NBSIR 75-668

Quieting: A Home Owner's Practical

Guide to Noise Control

Raymond D. Berendt, Edith L. R. Corliss and Morris S. Ojalvo*

Sound Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

*Engineering Division

National Science Foundation

Washington. D. C. 20550

March 1975

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 75-668

QUIETING: A HOME OWNER'S PRACTICAL

GUIDE TO NOISE CONTROL

Raymond D. Berendt, Edith L. Corliss and Morris S. Ojalvo*

Sound Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

*Engineering Division

National Science Foundation

Washington, D. C. 20550

March 1975

U. S. DEPARTMENT OF COMMERCE, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

QUIETING!

A Homeowner's Practical Guide to Noise Control

by

Raymond D. Berendt, Edith L. R. Corliss

and

Morris S. OJalvo

ABSTRACT

This publication is a guide offering practical solutions for the

ordinary noise problems that a person is likely to meet in his home, while

traveling and at work. The discussion describes the ways in which sounds

are generated, travel to the listener, and affect his hearing and well

being. Recommendations are given for controlling noise at the source and

along its path of travel, and for protecting the listener. The guide

instructs the reader by way of "Warning signs" on ways and means of

determining whether prolonged exposure to a noisy environment may be

hazardous to his hearing. General principles for selecting quiet

appliances are given. The remedies for noise problems deal both with

prevention and with selection of quiet alternatives to existing noise

sources. Ways of searching for the sources of noise and the paths over which they travel to the listener are described. A detailed index is given

for individual noise sources and the solutions to the problems they

present. General ways of looking for inherently quiet homes ajid travel

accommodations are described. In a final chapter, there are suggestions

for enlisting commvinity help where large external sources of noise must be

quieted, such as those arising from public tremsportation and public

utilities

.

KEY WORDS: Airborne and structure-borne sounds; annoyance; appliance noise;

health and hearing hazards; household noise; legal and community

action; loudness; noise control and abatement.

ii
CHAPTER 1

TABLE OF CONTENTS

Page

INTRODUCTION

WHAT IS NOISE? • 1-1

HOW DOES NOISE ORIGINATE? 1-1

THE CHARACTERISTICS OF SOUND OR NOISE 1-4

Decibel, usually written dB

Sound level meter

A-weightlng, dB(A)

Frequency and pitch

Loudness, soiind pressure and intensity

Phons

Pure tone and broadband noise

CHAPTER 2

NOISE AS A HEALTH HAZARD

PRECAUTIONS 2-1

WARNING #1

'

. . WARNING #2

WARNING

; HEARING PROTECTION 2-A

Situations to avoid

Signs of hearing loss

Noisy activities that should be limited

HOW TO AVOID RISKING YOUR LIFE AT NOISE LEVELS NOT

DAMAGING TO HEARING 2-5

Lesson 1 Provide for sounds of emergency vehicles

Lesson 2 Take frequent rests in quiet areas Lesson 3 Avoid startle reactions

. Lesson h Control noise at source

CHAPTER 3

BASIC PRINCIPLES OF NOISE REDUCTION ^

SOURCE-PATH-RECEIVER CONCEPT • . 3-1

NOISE CONTROL AT THE SOURCE 3-1

Select Quiet Equipment

iii
Page

REQUIREMENTS FOR QUIET OPERATION 3-2

1. Reduce Impact or Impulsive Forces

2. Reduce Speed in Machines and Pressure and

Flow in Fluid Systems

3. Balance Rotating Parts

h. Reduce Frictional Resistance

5. Isolate Vibrating Elements Within the

Machine

6. Reduce Radiating Area

7. - Apply Vibration Damping Materials

8. Reduce Noise Leakage From the Interior of

the Appliance

9. Choose Quieter Machinery When Replacing

Appliances

NOISE CONTROL OF THE TRANSMISSION PATH 3-10

FACTORS AFFECTING TRAVEL OF SOUND

1. Absorption: Soaking Up Sound

2. Sound Reflection: Bounding of Sound

3. Reverberation: The Re-echoing of Soiond

U. Diffraction: The Bending or Squeezing of

Sound

"QUIETING" IN THE PATH 3-15

1. Separate the Noise Source and Receiver as Much as Possible

2. Use Sound Absorbing Materials

3. Use Sound Barriers and Deflectors

h. Use Acoustical Lining

5. Use Mufflers, Silencers or Snubbers

6. Use Vibration Isolators sind Flexible

Couplers

7. Use Enclosures

PROTECT THE RECEIVER ..... 3-17

USE EAR PROTECTORS

ALTER WORK SCHEDULE

IS THERE AN ACOUSTICAL PERFUME?

CHAPTER h

NOISE CONTROL AT HOME

TRANSMISSION OF AIRBORNE AND STRUCTUREBORNE NOISE ..... 4-1

"SOUNDING BOARD" EFFECT 4-2
Page

FLANKING NOISE TRANSMISSION 4-3

GENERAL SOLUTIONS FOR NOISE CONTROL IN THE HOME 4-4

SOUND ABSORPTION VS SOUND INSULATION 4-5

KITCHEN NOISE . . • 4-6

INSTALL DOORS

CONTROL APPLIANCE NOISE

1. Vibration Isolate Appliance from the Floor

2. Isolate Appliance from the Wall

3. Isolate Appliance from Cabinet Enclosure

/ U. Isolate Cabinet Enclosiire from Wall

5. Isolate Small Appliances

6. Cushion Impact Noise in the Cabinets

?• Apply Vibration Damping Material

8. Install Acoustical Lining

9« Install Exhaust Fans on Rubber Mounts

10. Install Acoustic Ceiling

11 . Install Carpet or Foam-Backed Tile

12. Quieting of Large Appliances

RECREATION OR PLAYROOMS 4-11

CORRIDORS, HALLS, STAIRCASES 4-12

IMPROVING THE PRIVACY OF YOUR BEDROOM, STUDY OR

BATH AREA 4-12

IMPROVING THE SOUND INSULATION OF WALLS .......... 4-13

IMPROVING THE SOUND INSULATION OF FLOOR-CEILING

CONSTRUCTIONS 4-15

CONTROL OF FLOOR SQUEAKING . . . 4-16

CONTROL OF STAIR SQUEAKING 4-18

CONTROL OF HEATING, VENTILATING AND AIR-CONDITIONING

SYSTEM NOISE 4-18

CONTOOL OF PLUMBING NOISE 4-27

CHAPTER ^

HOW TO INSULATE YOUR HOME AGAINST OUTDOOR NOISE

Reducing the Intrusion of Neighborhood Noise 5-2

Reducing the Intrusion of Traffic Noise ......... 5-3

Reducing the Intrusion of Aircraft Noise 5-4

CHAPTER 6

SELECTING A QUIET HOME OR APARTMENT SITE

(or hov to avoid making the same mistake twice)

Selecting a Quiet Residential Area 6-1

Selecting a Quiet Location Within a Housing or Apartment

Development 6-2

Selecting a Quiet Apeirtment Unit Within the Building • • 6-3

V
Page

CHAPTER T

A TROUBLE-SHOOTING GUIDE

HOW TO LOOK FOR LEAKS 7-3

REMEDIES 7-4

LAST RESORTS 7-6

INDEXED CATALOG OF SPECIFIC NOISE PROBLEMS AND REMEDIES . . 7-14

CHAPTER 8

NOISE CONTROL AT THE OFFICE

NOISE SOURCES 8-1

REDUCING THE NOISE 8-1

EXTRANEOUS NOISE 8-3

PRIVACY BETWEEN OFFICES 8-3

PRIVACY IN OPEN-PLAN OFFICES 8-4

CHAPTER 9

NOISE CONTROL WHILE TRAVELING

AUTOMOBILES 9-1

1. Select a "Quiet" Automobile

2. Drive at Slover Speeds

3. Drive with Windows Closed

h. Use Air Ventilators

5. Use Slow Fan Speed

6. Turn Off the Radio

7. Select Quiet Tires

8. Balance Car Wheels

9. Reduce Windshield Wiper Noise

BUSES AND TRAINS 9-3

AIRPLANES 9-3

SELECTING A "QUIET" MOTEL OR HOTEL 9-3

SELECTING A "QUIET" ROOM 9-5

CHAPTER 10

POLITICAL AND LEGAL ACTION — WHEN ALL ELSE FAILS

INTRODUCTION 10-1

FEDERAL NOISE REGULATION 10-2

STATE AND LOCAL REGULATION 10-3

CORRECTIVE ACTION PROGRAMS ....... 10-4

LOCAL NEIGHBORHOOD NOISE PROBLEMS 10-5

BIBLIOGRAPHY B-1

vi

QUIETING

A HOME OWNER'S PRACTICAL GUIDE TO NOISE CONTROL

Raymond D. Berendt , Edith L. R. Corliss

and

Morris S. OJalvo*

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 2023^4

Chapter 1

INTRODUCTION

WHAT IS NOISE?

One humorous definition holds that "Noise is what your neighbor

makes." Of course, we all make noise ourselves, but we especially resent

the intrusion of sounds that we do not choose to hear. Thus, noise may be

defined as "unwanted sound."

So\ind becomes unwanted because it is capable of interfering with our ability to relax or to concentrate, to work or play, sleep, study, or

communicate. In short, it invades our privacy and disrupts the enjoyment

and full use of our surroiindings . At worst, it can affect our hearing,

performance, and behavior; noise can impair both physical and mental

well-being. Excessive noise represents a major public health hazard, and

indeed millions of workers risk permanent hesiring loss from exposure to

noise in their work.

Not only is much of this noise unnecessary, but it is avoidable.

Most experts will agree that modern technology for noise control can be

applied to reduce much noise to acceptable levels. Often noise arises

through thoughtlessness and neglect, and may be remedied by attention to a relatively few basic principles.

The objective of this Consumer Guide is to explain and illustrate in

a simple manner how many of the commonly encountered noise problems can be

alleviated or even eliminated.

HOW DOES NOISE ORIGINATE?

Generally speaking, noise is produced when an object or surface

vibrates rapidly enough to generate a pressure wave or distiarbance in the

surrounding air. Air is a rather springy, elastic substance composed of

small particles called molecules. The elasticity is due to the tendency of

these moleciiles to spring back to their original positions of rest whenever

they are deflected or displaced by some outside disturbance or force. As a sound wave travels through the air, the pressure fluctuations cause the

* Engineering Division, National Science Foundation, Washington, D. C. 20550

1-1
molecules to vibrate back and forth about their normal positions of rest.

In so doing, they bump neighboring molecules, imparting motion to them and

then, rebounding back and forth, return to their original positions. The

disturbed molecules collide with others in the same manner. The

disturbance travels through the air by successive collisions, much as a billiard cue ball will impart motion to a line of billiard balls. Although

each of the balls moves with the disturbance, each returns to its original

position after collision with the next successive ball; only the end ball,

which makes no further collision, moves forward beyond its rest position.

In a similar fashion, the vibration imparted to the air travels in a chain-reaction manner from one air molecule to another until it eventually

reaches our ears. Colliding molecules produce a pressure increase or a "compression" in the air; molecules rebounding away from each other produce

a lower pressure or a "rarefaction". In spice of all this motion, the

individual air molecules do not travel far from their original positions;

it is only the pressure wave or the compression/rarefaction disturbance

that moves outward, like the ripples in a pond into which a pebble is

dropped. We hear sounds because our ears respond to the pressure

fluctuations that have been set up in the air around us.

A few noises originate direc^l5>^y in the air. The most dramatic is the

thunderclap that originates from a discharge of lightning. The electrical

forces and the local heating create a sudden burst of overpressure that

compresses the air surrounding the path. This pushes the air outward, and

the motion persists until the surrounding air particles have been pushed

outward by the particles driven by the original stroke. By this time, the

column of air has been somewhat over-expanded, a process that cools it and

^ lowers the pressure within it. As a result, some air molecules are sucked

back into the column, and by the time they have collided with the central

part of the column, a pressure rise has been generated that again pushes

outward on the column. What started out as a pulse from a single

instantaneous heat surge becomes a succession of high-pressure pulses

separated by low-pressure pulses, which gradually diminish as the wave motion spreads outward from the column. These we recognize as the

compressions and rarefactions in a sound wave.

Another noise that originates directly in the air is turbulence. You

can see the swirls of turbulence that your breath generates if you blow

into an illuminated column of smoke or dust, such as one illuminated by a beam of sunshine coming through a window. The swirls that you see are

larger in diameter and slower in motion than the turbulence you can hear,

but have the same general form as the audible turbulence generated at the

edge of a jet-engine exhaust or the blades of a high-speed fan. The swirls

of turbulence originate whenever a fast flow of fluid goes past a stationary or slowly-moving surface of fluid. After many years we still

find the exact process a mystery, but we do know that turbulence is more likely as flow speed increases. In fact, once turbulence is started, it

increases rapidly as the flow speed is increased. The rapid changes in

direction and speed in a turbulent flow also result in rapid changes in

pressure, which we hear as noise.

1-2
Most noises are started by the transfer of motion fnm a vil:)rating

surface to the air lying next to it. If this motion is to be transferred

efficiently, the radiating surface must be large compared to the spacing

between successive pressure piilses. The pressure pulses travel through the air

at the speed of sound, 3^5 meters/second (1130 feet/second - a little slower

than a mile in fotir seconds). If the pressure can flow from the front to the

back of the surface in a very short time, it can restore the neutral condition,

because if the front surface of a moving object is compressing the air, the

back surface must at the same time be allowing the air behind it to expand.

For example, if you wave your heind slowly throvigh the air, it doesn't generate

any sound. The forward pressure causes the air to flow into the region of

reduced pressure behind your hand during the time it is moving; the entire

disturbance is confined to a small space about your hand.

As far as the listener is concerned, a sonic boom sounds very much like a loud thunderclap. Whereas the lightning generates an initial overpressvire by

electrical heating, a supersonic plane or the blade tip of a high speed

helicopter generates the overpressure by compressing the air in its path faster

than the high-pressure disturbance can flow away. This compression is called a "shock wave". Once the sonic boom has been created, the subsequent behavior of

the sound is similar to that of thunder.

You can generate sound pressures with the motion of a small surface if

there is little opportunity for the air to flow around and equalize the

pressure between successive motions. It's quite possible to generate a high

sound pressure if you box someone on the ear or strike a drumhead. There you

are changing the pressure in an enclosed volume, and the cancellation from the

w back surface cannot occur.

You can hear a bumblebee because his wings are vibrating so rapidly that

the individual pressure pulses, which can only move at the speed of sound, do

not have time enough to travel around the tips of his wings to interfere with

the rarefactions at the back of his wings. The beating of his wings generates

pressure waves in the air that propagate for some distance before they die out.

Since his wings beat at many times per second, we say he generates soxinds at

high frequency; we perceive these as being high in pitch, which is our subjective response to sounds of high frequency. In fact, we hear only the

higher-pitched parts of his buzz, when he is flying freely. VHien he strikes

against a window, for the duration of his contact with the window we hear the

low- frequency parts of his buzz enhanced, because the window offers an extended

surface over which cancellation of the lower- frequency (more slowly varying)

pressure pulses cannot occur.

Except for our own voices, which reach us primarily through the bony

structures in our heads, most sounds reach us through the air. We say they

are airborne. However, sounds travel rapidly and with little loss through

liqvdds and solids. As long as these offer an uninterrupted path, they

transmit vibrations readily. In liquids and solids the speed of sound is

1-3
from foiir to ten times as great as it is in air.

From experience, you know that if you press your ear against a wall

in your home or apartment, you can heeir noises arising from some distance.

You may be able to identify quite clearly your own dishwasher, a distant TV

set, or the compressor in the air-conditioner system. Often, when you

press your ear against a water pipe, you can hear the sound of running

water, perhaps originating at a neighbor's faucet. Some of us have had the

childhood experience of listening to the railroad track to hear whether

there was a train on the line. These are examples of structure-borne

sounds .

In each case, sound waves travel through the medium because a source

of noise or vibration in contact with the medium generates a disturbance . that displaces the molecules of the substance carrying the sound. The

disturbance continues to travel until it dissipates itself and becomes

indistinguishable from the random motions of the molecules. We hear the

sounds coming from a liquid or solid when they are transferred to ovir ears

as pressure fluctuations if they occur within the range of frequencies to

which our ears are sensitive. We do not normally hear the thermal

vibrations of molecules because they are too small and too random to

generate enough sound, and vibrations occur at frequencies for which our

ears are insensitive.

THE CHARACTERISTICS OF SOUND OR NOISE.

The various physical characteristics of noise or vibration, the way

they travel through materials, and how they react with the surrounding en- vironment can be measured. In many cases they can be predicted, analyzed

and explained.

When acousticians or noise control engineers get together in

technical discussions about noise, words like sound power, sound pressure

level, intensity, frequency and decibels frequently are mentioned. While

these terms are by no means household words, most people have a rough

understanding of what they represent. We perceive frequency as pitch,

intensity as loudness, and are likely to be concerned with the general

level of the noise rather then the absolute over- all sound power level.

Of all of these terms, the most confusing is likely to be the term

"decibel", although nearly all of us have some idea that it relates to

measuring sound levels. Except for experience, we should all have some

diffic\ilty with relating decibels to some familiar sound, for sound levels

in decibels do not translate directly into loudness. In fact, the first

use of decibels was in connection with telegraphy, and the engineers who

work in acoustics use the term in ways that communications engineers

dispute. So, rather than tell you in detail what the decibel scale is,

we'll tell you more of what it does .

Decibel, usually written dB:

Unfortunately, the decibel is not a linear unit of sound level in the

same way that a foot, inch, meter or centimeter are units of length. It is
a measTire of a ratio of the power of a sound relative to some reference

value. Usually the "threshold of hearing" is used as the reference.

Because it arises from the logarithm of a ratio, one decibel is not a fixed

difference, in the same way that all units of an inch or a centimeter are identical. Nevertheless, as we shall see, the convenience of the decibel

scale outweighs its difficulties.

Consider for a moment the range of sensitivity of the human ear. If we were to assign the value of one unit to the smallest sound power that

the ear can hear, commonly referred to as the "threshold of hearing", then

a value of one million million units would be given to the greatest sound

power that the ear can withstand without suffering discomfort, which

defines the "threshhold of^gain". (The ratio of one million million is

written by engineers as 10 , meaning that twelve successive

multiplications by ten of the threshold power would be needed to produce

the threshold of discomfort.) If one were to plot this enormous range on

graph paper with graduations of a millimeter per unit of sound pressure, it

woiild require a sheet of paper 10 kilometers (6.2 miles) long. And if we insisted upon soiind power , this would require 100 kilometers (62 miles).

On the decibel scale, however, the range of soimd power level between the

threshold of hearing and the threshold of pain would be compressed between

the limits of 0 dB and 120 dB respectively, and could be plotted easily on

a graph the size of ordinary tablet paper.

On this scale, the sound pressure level of 0 dB does not indicate the

absence of sound; it indicates a level of sound, at a frequency of 1000 Hz,

(cycles per second — see section on Frequency and Pitch) Just barely

audible to a normally sensitive ear. A 1-dB difference in sound level is

about the smallest relative change that the average person can detect. For

each 10-fold increase in sound pressure, there is a 20-decibel gain in

power level, that is, the new power is 100 times greater than the original.

If the so\md pressure is increased to 100 times the original pressure, the

power now would be 10,000 times greater, a gain of kO dB in power level.

Sound level meter:

Sound levels are measured with a sound-level meter, which is an instrument calibrated to read sound level directly in decibels. Basically,

the instrument is an electrical device. It has a microphone that converts

a sound-pressure variation in the air into an electrical signal, an amplifier powered by a battery to raise the signal level to produce enough power

to operate an indicator needle, and an attenuator to adjust the signal

level within the range of the meter's scale. For its basic setting, the

meter reads the total of all sound within the range of frequencies normally

heard by the h\iman ear. To give you a feeling for the meanings of the

meter indications, we are presenting in Table 1-1 the sorts of readings you

would see if you were to take a sound-level meter and expose its microphone

to common soiorces of so\ind in your environment.
Now, if your ear "behaved Just like the simple sound-level meter, the

decibel scale vould be all that you would need to measure the extent of a noise

problem. However, high-pitched sounds — the calls of birds, the upper notes

of a piano, insect chirps, the consonant sounds of speech, whispers — all can

attract your attention at low power levels , in fact at levels so low that

sounds of low frequency and similar intensity, as for example a distant

, airplane, might easily go unnoticed. The simplest way to adapt a sovmd-level

meter to the behavior of the ear has been to provide it with weighting networks

A-Weighting, dB (A):

We can give you a picture of the way in which the ear weights sounds of

equal level but different frequencies by showing you a set of "equal- loudness

contours". These values are measured by asking subjects to match the loudness

of a test sound against a standard sound. Usually the standard sound is a pure

tone whose frequency is 1000 Hz (about that of the top note of a soprano's

range). A set of these equal-loudness contours is shown in Figure 1-1, and we have superimposed some typical sound sources in their proper places in the

frequency and intensity scale. Until fairly high intensities of sounds are reached, the contours are more or less parallel to one another.

The A-weighting network on a sound level meter is designed to adjust the

sensitivity of the meter to sounds of different frequencies so that it behaves

more nearly like the human ear at moderate sound levels . The "A-scale"

/ weightings of a sound-level meter have been found to agree reasonably well with

subjective response to the loudness of soundo . When an A-weighting network has

been used with a sovmd-level meter, this fact often is noted by using the

w abbreviation dB (A). The hum of an air-conditioner might be read as TO dB with

a sound-level meter, and would be likely to read 58 dB (A) when the weighting

network was used.

At high sound levels (90 dB and above) the ear seems to behave more nearly

like a "flat" or unweighted sound-level meter. Sometimes this weighting is

called the "C" scale. There is also a B-weighting network that is used to

approximate the loudness behavior of the ear for a 60-dB contour ~ i.e. , it is

intermediate between A and C weightings.

This guide will follow the ordinary practice of reporting A-weighted sound

levels as dB(^). Many regulatory agencies of state and local government use only the dB(A) ratings when they are dealing with human responses. The "flat"

scale of the sound-level meter is also sometimes marked confusingly "linear";

when data are reported simply in dB notation, they represent the unweighted

readings of the sound-level meter, obtained with the flat setting of the meter.

Frequency and Pitch

The number of complete to-and-fro vibrations that a source of sound makes

in one second is called the frequency of vibration. For example, if a loudspeaker cone moves back and forth 100 times in a second, the frequency of

the tone it radiates is said to be 100 cycles per second, (the cone has

executed 100 cycles of the same motion within one second) or, in modern metric

1-6
terminology, 100 Hertz (abbreviated Hz). (Hertz was a nineteenth century scientist who discovered the alternating-current properties of spark discharges

and introduced communication by radio waves.)

Since the ear senses the frequency of a sound as the pitch, on a similar

though sensory scale, sounds with frequencies near 30 Hz are sensed as having

very low pitch, whereas sounds near the upper frequency limit of hearing at

15,000 Hz are judged to have a very high pitch. The noise of bacon sizzling in

a pan is Judged to be high-pitched, whereas the rumble of distant thunder is

low pitched. The 100-Hz tone we mentioned above is sensed by the listener as having a low pitch. The small, high-speed wings of a mosquito radiate a higher-pitched whine than do the larger, somewhat more slowly-vibrating wings

of a bumblebee.

The ear has another perception about pitch which is important from a musical standpoint: it recognizes the doubling of frequency as producing a repeating tone quality. To produce the same pitch in different parts of the

frequency range, the interval must be adjusted to be proportional to the frequency. The scale of frequencies in Figiu'e 1-1 is adjusted for this property

of hearing, and you may notice that each doubling of frequency teikes up the

same horizontal internal in the figtire. Musicians call this the octave scale.

Loudness, Sound Pressure and Intensity

Loudness may be described as human or subjective measure of the pressure

or intensity of sound. It can be ordered on a scale with limits ranging from

whisper-soft to painfully loud. We have already seen that the loudness of a sound of a given intensity depends upon its frequency or pitch. However, if we

present a sound of a given frequency at different levels and ask a person to

assign a number representing its loudness, we find that - as a "rule of thiomb"

- doubling of loudness corresponds roughly to a 10 dB increase in sound level.

(Experiments give from 10 to 12 dB). Table 1-2 relates changes in sound level

to the average person's perception of loudness.

You can see now that Figure 1-1 gives you a picture of how the ear weights

sounds of equal level but different frequencies. The ordinary noise sources

are shown at their typical sound-level meter readings in dB, plotted at their

dominant frequencies. These are the indications that the sound-level meter

would yield as measured at the position where the sound would be most likely to

be experienced: For some appliances, such as a blender or a power mower, at

the position of the operator; for vehicles on a highway, at curbside; for

aircraft overflights and neighborhood noise sources, outside the home; for such

sounds as the ocean, bird calls, or thunder, at the position of the observer

out-of-doors. Superimposed on this plot are contours of equal loudness for

pure-tone sounds, depicted by the solid curved lines. On a given contour any

pure tone at the sound level and frequency indicated will be Judged by the

average person to be equally as loud as any other tone along the curve. For

example, on the lowest contour, the "threshold of hearing", a 50-Hz tone at a level of about dB sounds equally as loud as a 500-Hz tone at 5 dB. The

audiofrequency spectrum from 1000 to 8OOO Hz (approximately the two top octaves

of the piano and the next octave beyond) covers the region where your ear is

most sensitive. Some of the more distressing sounds, such as the squeaking of

chalk on a blackboard lie in this region. It is in this region, also, that the

ear is most vulnerable to dajnage by noise or disease.

1-7
Phons

:

In Figure 1-1, the spacing of the contours is chosen to be in even increments of the 1000-Hz standard tone, as read on a soiind-level meter. The

contours connect sound level values where the loudness is alike. Each contour

is rated numerically for the sound-level of the 1000-Hz tone vith which other

tones on the contour are comparable. Although they, too, are written as dB,

the units related to the contours are no longer sound level, but "phons", and

now represent a level of loudness perceived to be equal in effect to the

1000-Hz tone through which the contour passes at a sound-level indicated in the

decibel scale on the left-hand margin of the graph.

Ptxtc Tone and Broadband Noise

Throughout this guide some noises may be described as pure tones, or as having pure-tone components, whereas other noises may be described as being

broadband in character.

Pure Tone:

A pure tone is the sound radiated by a source vibrating at a single

discrete frequency. For example, the sound emitted by a tuning fork that is

properly struck is remarkably pxire in tone. Similarly, striking a single key

on a piano or plucking a single guitar string produces a relatively pure tone.

The average person can produce a reasonably pure tone simply by puckering his

lips and whistling a note. A chord struck on the strings of a guitar is an example of a tone made up of a number of pure-tone components.

Broadband Noise:

Broadband noise, on the other hand, is a complex mixture of sounds of

different frequencies. Often these mixtures are changing rapidly with time.

The sound produced by a nearby waterfall or a pounding surf is relatively

broadband in character.

.. In many instances', noise so\irces radiate both broadband noise and puretone

components. A jet plane at take-off, for exajnple, radiates a combination of

such noises. There is the shrill whine of the turbine, which may have a pure,

whistle-like character, superimposed on the broadband roar of exhaust noise.

The vacuum cleaner emits a siren-like sound from its impeller, generates

whistling noise in some corrugated hoses, and also produces broadband airsuction sound. Wind blowing past overhead power lines often generates a puretone whistling sound which stands out against the background of the broadband

noise of the wind.

There is some evidence that pure tones are Judged to "grow" in loudness as they end\u"e over a time interval of a number of seconds, whereas broadband

noises soon reach a plateau of loudness. This is not indicated by the usual

methods of measuring equal- loudness contours because comparisons ordinarily are made between sounds of similar durations. However, this feature does have a bearing on the choice of procediires for noise abatement. Special effort to

remove pure tones is desirable.

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1-9
TABLE 1-2

SUBJECTIVE RESPONSE TO CHANGES IN SOUND LEVEL

Change in Sound Level Change in Loudness

+ 1 dB Requires close attention to notice

+_ 3 dB Barely perceptible

5 dB Quite noticeable

+^ 10 dB " Dramatic; nearly twice or half as loud

v, + dB Striking, fourfold change

1-10
FIG. 1-1 COMMON SOUND SOURCES PLOTTED AT THEIR DOMINANT

FREQUENCIES AND LEVELS AS TYPICALLY HEARD BY

THE OBSERVER.

1-11
\

4.
Chapter 2

NOISE AS A HEALTH HAZARD

When you are in a sotind field whose level as read on a sound-level meter

is TO dB or more, even though you know consciously that you are in no hazard,

some part of your "body tries to run away. The signs of this are the common

symptoms of nervous stress: Your heart beats more quickly; breathing becomes

shallower and faster; the pupils of your eyes dilate; the small blood-vessels

in your skin contract; your blood pressure rises. These are the actions of a body arousing itself to escape. In the seune experiment that showed this to

happen, the effects of noise on sleep were studied. Even though the human

subject didn't necessarily awaken, his body responded. The only difference was that during sleep the sound level needed only to exceed 55 dB.

You can become "accustomed" to the noises in your environment, but all

that this means is that you can become accustomed to eliminating the noise from

your conscious attention. The physiological effects persist. If you are compelled to work in noisy surroundings, the only warnings you may have of

acoustically-induced stress are signs of fatigue and nervous strain.

No one knows how many of the stress-induced diseases of our modern era are made more prevalent by the rising noise levels in our densely-populated cities.

Note that these levels do not affect your hearing in itself. Nor do the

results mean that all noise shoxild be excluded. Studies of the effects of

noise upon work indicate that some degree of ambient sound (which might as well

be pleasant, such as the sounds of a fountain, or background music) helps

maintain arousal during repetitious tasks ; only the very highly-demanding

mental tasks are done better in wholly quiet surroundings.

Noise damage to hearing is an insidious process. That is, the immediate

effects are not a good indicator of the ultimate results of the exposure.

Exposure to a mildly excessive noise level results in a temporary desensitization of the ear, the so-called "temporary threshold shift", a temporary loss of

the ability to detect faint sounds. Noises likely to cause a temporary

threshold shift are encountered during subway rides and airplane trips. Some

degree of temporary threshold shift may be detectable even on the day following

exposure, but ultimate recovery cein be complete.

However, this pattern of threshold rise and recovery sometimes goes on through a number of cycles without any further evidence of damage, and then

there may be a sudden failure to make complete recovery. This permanent effect

- "noise-induced permanent threshold shift", sometimes abbreviated in capitals

as NIPTS - is a sensorineural hearing loss. That is, the damage is located at

the auditory nerve, itself, with seriovis consequences.

PRECAUTIONS

WARNING #1: Because we have no reliable way to predict the degree of

permanent loss from temporary threshold shift, a conservative policy is to

avoid situations giving rise to temporary threshold shift . Any person whose

2-1
hearing does not recover within a few days after an exposure that induced a w threshold shift shoxild avoid any further exposure to sounds of that level, and

should take positive action to protect his hearing. He should not ret\irn to

that environment without protective equipment.

After exposure to sound levels of 85 dB and above for lengthy periods of

time, a significant number of persons will be found to have a permanent hearing

loss (NIPTS); this degree of exposure essentially doubles the incidence of

hearing loss beyond what would occur from mischance and disease in the course

of aging. For exposures above this level, the incidence of losses rises fairly

rapidly with the sound level to which persons are exposed. Since there is some

. reason to believe that 80 dB represents the point from which the damage risk

begins to be significant, it is obviously a good idea to avoid continuous

' exposure to any levels above 80 dB for any length of time competrable to a working day, and to wear ear protection if exposure is necessary. The

potential damage point is indicated fairly reliably by conversational effort.

WARNING #2: If you have to raise yoxu- voice to carry on a conversation at

a distance of 3-^ feet from the person with whom you are talking, you are being

sub.lected to a potentially damaging exposia'e. Not only does it inconvenience

, you in your conversation at the moment; it may make it difficult for you in the

future.

Figure 2-1 is a diagram of the process whereby the sounds arriving at your

ear through the air reach the auditory nerve at the entrance to your brain.

Like any well-engineered system, your ear has a few external protective

devices. If you are exposed to an excessively loud noise, the muscle tensing

*^ your eardrum pulls taut, desensitizing it. This "stapedius reflex" takes place

at sound levels between 80 and 95 dB. The point of onset of the reflex varies

with individual sensitivity. Some persons can operate the stapedius reflex at

will; from their experience it is evident that the desensitization is of the

order of 20 dB. Thus the protection afforded by the stapedius reflex is

.. important.

However, a burst of intense sound pressure too abrupt to give the stapedius reflex time to act can occur. This is particularly true of a shock- wave

from a gun-shot or a pressvire burst from a box on the ear. In that event, the

drum membrane is likely to rupture, causing a temporary loss of hearing and a hazard of middle-ear infection. However, if no infection follows the injury,

the membrane will heal. Except for the effect of the weight of the heavier

scar tissue that is likely to form, the ultimate senistivity of the ear will

have suffered little change. Desensitization due to scsir tissue may be. enough,

in some individuals, to lower the response of the ear to high-frequency sounds,

where the critical consonant sounds of speech are located, and where the cues

to musical tone quality are transmitted. (Since it is sometimes necessary to

lance the drvm membrane in cases of middle-ear infection, with a consequent

formation of scar tissue, it is clear that any ear infections must be attended

to at once to avoid a residue of permanent loss.)

It is damage to the hair cells in the inner ear that causes the irretrievable losses that are associated with noise damage. From experiments on

2-2
animals, it has been found that loss of 13-20% of the hair cells that respond

to high frequencies will produce a rise in threshold of about hO dB. This

loss, for hxaman beings, occurs first in the region most important for discrimination of the consonant sounds of speech - in the range from kOOO to 6OOO

Hz. If you look at the diagram in Figure 2-1, you can see that losing a fraction of the hair cells is comparable in some vays to the loss in vision

that would occur if scattered areas of your retina were destroyed. Although

the effect observed by measuring your threshold of hearing is simply that your

threshold has risen, which is the same sort of observation that would be made

if the injiiiy were in the drum or in the chain of bones in the middle ear,

something much more serious has been lost.

Loss of hair cells impairs the resolution that your ear can bring to bear

on sounds. Even after amplification, the loss of resolution remains. As you

can see from Figure 2-2, which shows the damage to hair cells as a result of

noise exposure, nerve endings have been put out of action. The loss impairs

the ability to understand conversation in the presence of noise. With a severe

loss of hair cells, although a person can use a hearing aid to permit him to

hear soimds at levels comparable to those heard by persons with normal hearing,

he may not be very successful at recognizing speech. The average person who

has suffered a sensorineural hearing loss that raises his unaided threshold

above the normal by 60 dB will generally have a significant degree of

difficulty in understanding speech even while he wears his hearing aid . Thus a permanent threshold shift produces a permanent impairment of hearing, and the

only practical remedy is prevention .

If you have been exposed to an excessively intense noise, you are likely

to notice a ringing in your ears as an after-effect. This is called

"tinnitus", and it seems to represent a spontaneous firing of signal impulses

by the hair cells. Also at sound levels that are potentially damaging to your

hearing, you may notice that music acquires a complex, sometimes discordant

sound. This is because the ear produces mixtures of tones instead of merely

transmitting the sound stimuli. Only the rhythmic patterns of music may remain

esthetically pleasing. At these levels, some effect is sensed on the semicircular canals of the ear that normally respond to orientation and balance.

This gives a sensation of dizziness, which is perhaps cultivated by devotees of

rock-music as a pleasurable sense of detachment, analogous to drunkeness. Like

the over-consumption of alcohol, continuous very loud sounds lead to an end-point of seasickness and nausea. You can literally experience an "acoustic

hangover"

WARNING #3: At still higher sound levels, a "tickle" sensation is felt in

the ear, and with another 10 dB rise of level, a sensation of pain intrudes.

The pain is an important though perhaps tardy warning. Very little exposure at

the threshold of pain is needed to produce a permanent hearing loss in sus- ceptible individuals . Another serious flaw in this warning system is the fact

that at present we cannot predict who is susceptible. (There is some reason to

suspect that susceptibility is enhanced by large-scale changes in the

physiology of the body, as in adolescence.

)
It is a fact that persons in noisy occupations and vith noisy avocations

are found generally to have various degrees of permanent, sensorineural hearing

loss. Among the pleasures having more devastating consequences are rock music,

target shooting and snowmobiling. Hearing loss due to gunshot in warfare is

very prevalent. You should also be aware that the readings of an ordinary

sound-level meter will fail to indicate the true level of rapidly peeiking

sounds because the needle of the meter is too sluggish to follow the sharp

pressure changes that occur on impulsive sounds like shots, or even the sounds

of a poorly-muffled internal combustion engine. (After all, it derives its

power from the explosions confined in its combustion chambers.)

We are hampered in preventing a great deal of hearing loss because of a degree of bravado that causes some people to shun wearing hearing protection.

Since hearing loss is subtle and invisible, perhaps it seems illogical to

choose a visible means of protection. Some types of ear protectors are shown

in Figiire 2-3. Simple insert-type ear protectors are usable where perhaps

10-20 dB of protection is sufficient to eliminate the chance of hearing loss.

In general, these are more effective for high-frequency sounds such as whistles

than for low-frequency sounds such as machinery noise or Jet turbulence. Cotton worn in the ears is not very effective, only a little better than nothing.

However, in a pinch, you can derive some real help from cotton soaked in

vaseline or soft wax (to increase its mass and sealing power), and pressed

gently into your ears. Commercial ear protectors of the deformable soft plastic type make still better protection. If you are concerned about appearances,

be assured that these are not as obvious as hearing loss, for a hearing loss at

high frequencies destroys the referee that enables you to monitor your own

speaJting. Not only do you have trouble hearing other people — because your

hearing loss slurs and obliterates the consonant sounds of speech, your own speech becomes like what you hear.

At most, you can count on internally-worn ear protectors for a 10-20 dB

reduction. Really effective protection is offered by over-the-ear muffs, which

look like a relatively large pair of headphones. You may have seen these on the personnel working at airports. For maximum protection, both muffs and

inserts may be worn. Even the combination of muffs and ear protectors, . however, can offer little more than ^0 dB protection, for sound caji enter the

body by other paths, entering via the chest cavity, the throat, and the bones

of the head. If you translate that information into the conditions of your

environment, you cannot remain for any length of time around sound levels in excess of 120 dB without walling yourself off from the source of sounds. In

operating noisy machinery, workmen may find it necessary to observe and control

the operation from the window of an isolation bpoth.

HEARING PROTECTION

How can you protect your hearing? The following notes may help:

Avoid Situations WTiere

1. You have to raise your voice to converse with anyone.

2. Ordinary melodic music sounds discordant.

3. You can't manage to talk over the telephone.

2-4
h. Sharp noises are repeatedly making your ears ring.

5. Everything seems too bright and too loud.

6. The racket makes it difficult to "think straight".

7. You begin to feel detached and a little dizzy.

8. In a short while you begin to feel tired and dazed.

9. The noise makes you feel seasick.

Your Hearing May Have Begun To Deteriorate When It Seems That

1. You have trouble recognizing what is said from the stage or pulpit.

2. You have to ask people to repeat what they say.

3. People ask you to repeat what you say.

h. You lose the thread of conversation at the dinner table.

5. The birds seem to have stopped singing.

6. You miss the telephone bell or the doorbell.

7. Your family repeatedly asks you to turn down the TV or radio.

8. People seem to have begun to mumble.

Be Cautious in the Use of These Devices

If you garden:

Power lawnmowers , chain saws, mulchers , lawn vacuums, lawn edgers

.

For the sportsman:

Guns, speedboats, snowmobiles, motorcycles, all-terrain vehicles.

Even if you are the sheltered, indoor type of person:

Power tools, "industrial vacuum-cleaners", superpowered Hi-Fi,

rock-music bands.

HOW TO AVOID RISKING YOUR LIFE AT NOISE LEVELS NOT DAMAGING TO HEARING

A high sound level can conceal the presence of rival sounds in your

environment, or reduce their apparent loudness, thus removing their capacity

for attracting your attention. This concealment can prove fatal.

For example, in a modern car with stereo and air-conditioning running, someone we know drove happily out of her driveway and collided with a fire

engine. The car was a total wreck. Two factors militated against her: In the

first place, the closed car windows attenuated exterior sounds. In the second

place, although the car radio masked the motor noises and the air conditioner

with pleasing sounds, it also masked out the warning siren and the engine noise

of the fire truck. Since the car noises were in themselves not negligible, she was of course actually operating the radio at unduly high sound levels. In

order to have overridden all this sound and caught her attention, the fire

engine's siren would have had to be intense enough to offer a risk of hearing

damage to the firemen themselves and to pedestrians on the street. The most

common function of a siren is to alert motorists and pedestrians to clear the

road for an approaching emergency vehicle. Tower or roof-mounted sirens, on

the other hand, alert the populace to some impending danger, such as an air

2-5
raid, or siaimnon volunteer fire fighters as the case may be. Althoiigh the noise

is intense enough to, and often needlessly does awaken large segments of a sleeping community, it fails all too frequently to achieve its main objective,

that is, to alert the motorist. This failure is due to one or a combination of

the following factors:

-vehicle windows are closed

-high noise level in vehicle due to operation of radio, fan or air

conditioning equipment or the intrusion of engine or traffic noise

-preoccupation or distraction of driver.

For the motorist, the ideal warning device would be a small buzzer or

' alarm with perhaps an intense flashing light installed on the dashboard of his

vehicle that could be triggered or set off by a short range radio frequency

transmitter on the emergency vehicle. Both the warning buzzer and light could

be modulated to buzz and flash at a gradually increasing rate as the emergency

vehicle approached to alert the motorist as to its proximity.

Similar warning systems could be installed in the station house and homes

of volunteer firemen. If the installation of such equipment were made

mandatory in all emergency and automotive vehicles, communities would benefit

from a dramatic c\irtailment in the use of a highly disturbing source of noise

pollution and perhaps a significant improvement in the safety of conducting

emergency or rescue missions.

Lesson 1: In order to hear sirens of emergency vehicles while you are driving an air-conditioned or heated car in city traffic, do not close it

tightly. Leave an opening of perhaps half an inch (about 1 cm) in the window

next to the driver's seat.

Leaving the window next to your ear raised enough to prevent "line-ofsight" access from the sounds of the road has some advantage. It will generally not interfere with the sounds of sirens and warning whistles, which are ordinarily pitched in the range from 500 to 3000 Hz, but some of the highfrequency road noises generated by tire treads and exhaust turbulence will be

kept from reaching your ear at levels high enough to induce acoustic fatigue.

Use your radio sparingly and at low volume when driving in any degree of

traffic. You have more at stake than your hearing. However, you must still be

alert because the partially open window offers no guarantee that you will hear

an approaching siren.

A careful industrial study has shown that persons in noisy environments

gradually require longer times to react to emergencies; we say their reaction

times have increased. This points to a special hazard: Reaction time is known

to have an influence on accident rate. (One of the important consequences of

the consumption of alcohol, and of such medicinal agents as tranquilizers and

antihistamines, is an increase of reaction time.) Further, in the noise

exposure cases it was found that although for the first day or two of exposure,

a rest period of an hour or more restores the reaction time, continued exposure

to noise in succeeding days is no longer compensated entirely by rest.

2-6
In the industrial experiment, persons working for an eight-hour day were tested before and after each four-hour work session, with a lunch hour between.

Each group in this study had Just returned from vacation. By Wednesday of each

week, the reaction time in the morning was lengthened a little, and full

recovery did not follow the noon hour. By Thursday, and even further on Friday, the reaction time was lengthened at all times, and recovery was poorer.

On Friday afternoon, the reaction time was nearly 50% longer than the normal

level following extended rest. This was not due to the work: Half of the

subjects of the study were merely sitting in the noisy environment beside their

working companions.

Lesson 2: For maximum safety, you should break up working spells in a noisy environment by taking a full day's rest at frequent intervals. It is

worth noting that you can enhance the safety of your family on long trips by

automobile simply by breeiking the trip for at least an hour in a quiet

surrounding after four hours' driving, and by making a stopover for more than a day at least every three days , preferably every two days

.

The definition of

"quiet" has been found by experiment, as well: Full recovery from acoustic

exposure demands a quiet area in which the ambient noise is less than 55 dB.

Since the lengthening of reaction time is primarily due to the exposure to

noise, changing of drivers among the travelers within the car will not avoid

this problem.

Another source of accidents that can be caused by noise not in itself at a physically dajnaging level is the "startle reflex". The normal human reflex at

a sudden loud noise is to cringe: The eyes blink and shift, the shoulders are drawn together, the head is moved downward and away from the sound, the long

muscles of the arms and legs pull them toward the trunk. Probably the

startling noise of a blowout is a large part of the problem of control of a car after a blowout has occurred.

Lesson 3: If you are driving a car and see a pedestrian about to cross

the street, you have to measure the possibility that by blowing your horn you

will trigger off a startle reflex in him and possibly in other bystanders, and

weigh it against the chance that you might lack enough control to stop before

you hit him. Bicyclists are very vulnerable to startle reactions because they

can lose direction as well as balance. If you are riding a bicycle, you should

be careful to remain in a lane clear of traffic to protect yourself against a sudden startle; for the same reason a passing motorist should allow a bicyclist

a wide lane, even though the small size of the vehicle does not require it.

A reflex known as "nystagmus", a sideward back and forth scanning of the

eyes, is triggered off by noise. For most persons it is unlikely to occur

until sounds reach quite a high level, but for susceptible persons it may

become troublesome at levels below those directly injurious to hearing.

Natiarally, this reaction interferes with visual acuity and the Judgment of

distance.

Lesson h: Since all the protection we can suggest is only a palliative

measure, it is clear that the best procedure for protection from noise is to

cut off excess noise at the source. Unfortunately, to many people, noise means

2-7
pover. Thus, there is some feeling that there may be a virtue in noisiness.

An adolescent who removes the muffler from his car feels it "sounds more

powerful", thus bigger and somewhat better than before. This is no different

from the reaction of the purchaser of a lawnmower or vacuum cleaner, who has a strong feeling that the sound indicates reserve power. Manufacturers of power

tools report that efforts to quiet the equipment do not pay; people feel that

the equipment is somehow less powerful.

Perhaps because the quieting of equipment often removes high-frequency

noise preferentially, the impression is created that the action of the equipment is stifled (as your speech would be smothered by a hand held over your

mouth, quieting the consonants more than the voice). This is very far from

true. Internal-combustion engines with properly resonated mufflers actually

fire better, make better use of fuel, and run more steadily. Thus, the

tradition among many cross-country truckdrivers of "cutting out" the muffler on open roads is actually count ereffective.

To re-establish a feeling for the magnitudes involved. Just remember that

a sound capable of damaging your hearing need have a power flux of no more than

one thousandth of a watt per square centimeter. Thus the amount of power

involved in generating noise is very small; a mechanism using very little power

can generate large amounts of so\md (ask any parent). Noise is thus no criterion for the availability of usable power.
2-9
H«l» CtlLS

I. «M(N«

CtlLS

P>l.l»R ClLlS NCRVC fllC«S

(A) NORMAL ORGAN Of CORTI

COll»PS£ Of OOGHN Of COiTi-

••*iS CtuJ »i$tNt - «CC£SSO<l» CtlLS swoiKN AND oiSTonreo

NtRVE FIBERS REOuCCO

IN MUM8E*

(C) SEVERE INJURY

I OliIfR MA, a CtllS ABSENT

OiSIORTl 0 CilLAR CEll SwOUtN

SUPPORIINC CCllS

(B) PARTIAL INJURY

ORGAN 0» COBfl AeSENI

NERVE fl«(RS ASSENT

(D) TOTAL DEGENERATION

FIG. 2-2 DRAWINGS OF THE HUMAN ORGAN OF CORTI ARE SHOWN THAT

ILLUSTRATE THE NORMAL STATE, PANEL A, AND THE INCREASING

DEGREES OF NOISE-INDUCED PERMANENT INJURY. PANELS B, C,

AND D. THIS IS WHAT YOU WOULD SEE IN A SECTION VIEW CUT

ACROSS THE REGION OF THE HAIR CELLS SHOWN IN FIG. 2-1,

INNER EAR.

2-10
2-i 1
i i
CHAPTER 3

BASIC PRINCIPLES OF NOISE REDUCTION

If you have a noise problem and want to solve it, you have to find out

something about what the noise is doing, where it comes from, how it travels,

and what can be done about it. A straightforward approach is to examine the

problem in terms of its three basic elements: i.e., sound arises from a source, travels over a path, and affects a receiver, or listener.

SOURCE-PATH-RECEIVER CONCEPT

The source may be one or any number of mechanical devices radiating noise

or vibratory energy, such as several appliances or machines in operation at a given time in a home or office.

The most obvious transmission path by which noise travels is simply a direct line-of-sight air path between the source and the listener; for example,

aircraft flyover noise reaches an observer on the ground by the direct

line-of-sight air path. Noise also travels along structural paths. In most

cases it travels from one point to another via any one or a combination of

several such paths. Noise from a washing machine operating in one apartment

may be transmitted to another apartment along air passages such as through open

windows, doorways, corridors or ductwork. Direct physical contact of the

washing machine with the floor or walls sets these building components into

vibration. This vibration is transmitted structiirally throughout the building

causing walls in other areas to vibrate and to radiate noise.

The receiver may be a single person, a classroom of students, or a suburban community near an airport or expressway.

Solution of a given noise problem might require alteration or modification

of any or all of these three basic elements:

(1) modifying the source to reduce its noise output,

(2) altering or controlling the transmission path and the environment to

reduce the noise level reaching the listener, and

(3) providing the receiver with personal protective equipment.

Let us examine the various noise control measures that can be applied in

each of these categories.

NOISE CONTROL AT THE SOURCE

Select Quiet Equipment

Basically, the best way of controlling noise at its source is to select

quiet equipment or appliances initially. When shopping, look for equipment

that carries a low-noise certification or rating - preferably backed with a

3-1
copy of the certifying laboratory's test report. Some appliances and equipment

feat lire or advertise noise-control design or construction - look for

descriptive terms such as "so\uad conditioned," "acoustically treated", "quiet

operation", and similar phrases that may be used in advertising copy or in

owner's manuals. However you must be on gueird because such descriptive phrases

as "whisper quiet" may well be deceiving!

Unfortunately, the selection of mechanical equipment and appliances that

feature noise ratings or that specifically call attention to noise control

design is extremely limited. Thus, the buyer must resort to his own wit or know what to look for in order to choose quiet equipment. The key words to

remember in making purchasing decisions are

" slower" and "lower ," particularly

as they apply to the operation of the equipment. The speed of moving parts,

flow velocities, gas or fluid pressure differentialp , and power ratings all

affect noise output. By looking for equipment displaying "slower" and "lower"

operation characteristics you can be relatively assured of quieter operation.

For example, large slow-speed fans are substantieilly quieter than small

high-speed fans for a given air flow; low horsepower motors are less noisy than

those with high horsepower ratings; likewise low-pressure, low-velocity air

ventilation or fluid distribution systems are virtually noiseless compared with

their high- pressure, high-velocity counterparts.

Whenever possible, the buyer should conduct a side-by-side comparison

noise test for various makes or types of appliances or equipment. This can best be done by dealing with a supplier who carries a wide selection of

appliances or equipment made by several manufacturers and who is willing to

demonstrate their operation in the show room. This, of course, is possible

when shopping for small domestic appliances such as vacuum sweepers, window air

conditioners, etc. However, large mechanical installations, such as central

heating or air conditioning systems can only be properly evaluated in-place.

In summary, the guidelines to use in selecting quiet equipment are:

(1) low-noise certification,

(2) advertisement of "quiet" operation, evidence of noise-control design,

(3) emphasis on "lower" and "slower" operating characteristics,

(h) comparative side-by-side noise tests in the dealer's showroom,

(5) Visit the site of actual installed equipment of the type you are considering, for purposes of making yovir own survey or subjective

evaluation of noise output.

REQUIBEMENTS FOR QUIET OPERATION

Most mechanical devices such as automated appliances and machinery are complex noise generators that contain numerous sources of noise. For example,

. the overall noise radiated by a clothes washer may be generated by the drive

3-2
motor, gear train, pioinp, pulleys, cams, bearings, electrical switches,

automatic valves, and water flow. Reducing the noise output of such a device

lisually requires a considerable amount of study to identify the major soiirces

of noise and their respective transmission paths. In other words, it is

important to know whether it is the motor, gear train or the puinp that is the

main cause of noise - and whether the noise is radiated directly from the

source into the air as airborne noise, or whether it is transmitted structurally as vibration to other parts and siarfaces of the machine which, in tiirn,

vibrate and radiate the noise.

A thorough study of_ the cause of machine noise is important because the

sound from major noise sources must be attenuated before reduction of the noise

from secondary sources, such as sixrface vibration, will have any significant

effect. The need for these investigations increases with increasing size and

con^jlexity of the machinery. In short, the larger and more complicated the

machine, the more difficult it is to quiet.

Obviously, the most effective way of manufacturing quiet equipment is to

incorporate good noise control techniques in the basic design stage. This is,

of course, a concern of the equipment designer and manufacturer. But if you,

as a consumer, are familiar with certain principles governing noise in

equipment operation you can know what to look for when making a purchase, or when attempting to control noise from appliances and equipment. Whether one is

concerned about designing quiet equipment or faced with the problem of quieting

an existing noisy device the following recommendations and corrective measures

should be considered and applied wherever possible.

1. REDUCE IMPACT OR IMPULSIVE FORCES

Many machines and items of equipment are designed with parts that strike

forcefully against other parts, producing noise. Often, this striking action,

or impact, is essential to the machine's function. A familiar example is the

typewriter - its keys must strike the ribbon and paper in order to leave an inked letter-impression. But the force of the key also produces noise as the

impact falls on the ribbon, paper and platen.

Other common devices that produce impact noise include qviick-acting

cut-off valves foiond in washing machines and furnace humidifiers. The loud

"th\imp" they often make can be startling, annoying or, in the case of furnace

noise, they can dist\irb sleep.

Several steps can be taken to reduce noise from impact forces. The

particular remedy to be applied will be determined by the nature of the machine

in question. Not all of the steps listed below are practical for every machine

and for every irnpact-produced noise. But application of even one suggested

measure can often reduce the noise appreciably. A knowledge of the principles

underlying inipact-noise reduction can also assist you in purchasing quieter

equipment

.

a) reduce weight, size or height of fall of impacting mass.
b) Cushion the impact by inserting a layer of shock-absorbing material

between the impacting surfaces. (For example, insert several sheets of

paper in the typewriter behind the top sheet to absorb some of the

noise-producing impact of the keys hitting against the platen.) In some situations, you may insert a layer of shock-absorbing material behind each

of the impacting heads or objects to reduce transmission of impact energy

to other parts of the machine.

c) VHienever practical, one of the impact heads or surfaces should be made

of non-metallic material to reduce "resonance or ringing" of the heads.

Fig. 3-1 shows the application of measures a, b, and c.

d) Substitute the application of a small in5)act force over a long time

period for a large force over a short period to achieve the same result.

. e) Smooth out acceleration of moving parts; apply accelerating forces

gradueLlly. Avoid high peak acceleration or Jerky motion.

f) Minimize overshoot, backlash, loose play in cams, followers, gears,

linkages, etc. This can be achieved by reducing the operational speed of

\ the machine, better adjustment, or by using spring-loaded restraints or

guides. Machines that are well made, with parts machined to close

tolerances generally produce a minimum of such impact noise.

2. REDUCE SPEED IN MACHINES, AND FLOW VELOCITIES AND PRESSURES IN FLUID

SYSTEMS

Reducing the speed of rotating and moving parts in machines and mechanical

systems results in smoother operation and lower noise output.

Likewise, reducing pressure and flow velocities in air, gas and liquid

circulation systems lessens turbulence resulting in decreased noise radiation.

(a) For quiet operation, fans, impellers, rotors, turbines, blowers,

etc. , should be operated at the lowest bladetip speeds that will still

meet Job needs.

(b) Use large-diameter low speed fans rather than small-diameter

high-speed units for quiet operation. In short, maximize diameter and

minimize tip speed .

(c) Centrifugal squirrel-cage type fans, sometimes used in furnaces or on exhaust ducts, are less noisy than vane ajcial or propeller type fans, all

other factors being equal, as illustrated in Fig. 3-2.

(d) Water pressure in individual home, office, or apartment plumbing

systems should be limited to 35 pounds per square inch (l800 Torr) and

flow velocities of the order of 6 ft/sec (2 m/sec) for quiet operation. A

competent plumber can perform these adjustments.

3-4
(e) In air ventilation systems, a 50-percent reduction in air flow

velocity may lower the noise output by 10 to 20 dB, or roughly 1/2 to 1/U

of the original loudness. Air flow velocities of 8-10 ft/sec (3 m/sec) as measured at a supply or return grille produce a level of noise acceptable

in most residential or office areas. Reduction of air flow velocity can

best be achieved by installing a greater number of ventilating outlets, or by increasing the cross-sectional area of the outlet grilles.

3. BALANCE ROTATING PARTS

One of the main sources of machinery noise is structural vibration caused

by the rotation of poorly baleinced parts such as fans, fly wheels, pulleys,

cams, shafts, etc. Measures used to correct this condition involve the

addition of counter weights to the rotating unit or the removal of some weight

from the unit as indicated in Fig. 3-3. You are probably most familiar with

noise caused by imbalance in the high-speed spin cycle of washing machines.

The imbalance results from clothes not being distributed evenly in the tub. By

redistributing the clothes, balance is achieved and the noise ceases. This

same principle - balance - can be applied to furnace fans and other common

sources of such noise. On some furnace fans driven by a single belt, an unbalanced load may be applied if the belt can move out of direct alignment

with the motor and fan pulleys; if the load is applied symmetrically through a pair of belts driving pulleys on either side of the fan and the motor shafts,

both shafts will tend to stay centered and the pulleys aligned, resulting in

less noisy operation and reduced wear.

h. REDUCE FRICTIONAL RESISTAKCE

Reducing friction between rotating, sliding or moving parts in mechajiical

systems frequently results in smoother operation and lower machine noise

output. Similarly, reducing flow resistance in air, gas and liquid

distribution systems results in less noise radiation. In most cases, applying

any one or a combination of the following corrective measures should provide a noticeable reduction in noise output.

Reducing Resistance In Mechanical Systems (See Fig. 3-^)

Lubricate : all rotating, moving, sliding, meshing or contacting parts

shoiild be lubricated with appropriate lubricant for quiet operation.

Align : Proper alignment of all rotating, moving or contacting parts

results in less noise output. Maintain good axial and directional

alignment in pulley systems, gear trains, shaft coupling, jxDwer

transmission systems, bearing and axle alignment, etc.

Polish: Highly polished and smooth surfaces between sliding, meshing or contacting parts are required for quiet operation, particularly where

bearings, gears, cams, rails, and guides, are concerned.
Balance : Static and dynamic balancing of rotating parts reduces

frictional resistance and vibration which result in lover noise output.

Avoid eccentricity or out-of-roundness : Eccentricity or off-centering of

rotating parts such as pulleys, gears, rotors, shaft/ bearing alignment

causes vibration and noise. Likewise, out-of-roundness of wheels,

rollers, and gears cause uneven wear resulting in flat spots which

generate vibration and noise.

Reducing Resistance In Air or Fluid Flow Systems (See Fig. 3-5)

The key advice to effective noise control in such systems is

"streajnline the flow" . This holds true regardless of whether one is concerned

with air flow in ducts or vacuum sweepers , or water flow in plumbing systems

.

Streamline flow is simply smooth, nonturbulent , low-friction flow, but it is

the essential requirement for quiet operation of any type of fluid flow system.

The two most important factors which determine whether flow will be

streamline or txarbxilent are flow velocity and the cross-sectional area of the

flow path - that is, the pipe diameter . The rule of thumb for quiet operation

is to use a low-velocity, large-diameter pipe system to meet a specified flow

capacity requirement. However, even such a system can inadvertently generate

noise if certain aerodynamic design features are overlooked or ignored. A

system designed for quiet operation will employ the following features

:

. Low- flow velocities : Low-flow velocities avoid turbulence, one of the

; main causes of noise. Flow velocities should be of the order of 8 to lO

feet per second (3 m/sec) in domestic forced-air heating and ventilation

systems and plumbing systems for quiet operation.

Smooth boundary surfaces : EKict or pipe systems with smooth interior

walls, edges, and Joints, generate less turbulence and noise than systems

with rough or Jagged walls or Joints.

Simple layout : A well-designed duct or pipe system with a minimvun of

•, branches, turns, fittings and connectors is substantiaJ.ly less noisy than

a complicated layout.

Long-radius turns : Changes in flow direction should be made gradually and

smoothly. It has been siiggested that turns should be made with a curve radius equal to about five pipe diameters or major cross sectional

dimension of the duct.

Flared sections : Flaring of intake and exhaust openings, particiilarly in.

• a duct system, tends to reduce flow velocities at these locations, often

'

. with substantial reductions in noise output.

Stream-Tine transition in flow path : Changes in flow path dimensions or cross-sectional areas should be made gradually and smoothly with tapered

3-6
or flared transition sections to avoid turbxilence. A good rule of thiimb

is to keep the cross-sectional area of the flow path as large and as W uniform as possible throiighout the system.

Remove unnecessary obstacles in flow path : The greater the number of

obstacles in the flow path, the more tortuous, turbulent and hence, the

noisier the flow. All other required and functional devices in the path

such as structiiral supports, deflectors, and control dampers, should be

made as small and as streamlined as possible to smooth out the flow

patterns

.

If you are building" or remodelling a home or other building tell the

architect or builder of your concern for achieving a quiet environment, and ask

specifically if these design features have been included.

5. ISOLATE VIBRATING ELEMENTS WITHIN THE MACHINE

In all but the simplest machines, the vibrational energy from a specific

moving part is transmitted through the machine structure forcing other

con^jonent parts and surfaces to vibrate and radiate sound - often with greater

intensity than that generated by the originating source itself. For example, a water pump fastened to a side panel of a washing machine will cause the panel

to vibrate and produce greater noise output as illustrated in Fig. 3-6.

The vibration generated by moving or rotating parts of a machine should be

confined as close as possible to the area containing the source of vibration.

In short, the vibrating unit must be isolated as much as possible from the

structural frame or machine housing. The most effective method of vibration

isolation involves the resilient moiinting of the vibrating component on the

most massive and structurally rigid peirt of the machine. All attachments or connections to the vibrating part in the form of pipes, cond\iits, shaft

couplers, etc., must be made with flexible or resilient connectors or couplers

- otherwise the vibrational isolation afforded by the resilient mounts will be

bypassed or shortcircuited. For example, pipe connections to a pump

resiliently mounted on the structural frame of a machine should be made of

resilient tubing, preferably as close to the pump as possible. Resilient pipe

supports or hangers may also be reqvdred to avoid bypassing of the isolated

system. In addition to these meas\ires it is often good practice in the case of

large machines or appliances such as washing machines, dryers, refrigerators or

air conditioning equipment to set the entire machine on resilient motmts to

prevent vibrational excitation of the supporting floor, and thus avoid

radiation of noise into the area below or adjacent areas. These measures are illustrated in Fig. 3-7-

6. REDUCE RADIATING AREA (See Fig. 3-8)

Generally speaking, the larger the vibrating part or siirface, the greater

the noise output. The rule of thiamb for q\iiet machine design is to minimize

the effective radiating s\irface areas of the parts without impairing their

operation or structviral strength. This can be done by making parts smaller.

3-7
removing excess material, or by cutting openings, slots or perforations in the

parts. For example, replacing a large vibrating sheet metal safety guard on a machine with a guard made of wire mesh or metal webbing might result in a substantial reduction in noise in some cases, because of the drastic reduction

in surface area of the part. (in other cases, parts with perforations, slots or other openings, permit air leakage through or around the part as it moves,

thus eliminating air pressure buildup, the chief cause of flexing emd

pulsation. Such action when there is no air leakage gives a popping sound - as the noise produced when squirting oil from an oil can.

)

.

, 7. APPLY VIBRATION DAMPING MATERIALS (See Fig. 3-9)

Since a vibrating body or surface radiates noise, the application of any

material which reduces or restrains the vibrational motion of that body will

decrease its noise output. Generally speaking, when such materials are applied

to a vibrating body they dissipate the vibrational energy in the form of

frictional heat which is generated by the flexing, bending eind rubbing of the

fibers or particles of the damping material. For example, these materials

could be applied to surfaces of washing machines, dryers, refrigerators, room

air conditioners, etc, to help control noise due to vibration. Of course, you

would probably apply the materials to the inside surface to preserve the

appearance of the appliance. Three basic types of vibration damping materials

axe available:

(a) liquid mastics which are applied with a spray gun and harden into

relatively solid materials, the most common being automobile

"undercoat ing"

(b) pads of rubber, felt, plastic foam, leaded vinyls, adhesive tapes or

,. fibrous blankets which are glued to the vibrating surface;

(c) sheet metal viscoelastic laminates or composites which are bonded to

the vibrating siu^face.

The type of material best suited for a particular vibration problem

depends on a number of factors such as size, mass, vibrational frequency and

operational function of the vibrating structure. However the following

guidelines should be observed in the selection and use of such materials to

maximize vibration damping efficiency:

(a) Damping materials should be applied to those sections of a vibrating

f surface where the most flexing, bending or motion occurs. These usually

are the thinnest sections.

(b) For single layer damping materials, the stiffness and mass of the

material should be comparable to that of the vibrating surface to which it

is applied. This means that single layer damping materials should be

about two or three times as thick as the vibrating surface to which they

are applied.
(c) Sandwich materials made up of metal sheets bonded to mastic

("sheet-metal viscoelastic composites") are much more effective vibration

dampers them single layer materials; the thicknesses of the sheet metal

constraining layer and the viscoelastic layer should each be about

one-third the thickness of the vibrating surface or panel of the appliance

to vhich they are applied.

8. REDUCE NOISE LEAKAGE FROM THE INTERIOR OF THE APPLIANCE

(See Fig. 3-10)

In many cases machine cabinets can be made into rather effective

soundproof enclosures through simple design changes, and the application of

some soiind absorbing treatment. Substantial reductions in noise output may be

achieved by adopting some of the following recommendations, especially if some

of the vibration isolations techniques discussed earlier are also used.

(a) Seal or cover all openings

(i) All unnecessary holes or cracks, particularly at joints, should

be caulked or closed off.

(ii) All electrical or plumbing penetrations of the housing or cabinet should be sealed with rubber gaskets or a suitable

non-setting caulk.

(iii) If practical, all other functional or required openings or ports which radiate noise should be covered with lids or shields

. edged with soft rubber gaskets to affect an airtight seal. For

exeimple, the lid of a top-loading washing machine may be fitted with

a rubber gasket or with rubber strips to prevent the escape of the

noise from the agitator.

(iv) Other openings required for exhaust, cooling or ventilation

purposes should be equipped with mufflers or acoustically lined

ducts.

(v) Relocate or direct openings away from operator and other people.

(b) Apply acoustical materials

(i) Install sound absorbent lining on inner siirfaces of cabinet to

reduce noise buildup in the reverberant cavities. (We will discuss

reverberation further in Section 3 under Factors Affecting the

Travel of Sound)

(ii) Apply vibration damping material to inner surfaces of all

vibrating panels.

3-9
9. CHOOSE QUIETER MACHINERY WHEN REPLACING APPLIANCES

This advice is, of course, of little comfort if you find yourself the

ovner of a new, noisy appliance. In due time, though, it will need to be

replaced, and this is an opportunity for choosing an effectively QUIETED

device. However, some minor changes in accessories can reduce noise problems:

(a) Replace plastic blender containers with containers made of heavy

glass. Often both alternatives are available; glass costs very little

more.

(b) Substitute rubber or plastic cans for noisy metal trash cans. Some

laminated metal trash cajis have been made for industrial use; the new

concern with quiet may make them desirable for ordinary domestic use.

(c) Use wood or fibreboeLrd cabinets instead of the noisier metal iinits.

(d) Select sliding or folding closet doors made of wood or laminate

.instead of metal doors which usually rattle or vibrate when moved.

(e) High velocity air flowing over the corrugated surfaces inside a hose

often generates a whistling noise. Replacing the corrugated hose of a vacuum cleaner with a smooth surface hose will reduce this noise.

(f) Replace small high-speed floor fans or exhaust fans with larger,

slower-moving units.

(g) Substitute a belt-driven furnace blower operated by a shock-mounted

motor for a direct motor-coupled blower.

NOISE CONTROL IN THE TRANSMISSION PATH

After you have tried all possible ways of controlling the noise at the

source, your next line of defense is to set up barriers or other devices in the

transmission path to block or reduce the flow of sound energy before it reaches

your ears. This can be done in several ways:

you can absorb the sound along the path,

you can deflect the sound in some other direction away from you by placing

a reflecting barrier in its path, and

you can contain the sound by placing the source inside a so\and- insulating

box or enclosure.

Selection of the most effective technique will depend upon various factors

such as size and type of source, intensity and pitch of noise, and nature and

type of environment. In addition one shoiild have a basic understanding of the

characteristics and behavior of sound that influence its propagation or travel

through the air.

3-10
As we mentioned before, a sound wave traveling through the air creates a succession of compressions — high-pressure waves — followed by rarefactions,

or low-pressure waves. These waves move away from the source in an alternating

manner much like the spreading of ripples in a pond into which a pebble was

dropped, as Illustrated in Fig. 3-11. The distance between adjacent peaJcs of

the high pressure waves is the wavelength of the sound. The frequency of the

sound "f" and its speed of travel "c" determine "x" the wavelength. These

three quantities are related by the equation c = fX. Since the speed of sound

in air is relatively constant for all frequencies, the wavelength decreases as frequency increases. Sound travels at a speed of about 1130 feet (3^+5 m) per

second. Therefore, the wavelength for a 100 Hz tone would be approximately 11

feet (3.^5 ni) whereas for a 1000 Hz tone it would be about 1.1 feet (3^.5 cm).

As we shall see, both frequency and wavelength affect the propagation of sound

in air and the manner in which it interacts with the environment.

FACTORS AFFECTING TRAVEL OF SOUND

1. Absorption: Soaking Up Sound

We know from experience that air absorbs sound, especially high-pitched

sounds. That is why we hear only the low-pitched roar of exhaust noise of a high-flying Jet plane and not the shrill high-pitched turbine noise we normally

hear at the airport when the plane takes off. The low pitched rumble of

distant thunder sounds almost harmless compared to the sharp terrifying crack

of thunder when heard close by. The high pitched components of a thunderclap

are absorbed by the air before they reach a distant listener.

Air absorbs high-pitched sounds more effectively than low. However, if

the distance between a source and a listener is great enough, low-pitched

sounds also will be absorbed appreciably by the air. For example, we might not

hear any sound at all from a Jet plane flying at an altitude so great that only

its vapour trail is visible.

Unfortunately, in most buildings, the masses of air are inadequate to

provide any useful sound absorption. With the exception of very large

auditoriums, convention halls, or sport arenas, the absorption of sound by air

within typical buildings or rooms is negligible. However, in most buildings

and rooms a significant degree of sound absorption can be achieved through

proper furnishings. Because of their soft porous qualities, such materials as draperies, carpeting, and exposed towelling are excellent sound absorbers.

Upholstered furniture and bed furnishings also have good sound absorbing

characteristics. However, the installation of acoustical tile on ceilings in

rooms, corridors and staircases is a practical method of controlling noise

along its path of travel. Depending on the type of installation, and the

frequency distribution of the noise, acoustical ceilings can absorb from 50 to

Q0% of the sound energy that strikes the surfaces. A soft, thick carpet with

felt padding placed on the floor will absorb about 50 to 60% of airborne sound

energy striking it. In addition, it will muffle impact and footstep noise very

effectively. Pleated drapery will absorb about as much sound energy as carpet

3-11
for the same amoxint of surface coverage. With these materials on ceilings,

^ floors and walls, much of the sound energy is absorbed along the path before it can cause annoyance in other areas.

Unfortunately, like air, drapery and carpeting absorb high-pitched sounds

much more effectively than low. When sound waves strike a fabric, they

penetrate into the pores and air pockets of the material. There they bounce

around haphazardly causing air in the pores and the fibers of the material to

vibrate; this motion dissipates the sound energy in the form of heat because of

frictional resistance between air molecules and fibers.

Because of their long wavelengths, low-pitch sound waves require materials

that are many times thicker and have much larger pores and air pockets than

those used for absorbing high-pitched sounds. For efficient absorption of low

fl'equency sounds, the thickness, openings and pores of the acoustical material

.. should bear the same proportion to the wavelengths of these sounds as the

-thickness, openings and pores of absorbers for high-frequency soiinds bear to

their respective wavelengths. Unfortunately materials for absorbing

low-frequency sounds are somewhat impractical because of their large size and

bulklness

.

Although sound waves generally keep on traveling in the direction in which

they originally started, high-pitched sounds tend to follow a path that appears

to be narrower and somewhat straighter than a low-pitched sound path. We have

noticed how highly directional the sound of a "hiss" or "psst", or a whistling

tea kettle is compared, for example, with the rumbling sound of a washing

machine. This is due to the fact that because of their short wavelengths,

high-pitched sounds are propagated in a beain-like manner with very little

spreading. Low-pitch sounds, on the other hand, tend to spread out uniformly

in all directions from the noise sotirce because of their long wavelengths.

The assumption that sound travels in straight lines is valid for wavelengths that are short compared to the dimensions of open spaces, rooms or passage ways. Sound waves travel in straight lines until they encounter some obstacle in their path. If the obstacle is small compared to the wavelength of

the sound, its direction of travel will hardly be disrupted. On the other

hand, if the obstacle is large compared to the wavelength of sound, the wave

will be deflected in its direction of travel.

2.. Sound Reflection: Bouncing of Sound

When a sotind wave strikes a solid flat surface that is large compared to

the wavelength of sound, the wave is reflected simileir to the way a sunbeam is

reflected from a window pane — or a ball bounces off the walls of a handball

court. As sound waves strike a flat surface, they reboiand at an angle equal to

the one at which they originally struck the surface, as shown in Fig. 3-12.

A listener exposed to both the direct waves and reflected waves from a distant sound source will perceive the direct wave to be much louder than the

reflected wave. At one time or another, you might have noticed that an echo of

3-12
a person's handclap or a yell in a large hall or canyon seemed to be much less

intense than the original sound. This reduction in loudness of the reflected

vave or echo is due to the longer distance it traveled, and also to the loss of

energy due to absorption by both the reflecting surface and perhaps the air.

However, in a reverberant room or space, the reflected and direct sound waves tend to merge to produce a sound that is louder than the direct sound alone.

So\and reflection frequently is not only desirable but can be put to

practical use. When properly used it will enhance the sound of music, or, as in the case of a band shell, it will amplify the music reaching the audience.

You, perhaps, have taken advantage of this phenomenon, if you have mounted

your stereo loudspeakers on a wall or in the corners of a room to get greater

sound intensity for the same setting of the volume control.

3. Reverberation: Re-echoing of Sound

Have you ever noticed upon entering a bare, unfurnished room how much

louder your voice appears to be? This is caused by the repeated reflection of

the sound waves by the surfaces of the room. The merging of these reflected

waves builds up the noise level. This effect, which is called "Reverberation",

is most prominent in rooms with hard reflecting surfaces such as a typical

bathroom with its ceramic tile and plaster surfaces. This phenomenon, more so than any other, gave birth to the so-called BATHROOM BARITONE. Rooms like the

bathroom, which are highly reverberant, woixld be described as being

acoustically "Live". Many basement areas and recreation rooms would fall in

this category. Bedrooms and living rooms, on the other hand, would be

considered as acoustically "Dead" because of the large amounts of sound

absorbent materiaJ.s normally found in these rooms. Obviously, the Bathroom

Baritone rarely performs in such rooms because his powerful voice suddenly

would sound weak or dead. Just like the environment.

Highly reverberant rooms tend to be excessively noisy. The most effective

method of dealing with this problem is to install a large amount of sound

absorbent treatment in the form of carpeting, drapery, upholstered furniture or

an acoustical ceiling. As a rule of thumb, if the soiond of a person's handclap

or a shout in a particular room takes longer than a second or two to die away,

the room is too reverberant, and should be acoustically treated .

Although excessive reverberation of sounds in most instances is a problem

associated with the interior of buildings or rooms, it can occur in the

outdoors as well. The most common example is the reverberant echoing and

rumble of thunder in mountainous areas. The high noise levels caused by the

reverberation of traffic noise between tall buildings in major cities is

familiar to all of us. The court areas of U shaped apartment buildings tend to

be excessively reverberant and noisy, particularly if they are used as recreation areas or if they face traffic arteries. Very little can be done to

remedy problems of natural origin; however, man-made problems can be avoided

through proper planning in the design stage. For example, a U shaped court

yard shoxild not front on a traffic artery.

3-13
^4 , Diffraction: Bending or Squeezing of Sound

When a sound wave encounters an obstacle or an opening which is comparable

in size to its wavelength, the sound will bend around the obstacle or squeeze

through the opening with little loss of energy, as in Figs. 3-13a, 3-13b. This

action is known as "Diffraction". Diffraction occurs when soiind waves strike

the edge of a solid barrier. This edge acts as a focal line from which a new

train of waves is generated. These new waves which spread out into the area behind the barrier are of the same frequency as the original waves but lower in

intensity. This explains why we can hear traffic noise from a busy highway

even though it is hidden from view by a large building or a hill.

With regard to sound passing through small openings, you may have noticed

how readily sound passes through a door that is slightly ajar. With the

conventional practice of installing doors with a 1/2 to 3/U inch (13-19 mn) air

space at the bottom to provide for the circulation of return air, it is not

surprising that we get no privacy even when the door is closed. The anwunt of

sound energy that passes through a small hole or hairline crack in a wall is

far greater than one would predict based on the size of the crack. This points

out how important it is to caulk or seal all cracks or openings in walls,

doors, etc., which separate areas where privacy is desired.

Inside buildings, the combined effects of diffraction and reflection

explain how sounds travel along winding corridors, up staircases and through

duct systems with surprising ease.

In open spaces, sound coming from a point sovirce tends to spread out in a front that is spherical in shape. The power at any point away from the source

drops in proportion as the surface area of a sphere centered at the sovirce

increases. For each doubling of distance, the surface area increases fourfold.

Consequently, for each doubling of the distance from the point at which the source is located, the power drops to one-fo\irth; the power level drops by 6

dB.

By a point source we meein any noise source that radiates noise uniformly

in all directions. Almost any source that is located at a distance from the

observer that is large compared to the size of the source acts like a point

source, even though the source itself may be relatively large. Thus, a power

mower located at a distance of 100 feet (30 m) from the listener, and a large

noisy factory located at a distance of 1/h mile {O.U km) from the listener

could both be considered as point sources so far as the listener is concerned.

Increasing your distance from a source of noise is a practical means of

noise abatement, if you can manage it. If you can quadruple yo\ir distance from

a point source of noise, you will have succeeded in lowering its loudness by at

least one-half or roughly 12 dB. If you have to contend with an extended or a line source such as a railroad train, the noise level drops by only 3 dB for

each doubling of distance from the source. The main reason for this lower rate

of attenuation is that line sources radiate sound waves that are cylindrical in

shape. The surface area of such waves only increases twofold for each doubling

of distance from the source. However, when the distance from the train becomes

3-14
comparable to its length, the noise level will begin to drop at the rate of 6

^ dB for each subsequent doubling of distance. Figures 3-l^a and 3-l^b

illustrate how the noise levels drop as distance increases from both types of

noise sources.

If due consideration is given to controlling the noise at the source, and

fiirther noise reduction is required, then the transmission path between the

noise source and the receiver must be altered or modified in order to reduce

the flow of sound energy reaching the receiver. This can be done in a number

of ways . .

"QUIETING" IN THE PATH

1. Separate the Noise Source and Receiver As Much As Possible

In open air, the noise level drops roughly 6 dB for each doubling of the

distance from the sovirce to the receiver. Indoors, the noise level generally

drops from 3 to 5 dB for each doubling of distance in the near vicinity near

the sotirce. However, further from the source, reductions of only 1 or 2 dB

occTir for each doubling of distance, due to the contributions from the

reflection of sound off hard wall and ceiling surfaces.

2. Use Sound Absorbing Materials

Sound absorbing materials such as acoustic tile, carpets, sind drapes

placed on ceiling, floor or wall surfaces can reduce the noise level in most

rooms by about 5 to 10 dB for higher pitched sounds , but only by 2 or 3 dB for

lower- pitched sounds. Unfortunately, such treatment provides no protection to

an operator of a noisy machine who is in the midst of the direct noise field.

For greatest effectiveness, sound absorbing materials should be installed as close to the noise source as possible. However, because of their light weight

and porous nature, acoustical materials are ineffectual when applied to wall or ceiling surfaces to prevent the transmission of either airborne or structure-borne sound from one room to another. In other words, if you can

hear people walking or talking in the room or apeirtment above, installing

acoustical tile on your ceiling will not reduce the noise transmission. In

most cases, the installation of a soft, thick carpet on the floor above will

reduce the transmission of footstep noise substantially. However, reduction of

both footstep and conversational noise might reqiiire the addition of either a floating floor or a resiliently suspended gypsiun board ceiling to the existing

floor-ceiling construction.

3. Use Soiind Barriers and Deflectors

Placing barriers, screens, or deflectors in the noise path can be an effective way of reducing noise transmission, providing that the barriers are large enough in size, and depending upon whether the noise is high-pitched or low-pitched. Wood or metal panels lined with acoustical materials and placed

in front of or around some noisy machine might attenuate the noise reaching a worker on the other side by about 10 to 15 dB if the noise is high-pitched.

For example, in a room relatively free of echoes, the noise from a card-punch

3-15
machine, which as a fundamental frequency of about 3000 Hz can be reduced in

the shadow of a barrier about 5 feet (1.5 m) on a side by at least 10 dB.

Low-pitched noise, however, might be reduced by only i+ or 5 dB. Fig. 3-15

illustrates the application of measures 1, 2, and 3.

If intruding sound originates out-of-doors, you may be able to quiet the

interior of your house by increasing the degree to which it is sealed off from

. its environment. Windows and doors are common leaks for both sound and heat.

Properly fitted and sealed storm windows and doors will cut down the intrusion

of outdoor sounds as well as reduce heat transfer.

,k. Use Acoustical Lining

Noise transmitted through ducts, pipe chases, electrical channels, or other passages can be reduced effectively by lining the inside surfaces of such

passageways with sound absorbing materials. In typical duct installations,

noise reductions of the order of 2 to 3 dB per linear foot of l" (2.5 cm) thick

acoustical lining are quite possible for high-pitched soiinds. (In metric

units, the reduction is about 10 dB/ra for an acoustical lining 2.5 cm thick.) A

comparable degree of noise reduction for the lower pitched sounds is

considerably more difficult to achieve because it usually requires at least a doubling of the thickness and/or length of acoustical treatment. Various types

:

. of duct lining and silencers are illustrated in Fig. 3-l6.

5. Use Mufflers, Silencers, or Snubbers

Mufflers or silencers should be installed on all gasoline or diesel

engines, regardless of size, including those used in model airplanes, toys,

power tools, etc. Such devices should also be used in all installations in

which large quantities of high-pressure, high-velocity gasses, liquids, steam

or air pass through narrow openings or are discharged into the open air as illustrated in Fig. 3-17.

6, Use Vibration Isolators and Flexible Couplers

In cases where the noise transmission path is structure-borne in

character, vibration isolators in the form of resilient mountings, flexible

couplers, or structural breaks or discontinuities should be interposed between

the noise source and receiver. For exeimple, spring mounts placed under an appliance or machine may prevent the floor from vibrating; or an expeuision

joint cut along the outer edges of a floor in a mechanical equipment room may

reduce the amount of vibration transmitted to the structural freime or walls of

a building. Such measures are illiistrated in Fig. 3-l8.

7. Use Enclosures

Sometimes it is much more practical and economical to enclose a noisy

machine in a separate room or box than to quiet it by altering its design,

operation or component parts. The walls of the enclosure should be reasonably

massive, and airtight to contain the soiand. Absorbent lining on the interior

surfaces of the enclosure will reduce the reverberant buildup of noise within

3-16
it. Structural contact between the noise source and the enclosure must be

avoided, or else the source vibration will be trgmsmitted to the enclosure

walls and thus short circuit the isolation. Figvires 3-19 and 3-20 show

the design and effectiveness of various enclosure configurations. Total

enclos\ires should be used where large noise reductions are required, i.e.,

exceeding 15 dB. Partial enclosures of "L" or "U" shaped configurations may be

adequate in areas requiring smaller noise reductions.

PROTECT THE RECEIVER

When exposure to intense noise fields is required, as when operating chain

saws or other very noisy equipment, measures must be taken to protect the

receiver from hearing dajnage. This can be done by employing some of the

following techniques.

USE EAR PROTECTORS

Molded and pliable earplugs, cup type protectors, and helmets are

conmiercially available as hearing protectors. Such devices may provide noise

reductions ranging from 15 to 35 dB. However, such devices should be used only

as a last resort, after all other methods have failed to lower the noise level

to acceptable limits.

ALTER WORK SCHEDULE

Suppose you have done all that it is possible to do to quiet an appliance

- and still it makes noise! You may be able to choose the times of its

operation to minimize the disturbance of your life and that of your neighbor.

Waiting until later on Saturday and Siinday mornings to operate your lawn mower

and power saw won't reduce their noise levels, but it may reduce the intensity

of objections. Inherently noisy operations, such as street repair, municipal

trash collection, factory operation and aircraft traffic should be curtailed at

night and early morning to avoid disturbing the sleep of the community.

Limit the ajnoiint of continuous exposure to high noise levels. In terms of

hearing protection, it is preferable to schediile an intensely noisy operation

for a short interval of time each day over a period of several days rather than

a continuous 8-hour run for a day or two.

At home there are several intensely noisy chores such as gardening or lemdscaping with power mowers, tillers, and chain saws to name a few. If the

home owner is concerned about protecting his hearing, he should intersperse

periods of quiet activity during such chores to rest his ears. In short, he

sho\ild avoid finishing intensely noisy jobs in continuous or overly prolonged

runs, unless, of course, he is weeuring ear protectors.

In an industrial plant employing a large number of people, such a schedule

would benefit not only the operator of the noisy equipment but also other

workers in the vicinity. Indeed, this practice would be even more beneficial

if the noisy work were performed at night or at some other time when a minimiam

3-17
number of employees would be exposed. This assumes, of course, that noise

created at night would be confined to the plant area and thus not disturb

residential areas.

IS THERE AN ACOUSTICAL PERFUME?

Masking is a very prominent feature of the behavior of our ears. If you

listen to a pure tone against a background of rival sounds, it will seem to

fade as the rival backgrovmd increases. In fact, the sounds of ordinary

surroundings are sufficient to obscure recognition of our heart beats and

breathing, which are quite audible in a very quiet place. For some people, the

awareness of breath sounds is enoiigh to break up the rhythm of breathing, and

this becomes a source of discomfort.

However, sounds are masked only by rival sounds that are quite near them

in pitch. Thus, the songs of birds cannot obscure the snoring of a person

sleeping. Althoiigh lower-pitch masking has a greater effect on high-pitch

sounds, the requirement that the masker must be in the pitch range of the tone

to be masked is dominant, as we can recognize from the fact that orchestral

music is hear as an ensemble. Effective masking requires a broad-band source

of masking sound, if you can't predict the frequency range of the noise, or have to deal with broad-band interference.

In order to make conversational speech less obtrusive, as in a crowded

restaurant, some use has been made of background music as an "acoustical

perfume". Clearly the requirement for broad-band masking imposes the use of*

relatively bland, complex harmony, with limited rsinge of volume. Other usable

sources of acoustical perfume are rippling brooks and splashing fountains.

However, efforts to use acoustic perfume for reduction of noise annoyance

are not likely to succeed if the noise levels rival the levels of

conversational speech. Ir^ order to override these levels, the soxmd background

must begin to Intrude into the higher levels where the ear's behavior is

nonlinear. As a result, sounds would no longer necessarily retain their

harmonious character. Where people working in noisy areas have been allowed to

bring in radios, it will be observed that the listeners prefer strong rhythmic

patterns and solo melodies.

A general characteristic of acoustical perfume is evident: it can be used

to enhance the s\irroundings in an excessively quiet environment. People prefer

some noise as opposed to not enough noise or too much noise. Most people feel

quite comfortable in an environment with a low level, steady, soothing,

unobtrusive sort of background noise, such as can be found along secluded

beaches, forests, or quiet countrysides. However, it is impossible to produce

a peaceful environment in an already noisy place merely by obscuring the sounds

with rival stimuli.

Although the use of masking noise can be beneficial in certain cases, it

has been extended and overemphasized to the point where it fails more

frequently than it succeeds. The concept of "masking noise" in this context

3-18
simply involves using an artificially induced noise or the ambient acoustical

environment beneficially for "masking" or overriding annoying intruding soiands

.

A descriptive definition of masking noise might be any steady sound which has

the following pleasing characteristics:

(a) low intensity with a wide-band frequency distribution, void of any

pLire-tone components;

(b) an omnidirectional source, such that its location is not evident to

the observer;

(c) the ability to over-ride or mask intruding noise without becoming

annoying itself.

Majiy examples of sources of masking noise are given in the literatvire; the most

commonly mentioned being vehicular traffic and heating and air conditioning

equipment. Unfortunately neither is suitable. Traffic noise is seldom steady

and heating or air- conditioning equipment is cyclic. Hence such masking noise

may itself become a source of annoyance. Likewise, using acoustic perfume to

"trade off" or compensate for acoustically inferior party walls in the design

of apartment buildings usually backfires. However, commercial devices which

electronically produce masking noise can be used to improve privacy in

specialized situations. For example, using acoustic perfume in the reception

or waiting room of professional offices of doctors, dentists, or lawyers

provides additional privacy for the patient or client.

However, the presence of masking noise by whatever name interferes to some extent with the ability to discriminate sounds. Thus, the presence of acoustic

perfume in a doctor's office might interfere with his stethoscopic examination

of a patient, for example. Physicians have reported, for example, that it

becomes difficult to interpret the sounds from a stethoscope if the surrounding

so\ind levels exceed U5 dB.

3-19
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3-22
FIG. 3-4 REDUCING FRICTION OF ROTATING AND SLIDING PARTS

3-2 3
3-24
3-25
i-26
J- 2 7
3-2 8
1 install motors, pumps, fans etc on most massivo part of the machine.

2 Install such components on resilient mounts or vibration isolators.

3. Use belt drive or roller drive systems in place of gear trains.

4. Use flexible hoses and wiring instead of rifid piping and stiff wirin|.

5. Apply vibration damping materials to surfaces undergoing most vibration.

6. Install acoustical lining to reduce noise buildup inside machine.

7. Minimize mechanical contact between the cabinet and the machine chassis

8 Seal openings at the base and other parts of the cabinet to prevent noise

leakage.

FI6 3 7 TECHNIOUES TO REDUCE THE GENERATION OF AIR80RNE AND

STRUCTUREBORNE NOISE IN MACNfNES AND APPLIANCES

J-29
VIBRATING

SURFACES

REDUCE SIZE Of PART Oil

CUT OUT EXCESS MATEMIAL

FIG. 3- a REDUCE RADIATING AREA QF VIBRATING PARTS.

3-30
3-31
3-32
3-33
3-34
3-35
3-36
3-37
3-38
3-39
SINGLE « DOUBLE WALL LINED DUCTS

FIG. 3-16 VARIOUS TYPES OF ACOUSTICAL DUCT LINING,

BAFFLES, AND SILENCERS .

3-AO
THIS siltncer

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QUIET FLOW

open air discharge

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FIG 3 17 SILENCER FOR HIGH PRESSURE EXHAUST LINES

3-41
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3-43
3-44
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3-45

Chapter h

NOISE CONTROL AT HOME

The peace and quiet traditionally associated with the home is fast

disappearing. Indeed at times the noise levels within and outside the home or apartment approach those foiuid in industrial plants. As a consequence, the

typical homeowner or apartment dweller finds it rather difficult to isolate

himself from the noise. This unfortxinate situation is due primarily to the

following factors:

(a) Increasing use of noisy appliances in virtually all areas of the home.

(b) The open-space layout of many homes. Wide doorless passage ways

between rooms, waist-high partial walls, and open screen room dividers obviously

permit noise to travel freely to all areas of the home.

(c) The poor sound insulation provided both by the exterior shell of the

dwelling and by the partition walls, floors, and doors within.

(d) The intrusion of neighborhood noise, the level of which unfortunately

is increasing with the growth of automobile and aircraft traffic, and with the

use of outdoor powered equipment and appliances.

Figures ^+-1 and h-2 illustrate some of the more common indoor and outdoor

sources of noise that the typical apartment dweller or homeowner is exposed to

on a daily basis

.

If you expect to be successful at controlling noise in your home, you must

have a basic understanding of how noise travels from one area to another within

the home.

TRANSMISSION OF AIRBORNE AND STRUCTUREBQRNE NOISE:

The control of noise in the home involves reducing the travel or transmission of both airborne noise and structurebome noise , whether generated by

sotirces within or outside the home. By airborne noise we mean noise that is

produced initially by a source which radiates directly into the air. Many of

the noises we encoiinter daily are of airborne origin; for example, the roar of

an overhead Jet plane, the blare of an auto horn, voices of children, or music

from our stereo sets. Airborne sound waves are transmitted sin5)ly as pressTire

fluctuations in the open air, or in buildings along continuoiis air passages such

as corridors, door ways, staircases and duct systems.

The disturbing influences of airborne noise generated within a building

generally are limited to the areas near the noise sources. This is due to the

fact that airborne noises usually are of much smaller power and are more easily

atten\iated than structurebome noise. The sound from yo\ir neighbor's stereo

system may caiise annoyance in rooms of your apartment which are adjacent to his,

but rarely in rooms farther removed Tinless doors or passageways are open.
Structuretorne noise occurs when wall, floor or other building elements are

set into vibratory motion by direct contact with vibrating sources such as mechanical equipment or domestic appliances. This mechanical energy is

transmitted throughout the building structure to other wall and floor assemblies

with large surface areas, which in turn are forced into vibration. These

vibrating svirfaces, which behave somewhat like the soionding board of a piano,

transmit their motion to the surrounding air causing press\ire fluctuations that

are propagated as airborne noise into adjacent areas.

The intensity of structureborne noise generally is much higher than that

produced by a wall or floor structTire when it has been excited into vibration by

an airborne sound wave, because the vibrating source is more efficiently coupled

to a structural member than it is to the surrounding air. Unlike sound

propagated in air, the vibrations are transmitted rapidly with very little

attenuation through the skeletal frame of the building or other structural

paths. These vibrations frequently reach large light-frame structures which

perform rather efficiently as sounding boards, and radiate the noise at high

levels

.

"SOUNDING BOARD" EFFECT

It might be well to consider briefly the so-called "sounding board effect",

- a reinforcement or amplification of sound, which so frequently is involved in

the radiation of structureborne noise. Generally speaking, the efficiency of a soxmd radiator varies directly with the ratio of its surface area to the

wavelength of sound; the larger the area of a radiator the greater its

effectiveness. A sound source with a small radiating surface, such as water

- pipe, produces relatively little airborne sound; but on the other hand, it will

radiate higher pitch sovinds more efficiently than lower pitch sounds, all other

factors being equal. If a small vibrating source, which by itself radiates

little airborne noise, is rigidly or mechanically coupled to a large surface

such as plywood or gypsum wall panel, the intensity or volume of sound will be

substantially reinforced or amplified. A piano provides an illustration of this

effect. If we were to remove the sovinding board of a piano, the sound generated

by the vibrating strings would be almost inaudible, because of their small

radiating surface.

Under certain conditions, airborne noise may produce structureborne noise

which in turn may be radiated again as airborne noise. For example, an airborne

sound wave striking one side of a wall may cause the entire wall to vibrate like

a solid panel. Thus, the sound is transmitted to the other side of the wall

from which it is radiated as airborne sound. However, some of the wall

vibration will be transmitted to the supporting floor, adjacent walls, and

through other structural members to various parts of the building where it

eventually emerges as airborne sound.

There are many noise sources which generate both airborne euid structureborne noise simultaneously. In fact, this type of noise source is very common. Sources usually considered to be strictly airborne noise generators may produce

a substantial amovint of structureborne noise and vibration if they eire fastened

4-2
rigidly to wall and floor structures. For example, a high-pover loudspeaker

'bxiilt into a wall enclosure might cause not only the wall to vibrate "but perhaps

the rafters as well. Every noise source has vibrating elements which radiate

noise. A window air conditioner suspended in mid-air would produce a substantial amount of airborne noise; however, when the unit is moxonted in a conventional manner a combination of both structureborne ajid airborne noise of

greater intensity is produced, due to the induced vibration of the window and

supporting wall. Occasionally, a noise source may produce vibrations so low in

frequency that they can be felt but not heard. In some instances, such a source

may induce a wall or floor structure to resonate at its own natural frequency,

which may be in the audible range. Thus, the low-pitched drone of a passing

airplane may cause a wall or window to resonate at a higher pitch than that

radiated by the plane itself.

Since both airborne and structureborne noise cause pressure fluctuations in

the air which can be perceived by the ear as sound, it is not easy to tell

vrfiether sound has reached you mainly through a structural path or thro\;gh the

air.

Sometimes location of the source of sound requires considerable search.

For example, there was a man, living in an apartment building, who was haunted

by a "ghost" piano. From time to time, it played softly in his living room, but

when he walked up and down the corridor outside his apartment, it was gone.

Eventually, bothered not by its intensity, but by its mysterious origin, he

hired an acoustical engineer to locate the source. The puzzle remained until

the architect's drawings were examined. The sound of the ghostly piano reached

him through a main load-bearing beam, anchored at one end to the exterior wall

of his living room, and at the other end to the outside wall of the apartment on the opposite side of the building. There, a grand piano sat, with two of its

legs positioned over the beam. The vibrations of the piano that were

transmitted via the beam induced a wall in the man's apartment to vibrate and

thus to radiate the sound.

FLANKING NOISE TRANSMISSION

The movement of noise from one completely enclosed room to an adjoining

room separated by a continuous partition wall may be either by direct

transmission through that wall, or by indirect transmission through adjoining

walls, ceilings and floors common to both rooms or through corridors adjacent to

the room. Noise transmission by indirect paths is known as "flanking

transmission." Quite frequently one is faced with a noise transmission problem

that involves a combination of both direct and indirect transmission paths, and

in which noise from the indirect path may be the more serious offender. Such

indirect or flanking transmission commonly occurs with structureborne as well as airborne noise.

The chief flanking tremsmission paths of airborne noise between two

adjacent rooms usually involve common corridors, ventilation grilles, duct

4-3
systems, open ceiling plenums which span both rooms, louvered doors, and close

spacing of windows between rooms. In addition to the flanking paths, there may

. Z**^ be noise leaks, particularly along the ceiling, floor and side wall edges of the

partition wall. Also, noise leaks may occur frequently around pipe and conduit

. penetrations, back-to-back installations of cabinets and electrical outlets in

the partition wall. Imperfect workmanship may result in serious noise leaks,

e.g., poor mortar Joints in masonry core-walls which often are concealed behind

furred walls, panels or built-in cabinets.

As we see in Fig. h-3 airborne noise may travel from one room to another

over any number of different paths, some of which are not only complicated but

often hidden from view.

Flanking transmission paths of structureborne noises, as illustrated in

Fig. h-hy are about as numerous and difficult to trace as those of airborne

noise. Noise and vibration-producing equipment such as fans, compressors,

pumps, ventilation and plumbing systems readily communicate their vibrational

energy to the building structure if no precautionary measures are taken. The

vibration travels quickly over long distances through the skeletal building

structure with no appreciable attenuation, forcing other building elements like

- wall and floor assemblies in other parts of the building to vibrate and to

radiate noise. While noise or vibration transmission problems between adjacent

rooms are relatively simple to resolve, it may be extremely difficult to

determine the reasons for excessively high noise or vibration levels in rooms

far removed from the noise sources. The difficulty arises in tracing the

specific flanking paths and identifying the operating equipment at fault.

However, a good rule to follow is to conduct an inspection of the apartment

w building in order to locate all excessively noisy areas; identify and examine

: . the major noise sources in each area, including their mountings and other

accessory equipment and hardware to which they are connected. Then starting

* with the noisiest source try to reduce as much as possible the airborne noise

radiation and vibrational motion of the source, using the various techniques

discussed throughout this guide. This, of course, presupposes that the building

owner or management will permit such a survey to be done. However, most owners faced with noise complaints can be induced to cooperate, especially if the

chances are good that the installation of some inexpensive treatment or simple

devices would alleviate the noise problem, as for example inserting vibration

isolators under a pump or elevator motor; or perhaps installing pressure

reducing valves in certain locations of the building plumbing system.

GENERAL SOLUTIONS FOR NOISE CONTROL IN THE HOME

General solutions for the control of noise in the home or apartment involve

a three step approach, namely:

(l) Stop or reduce the transmission of airborne sound by installing a wall

or floor structure in its path. Ideally, the structure should reduce

the level of intruding sovind sufficiently to make it inaudible, or at

4-4
least nondisturbing in areas where privacy is desired. The so\ind

insulating effectiveness of a single wall is weight dependent. Based

on the mass law, there is a gain of about 5 dB in sound insulation or transmission loss for each doubling of the weight of the wall.

However, single walls are not very effective where a high degree of

sound insulation is required. For the same overall weight, a double

wall or one using resilient studs or channels can be made to provide a higher degree of sound insiilation than a single wall.

(2) Stop or reduce the transmission of impact or structureborne noise by

installing a structure, whether a wall or a floor, that will cushion

the impact or interrupt the path of vibration. In the case of a concrete floor slab, a thick soft carpet with felt or rubber padding

will be adequate. In addition to the carpeting, a floor of light-frame

construction might require a gypsum board ceiling suspended on resilient channels to achieve the same degree of impact isolation.

(3) Stop or reduce sound reflection which tends to amplify or buildup the

level of noise, particularly in rooms. Ordinary room furnishings like

carpeting, drapery and upholstered furniture are effective sound

absorbers and should, therefore, be used to control excessive

reflection. Sound reflection off hard ceiling surfaces can be

minimized by the installation of an absorptive ceiling.

Application of these three principles is illustrated in Fig.

SOIMD ABSORPTION VS SOUND INSULATION

The reduction and control of noise, whether in machinery, buildings, or rooms, generally involves the use of sound absorbing materials and sound

insulating materials. Contrary to public opinion, these materials have different

properties and are used for different purposes, which can not be interchajiged.

But due to confusion, both materials often are misused.

It may be well to clear up the popular misconception that sound absorbent

materials also are effective as sound insulators, i.e., materials which prevent

the transmission of sound through them. Unfortunately that is not the case.

Acoiastical tile applied to the walls of a noisy room will reduce the noise level

within the room appreciably, but will provide only a trivial reduction in the

amount of noise normally transmitted through the wall to an adjoining room. This

seemingly odd behavior can be explained as follows.

At a speed of about 1130 ft. /sec. (3^5 m/sec), a sound wave might be

reflected 10 or more times from the surfaces of a typical room in Just a fraction

of a second. With each contact with an absorbing surface, the soxind wave loses

some of its energy. Thus, the listener perceives a noticeable reduction in the

noise level within the room. But consider for a moment the very first contact of

the sound wave with the absorbing surface. The wave enters the material, loses

perhaps 2 to 3 dB in sound energy, which is hardly noticeable, strikes the wall

and is transmitted through it.

4-5
Sound absorbing materials like acoustical tile, carpeting and drapery are poor so\ind insulators because of their soft, porous and lightweight

. construction. Consider a wall made of such materials; it is quite obvious that

such a wall would provide virtually no resistance to the passage of sound

through it. A brick wall on the other hand, is a very poor absorber of sound

but, it is an extremely effective sound insulator. Because it is massive, it

resists the passage of sound. Perhaps a better example illustrating the

difference between absorption and insulation is the ordinary blotter. The

blotter is a very good absorber of liquids, but one would never consider using

..blotting paper to form the walls of a swimming pool. When the blotter absorbs

the liquid to its saturation point, the liquid readily passes through it and

leaks away.

WARNING! Because they act as poor barriers to the transmission of sound,

acoustical absorbers should never be used on walls and ceilings for the sole

purpose of preventing the transmission of sound throiagh such structures.

' KITCHEN NOISE

With rare exception, the kitchen is the noisiest room in the home. This is

due in part to its reverberant characteristics, but primarily to the frequent

. and oftentimes simiiltaneous operation of the various types of very noisy

. power-driven appliances ordinarily found in the kitchen. These include garbage

disposers, dishwashers, blenders, mixers, can openers, ice crushers, exhaust

. fans, etc. Although kitchen noise generally subsides before bedtime and thus

rarely causes any problems of interference with sleep, it ranks as one of the

most irritating disturbances during daytime or early evening periods of

relaxation and entertainment. Even though most kitchen appliances are operated

for relatively short periods of time, it is the intensity, random intermittency

and the periodic or cyclic characteristics of the noise that are especially

annoying, as for instance the noise associated with filling, washing, draining

and rinsing cycles of a dishwasher. Kitchen noise like most building noise

. problems can be avoided if good noise control techniques are incorporated early

in the design stage of the home. This cein best be done by adopting the

following design and noise control features.

(1) Choose a floor plan which locates the kitchen as far as possible from

such noise sensitive areas as bedrooms, studies or formal living rooms.

(2) Design the kitchen as a completely enclosed sound insulated room.

(3) Select "quiet" appliances and insist on proper vibration isolated

mounting or installation, and

{h) Install sound absorbing materials on room surfaces to reduce the noise

buildup due to excessive reverberation. Materials such as acoustical

ceiling tile, draperies and curtains, carpets or throw rugs and even racks

of exposed towelling can provide a considerable reduction in kitchen noise

level.

4-6
V/liat can "be done to control the noise from an existing kitchen with typical

appliances and furnishings? A significant reduction of both the level of noise

in the kitchen area and the amount of noise escaping to other areas of the home

can be achieved by adopting the recommendations preferably in the order

illustrated in Fig. and described in greater detail below.

Install Doors

Completely enclose the kitchen area by installing doors in all passageways

.

Doors should be of solid core construction and equipped with soft rubber or plastic gaskets at the top, sides and at the bottom, as illustrated in Fig. h-f

.

Hinged or sliding doors may be used, providing good edge seals are maintained.

Such an installation will confine the noise to the kitchen area.

Control Appliemce Noise

1. Vibration isolate applieince from the floor

Place pads of resilient materials such as sponge rubber, ribbed

neoprene or solid rubber under the legs or corners of large, heavy

appliances like wash machines, dryers, and refrigerators to prevent

the transfer of machine vibration to the supporting floor. Pads

measuring 1/h to 1/2 inch (a^ut 10 mm) in thickness with an area of

about 2 square inches (13 cm ) should provide adequate vibration

isolation for most large appliances. Placing a metal plate on top of

the pad will tend to distribute the load more uniformly, especially if

the appliance is equipped with leveling-screw legs.

2. Isolate appliance from the wall

Under no conditions should any appliance make rigid contact with a wall. A space of at least 2 inches (5 cm) should separate the

appliance from the wall. Flexible plastic or rubber hoses shoxild be

used in the installation of food waste disposers, and of dish or clothes washers to avoid the treinsfer of machine vibration to the

walls containing the pliimbing outlets or fixtures. Otherwise, the

vibrating walls acting like sounding boards would tend to amplify the

machine noise.

3. Isolate Appliance from Cabinet Enclosure

Appliances such as dishwashers, disposers, compactors, etc. which are built into or enclosed by counter-type wall cabinets shoiild preferably

be installed with a perimeter strip type gasket or spacers made of

soft rubber to vibrationally isolate the cabinets from the machine. A

strip gasket 1/h inch (6 mm) thick and 1/2 inch (13 mm) wide attached

to the top and side edges of the cabinet opening into which the

appliance is to be installed would provide adequate isolation.

Small countertop appliances such as blenders, mixers, ice crushers,

can openers, etc. should be placed on small pads or fitted with

button- type feet of soft rubber to prevent the transfer of vibration

to the countertop.

4-7
As a temporary measure, folded towels placed \inder small appliances

can be effective. However, in using these schemes, one must be

careful to avoid blocking any air vents used for cooling purposes that

might be located in the base of the imits . Otherwise, the appliances

might tend to overheat with prolonged use.

A soft rubber sleeve-type gasket inserted between the mounting flajige

of a waste disposer and a sink basin will tend to prevent the sink

from vibrating and thus amplifying the disposer noise, as illustrated

in Fig. U-8.

k. Isolate cabinet enclosure from wall

. Countertop wall cabinets with built-in appliances tend to vibrate

excessively when the devices are used. To prevent the transmission of

the vibration to the back wall, strip gaskets, as described above,

should be inserted between the back of the cabinet and the wall. This

will eliminate the tendency of the wall to act as a soundingboard.

Such gaskets will also reduce impact noise radiation caused by

stocking of cabinet shelves, closing of drawers and cabinet doors.

3. Isolate small appliances

In most cases it is extremely difficult to reduce the noise output of

the small countertop applieinces that you presently own; the devices

usually are built so compactly that it is virtually impossible to

vibration isolate the case or housing from the motor and gear trains, ^ which as a rule are the main sources of noise. The lack of room also

precludes lining the case with sound absorbent material. Sometimes

lining the inside surfaces of an appliance with a metal or lead foilbacked adhesive coated tape will damp the vibration of the case and

^ thus resTilt in some reduction of the noise. Aside from operating the

units at low speeds, about all the owner can do is to vibrationally

isolate the units from the counter tops by placing soft rubber pads

under the base. This scheme at least prevents the counter top from

amplifying the noise as a sounding board and thus results in a noticeable reduction in the overall noise.

Placing rubber mats in sink basins, and on countertops alongside the

cook range, and under dish drying racks or baskets will cushion or absorb the impact noise caused by handling of dishes, pots and pans;

further, such mats will tend to suppress the drtmihead type

amplification of impact noise by the hollow reverberant cabinets.

6. Cushion impact noise in the cabinets

Install soft rubber or cork tile on the shelves and back s\arfaces of

the kitchen cabinets to minimize the impact noise caused by placing

dishware or food supplies in the cabinets. The tiles will cushion or absorb the impacts caused by such chores.

4-8
Placing soft rubber bumpers or small strips of foam rubber on the

inside edges of the cabinet doors will reduce the noise caused by the

closing or slamming of the doors.

7. Apply vibration damping material

Sink basins equipped with a food waste disposer should be iindercoated with a thick layer of a mastic type vibration damping

material or other types of vibration dampers as illustrated in Fig.

3-9 • Such treatment will suppress the vibration of the sink and

resulting noise caused by operation of the disposer.

Damping treatment applied to the interior surfaces of the metal

cabinets and tiomblers of larger appliances, especially washing

machines and dryers, would result in a noticeable reduction of

noise due to cabinet vibration.

8. Install acoustical lining

Installing acoustical tile on the interior walls of the sink

cabinet will minimize the noise buildup in the hollow reverberant

enclosure. If space permits, this treatment should be applied to

the cabinet that encloses the dishwasher or any other appliance.

9. Install exhaust fans on rubber mounts

Most ceiling exhaust systems use high speed, noisy propeller fans

that are moimted rigidly to the ducts, which in turn axe connected

to the ceiling by means of the fsji grilles. These structural paths

carry the fan vibration to the ceiling, which acts like a large

soiaiding board and eunplifies the noise. You can reduce the noise

level noticeably by following this three-step procedure: If

possible, remount the fan on rubber grommets or spacers to isolate

it from the duct, as shown in Fig. U-9. In addition, try to break

contact between the duct and the ceiling by inserting a soft sponge

rubber gasket or spacers between the grille and the ceiling.

Operate the fan at its lowest speed.

In the case of a hood type fan installed directly above the stove,

it is unfortunately much more difficult to reduce the noise output

because of the severe space limitations. In most situations, the

only measures you can use to lower the noise are to operate the fan

at its slowest speed, and to keep the oil and grease from

accumulating on the fan blades and clogging up the pores of the

filter pack. If it is at all possible to do so, install the fan on rubber mounts; this will reduce the noise due to hood vibration.

When replacement of a ceiling or hood exhaust fan is due, remember

that squirrel-cage type fans are less noisy than propeller blade

units

.

4-9
The ideal solution to avoid exhaust fern noise is to install a squirrel- cage fan on rubber mounts at the discharge end of the duct

instead of at the intake end in the kitchen ceiling. These measures combined with some acoustical lining near the fan and a flexible link

between the duct and the ceiling would result in a relatively

noiseless operation. These measiores should be used in the

installation of bathroom exhaust fans as well.

10. Install acoustic ceiling

The installation of an acoustic ceiling in the kitchen area will

absorb a noticeable amount of noise. For ease of cleaning and

maintenance, vinyl or membrane faced tile are available. Draperies,

~' curtains and racks of exposed toweling also are good sound absorbers,

particularly at high frequencies.

11. Install carpet or foam-backed tile

Installation of foeun-backed tile or an indoor/out door type carpeting,

which is stain resistant, is an effective way of reducing impact noise

caused by footsteps and dropped objects.

12. Quieting of large appliances

-

: The application of basic noise-control principles in the early design

stages of large appliances woiild eliminate much of the noise and dis-

. • t\irbance such devices cause. This, of course, is a corporate W responsibility which manufacturers may choose to neglect or ignore as long as it does not interfere with market sales. The consumer,

unfortTinately , has neither the technical backgro\ind nor the equipment

•

. or supplies to effect any substantial reductions in noise output. The

only noise control measures he can employ are:

(a) install ribbed neoprene or soft rubber pads under the units.

(b) adjust screw-leveling legs to prevent units from wobbling.

(c) tighten all loose parts and panels to prevent them from rattling.

(d) install soft foam rubber gaskets along the perimeter edges of

, doors, of washing machines, dryers, and dishwashers to prevent noise

from inside the machines.

(e) with such units in operation, run your fingers lightly over the

surfaces of the machines to find areas of greatest vibration. At

these points install vibration damping materisLls on the inside

surfaces. This will tend to supress the vibration and reduce the

noise output.

(f) apply glass fiber board on the interior surfaces of the cabinets

to reduce the noise buildup in these reverberant enclosures.

4-10
(g) the more technically competent person might try moimting motors

and pumps on resilient isolators and inserting rubber sleeves around

pipes and conduits at points of support or contact with large cabinet

surfaces

.

Incorporation of the above acoustical measures will make a substantial

reduction of the noise in the kitchen area.

RECREATION OR PLAY ROOMS

Other rooms of the home can be as noisy as the kitchen. These rooms are the

family or recreation rooms, where members of the family, especially children, are permitted to watch television programs, listen to their stereo sets, play games

or practice their music lessons. Such rooms tend to be somewhat reverberant and

noisy because the wall and floor surfaces and furniture generally found in these

rooms are made of hard materials designed to be stain resistant and unbreakable.

Installing acoustic tile on the ceiling, drapery on the walls, and perhaps

placing a few pieces of shag carpeting on the floor will reduce the noise

biiildup, and the resultant distraction and annoyance.

Popular games like darts, table tennis, and billiards commonly fo\ind in

recreation rooms can be made less disturbing, without detracting from the fun, by

placing a rubber pad behind the dart board, undercoating the tennis table with a vibration damping compound, and by placing rubber pads at the bottom of the

billiard pockets and lining the ball ret\irn chutes with rubber or cork tile.

Such treatment will cushion the impacts and muffle the resultant noise and

distraction.

The use of earphones or headsets by family members listening to TV or stereo

will reduce the noise level appreciably in the recreation room.

However, while such meas\ires will reduce noise levels in the recreation

room, they do little to keep the noise from spreading to other areas of the home

where privacy may be desired even during daylight hours. The most effective

measure to decrease the leakage of noise from the room is to seal it off with

sound insiilating doors, as was recommended in the case of the kitchen area.

Basement Recreation Rooms

In one story homes, special attention must be paid to prevent the

transmission of so-und from recreation rooms located in basements to noise

sensitive areas on the floor above. In many cases, recreation rooms are located

directly below bedroom and study areas where privacy is most desired. The

installation of a so\jnd insulating ceiling assembly will alleviate such problems.

A ceiling assembly which will provide adequate sound insulation \inder most

circumstances would consist of the following construction as illustrated in Fig.

k-10.

(a) if the floor Joists are exposed, install a 3 inch (T-6 cm) thick layer

of glass fiber insulation between the joists.

4-11
(b) attach metal resilient channels to the iinder edges of the joists. The

channels should be installed so that they are perpendicular to the

Joists and spaced 2 feet (60 cm) apart.

(c) Attach a 5/8-inch (l6 mm) thick layer of gypsum boeird to the resilient

channels with self-tapping screws.

(d) Provide a l/^t-inch (6 mm) clearance around the perimeter edge of the

ceiling to. avoid contact with the walls, and fill the space with a resilient non-setting caulk.

(e) To reduce excessive reverberation in the recreation room, cement

acoustic tile to the gypsiamboard surface. As mentioned previously,

the application of the acoustic tile will not improve the sound

insiilation of the new ceiling construction, but will only reduce the

, ,, ... noise level in the recreation room.

Install a sound insulating door with proper gaskets at the entrance to the

staircase leading to the basement recreation room. This measure will confine the

noise to the recreation room area.

Install carpeting on the stairs to absorb both airborne noise and the impact

noise of footsteps.

CORRIDORS, HALLS, STAIRCASES

In most apartments and homes, corridors or halls separate the noisy kitchen

and family areas from the bedroom and study areas where a relatively high degree

of privacy and quiet is desired. The most effective way of preserving this

privacy is to install a solid core door at the entrance of the hall leading to

the bedroom area. Such doors, when installed with proper gaskets, become very

effective barriers against the noise escaping from the kitchen or family room

areas of the home. In addition, installing a soft thick carpet in the hall and

staircase will muffle the inipact noise of foot steps and reduce reverberation

thus leading to a quiet environment.

IMPROVING THE PRIVACY OF YOUR BEDROOM, STUDY AND BATH AREAS

Although interference with a person's sleep is least to be tolerated,

especially at night, there are times when one desires quiet and privacy d\iring

the day. Areas requiring such privacy are the bedroom, study, and bathroom

areas. Unfortunately, in most homes and apartments the lack of privacy in these

areas is obvious. This arises from the use of the following building

constructions and practices:

(a) thin, veneer, hollow-core doors,

, 1 (b) open air spaces under doors that provide for the circulation of return

air, and

(c) the poor sound insulation provided by light interior walls throughout

the home, particularly in bedroom areas. 4-12
The most common practice of installing a forced-air ventilation system in some central closet location in most homes and apartments is largely responsible

for the lack of privacy in many areas of the home. Such a system relies upon

using a central hall or corridor as the main air return duct. All other rooms bordering on this hall vent the return air through open air spaces under the

doors

.

The obvious solution to this problem is to:

(a) install solid core doors with perimeter gaskets and a drop closure,

(b) if possible, install separate return air ducts in each rooms. Sometimes this can be done in one-story houses, if the floor Joists and

ductwork are exposed in the area below. If this is not possible, install

acoustically lined air transfer grilles or ducts, which are commercially

available, as illustrated in Fig. i+-ll.

During construction of the house, similar return air ducts could have been

built between the studding of the bedroom walls, by simply lining the inside

surfaces of the wallboard with acoustical duct liner and providing an outlet

grille at the top of the duct on the hall side of the wall, and an intake

grille at the bottom of the duct on the bedroom side of the wall.

The sound insulation of the existing wall may be improved by eliminating

sound leaks or by adding another layer of wallboard.

If a higher degree of sound insulation is required, laminate a 1/2" (13 imn)

thick layer of gypsum wallboard to the existing wall with a resilent non-setting

adhesive as illustrated in Fig. U-12. Provide a l/i+" (6 mm) air space along the

perimeter edges of the wall and fill the space with a non-setting caulk compound.

If one is disturbed by conversation, TV noise, etc., coming through the

walls in bedroom areas, he should also look for noise leaks at the base of the

walls and at electrical outlets.

II-IPROVING THE SOUND INSULATION OF WALLS

Many walls, especially party walls separating appartment units, are particularly vxilnerable to noise leakage. The installation of back-to-back

electrical outlets, medicine cabinets, and master TV outlets are common causes of

noise leakage. Openings around pipe penetrations and duct work are also causes

of noise leakage. Cracks at the ceiling and floor edges of walls caused either

by settlement or poor construction allow the transmission of noise from one space

to another.

4-13
The sound insulation of many such walls cbji be improved simply by

eliminating the noise leaks and flanking paths.

(a) Sealing holes and cracks:

All holes or openings around plumbing fixtures, piping and drain pipes

should be enlargened slightly to provide a clearance aroiind the pipe.

The opening should then be filled with a fiber glass packing and

sealed completely with a resilient caxilk. This same treatment should

be used in openings around ducts and grilles.

Settlement cracks at the ceiling edge of a wall should be sealed with

a resilient caulk, preferably applied under pressure with a caulking

gun. Cracks at the floor edge of the wall should be handled in the

same manner, although it might require removing the toe molding and

base boards to do a thorou^^h Job.

(b) Sealing leaks behind back-to-back outlets and cabinets:

If you hear your neighbor's noise coming through an electrical outlet,

remove the cover plate and examine the opening. If necessary, remove

i your outlet box, pack glass fiber wadding around the remaining outlet,

and insert a l/l6-inch (l mm) thick sheet of lead to form an airtight

barrier walls. Reinstall your outlet box, fill the remaining voids

h with the glass fiber and put the cover plate back on.

If the party wall is of wood stud construction, you may be able to

rewire and install your outlet in the adjoining stud space. Fill the

voids around both outlets with the glass fiber wadding and seal the

former opening with a piece of wallboard.

Noise transmission through recessed medicine cabinets can be handled

in a similar manner. However, if space permits, you may be able to

insert a gypsum board or a sheet of plywood as a barrier between the

two cabinets. In this case you should caulk the perimeter edges of

the intervening barrier before installing your cabinet.

(c) Eliminating flanking paths:

The chief flanking paths in homes and in apartment buildings are open

ceiling plenvims, attic spaces, basement areas and crawl spaces which

span freely across dwelling units or adjacent rooms. Such areas should be completely subdivided with f\ill height partitions or barriers installed directly above and below the party walls separating

the dwelling units or rooms in question.

Measures for control of noise leaks and flanking paths described in items

(a), (b), and (c) are illustrated in Figures h-13 and U-lU.

If the above recommendations fail to improve the sound ins\ilation of the

party wall, then modifications to the existing wall must be made. For moderate

4-14
annoyance, the attachment of an additional layer of gypsum hoard to the existing

wall, as illustrated in Fig. U-12, would be adequate. A much higher degree of

privacy would require the attachment of a wall of special design to the existing

wall. The new wall, as shown in Fig. U-15, would be constructed as follows:

(a) fasten wood furring members, spaced l6" (Uo cm) on centers vertically,

to the existing wall.

(b) nail resilient metal channels perpendicularly to the furring members;

channels should be spaced 2U" (60 cm) apart.

(c) fill the space between the existing wall and the channels with a glass

fiber blanket.

(d) attach 1/2" (13 mm) thick gypsum wallboard to the metal channels with

self-tapping screws.

(e) provide a 1/U" (6 mm) clearance around the perimeter edge of the wallboard to avoid restraining contact with adjoining siirfaces of the

room; fill the clearance gap with a resilient non-setting caulk.

IMPROVING THE SOUND INSULATION OF FLOOR-CEILING CONSTRUCTIONS

A floor-ceiling construction separating two rooms or apartment units will

provide adequate sound insulation or privacy, if it can reduce the intrusion of

conversational or TV noise and footstep or impact noise to non-disturbing levels.

If you are disturbed by the transmission of only footstep or impact noise

from the room above, the installation of a soft thick carpet, preferably on a felt or foam rubber pad on the floor above will eliminate the problem in most

cases.

If both footstep and conversational or TV noise from the room above annoy

you, modifications to the existing ceiling must be made to remedy the problem. A

gypsum board ceiling supported on resilient channels should be attached to the

existing ceiling. This second ceiling, which is illustrated in Fig. k~l6 wotild

be constructed as follows:

(a) attach wood furring members, spaced l6" {hO cm) on centers to the

existing ceiling.

(b) nail resilient metal channels perpendicularly to the furring members;

channels should be spaced 2)4" (60 cm) apart.

(c) fill space between the existing ceiling and the channels with a glass . fiber blanket.

4-15
(d) gypsum wallboard, 1/2" (13 mm) thick should be fastened with

self-tapping screws to the resilient channels.

(e) provide a l/ii" (6 mm) clearance around the perimeter edge of the wallboard ceiling to avoid contact with the walls, and fill the gap with a

! vT' resilient, non-setting caulk.

This ceiling assembly should not only eliminate the airborne noise transmission,

but shovild meike a substantial reduction in the footstep noise level. However, if

additional reduction in footstep noise is desired, then a carpet and pad placed

on the floor above will solve the problem.

CONTROL OF FLOOR SQUEAKING (See Fig. U-l?)

Squeaking floors cause considerable irritation because they generally

produce high-pitched noises to which the average person's hearing is highly

sensitive. Althoiogh the squeaking floor problem is more commonly found in homes

of wood frame construction, it occurs quite often in apartment buildings with

concrete floors surfaced with wood block or strip flooring.

Causes of Floor Squeaking:

In general, floor squeaks are caused by the rubbing or sliding of sections

of finished flooring over the subfloor. Movement between adjoining wood blocks,

strips or sections of both sub-flooring and finish floor also cause squeaJcing.

This problem usually is the result of faulty workmanship, the use of defective

materials or poor structural design, such as:

(a) poor nailing : The most frequent cause of floor squeaking is the

failure to nail the sub and finish flooring materials tightly and

securely together and to the supporting Joists or structural floor.

This failure results from the use of undersize or improper nails,

V..I excessively wide spacing of the nails and faulty nailing practices in

general.

(b) defective materials : Another cause of floor squeaking is the use of

warped or twisted floor Joists, buckled or bowed subflooring sheathing

or wood block or strip flooring with defective tongues and grooves.

• When layers of such materials are fastened together, air-pockets or

gaps form between them resulting in poor support. This allows the

~ materials to rock, move or deflect under foot which caused the

squeaJcing. Excessive moisture or humidity: The installation of dry

flooring in damp areas often resvilts in squeaking floors because the

absorption of moisture by the flooring causes it to swell or buckle.

(c) poor structural design : Although a floor Joist system may be

adequately designed in terms of structural and load requirements, it

may deflect sufficiently under foot traffic to permit movement of the

surface flooring; this generally occixrs when either the depth of the

4-16
Joist is too shallow or the spacing between Joists is too wide for a given floor span.

For reasons of economy, the practice of inserting a layer of building

paper between the finish and sub-flooring surfaces to avoid sliding or rubbing contact has been largely discontinued.

Methods of Avoiding Floor Squeaking:

If you plan to build your own home, remember that the best way to eliminate

the problem involves

(a) using straight, true, properly seasoned flooring materials and joists,

(b) bxiilding a rigid well-constructed and properly supported floor system,

(c) controlling proper moist\ire content of flooring prior to installation,

(d) inserting building paper or felt between finish and subfloor layers to

eliminate rubbing or sliding contact,

(e) employing good nailing techniques.

Ways to Remedy Existing Problems:

If you have floors that squeaic, the following recommendations should help

you correct the problem.

(a) With someone walking over that section of the floor that squeaks,

closely examine the finish floor to see if it moves excessively.

The light beam from a flashlight placed on the floor will tend to show

floor deflection or motion more vividly.

(b) If your finish floor consists of wood block or strip flooring, and you

detect no movement, lubricate the tongues of wood blocks or strips

with mineral oil applied sparingly at the seams between adjacent

boards

(c) Loose or bowed finish flooring may be securely fastened to subflooring

by siirface nailing with ring type or serrated nails into the subfloor

and preferably the Joists. Recess the nail heads and fill the hole

with a wood sealer that matches the floor color. If the nails tend to

split the flooring, predrilling a very fine hole through the finish

floor before nailing will eliminate the problem.

(d) If the floor Joists are exposed, and the finish flooring is warped,

you can drill clearance holes through the subfloor and drive wood

screws through the holes into the finish floor. The screws will draw

the two layers of flooring tightly together.

4-17
(e) In places where the joists are warped or bowed, gaps will occur

between the subflooring and the joists. Inserting wedges or shimming

material tightly in the gap usually will remedy the problem. If the

gap is very long, a 2" x U" brace pressed up against the subfloor and

nailed securely to the warped Joist will provide adequate support.

, (f) Excessive deflection of the structiiral floor due to lightweight or widely spaced joists may be corrected by the insertion of a few extra

joists, if the under surface of the floor is exposed. However, if

there is a finished ceiling below the floor, cross- beajiiing with

support columns may be the most expedient corrective measure.

CONTROL OF STAIR SQUEAKING (See Fig. h-lQ)

Stair squeaking may be caused by:

(a) loose or warped treads (the flat horizontal steps), or

(b) the binding and rubbing of the treads against the top or bottom edges

of the risers (the upright or vertical boards).

Remedies:

(a) If the treads are loose, they should be nailed secvirely to the center

and side stringer (the saw tooth side frame that supports the

staircase).

(b) If the treads are warped, inserting wedges between the tread and

stringer usually will eliminate the rocking motion of the tread when

^ it is stepped on. Drilling clearance holes throiigh the treads, where

• ,' they are supported by the stringer, and driving long wood screws through the holes into the stringers will pull a warped tread down

tightly onto the stringer.

(c) Lubricating the top and bottom of the risers edges with mineral oil or

spray silicone often will remedy the squeaking problem.

(d) Sometimes nailing the front edge of the tread to the riser or inserting thin wedges at the bottom of the risers will correct the

squeaking problem.

(e) If the backside of the stairs is accessible, the back edges of the

treads may be nailed to the risers. Additional bracing also may be

added by fitting a 2" x U" brace between the stringers, pressing it up

against the bottom edge of a riser ajid nailing it securely to the

stringers.

CONTROL OF HEATING, VENTILATING AND AIR-CONDITIONING SYSTEM NOISE:

(See Figures h-19 and U-20)

The noise problem associated with heating, ventilating and airconditioning systems is due primarily to the current trend of installing, in

4-18
homes and apartments, small compact units driven by noisy high-speed,

motor-coupled blowers. The blowers usually are coupled to short unlined supply

ducts, and open corridors serving as centralized air return ducts, which

aggravate the problem.

The problem reaches serious proportions when, for economic reasons, such

units are installed in a closet centrally located in a house or an apartment.

The typical closet provides virtually no soiind attenuation. Because of its

light-frame construction, louvered door, and large return air grille, the noise

radiates with undiminished intensity throughout the home or apartment.

Homeowners and tenants alike often complain that their sleep is seriously

disturbed throughout the night because of the noisy equipment. The noise also

is a constant source of irritation and annoyance to them even during their

leisure hours. However, they have no choice but to tolerate the noise or else

suffer the discomfort of a poorly heated or air-conditioned dwelling, if they

turn off the equipment.

Causes of the Noise

(a) Motor and Blower: In a typical installation, the high-speed motor and

blower, which generally are coupled together, are the main soiirces of

noise. The mechanical noises of bearings, brushes and switches and

the siren-like "blade-frequency" noise of the blower is transmitted

both by air through the duct passages and by vibration of the ductwork

to supporting wall and floor structures. The "blade frequency" noise

^ of the blower may be determined by multiplying its number of

revolutions per minute, by the number of blower blades and dividing

the product by 60.

(b) Noise Resulting from Air Flow and T\irb\ilence : Ventilation systems

using high-speed blowers are characterized by high air- flow

velocities. High velocity air flowing past obstacles in the duct air

stream (sharp corners, ragged Joints, dampers and grilles) generate a considerable amount of turbulence. The highly turbulent air flow,

which usually occurs at the discharge port of the blower, is the

predominent cause of duct vibration in most ventilation systems.

(c) Rigid Mounting of the Equipment: In most installations, the heating

and air-conditioning equipment is mounted directly on the floor with

all ducts coupled directly to wall and floor structures. As a consequence, the wall and floor structures are set into vibration and

radiate the noise with increased intensity throughout the dwelling.

(d) Central Air Return Duct: The installation of the central return duct

of a typical home size unit has two serious short-comings. The return

duct usually is coupled to the blower by a short- length, unlined duct

with a relatively large cross-sectional area. As a result, the grille

end of the duct radiates the noise from the motor-blower and air

turbulence with undiminished intensity. Since there often are no air

return ducts in individual rooms , entrance doors are undercut

4-19
approximately one inch at the bottom to provide passage of the air and

thus complete the circulation system. Unfortunately, the large air

gaps under the doors are extremely efficient flanking noise paths

which allow the noise to intrude into bedroom or other rooms where

privacy is most desired.

If you are planning to build a home, insist that the builder selects quiet

equipment and installs it properly for quiet operation. Equipment should be

selected on the basis of low noise output. The more progressive manufactiirers

provide soiind power ratings of most types and sizes of equipment they market.

Such ratings, which frequently contain soxind power levels in various frequency

bands under different load conditions, eire useful for acoustical design

purposes. A few salient points worth remembering are:

(1) It is less expensive to install quiet equipment than to reduce the

noise output of a cheaper unit by costly acoustical treatment or construction.

(2) Centrifugal or squirrel-cage fans are less noisy than vaneaxial

propeller fans, all other factors being equal.

•; (3) For a given air flow capacity, large-diameter, slow-speed, beltdriven blowers are substantially less noisy than small-diameter,

high-speed motor-coupled blowers.

(h) Basement or slab-on-grade locations, far removed from living quarters,

are preferred for the typical heating and cooling equipment

installations. Attic locations should be avoided.

(5) For purposes of noise control, it is more advantageous to install

equipment with output capacities which are greater than required,

' instead of installing smaller units which must labor continuously at

maximum speed in order to meet the building's minimal heating or

' * cooling requirements.

Although the above advice may be useful to the potential homebuilder, it

unfortunately offers no comfort to the family who has a noisy heating and

air-conditioning system in their home or apartment.

If you have a noisy heating and ventilation system, check the following

listing of possible noise sources; adopting some of the recommended remedies may

reduce the noise output significantly.

Remedies :

Motor and Blower:

(a) lubricate or oil bearings,

(b) clean blower blades.

4-20
(c) if blower is belt driven, replace worn or frayed belts, adjust

tension on belt to prevent belt resonance "druimning" and check

pulley alignment

,

(d) mount motor and blower on resilient isolators, if possible,

(e) reduce the rotational speed of the blower, a 23% reduction may

decrease the total noise output as much as 8 dB. However,

consult with a professional heating and air-conditioning

engineer for proper advice and instructions, especially if

rewiring _of motor connections is required.

(f) install acoustical duct liner on the interior surfaces of the

motor-blower enclosure.

Mounting of Equipment:

(a) Place vibration isolators under both the motor blower and the

heating and air-conditioning equipment. Sufficient isolation

may be obtained by mounting all the equipment on a 5/8" (l6

mm) thick plywood base resting on a 5/8" (l6 mm) thick pad of

glass fiber.

A 2-1/2" (6 cm) square, 5/8" (l6 mm) thick pad of ribbed

rubber or neoprene covered with a hardboard or metal plate

placed under each corner of the equipment would also provide

adequate isolation.

(b) Insert flexible canvas or plastic connectors at the blower end

of both the supply and return ducts.

The above measures should reduce the noise output significantly.

Central Return Air Duct:

(a) All interior surfaces of the return air duct should be treated

with acoustical duct lining, or

(b) the duct should be fitted with a suitable prefabricated

silencer.

Central Closet Installation:

(a) Replace the louvered door with a solid core door equipped with

a perimeter rubber gasket and a threshold drop closure.

Caution: The door louvers provided the ventilation of the

closet for proper heating and combustion. It is necessary

that the ventilation be maintained by other means. See next

item.

(b) If the wall studs are exposed, build or install an acoustically lined air transfer grille, as illustrated in Fig.U-ll.

to preserve the required ventilation and noise isolation.

4-21
(c) Nail resilient channels horizontally to the studding, spaced

2U" (60 cm) apart; fill space between the channels and the

"backwall with glass fiber blanket; attach 1/2" (13 mm) thick

gypsum wallboard to the channels with self tapping screws.

(d) Install a ceiling of construction similar to item (c) in the

closet.

(e) Apply acoustical tile to both ceiling and wall surfaces in the

closet to reduce noise buildup.

The above measures, most of which are illustrated in Figs. U-20, 21 and

22, should improve the sound insulation of the closet walls substantially.

CONTROL OF DUCT NOISE: (see Figures k-21 and I*-22)

Because metal ducts are extremely efficient transmission paths of airborne

• noise and vibration, considerable attention must be given to the proper design,

construction and installation of duct networks.

Equipment Noise

Airborne noises such as motor hum, blower-blade noise, bearing or piilley

noise furnace ignition, flame noise, the creaking and snapping noise due to the

expansion and contraction of metal parts are easily transmitted throiogh the

ducts.

If any of these noises are a source of annoyance, you can reduce the level

of noise output substantially by installing sound absorbing lining material or

a prefabricated silencer in the ductwork. Such treatment is most effective

when it is installed in both supply and return branch ducts serving the

individual rooms, and preferably at the open or grille end of the duct. The

installation of a ten-foot length of duct liner, as measured from the grille or diffuser, may reduce the loudness of the noise as much as 50% or 10 dB.

Cross Talk

Metal ducts carry noise like speaking tubes on a ship. Thus noise from

one room may be carried to another room through an unlined duct serving both

rooms. For example, this problem of "Cross Talk" frequently occurs in a common return duct serving back-to-back bathroom installations, or in common ducts in

which the grille openings serving separate rooms or apartment units are too

closely spaced. Such problems also arise in exposed, thin-wall main ducts

which span across adjacent apartment iinits, even though such ducts might not

have any grille openings. Household noises may penetrate the thin walls of the

ducts in one apartment, travel through the short duct passage through the party

wall and emerge through the thin-wall duct of the adjoining apartment. Noise

transmission from one room to another may also occur by way of openings and

holes around poorly sealed duct penetrations throiigh wall and floor structTores

.

4-22
Such noise transmission paths short-circuit the sound insulating effectiveness of the intervening party walls and floor structures

.

If you are distxirbed by noises from an adjoining room or apartment that seem

to be coming through a ventilation grille or the walls of the duct in your room,

try one or more of the following remedies to alleviate the problem.

(a) Line the intervening duct run with acoustical material or install a sound silencer, preferably at the wall junction.

(b) Remove existing grille, seal opening, and reinstall grille in the duct

at a location as far as possible from the party wall.

(c) Seal all openings where ducts penetrate through the wall.

(d) If the noise is coming through the duct wall enclose the duct in a box

made of gypsum wallboard.

Duct Noises

The creaking and snapping noises caused by the expansion and contraction of

ductwork due to temperature variation often are a source of disturbance.

Likewise the booming noise caused by the ballooning and collapsing of

thin-wall ductwork as the "blower" cycles on and off may be loud enough to

interfere with a person's sleep.

If you are troubled by noisy ducts, the following measures may be useful in

reducing or controlling the noise:

(a) Support ducts on resilient mounts or hangers to prevent wall and floor

structure from amplifying the noise. The resilient mounting will

permit the ducts to expeind and contract without binding against some wall or floor construction.

(b) Wrap the ductwork with two or three layers of building paper which will

act as a vibration dajnper . The paper may be taped in place or held

with wire ties. This treatment will tend to suppress any vibration set

up in the duct walls and restrain the "ballooning" action of the duct

by adding some much needed mass and bracing to the flimsy duct work.

(c) Install 3/^" (19 mm) thick glass-fiber-board sound absorbing lining on the inside surfaces of the ducts where "ballooning" occurs. The

glass-fiber board, which is rigid enough to support the duct walls, and

to act as a vibration damper, will also absorb some of the noises

generated within the duct system.

(d) Using sheet-metal screws, install braces made of metal bars or folded

strips of sheet metal across the largest or widest sections of ductwork

or at places wherever "ballooning" occvirs . The braces will provide

adequate support of the duct walls and thus prevent this type of

motion.

4-23
Air Flov Noise

High velocity air flow generates noise not only within the ducts but at

the face of the outlet grille or diffuser as well. The intensity of flow noise

: is strongly velocity dependent. For a given duct area, decreasing the flow

velocity 30% may decrease the output noise level as much as 15 to 2h dB.

Air flow velocities of about 15 feet (U.5 m) per second are quite

acceptable for most homes and apartments. However, to be on the safe side,

flow velocities in noise sensitive areas should be lowered to about 8 or 9 feet

(2.5-3 m) per second.

The most expedient way of reducing air flow velocity is to decrease the

rotational speed of the blower, providing that it does not interfere with the

heating or cooling efficiency of the system.

Grille Noise

Noises generated within induction units or at the faces of outlet grilles

or diffusers give rise to numerous complaints from tenants. The intensity and

. characteristics of such noise are dependent upon the airflow velocity and the

size and design of the outlet units. For example, high velocity air striking

the face of an outlet grille often generates a high-pitch whistling noise.

Removel of the grille is a simple expedient test to determine the cause of

noise. If there is no appreciable reduction in the noise output without the

grille, the noise may be due to turbulence within the discharge duct or some other source farther back in the duct system. If there is a marked reduction

• in the noise output without the grille, it is evident that the grille was at

faiilt and therefore should be replaced with one of better design, or the air

flow speed should be reduced if practicable.

The following points are worth remembering when choosing outlet grilles

and diffusers for quiet operation.

(a) Grilles or diffusers which radiate little noise are made of

heavy-gage metal with widely-spaced streamlined deflectors devoid of

any sharp corners or edges

.

(b) A low-spread air diffuser will generate substantially less noise

than a large spread unit, all other factors being equal.

(c) Grilles constructed of wire mesh or perforated metal facings with

large openings are less noisy than those with tightly woven or small

. openings which restrict the air flow.

Furnace Combustion Noise

There are two types of noise associated with furnace combustion that

sometimes cause annoyance. They are the muffled explosion noise when the gas

or oil is ignited and the very high-pitched whistling noise caused by

w high-velocity gas flow through the fuel nozzle or burner Jets.

4-24
The most expedient way of dealing with this problem is to have a heating

engineer adjust the fuel pressure or install nozzels with proper openings for

quiet operation.

If the furnace operation is still too noisy following such adjustments, the

installation of sound absorbing material in the ductwork will reduce the noise

to acceptable levels

.

Steam Heat Noise

The hammering and knocking noises in steam pipes and radiators may result

from water being trapped in the lines. This frequently is caused by vapoi* lock,

partially open valves or improper drainage of pipes and radiators.

If you have noisy radiators, you may alleviate the problem by:

(a) Opening all valves completely to allow trapped water in the system to

drain back to the boiler.

(b) Placing thin blocks or wedges under the legs of the radiator opposite

the input end to increase the drainage angle, and thus allow any

trapped water to drain away.

(c) Replacing faulty pressure release valves.

(d) Inserting heat-resistant resilient material around the pipes at points

of support or penetrations through walls or floor structures, to

eliminate the rubbing contact and the resulting noise caused by the

expansion and contraction of the pipes.

Noise from Baseboard Heating Systems

Homeowners and apartment dwellers alike frequently complain about the noisy

operation of baseboard heating systems, in particular the hot water heating

system and the electrical heating system.

Hot Water Baseboard Heaters

Causes of Noise

The noise produced by such heaters generally is caused by:

(a) the expansion and contraction of pipes, heater components and

hoiising.

(b) water flow and turbulence, and

(c) pump and motor vibration.

Remedies

(a) Heaters and associated piping generally creak at Joints, con- nections and points of support or contact with building

structvires during expansion and contraction due to temperature

4-25
variation. When the units are rigidly connected to walls and

floors, these structures behave like soiinding boards and ampl i fy

the noise. Therefore, in order to minimize this problem,

heat-resistant resilient sleeves or collars should be placed at

all pipe clamps, supports and penetrations through wall and floor

structures. Similar measures should be teiken to isolate the

heater units from the walls and floors using heat-resistant

resilient spacers and leg mounts. Soft asbestos pads may be used

for this purpose.

Reducing the expansion and contraction noise of the heater

assembly itself is somewhat more difficult to achieve. Sometimes , attaching braces of folded sheet-metal strips to the long

narrow panels of the heater assembly will suppress the noise due

to buckling and popping of the panels during the heating cycle.

Securely fasten all loose panels and hardware on the heater

assembly to suppress buzzing and rattling noises.

(b) If the pipes tend to "sing" a high-pitched noise, this is an indication that there is high-velocity, turbulent flow in the

system, which generally is caused by using an oversize, highspeed piimp and undersize piping.

This problem can best be alleviated by decreasing the rotational

speed of the pump or replacing it with a slow-speed model

(c) Pumps and driving motors should be mounted on resilient pads to

prevent vibrational excitation of the floor.

Flexible hoses similar to auto heater or radiator hoses should be

installed in a "u" shaped configuration between the pump and pipe

system to suppress the transmission of pvunp vibration to the pipe

system.

Installing a siirge tank in the system at the discharge end of the

flexible hose will further suppress vibrations from the pump and

dissipate pulsation from the impeller.

Electrical Baseboard Heaters

Causes of Noise

(a) The major source of noise is the expansion and contraction of the

heater assembly and component parts and the eimplification of the

noise by wall. and floor structxires in direct contact with the

heating system.

(b) Another source of annoyance is a low frequency resonance of the

heater assembly, which sounds like the low-pitched hum of a transformer

.

4-26
(c) Some installations have individual thermostat controls in each

room. The clicking of a thermostat in the still of the night can he extremely irritating, partictilarly if a person is trying to

sleep.

Remedies

(a) To alleviate the noise of expansion and contraction of the heater

assembly, use the method discussed above for hot vater heaters.

(b) In a typical installation, the low-pitched humming noise

generally is radiated at amplified levels by a large wall which

is directly connected to the resonating heater assembly.

Structurally isolating the heater from the floor and wall with

heat-resistant, resilient spacers and leg mounts should reduce

the noise output to acceptable levels.

Attaching braces of folded sheet-metal strips to the long narrow

panels of the heater assembly will further suppress the

low-pitched humming noise or resonance.

(c) If yovir thermostat is excessively noisy, remove the cover plate

to determine what type of unit was insteilled. The noisy

thermostats generally use bi-metal, electromagnetic- assisted

contact elements which operate off high or line voltage. The

"Silent" thermostats use mercury-filled tubes as the contact

elements and operate off a low voltage supply. Consult with your

heating engineer for advice regarding replacement or interchange

of such units.

There are a number of methods that may be used to reduce the

clicking noise of thermostats. However power must be shut off

before the following methods can be tried.

(1) Remove the cover plate and remove the thermostat from the

electrical box. Reinstall the unit with rubber grommets or other resilient mounts to isolate it from the box and wall

structiire. Replace the cover plate.

(2) If additional noise reduction is desired, wrap the outside

surfaces of the electrical box with a thin layer of lead or metal foil-backed tape to damp the vibration. Place lead or tape on the back of the cover plate.

CONTROL OF PLUMBING NOISE

(See Figs, k-23, 2U, 25, and 26)

Most homeowners and apartment dwellers readily admit that noise arising

from the use of plumbing facilities anywhere within the home generally can be

heard throughout the dwelling, and frequently in adjacent dwelling vinits as

4-27
well. Probably because of this characteristic invasion of a person's privacy,

plumbing noise ranks not only as an irritating disturbance but as the most

bffensive noise to which building occupants are exposed.

In any case, it is extremely difficult to isolate yourself from plumbing

noise or to prevent it from disturbing other occupants in the building.

Causes of Plumbing Noise and Methods of Control

Water pipes and fixtures are rather ineffective noise radiators because of

their small radiating areas. The major problem arises when such sources are rigidly coupled to large efficient noise radiating surfaces such as wall,

ceiling and floor structures. Such surfaces, acting as sounding boards, radiate

the noise at amplified levels.

Techniques for the reduction and control of common types of plumbing noises

are given below. They are listed in preferential order and should be combined

for greatest effectiveness.

.

• Isolation of Pl\mibing System

Unfortimately , most of the plumbing system is installed within the

walls and is thus inaccessible to the home owner or apartment dweller. He,

therefore, is somewhat limited in the measures he can take to correct the

major cause of plumbing noise problem, that is to vibration isolate the

piping from all large wall and floor surfaces which act as sounding boards.

However, he shoiold make every attempt to isolate exposed piping with bands

or sleeves of rubber, neoprene or glass fiber at all points of support.

Including pipe clamps, straps, and penetrations through wall and floor

structures. If necessary, oversized clamps should be used to accommodate

the thickness of the resilient sleeve.

Expansion and Contraction of Pipes

The expansion and contraction of pipes produce a staccato-like series

of creaking, squeaking and snapping noises which are caused by the sliding

or binding of the pipes against studding or other supports. Isolating the

pipes from building structures as described above will alleviate the

problem.

Noise from Turbulence and High-velocity Water Flow

High water pressures with resultant high flow velocities cause

turbulence particularly around bends, valves, taps and connectors which

usually contain many sharp edges and constrictions. The familiar hissing

noise, occurring frequently at partially opened taps, is associated with

turbulence. It has been s\iggested that this noise is due to the combined

action of eddies and collapsing water vapor bubbles.

Although t\irbulent flow is considered to be the chief cause of

plumbing noise, the onset of cavitation in a plumbing system will result in

much higher noise levels. Both conditions may exist simultaneously.

4-28
especially arovmd restrictions in high pressure systems. Cavitation is

associated with the collapse of vapor bubbles, which are formed at some restriction by a critical combination of high velocity and low pressure.

High velocity flow in a plumbing system, due chiefly to undersized

piping, gives rise to turbulence which frequently generates excessive

noise. A noticeable reduction in noise level may be obtained by using

proper size piping to lower the water velocity. Flow velocities of the

order of 6 ft/sec (2 m/sec) or less in domestic systems have been found to

be quite acceptable. Specified flow capacity requirements caji be met and

a substantial reduction in noise can be obtained by using both pressure

regulators and larger diameter piping in the plumbing system.

High-pressiore plumbing systems are inherently noisy, due to the

resultant turbulent flow generated within such systems. The static

press\jre of main water-supply lines of buildings with three stories or less should be regulated so that it will not exceed 50 psi (2500 Torr)

.

The water pressure in branch lines serving individual apartment units

should not exceed 35 psi (l800 Torr). In high-rise structures where

high-pressure main supply lines are required, pressure reducers or regulators should be used in supply branches at various floors to maintain

water pressure within the above limits.

Pipe Hammering, Chattering and Vibration

The noisy hammering of a plvunbing system is usually caused by the

sudden interruption of water flow; for exeimple, by a quick-closing tap.

The sharp pressure build up at the point of interruption forms a shock wave which reflects back and forth in the system. The multiple

reflections, produce a series of hammer-like noises which gradually

decrease in loudness as the energy of the shock wave is dissipated. The

sudden release of pressure by a quick-opening valve which discharges into

a section of piping with a narrow restriction, elbow or tee connector also

may cause hammering of the plumbing system.

Noise in plumbing systems is frequently caused by motor driven pumps

which, by virtue of rigid mechanical coupling, transfer the vibrational

energy of the motor, or the pvmp to the piping system.

Noises due to such sources are easily recognized, since they consist

mostly of pure tones associated with the rotational speed of the pumps or

motors. The current trend toward using miniaturized, high-speed,

shaft-coupled motor pumps has intensified this problem.

Defective, loose or worn valve stems, faucet washers or seals give

rise to intense chattering of the plumbing system. The defective device

frequently can be pinpointed without difficulty, since immediate use of

the device causes the vibration which generally occiirs at some low flow

velocity setting and diminishes or disappears at a higher flow setting.

For exajcple, if vibration occurs when a particular faucet or tap is opened

partially and diminishes when fully opened, the faucet more than likely

has some loose or defective parts.

4-29
The above pipe noise problems generally can be alleviated by using

flexible connectors and air chambers in the piping system and by replacing

worn or defective valves, faucet vashers and refinishing pitted valve and

washer seats.

Flexible connectors shoiild be used in coupling sirpply and drain

pipes to vibrating appliances such as pumps, garbage disposers, clothes

and dishwashers. Since such appliances frequently have electrically

operated shut-off valves, air chambers or other shock absorbing devices

should be installed in supply and drain lines to prevent water hammering

of the plumbing system. The air pockets, rubber inserts or spring

elements in such devices act as shock-absorbing cushions.

Noise from Draining and Dripping Water

The draining of water from bath tubs, basins and toilets produces

gurgling noises which frequently are more annoying than those associated

with the filling of such units. The noise problem is intensified when

vertical drain systems do not run directly to the basement, but branch off

into horizontal pipe rvins which usually are supported from floor Joists.

Falling water striking the horizontal piping sets the drain system into

vibration which in turn is transmitted to the building structure.

The noise of splashing of water such as that associated with filling

a bath tub can be irritating. Attaching a long resilient hose to the

faucet which will reach the bottom of the tub, is an effective way of

eliminating this noise problem. In the case where the noise of a dripping

faucet is a source of annoyance in the still of the night, as a temporary

solution, attaching a string or draping a wash cloth from the faucet will

channel the water drops to the drain without noise. Of course, replacing

the worn washer seal would be a more permanent solution.

. .1. Noise Due to Entrapped Air in Pipes

A relatively common noise problem generally confined to newly

constructed buildings is that caused by entrapped pockets of air in the

plumbing systems. The combined action of water pressure and compression

of the air pockets may produce intense noise and vibration disturbances

which are characterized by explosive bursts, spewing and spitting of water

and air from open faucets or taps and hammering or knocking of the piping

system. Such problems seldom are a source of complaints, \inless they

persist for extended periods. Generally speaJcing, the problem eventually

corrects itself by gradual release of the entrapped air through continued

use of the plumbing services.

4-30
HOW TO DESIGN A QUIET PLUMBING SYSTEM

If you are planning to build a home with a quiet plumbing system,

you must incorporate the following design elements in the early stages

of your building plan.

(a) Vibration Isolate all Plumbing Systems:

A typical modern home or apartment may have three separate

piping systems; the hot and cold water supply system, the

drainage and venting system, and the hydronic piping system,

which includes air-conditioning, and steam and hot water

heating systems. One of the most effective solutions to pipe

noise problems is to keep the pipe isolated with resilient

sleeves and hangers from building structures with large

radiating surfaces such as walls, ceilings and floors. Pipes

in buildings behave like tuning forks using such structures

as sounding boards to amplify the noise levels.

(b ) Use a Simple Plumbing Layout

A well designed plumbing system with a minimum of fittings

and bends is substantially less noisy than a complicated

layout. Proper size fittings and large-radius elbows or bends should be used for quiet performance. Large diameter

piping should be used for all main supply lines. Separate

branch lines of smaller diameter should be installed to serve each individual area where required.

(c ) Install Pipes Away from Quiet Areas

Pipes should not be installed in any walls, enclosing bedrooms,

living rooms , studies or other rooms where privacy and quiet

surroundings are essential. For example, in order to prevent

the transmission of noise into bedroom areas, supply and drain

pipes should not be installed in walls separating bathrooms

and bedrooms. Piping should be installed in partition walls

which separate adjacent bathroom or kitchen areas. Supply emd

drain pipes must be isolated from internal studding or wall

surfaces

.

(d) Install Quiet Fixtures:

Siphon-jet toilet and flush tank fixtures with adjustable flow

valves are considerably less noisy than conventional models.

Taps and faucets using full-ported nozzles and equipped with

anti-splash or aeration devices produce little noise.

4-3L
(e) Install Bathroom Fixtures on Resilient Bases and Mounts:

Bath tubs, toilets and shower stalls should be set on underlayments

of cork, rubber, neoprene or other resilient materials or installed

on floating floors to reduce the transmission of noise due to

falling water. Likewise, the fixtures should be vibration isolated

from supporting walls by means of resilient gaskets. Such mounting

precautions should be observed with respect to installation of wash

basins and faucet fixtures as well.

(f ) Seal Air Leaks Around Pipe Penetrations

:

To prevent noise leaks, seal all openings around pipe penetrations

: through wall and floor structures with a non-setting waterproof

caulking compound. Party walls between bathrooms should be

completely finished to floor level on both sides, particularly in

back-to-back tub and/or shower installations. Failure to s\irface

th^ walls behind tubs results in serious noise transmission

problems. Likewise, both subflooring and finish flooring in

bathroom areas should be completely finished before tubs and shower

stalls are installed.

(g) Enclose Large Pipes:

Large diameter pipes in high pressure systems, frequently radiate

considerable noise, especially when they are exposed. Such pipes

should be boxed in gypsum board enclosures, preferably lined with

- acoustical material. An alternate, though somewhat less effective,

technique is to enclose the pipes in thick glass fiber jackets with

. heavy impervious outer coverings of plastic or leaded-vinyl

materials. It has been siiggested that the glass fiber Jackets

should have a density of about 6 Ib/cu ft (96 kg/m ) and a thickness of at least 3 inches (I8 cm). ^The impervious covering

should weigh at least 1 Ib/sq ft (5 kg/m ).

4-32
4-33
4-34
4-35
FIG. 4-4 COMMON VIBRATION AND NOISE PATHS IN BUILDINGS.

4-36
NOT AUDIaU

The objective Is to reduce level of the

transmitted noise below

level of background noise.

1.1 lir' m

MASSIVE WAli

1)))

& ISOLAUD SURfACt C DOUBU WAa

Techniques for the control of airborne noise

IL SOUND ABSORBER

IM CAVITY

E. SEAi HOUS

AND CRACKS

A. CUSHION IMPAa L aoATaooa

i

C SUSPEND CEILINC Bt SOUND ABSORBER,

IN CAVITY

Methods for the control of impact noise; the objective Is to absorb the impact

and to break direct structural connections.

carpet

acous celling

tic A

drapes

Reducing reflection and noise buildup with sound absorbent furnishings.

FIG. 4-5 GENERAL SOLUTIONS FOR NOISE CONTROL IN THE HOME.

4-37
4-38
USE IN ENTRANCE. BEDROOM & BATHROOM

AREAS

SOLID CORE DOOR HOLLOW CORE DOOR

DOOR

OPEN

METAL

STRIP

13

SOLID RUBBER

STRIP DOOR JAMB CASKETS

AUTOMATIC I «v DROPLAP

JOIN!

TUBE /

;

CASKET V

IN SI

RUBBER

TUBE

ET ' SWEEP y

,

U J STRIP ]\J/

DOOR SILL CLOSURES

FIG. 4-7 PROPER INSTALLATION OF SOUND INSULATING DOORS,

4-39
A- RUBBER GASKET B- SINK C- ACOUSTIC HAT'L D- CA6II1ET E- HASTIC COAT

F-RING PLATE G- DISP'L- FLANGE H- STEEL WASHER

I- RUBBER MASHER J- HUT

K- RING CLAUP L- HETAL COVER M- CLASSVOOL N- OlSP'L- HOUSING 0- RUBBER SLEEVE P- RUBBER HOSE

FIG. 4-8 DESIGN AND INSTALLATION OF A GARBAGE DISPOSER

FOR QUIET OPERATION .

4-40
4-41
wood floor joists

wood subfloor

wood finish floor

glass fiber blanket, 3 in thick

5. resilient metal channels

6. gypsum board, 5/8 in thick

7. acoustical tile

FIG. 4-10 DESIGN OF A SOUND INSULATING CEILING FOR A BASEMENT

RECREATION ROOM.
4-43
c

4-44
o <u O Ol 11 / n m I ' r—

CO

1—

3 O LU

XX^s*

LxJ

ixl •r~ +J O O O ^ tn

•1- o O U. -r- O t_

(A +-> CD

(/) (J Z <a 0) l-H _J

CD UJ <LlI to • •

ro1 Q.

lO

i- CD

•—1 U.

r— -a

<0 0) CJ _J

1— CM

4-45
DO

CtlllNCSlAB

caulk

APt B

PARTITION WAOS BIWH

APTS. SHOUlOaTENO

FROM nOOR SLAB TO CEILING SLAB

FLOOR SLAB /APT. A

DONT

1 I 'Ca

^ CrPSUM BQ.

NOISE PAW 'ar

AVOID EXTENDING WALLS TO UNDERSIDE

Of SUSPENDED aiLING

Art A rf APT. B

ROOF

ATTIC SPAa

GYPSUM bd: CEILINGcaulk

7

FLOOR-aiLING ASSEMBLY APL A \

SOUND BARRIER ^ k\ t;; „

EXTEND WAU TO ROOF OR DIVIDE AniC SPAa

WITH FUU-HEICHT BARRIER

, PARTITION WAU

APT. B

APT. C APT. 0

APT. A APT. B

caulk

PARTITION WALL' caulk

1

APT. C

CRAWL SPACE OR BASEMENT

DIVIDE CRAWl SPAa

OR BASEMENT AREA WITH FUU-HEICHT BARRIER

APT. 0

• SOUND BARRIER

AniC OR PUNUM

r i

AVOID OPEN Ante SPACES M PLENUMS

APT. A APT. B

APT. C APT. D

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CRAWl SPAa OR BASEMENT AREA ^® • * O - - o

FIG. 4-14 METHODS OF CONTROLLING FLANKING SOUND TRANSMISSION PATHS.

4-A6
4-47
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4-48
Loose-finish flooring

Warped-finish flooring

t

Bowed subflooring Bracing of sagging floor

Warped Joist

(1) Serrated or ring-type nails (5) Cross brace inserted

(2) Mineral oil in grooves (6) Extra joist inserted

(3) Wood screws (7) Full-length straight

(A) Clearance hole board nailed to Joist

FIG. 4-17 TECHNIQUES FOR THE CONTROL OF SQUEAKING FLOORS .

4-49
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Selecting proper location of closet-installed furnace unit.

CI0KT IHSTAUATKM

meant sim«mu

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Recommended design of closet and installation of furnace unit,

2 Uknn Pirwooo MINTS SUCCMIIK

SUIFUXM

FIG. 4-19 RECOMMENDATIONS FOR NOISE CONTROL OF CLOSET-INSTALLED

FURNACE AND AIR CONDITIONING UNITS.

4-51
Attic installation

Basement installation

CflLINC SLAB

STRUCruUAL SLAB

FIG. 4-20 TECHNIQUES FOR THE CONTROL OF NOISE FROM EXISTING ATTIC OR

BASEMENT INSTALLATIONS OF FURNACES AND AIR-CONDITIONING

UNITS.

4-52
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4-53
THIS NOT THIS

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FIG. 4-22 METHODS OF CONTROLLING CROSS TALK AND THE TRANSMISSION

OF FLANKING NOISE IN DUCTS.

4-54
I FIG. 4-23 TECHNIQUES FOR CONTROLLING NOISE IN PLUMBING SYSTEMS .

4-55
.M>» lam

liTd nn

CAULK

CAULK

1/8' CLEARANCE UNDER FLANGE

FLOATING FLOOR

RESILIENT MATERIAL

SUB -FLOOR

rubber

sleeve or glass fiber

packing

pipe ^^^^v-'^ clamp

in rubber sleeve

IVBIll euiET

laaia p«i

FIG. 4-24 METHODS OF INSTALLING PIPES FOR QUIET OPERATION .

4-56
APT. A APT B

FIG. 4-25 PROPER INSTALLATION OF BATH TUBS AND WASH BASINS.

1

4-57
3/16- KOnm PAD

RESILIENT PAD

IN PIPE HANGER

SOIL PIPE

NEOPRENEOETAIL 'A'

FIG. 4-26 PROP ER INSTALLATION OF A TOILET FOR QUIET OPERATION .

4-58
Chapter 5

HOW TO INSULATE YOUR HOME AGAINST OUTDOOR NOISE

As we know from experience, residential areas that formerly were

quiet and peaceful, frequently have become engulfed by highly disturbing

sources of noise.

Changes in zoning ordinances often permit development of noisy industrial parks or shopping centers on the outskirts of residential areas.

Ordinary highways eventually become high-speed noisy expressways

which invade the peace and privacy of quiet communities and suburban areas

that often are encircled or flanked by the roadway.

In some cases, local neighborhood noise caused by community traffic,

homeowners' use of outdoor power applicances such as lawn mowers, chain

saws, or perhaps children at play, barking dogs, etc., may be the most

disturbing problem.

In other cases, noise from community swimming pools, playgrounds,

athletic fields, amusement parks or sport arenas may be the major source

of annoyance.

The outdoor noise levels generated in neighborhood environments by

the various sources cited above might be described as being in the moderate

to high level range, or roughly 70 to 95 dB.

However, the greatest number of noise complaints come from home owners

and apartment occupants living in residential areas near airports. The

expansion of medium jet airports into international airports handling much

larger and noisier aircraft has created noise problems affecting much

larger communities and populated areas. The expansion of small private

airports to handle the new breed of small business jet aircraft has

created similar noise problems. in small, relatively quiet communities.

Aircraft noise levels at the location of the home or apartment site

will vary depending chiefly on its distance from the airport or flight

path, and type and altitude of aircraft among other factors. In any

event, dwellings near large airports or directly under flight paths may

be subjected to rather intense levels of noise ranging from 90 to 110 dB

or more.

We will discuss first the steps for improving the sound insulation

of houses in moderately noisy neighborhood environments, and deal

separately with the more difficult problem relative to aircraft noise

intrusion at the end of this section. Illustrations of building modifications and sound-insulating construction discussed in this chapter are given at the end of the chapter.
Generally speaking, most single-family dwellings are an assemblage

of light-frame interior partitions enclosed and supported by a light-frame

exterior shell. If this shell were continuous and provided an air-tight

seal for the enclosed space, it would provide at best only a fair amount

of sound insulation. However, this shell not only is covered by a thin

roof of even lighter-weight materials but also contains a number of windows

and doors with their customary air and noise leaks. These structural

assemblies tend to reduce substantially the sound-insulating capabilities

of the dwelling. The following information will suggest ways of improving

the sound insulation of the house to provide adequate privacy in typical

noise environments.

Reducing the Intrusion of Neighborhood Noise

If you have a home in a noisy neighborhood and are disturbed by the

exterior noise intrusion, the following recommendations may alleviate the

problem.

(1) The first rule of thumb is to install a central heating and air

conditioning system in the house. This will eliminate the need to open

windows and doors for ventilation purposes and thus reduce considerably the

intrusion of outdoor noise.

(2) Existing windows should be caulked or equipped with gaskets to

provide an air-tight seal.

(3) If the noise source is high pitched and very directional, install storm windows with caulk or gasket seals on the side of the house

facing the source. However, it is more beneficial to install storm

windows, properly sealed, on all existing windows. This will provide

additional insulation against low-pitch noise as well as noise approaching

from other directions.

(4) Exterior doors should be provided with soft resilient gaskets

and threshold seals. This applies to sliding doors as well.

(5) Install storm doors equipped with resilient gaskets and threshold seals. Sliding storm doors also should be installed.

(6) Seal or caulk all openings or penetrations through walls particularly around water or gas pipes, electrical cables, and refrigerant

lines.

(7) Cover mail slots in doors; install hinged cover plates on clothes dryer heat vents, bathroom and kitchen exhaust ducts, and central

vacuum system dust discharge chute.

(8) Close fire-place damper, clean-out cover plates and install a 1/2-inch (13 mm) thick plywood barrier in front of the fire-place opening.
Adoption of the above measures would improve the sound insulation

of the exterior shell of the house about 6 dB for low-pitched sound and

above 10 dB for high-pitched sounds; this would reduce the loudness of the

intruding noise about 25 to 50 percent, respectively.

Reducing the Intrusion of Traffic Noise

Homes or apartments of conventional construction that are located

very near to heavily traveled roadways or expressways are particularly

vulnerable to the intrusion of excessively high levels of noise. Since

the sound proofing of such dwellings would be costly and impractical, the

occupants should choose those solutions which provide the most noise re- duction at least cost. In addition to the recommendations described

above, the homeowner should incorporate, on a step-by-step basis, the

following noise control measures, until the noise has been reduced to a tolerable level.

(1) In existing windows, install glass panes of double thickness

on the side of dwelling facing the noise source.

(2) Lifewise, install storm windows over the same windows. Select

storm windows which have glass panes mounted or encased in rubber gaskets.

(3) Line perimeter surfaces between the existing windows and storm

windows with acoustic tile or sound absorbent lining.

(4) Replace existing hollow-core entrance doors with solid-core,

sound-proof doors provided with perimeter gaskets and drop closures.

(5) If intruding traffic noise disturbs your sleep and your bedroom

faces the roadway, choosing a bedroom which is located on the opposite

side of the house may reduce the loudness of intruding noise an additional

50 percent or about 10 dB or more. Selecting a bedroom on the side of the

house that is partially shielded from the noise source should reduce the

loudness of the intruding noise about 25 percent or 6 dB.

(6) Install a barrier wall or fence between your house and the

roadway. To be effective, the fence should have a solid, continuous

surface without any openings or holes. The fence should be relatively

long and tall enough to shield, or hide, the entire roadway when viewed

from the nearest side of the house. The barrier or fence can be made of

relatively light material such as 1-inch (25 mm) thick boards, because

in such circumstances a noise reduction of only 5 to 10 dB may be

obtained.

5-3
Reducing the Intrusion of Aircraft Noise

If you are one of many home owners who now find themselves constantly

exposed to intense and highly disturbing aircraft noise, you should con- sider carefully the fol-owing four basic facts before you decide on any course of action to resolve the problem.

(1) The cost of soundproofing an existing home against intense aircraft noise is exceedingly high.

(2) Although soundproofing your home will reduce your annoyance

indoors, it does nothing to improve the noise environment outside the

home. Therefore if you enjoy gardening, patio parties or backyard

barbecues, you will have to tolerate the aircraft noise as before.

(3) The probability is rather low of gaining noticeable relief from

the noise through the development of quieter aircraft or changes in aircraft landing or takeoff flight patterns. In fact, the noise environment

near a large airport generally tends to grow worse in time, with the inevitable expansion in aircraft size and flight operations.

(4) The most effective solution is to move to a more quiet area, even though it might entail some financial loss in the sale or rental of

your home.

The following is a discussion of the various sound insultating

modifications that may be used to reduce the intrusion of intense aircraft

noise into the home. Figures 5-1 through 5-12 illustrate the structural

details of such modifications.*

Major Sound Insulating Modifications:

(a) Incorporate the noise-reduction recommendations given above

relative to reducing the intrusion of neighborhood and traffic noise.

(b) Windows

Windows are the weakest acoustical barrier in the exterior

shell or surfaces in most homes.

Ordinary double-hung, locked windows generally provide an average noise reduction of about 18 dB; the addition of a storm window

will increase the sound insulation about 6 dB. Caulking of both windows

improves the sound insulation about 3 dB at the higher frequencies. However, if the aircraft noise still seems to be coming through the windows,

despite the fact that they were equipped with storm windows and sealed

air tight, then the existing window installation will have to be replaced

with fixed, non-operable, double windows throughout the house.

*Figures 5-1 through 5-12 are courtesey of the Department of Housing and

Urban Development.

5-4
The window installation would consist of two 1/A-inch (6 mm)

thick panes of glass, each encased in a "U" shaped soft, resilient gasket

with a 4-inch (10 cm) air space between panes. Line perimeter surfaces

between panes with acoustic tile or other sound absorbent material.

This double-window installation would increase the sound insulation approximately 10 dB above that provided by ordinary windows

protected by storm windows.

(c) Exterior Doors

If the noise now seems to be coming through the doors, remove

the moulding from the door frame to see if there are any air gaps or noise leaks between the door frame and the wall. The conventional practice of installing prefabricated door kits, in which the doors are premounted in a door-frame assembly, often causes serious sound transmission

problems. Builders generally provide an oversized opening to receive the

preassembled door and fasten the assembly into place with a few wedges

and nails, and completely ignore any resulting air gaps or leaks. These

are conveniently covered and hidden from view by the thin finish moulding.

However, such leaks must be sealed if any improvement in sound insulation

is to be expected, and certainly before any existing doors are replaced

with soundproof doors or equipped with gaskets.

Replace existing doors with 1-3/4 inch (4.5 cm) thick solid-core

doors with soft, resilient, perimeter gaskets and threshold seals. Install storm doors with 1/4-inch (6 mm) thick glass and weather stripping.

It is estimated that the noise reduction provided by this combination of

doors would be about 20 dB greater than that of a conventional exterior

door.

(d) Exterior Walls

Generally speaking, exterior walls constructed of poured con- crete, cinder block, brick or other masonry materials provide sufficient

sound insulation against aircraft noise, if all penetrations through the

walls have been properly treated and sealed. For example, ventilation

ducts and exhaust vents must be lined with sound absorbent material or equipped with sound silencers; holes around penetrations of gas or water

pipes, electrical conduits and refrigerant lines must be sealed airtight

with a resilient, non-setting caulking compound. Settlement cracks in

the walls or gaps around framing of windows and doors should be caulked

or sealed in the same manner.

No structural changes or modifications should be made to the

exterior walls until you are sure that the noise is not entering the

house through the basement, crawl space or attic areas. Exterior walls of light-frame construction consisting of wood

studding faced on the inside with gypsum board and on the outside with

insulation board and wood, metal or stucco siding, are inherently incapable of providing adequate sound insulation against moderately high
levels of noise, much less intense levels of aircraft noise intrusion.

Such walls would have to be capped on the outside with a 4-inch (10 cm)

thick wall of brick veneer before the aircraft noise could be reduced

to a tolerable level inside the house.

(e) Roof and Ceiling Modifications

Ventilated attic space

If the attic is to be used as a wlak-in storage area, install subflooring on top of the ceiling joists and cover with 5/8-inch

(16 mm) thick gypsum board. Tape and seal the edges and joints of the

gypsum board layer. Otherwise, the gypsum board may be installed

directly on top of the ceiling joists.

Install a metal duct with 1-inch (2.5 cm) thick glass

fiber liner at all air-circulation vents or openings.

Plank and beam vaulted ceiling or flat roof

Attach wood furring or preferably metal resilient channels

to the existing ceiling. With self-tapping screws, fasten 5/8-inch (16

ram) thick gypsum board to the furring or metal channels. Tape and finish

joints and edges of the gypsum board in the conventional manner.

(f) Basement Areas

Caulk or weatherstrip existing windows and install storm

windows

.

Weather-strip existing hinged or sliding doors and install storm

doors

.

(g) Crawl Spaces

Install a metal duct with 1-inch (2.5 cm) thick glass fiber

liner at all air-circulation vents or openings.

Install 5/8-inch (16 mm) thick exterior plywood or moistureproofed gypsum board to the underside of the floor joists.

5-6
5-7
FIG. 5-2 HOUSE WITH A CRAWL SPACE AND VENTILATED ATTIC.

5-8

FIG. 5-4 HOUSE WITH SLAB ON GRADE AND FLAT ROOF.

5-10
Install new ceiling of 5/8"

gypsum board at bottom of

roof rafters

Lay 5/8" gypsum board over

ceiling joist and tape all joints

(For alternative treatment,

tee Case C)

Install r>ew ceiling of 5/8"

gypsum board on 1" x 3"

furring below existing

ceiling

c - Flat roof

FIG. 5-5 ROOF AND CEILING MODIFICATIONS,

5-11
•V

'

a - Added floor construction

b - Vent ottenuators

FIG. 5-6 CRAWL SPACE MODIFICATIONS.

5-12
5-13
1 3/4" Solid - Core Door

Storm Door

Install gasket or weatherstrip

to close joints on all sides

around both doors.

FIG. 5-8 DOOR MODIFICATIONS.

5-14
Caulk any op«n joints around

door frame

1 3/4" thick $olId - core door

At head and jambs - install closed -cell polyurethane

foam compression gasket or interlocking cloth-lined

weother strip to close joints

around both doors

At double doors, install resilient vinyl or r>«oprene gaskets

At threshold. Install either

resilient bumper strip or automatic drop - seal

FIG. 5-9 DETAILS OF DOOR MODIFICATIONS.

5-15
4" Airspace between glazing

1/4" Glass installed with neoprene

"U" gasket or glazing cofnpound,

Gasketing or weather strip to close

joints around both windows

Brick or concrete block veneer

installed outside existing wall

FIG. 5-10 INSTALLATION OF BRICK VENEER AND DOUBLE 1/4-INCH

WINDOW GLAZING.

5-16
HEAD

JAMff

SILL

4" Air space between glazing

1/4" Glass in naoprene gasket

Continuous ecjge gasket around

sash

3/16" diameter vent holes (2 per

sash) with glass fiber plug

Step B - 1/4" Glass in separate sash added to form

4" Airspace between the two windows.

FIG. 5-n DETAILS OF DOUBLE 1/4-INCH WINDOW GLAZING .

5-17
5-18
Chapter 6

SELECTING A QUIET HOME OR APARTMENT SITE

(or how to avoid making the same mistake twice)

If you are planning to move to a new home or apartment and desire more peace

and privacy than you have at present, the following recommendations can help

you to select a quiet location.

1. SELECTING A QUIET RESIDENTIAL AREA

(a) Obtain Maps of the Area

Obtain a recent edition of a detailed map of the area that you

propose to live in and study it carefully for the location of major

sources of noise. Look, particularly, for such major sources of

noise as airports, railroads, expressways, and industrial areas.

Airports : If possible get a sectional aeronautical chart of the area to determine the location of all airports and their respective

flight patterns and air routes relative to the proposed building

site. Such charts may be obtained from local airport authorities

or the Aircraft Owners and Pilot Association, Washington, D. C.

20011;

.

Sites near large commercial, international or military airports

should be avoided completely. Residentisd buildings directly in

line with prescribed runways , take-off and landing patterns or flight paths would have to be located at least 15, and preferably

20 miles {2h to 32 km) away from the airport before the noise from

jet aircraft fly-overs would be tolerable to the occupants, as illustrated in Fig. 6-1.

Near an airport, but off to the side of the runways, buildings

would need to be a lateral distance of about 3 to U miles (5 to 6

km) from the flight path before the noise would drop to a level

tolerable at the building location.

(Railroads, Expressways eind Industrial Areas) : If annoyajice or disturbance from these excessively noise sources is to to be

avoided, residential buildings should be located at a distance of

at least one mile and preferably two miles (1.5 to 3 km) from the

sources

.

(b) Check With City Zoning or Planning Authorities

Consult with local city or county plsinning authorities regarding

future development plans for the area. As a result of futvire

rezoning action, quiet residential areas frequently are boardered

by noisy indvistrial parks or huge shopping malls

.

6-1
(c) Consult With City or County Transportation Authorities

Such authorities should be consulted relative to the status and

location of existing and proposed expressways, mass transit systems

and changes in aircraft flight paths, procedures and operation.

( d) Conduct An On-Site Examination:

Conduct several on-site examinations of the area during daylight

and especially also after midnight to assess the outdoor noise

environment. Be especially alert for the location of fire and

police stations, schools and athletic fields, hospitals, sport

arenas, race tracks, shopping centers and amusement parks.

Although ordinarily these civic centers and activities may be

considered secondary sources of noise, they could well become,

depending on their proximity to your location, the major source of

noise and disturbance for you.

(e) Consult With Residents Living In The Area

It often pays to talk to people living in the area to determine

whether or not they are disturbed by noise, especially at night.

2. SELECTING A QUIET LOCATION WITHIN A HOUSING OR APARmENT DEVELOPMENT

(a) Select and inspect an apartment development which advertises

"soiuidproof" wall and floor construction, quiet, efficient central

airconditioning systems and fully carpeted interiors, including

entrance foyers, corridors and hallways. Such construction and

furnishings usually provide a quiet indoor environment, adequate

privacy and negligible noise intrusion or disturbance from

neighboring dwelling units or other areas within the building. The

intrusion of outdoor noise also may be substantially reduced,

especially if the building is equipped with heavy glass windows

that are fixed or non-operable and which are installed with

weatherproof, airtight seals.

(b) Avoid home or apartment sites which are along main traffic arteries

or bus routes through the development. Early morning traffic noise

may be a source of annoyance, as illustrated in Fig. 6-2.

(c) Select buildings which face wide open spaces such as parks, golf

courses , rivers , lakes and seashores . Such areas usually are very

quiet, especially at night.

(d) Select a building site which is located as far as possible or is

acoxistically shielded from a major source of noise by other

bioildings, natural landscaping or wooded areas, as illustrated in

Figs. 6-3, 6-k.

6-2
* 3. SELECTING A QUIET APARTMENT UNIT WITHIN THE BUILDING

(a) Avoid apartment units vhich are adjacent to elevators, mechanical

equipment rooms , laundry rooms , or indoor garages , roof-mounted

ventilation equipment, such as chiller pumps, compressors or cooling towers. Rarely are such powerful sources of low-frequency

noise and vibration properly isolated in sound-insulating

enclosures or vibration-isolated from the building structure by

means of resilient mounts. As a consequence dwelling units

adjoining such sources may be subjected to intermittent

round-the-clock intrusion of excessively high noise levels. These

dwellings can readily become an acoustically intolerable

environment.

(b) Avoid apartments that overlook parking lots, thoroughfares or through streets, play grounds and swimming pools. Noises caused by

automobile operation such as starting of engines and door slamming,

particularly during the early moniing hours, can be a source of

annoyance. Likewise, the voices or shouting of children at play

throughout the day eind evening may be disturbing.

The best way of avoiding such problems is to select an apartment

unit on the "quiet" side of the building; that is, one which faces

away from such noise sources.

(c) Avoid apartments which face "U" shaped courtyards. Such areas tend

to be quiet reverberent and noisy, particularly if they are used as recreation or play areas or face traffic through streets.

6-3
6-4
AVOID BUILDING SITES AT INTERSECTIONS liSS NOISY THAN SITES IN CONGESTED

OF MAJOR TRAFFIC ARTERIES. SUCH SITES BUILDING AREAS.

ARE EXTREMELY NOISY DUE TO ACCELERATING.

DECELERATING, AND BRAKING VEHICLES.

BUILDINGS ARE QUITE NOISY. AVOID BUILDING SITES OPPOSITE TALL "'^"^^ BUILDING SITE IS LESS NOISY

BUILDINGS IN SUCH CASES. THAN A DOWNWIND SITE.

AVOID BUILDING SITES ON THE CRESTS OF HIUY AVOID HOLLOWS OR DEPRESSIONS

TRAFFIC ARTERIES. SUCH SITES ARE VERY NOISY THEY ARE GENERALLY NOISIER THAN FLAT DUE TO LOW GEAR ACCELERATION NOISE. OPEN LAND

FIG. 6-2 EXAMPLES OF APARTMENT SITES THAT SHOULD BE AVOIDED.

6-5
A THICK GROWTH OF IXAFY TREES & UNDERBRUSH REDUCES NOISE ABOUT

6 to 7 Ob. / 100 ft. (AVERAGE OVER

AUDIBLE FREQ. RANGE) LOW FREQ. LOSS:3-4 db HIGH FREQ. LOSS: 10- 12 db

HIGH FREQ. REDUCTION 3-4 db SINGLE ROW OF TREES IS WORTHLESS

AS NOISE BARRIER. DUE TO INTER-REFLECTION MUITI-ROWS OF TREES ARE MORE EFFECTIVE:

FIG. 6-3 ACOUSTICAL SHIELDING PROVIDED BY LANDSCAPE AND NATURAL

AND MAN-MADE BARRIERS.

6-6
NOT THIS THIS

6-7

Chapter T

A TROUBLE-SHOOTING GUIDE

In solving noise control problems, it is best to employ the SOURCE - PATH

- RECEIVER concept introduced in Chapter 3. You can trace the travel of the

offending noise back to its source with some very simple equipment if you pay

attention to what you hear. Working in this manner, you will be following the

footsteps of a renowned acoustical engineer - Lord Rayleigh - who did some of

his best research with only the materials he had in his posession: his ears, a duck call, tennis and croquet balls. Having located the source of noise and

its path, you can use this guide for help in eliminating the annoyajice. For

your convenience, we have a detailed index at the end of this chapter.

First of all: Do you have a problem that is hazardous to hearing, or does

the noise merely bother you? You can use your own ears for a sound- level

meter. We have already mentioned the first step: Do you find conversation

possible? From just one further step you can estimate the sound level in yoiir

vicinity: Over what distance is conversation possible?

Figure 7-1 shows the experimental relationship that has been found between

the recognition of spoken words and the typical dB(A) reading of a sound-level

meter. As an example of the use of this graph, suppose you are standing

talking to another person at a customary distance of from 3-5 feet (l - 1.5 m)

from him. If you are comfortably able to carry on your conversation - no unusual effort to hear him, no feeling that you are pushing your voice to a higher level - then it's likely that the sound level doesn't exceed 6T dB(A)

where you are standing [point (l), Figure 7-1 ]. Suppose, now, you are at a stand-up dinner or a cocktail party, where a typical level shortly after the

beginning of the party might be 7^ dB(A) both of you may have to raise your

voices [point (2)], but you covild still expect to understand one another.

However, to attract the attention of someone at the other end of the living

room (20 feet or 6 meters) you would have to shout [point (3)]- However, since

shouting raises only the voice sounds, but contributes almost nothing to the

power of the consonant sounds upon which the meaning of speech so often

depends, you would also have to confine your remarks to the simplest subjects:

scarcely more than "Hi!" could get across. At about 80 dB(A) , a level reached

by some guests and some parties, even the normal conversational distance

becomes impossible for conversation; at this level, continued exposure for many

hours might offer some risk to hearing, and it's advisable to leave.

To use Figixre 7-1 as a guide to sound levels, you can start a conversation

with a companion, and then back slowly away. You can signal one another the

moment you feel that extra effort is involved, either in speaking or listening.

At this point, if neither of you has a hearing loss, tbe distance between you

can be noted on the horizontal scale on the chart. From the solid line on the

chart you can read off the effective sound level in dB(A) along the vertical

scale. This will work even when you are in a fairly reverberant space; only a very long echo time, as in a concert hall or church, will cause you to

overestimate the sound level.

7-1
The reason that this process works rather well is that the A-weighting

network of the soxind-level meter parallels quite closely the sound distribution

in conversational speech. Speech has another great advantage: we all are expert listeners. You can use your recognition of speech sounds to tell you

more about the noise source, itself. To allow you to translate your

recognition into the terms used by acoustical engineers, we have shown some of

the characteristics of speech sounds in Figure 7-2. If you listen closely to

the noise, you may be able not only to recognize the source, but may be able to

recognize the principal pathway through which the noise is reaching you.

For example, suppose you live in an apartment building, and the soxinds

from neighboring apartments annoy you. Are they coming through the air, or via

the structure? If footsteps sound more clearly than voices, and you can hear

the voices but can't make out what is said, the chances are that the sound is

traveling as vibrations along the floor, or through the walls and ceiling.

High-frequency sounds, such as those of the consonants that carry most of the

meaning of English speech, do not pass as readily through structures as do the

low-frequency sounds of footsteps and the voice melodies and vowel sounds of

speech. If speech comes through as though it were passing down a "speaking

tube" , you should expect to find airborne sound paths - actual sound leaks .

Sometimes, however, the character of the sound is so altered that you

can't recognize its origin. A floor lamp may "sing" if you set it at some points on the floor, but be quiet in other positions. There you are dealing

with a resonance in the structure of the lamp that permits it to resonate when

excited by a vibration from the floor that would otherwise be inaudible. A

possible source of this vibration might be the compressor of your refrigerator;

in that case the lairrp would sing only when the compressor is working. Simply

changing the bulb in the lamp might eliminate the trouble, or tightening up the

screw on the base of lajnpshade. Here, the chart in Figure 7-2 can prove

helpful. You can shout various words at the lamp and see whether some words

will set it singing. The chart in Figure 7-2 will then allow you to estimate

the frequency of the vibration that is triggering off the singing of the lamp.

Armed with these charts for analyzing the problem, you now need some simple tools. Most of these are at hand, in almost any household. For

example, you can look for sound leaJcs with a flashlight. Light coming through

the edges of a closed door is following a path that soiinds can travel along as well. Another place to look for a light leak is along the edge of the doorway

molding. Sometimes the opening cut for a doorframe has been larger than

needed, and inadequately filled in.

Of course, sounds can worm their way around corners too abrupt for light

beams. To locate these, you need a sound probe. A very useful device for

conducting soiinds to your ears from a definite location is a stethoscope. The

child's toy sold in some "educational" kits is good enough. In a pinch , you

can follow the lead of the originator of the stethoscope, and use a hollow

tube. You can use the central tube from a roll of paper towels, or a mailing

tube of about that diameter. This is Just about the right size to accommodate

one ear, and is long enough to enable you to move about freely while you look

7-2
for soiind leaks. With a small lump of caulking compound, modeling clay, or putty at hand, you csm make temporary closures of the leaks you find, thus

making it easier to locate secondary leaks.

For any extensive search, you need devices for generating sounds and

vibrations of relatively high intensity. The noise source that bothers you may

not he obliging about generating enough noise Just when you are in a position

to look for it. Even with a continuous noise, it is sometimes useful to

recognize that the noise path is reversible. If sound is reaching you through

a leak from outside, you can make a noise inside the room, and look for that

noise on the outside.

A portable transistor radio makes a convenient soiind source. Several

ordinary appliances make convenient vibrators. If you remember that it is

designed for brief spiirts of service, and can overheat if operated too long, a household blender makes a good source of vibration running under a mixing load.

A mixer on a stand, working on a moderate load, is less intense as a rule, but

aJ-SO usef\il. Other devices you might have about the house make fairly good

vibration sources: a vacuum sweeper with a rug beater, an electric shaver, a scroll saw, a portable drill.

Your stethoscope will help you locate vibrations as well as sounds.

Another sensitive vibration detector that you casi use is the sound conduction

path through your forehead. Just by resting it against a wall. Another

somewhat more sensitive area for picking up sounds is the mastoid bone behind

your ear. (You can lean it directly up against a door frame, for instance.)

For low- frequency vibrations, your fingertips are a sensitive pickup when held

lightly against the vibrating siorface.

HOW TO LOOK FOR LEAKS

First of all, try to estimate whether the intruding sound is arriving by

structural vibration or directly through the air. Compare the loudness when

you are in direct contact with the wall with what happens if you pull your head

Just slightly away.

If the sound seems to be coming through the air, explore wall cracks,

window-frame openings and door frames. You will find that the tube or the

stethoscope will allow you to locate specific leaks. You can mark them with

chalk, or, even better, plug them temporarily with whatever plug or ca\ilk

material you have conveniently at hand. Since you have to find the dominant

lesLk before the general noise level changes very much, it may take a little

time to find the worst leak. That is why plugging leaks as you go along is a great help. If you have access to both surfaces of a room wall, it is also

practical to explore for suspected leaks with your flashlight, having both

spaces darkened. For remote corners or inconvenient places, a hand mirror is

usefiil. You may find that a surprising amount of sound can leak through a little hole.

7-3
The stethoscope will also allow you to find the particular wall surface

through which vibrations are being radiated into the room. You can perhaps

determine whether you have any hope of removing the noise yourself, or whether

you may have to ask the upstairs neighbor to lay down a rug in his living room.

If you are searching for leaks during a period when the source is quiet,

you may have to make some noise yourself. Remember, for convenience, that it

is possible to reverse the source and the receiver in searching for a noise

path. You may be able to persuade someone to help you by pounding on an adjacent wall, or you may want to resort to one of the noisemakers we have

suggested. You can set a radio on a table, and then explore the exterior of

the room for soiind leaks. If you think sounds may be coming through by

vibration, you can set the radio on a pillow, and notice whether this makes the

sound coming through less intense. If the pillow reduces the soimd, you can resort to one of the vibration sources suggested, and then explore with your

stethoscope for the paths by which the vibrations travel.

You can explore for leaks using any simple device that generates air

press\ire, such as a small hand-held hair dryer or a vacuum cleaner with a long

narrow crevice tool fitted at the end of the hose. You can aim them at the

places "vdiere you suspect noise leaks, and explore for drafts on the far side.

You can use a wetted finger, or a candle flame (if you are cautious about the

fire hazard) to locate and trace out the pattern of the leak.

Your problem may be that both airborne and structure borne sounds are coming through. In that case, you have to make a trial estimate of which path

is dominant, for you have always to quiet the most potent source of noise

before you can proceed to the next remedy with einy hope of success.

Table 7-1 shows the way in which a listener may describe an irritating

noise problem, and lists the environmental qualities that lead to his complaint. Notice that some of the complaints are based upon secondary effects of

the interference, such as the "liveness" of a room and its noisy character.

REMEDIES

Often the remedies for quieting noise sources aj*e as simple and accessible

as the tools we have suggested for locating the troubles. You do have to keep

in mind the difference between absorbing sounds (to reduce echoes) and keeping

sounds away. It's like the difference between blotting paper and a slate roof.

You do have use for soiind absorbers to reduce room resoneinces, making for a quieter, less echoing environment. Often they do much to reduce the annoyance

from high-frequency sounds, although they are much less effective over the

entire sovind range than removal of the source of noise.

Just to give a general idea of the strategies involved in removing the

difficulties from noise, we present a table of noise abatement techniques in

/ Table 1-2. Because we pay most attention to the loudest noise sources in our environment, the order in this table is also approximately the order in which

remedies need to be applied for maximum effectiveness. It may seem to you that

7-4
some of these efforts are quite extensive, and yet may reduce the sound level

"by "only" 6 dB. If you recall what the decibel scale means, however, you will

see that a reduction of 6 dB means that you have succeeded in removing 75^ of

the noise power. No wonder it is important to select the remedies for noise

problems in the order of their likelihood for success. As you can see from the

arrangement of this bulletin, and from Table 7-2, you start by removing

resonances, reducing the probability of generating noises such as turbulence

and vibration, try to remove pure-tone components, and end by "decoupling" the

source from the path — either by enclosing it in a sound-resistant box or by

introducing sound or vibration attenuators, such as mufflers or resilient

mounts. ,

Most of the suggested remedies deal with breaking the path. As a result,

most of the techniques are those of sealing off and shock-mounting noise

soiirces. The materials for these processes are often readily at hand.

Old automobile tires and inner tubes make excellent shock mounts for

fairly large appliances, such as freezer chests or large compressor units for

air conditioners. Sections of automobile tire can be mounted as bumper strips

on the bottom of overhead garage doors. Discs cut out of old tire casings can

be used under casters on pianos, to reduce transmission of vibration to the

floor. (They also will spread the load over a wider area of a thick rug,

forming a protective surface as well as a resilient mount.)

Refrigerator supply stores and plumbing supply shops have various styles

of gasketing that can be used to seal door closures, making it easier to seal

off noise that is reaching an apartment from the outside corridor when the

leaks come through the doorway.

Household supply stores and plumbing supply shops stock various types of

non-hardening caulking compound. In addition to cutting down thermal losses

and reducing cold drafts, various sorts of weather stripping remove the rattle

from windows and help to cut down the conduction of sound from out-of-doors.

"Safety-glass" laminated window panes can be made up for replacement in window

frames to replace large areas of overly-thin glass, where the windows of a house must also cut down the intrusion of outdoor noise. Automobile glass

shops stock these sandwich glasses in large sizes, from which they may be cut

to fit your window freimes .

Bathtub mats and floor mats made of sponge or foam materials make area

shock mounts that can be placed under lighter appliances. You can make most

effective use of these mounts by choosing materials that are only partially

compressed by the load. Once the material has become greatly compressed, its

value as an isolator may be lost. The choice of padding depends upon the

weight of the load.

Some of the "closed cell" foam materials sold for upholstery and padding

make good gasketing when cut into strips. For instance, you can use a thin

strip of foam under the lower part of a double-hung window set between the

lower edge of the window and the top of a window air-conditioner unit. Not

only will it serve as weatherstripping , but because of its resilience, if

7-5
properly installed it will keep the air conditioner from rattling the

windowpanes . You do have to be carefiil to choose fire-resistant foam material

if you mount a window ventilation fan near a cookstove. Some types of

upholstery padding are not sufficiently heat-resistant for this service.

For a kitchen appliance shelf, consider setting down a slab of marble or other heavy material over a pad of soft rubber, and operating such appliances

as the blender on it. This treatment will reduce the "drumming" transmitted to

the rest of the cabinet, and can be cleaned fairly easily. The principle here

is that the marble is massive, the rubber is resilient, and only the

lowest-frequency vibrations can be transmitted to the rest of the cabinet.

Since the marble is heavy, the power needed to set it into motion would be

great; it tends to be moved only slightly by the unbalance of the blender load,

and that little motion is absorbed by the rubber. Detailed remedies for

specific noise problems are given in an indexed catalog at the end of Chapter

7, which presents an alphabetized list of common noise sources, and suggests

ways for reducing their impact upon your senses. Where a remedy has been

discussed in the text, you will find a page reference. If you find only a number following the entry, it means that there has been a detailed discussion

on that page in the text. Finally, you have another opportunity to look up

quieting in general within the final index, which includes a comprehensive list

of the topics disciissed, arranged alphabetically and interleaved with the page

references for the alphabetic index of common noise sources and their

abatement

.

LAST RESORTS

When the source of noise is beyond your control and you have done all that

is possible to break the transmission path, you have to do whatever is possible

to protect the listener if the noise level is still high enough to present a hearing risk or serious disturbance. In the next chapter, we will take up

community action, but on a more individual basis you have still the following

remedies at hand: Use noise appliances only at particularly insensitive times

of day, and provide numerous respites from the so\ind. 'Protect the user of the

appliance by ear plugs if possible. If the noise source is relatively mild,

but distracting, consider some favorable masking sounds, such as a splashing

fountain or a source of quiet music.

Brief intrusions of high-level sounds are among the most troublesome to

remedy. A recent study of aircraft flyover noise showed that reports of

annoyance tended to increase by a factor of only two when the flyover rate

increased by a factor of eight. Read optimistically, this means that if you

can tolerate one intrusion, you probably can tolerate two. From the standpoint

of an acoustical engineer who must quiet an airport area, and the commianity

that must live within the area, the situation must be viewed pessimistically.

Reducing the number of landings and departures per hour to one-half their

original number may leave a large number of delayed and disgruntled passengers

in remote airports that they did not wish to see, but still produce only an insignificant dent in the number of complaints from the residents. For a householder, this statistic is also important. If you must operate a noisy

tool, even though very briefly, it is important to try to stop the noise at the

source. Otherwise, you may find yourself the recipient of a number of

complaints despite the limited diiration of the noise involved.

7-6
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INDEXED CATALOG OF SPECIFIC NOISE PROBLEMS AND REMEDIES

ABSORBERS, SOUND

Materials: Acoustic tile, prefabricated silencers, fiber glass,

carpets, drapes, upholstered furniture. See Chapter 3.

Application: On ceilings and walls of noisy rooms, inside noisy

ductwork, appliances. See Chapter 4.

Function: To reduce noise buildup and reflection of sound, not

transmission. See Chapter 4.

AIR CONDITIONER, Central (See Chapter 4)

Compressor: Select low noise-rating number, shock mount.

Grilles, Diffusers and Convector: Select streamline units with

smooth, wide openings and low-spread discharge.

Fan: Choose slow-speed large diameter bearings and balance.

Motor: Choose symmetrical belt drive, large diameter pulleys, shock'

mount.

Ducts: Treat ducts and dampers with sound-absorbent material; use slow, large volume air-flow in preference to small, high-speed

flow.

AIR CONDITIONER, Room or Window (See Chapter 4)

Compressor: Select power adequate for job. Oversized compressor

more noisy than needed.

Fan: Large diameter, squirrel-cage type.

Gasket: Install perimeter gasket of soft rubber.

Mounting: Mount on resilient pads.

Thermostat: Starting and stopping noise more troublesome than

steady running: avoid over-power unit.

Air Filter: If the air filter in the unit becomes loaded with dust,

condensate may freeze on expander tubing and cause whistling

noise. Clean filters weekly during season to retain free air

flow.

7-14
AIRCRAFT NOISE

Note alignment of main runways and flight patterns of commercial or military airports.

Methods of avoiding; see Chapter 5.

Recommended dwelling locations: see Chapter 6.

Sound insulation - requirements of dwellings: see Chapter 5.

Recommended seat location for passenger: see Chapter 9.

AIR HAMMERS

Select units with exhaust silencer and sound Insulating jacket.

Choose minimum stroke needed to perform work. See Chapter 3.

ALARMS

Emergencey vehicles: see Chapter 2.

Noise levels: see Chapter 2.

Startle effects: see Chapter 2.

Traveling: see Chapter 2.

APPLIANCES (See Chapter 3 and 4)

Choose low noise-rating number where given.

Install properly: Use vibration mounts, resilient pads, flexible

connectors, vibration damping coatings.

Look under individual appliances by type.

BIRDS

(See Chapter 5.)

Reducing noise Intrusion: Caulk or gasket existing windows; install

storm windows. (This will also conserve energy by minimizing

temperature variation in the home.

7-15
BLENDERS

Select unit with low noise rating; see Chapter 4.

Container: prefer glass.

Housing or base: choose metal instead of plastic.

Mounting: place on resilient pads.

Use as a vibration source for troubleshooting noise problems; see Chapter 7.

BLOWERS

Choose slow speed, large diameter fan with wide blades or squirrelcage design; prefer belt-drive to direct drive. See Chapters 3

and 4

.

BOWLING ALLEY (See Chapters 3 and 4)

Reduce noise buildup and reverberation by sound-absorbent treatment

of walls and ceiling. Avoid areas where conversation can be

done only by shouting.

Alley must be vibration-isolated from building structure by means

of resilient mounting.

BUSSES

Avoid residences near major bus routes. Motors should be well

tuned, well muffled (see Chapter 6).

Tires should be selected for quiet treads; see Chapter 9.

Brakes should be adjusted and properly maintained to avoid

squealing.

Choose seats near center; see Chapter 9.

CABINETS

Choose solid, well-damped door material; see Chapter 4.

Apply mastic to inner panels; see Chapters 3 and 4.

Tighten loose strike plates.

Line shelves and backs of cabinets with cork or rubber tile to

absorb impact noise; see Chapter 4.

7-16
CAN OPENER

Place on soft rubber pad. See Chapter 4.

CAT FIGHTS, CATERWAULING

(See Chapter 5.)

Reduce noise intrusion: caulk or gasket existing windows, install

storm windows.

CHAIN SAW

Select quiet unit with adequate power; see Chapters 3, A, and 5.

Wear ear protection; see Chapter 2.

CHILDREN, VOICES AND PLAY NOISES (See Chapters 4 and 5)

Avoid play in reverberant spaces; reduce noise buildup by soundabsorbent treatment of playrooms and classrooms,

close off sleeping quarters with well-fitted windows, gasketed

doors; treat ventilation inlets with sound-abosrbing lining

CLOCKS, Alarm (See Chapter 4)

Give preference to the types of alarms that chime or turn on radios,

if you live in a multiple dwelling. Place alarm clock on a padded surface. Be especially careful not to set the alarm on

a surface leaned against a party wall between your apartment

and the one next door, or on a wall adjoining another sleeping

room.

CLOTHES DRYER AND WASHER (See Chapter 4)

Select units with low noise ratings. Vent clothes dryer where

noise will give minimum disturbance. Isolate laundry room as much as possible from other living space.

Install units on resilient pads or mounts.

Use sound-absorbing and vibration damping materials on inside

surfaces

.
COMBUSTION NOISE - FURNACE (See Chapter 4)

Have fuel-nozzle adjusted for minimum noise (this can be done with

no loss of burning efficiency). Separate furnace room from

rest of residence with fireproof partition, if possible. Air

intake in most residential furnaces is direct from cellar;

replacement with duct from outdoors can reduce noise entry into

rest of house, also might reduce need for humidifying heated

air in the house.

Flexible connector and sound-absorbing

reduce transmission of combustion

' room areas

.

COMPACTOR

Vibration isolate the unit from enclosing cabinet and floor by means

of resilient mounts and gaskets; see Chapter A.

'

. COMPRESSED AIR LINE

Select quiet blower nozzle; install silencer on exhaust port; keep

tight couplings (see Chapter 3).

. Maintain uniform diameter; avoid abrupt changes in cross-section.

V^i*^ Avoid rigid connection between pipe and wall, to prevent

"soundingboard" effect. (See Chapter 3.)

COMPRESSORS

Use muffler on air intake to reduce radiation of whistling noises,

see Chapter 3.

lining in air ducts can noise from the furnace to

Choose rotary pump rather than reciprocating pump; balance carefully.

Vibration isolate unit from surrounding structures by resilient

mounting; install flexible connectors in lines. Place unit in

sound-insulated enclosure. (See Chapter 3.)

CORRIDOR NOISE

Treat corridor floor with carpeting, ceiling with sound-absorbent

acoustic tile. Install sound insulating doors with gaskets to

reduce sound leakage into corridor space. Walls of apartments

that are common with corridor walls should be of sound-insulating

construction. (See Chapter A.)

7-18
COURTYARD NOISE

Courtyards tend to be reverberant and noisy.

Seal windows (see Chapt. 5 & 6 ), draw ventilation from other exposures. If necessary, increase weight of glazing in windowpanes

Some reduction of noise level can be obtained in a large courtyard

by planting trees and shrubs.

Avoid installation of air conditioners in areas with courtyard

exposures.

CREAKING

Common causes of creaking in a house are loose wood joints. For

floors, see a separate entry under "floors", also see Chapter A

For creaking door hinges and blinds, lubricate hinge pins. Weatherstripping improves the door seal and also restricts its freedom

to move and generate creaking sounds. Refit latches and locks.

Creaking of ductwork is caused by thermal expansion and contraction.

Mount ductwork on flexible hangers. Flexible expansion joints

may help relieve the problem.

"CROSSTALK"

Install acoustic barriers in ceiling plenums, crawl spaces, and

ventilation ducts. (See Chapter A.)

Flanking transmission (see Chapter 4 ) and small acoustic leaks

are common causes of sound conduction from supposedly Isolated

adjoining spaces. See Chapter 7 and general discussion of

"Troubleshooting" for leak-finding techniques.

DAMPER NOISE

Dampers are the vanes used to control the flow of air in ventilation

and heating ducts. Damper noise Is typically a whistling or hissing sound, and may be reduced by slowing air flow, see Chapter 4. Some improvement can be obtained by coating the

damper with a sound-absorbent coating (this, however , may impede

the flow)

.

Some flutter noise may be generated in a flexible damper; substitutl

of more rigid, heavier, or better-shaped dampers may help.

7-19
DIFFUSER NOISE

Dlffuser outlets in ventilating systems are frequent sources of

whistling or hissing. Reduction of air flow velocity is the

most effective remedy. Replace existing diffuser with a large-diameter, low-spread , better-streamlined unit. In a pinch, removing the diffuser altogether and replacing it with

a "spreading plate", i.e. a panel - treated with sound-absorbing

material on the sie toward the duct opening - suspended 4-6

inches below the opening, can be used to diffuse the air flow

without whistling. See Chapter A.

DISHWASHER

Generally, choose a dishwasher after a demonstration for quiet operation. Built-in dishwashers should be quieter because of the

limited surface for radiating sound. However, rigid pipe coupling

and drain coupling can transmit noise to the household plumbing.

Install flexible connector in pipe and drain lines to interfere

with the vibration conduction path. Load dishes so that they are

not free to flap in the washing stream. Tighten loose fittings,

especially door latches and shelf supports. See Chapter 4.

DOG BARKING (See Chapters 5 and 10)

Voice your complaint to the neighbor. Dogs likely to bark should

not be left out in the yard at night, out of consideration for

the neighbors. Your own dog makes a fine burglar or fire alarm

in your house.

Caulk or gasket windows; install storm windows.

DOOR KNOCKER (See Chapter 4)

Replace device with a door chime. Door knockers that strike too

heavily may be relieved by putting a small resilient felt or rubber pad at the point where it contacts the strike plate.

The knocker itself may be replaced by a lighter-weight part.

DOOR SLAMMING (See Chapter 4)

Install door closure dampers on all spring-loaded self-closing doors,

such as screen doors. A resilient strip (or weatherstrip)

surrounding the door closure will reduce the impace noise, as well as help seal the door against acoustic leaks. Substituting

a solid-core door for a hollow-core door may help to relieve

door-slamming and door-rattling noise.

7-20
DRAIN PIPES

The principal generator of noise In drain pipes Is turbulence from

rapid and unsteady flow. The noise, however, generally becomes

annoying because the drain pipe is fastened rigidly to some surfaces capable of serving as sounding boards. Insertion of

resilient pads in the pipe supports should reduce noise, as should spacing the pipe from floor supports by means of resilient

padding. Where a choice is available, use the largest diameter

of pipe, to maintain relatively slow, smooth flow; see Chapter 4. Use heavy-walled pipe such as ceramic or metal pipe

rather than plastic pipe.

DRILLS, PNEUMATIC

Drills with exhause silencers and sound-insulating jackets are available

.

Sounds of road-making machinery are difficult to eliminate. Repairs

on city streets using pneumatic drills should not be carried out

during sleeping hours; see Chapter 10. In many cities,

ordinances forbid such noise during night hours.

Caulk or gasket existing windows facing source; Install storm

windows

.

DRUMMING, BELT (See Chapter 3)

Looseness makes belt drumming and slapping more likely. Adjust

tension for minimum noise. If necessary, a damping idler wheel

may be installed to maintain belt tension while reducing belt

vibration.

DUCT NOISE

The principle causes of duct noise are creaking, rubbing and snapping

noises due to expansion and contraction. See Chapter 4.

Turbulent flow through ducts causes roaring sounds; see Chapter 4. Sound conducted through the ductwork as though it

were a speaking tube can be minimized by installing soundabsorbing material and sound baffles.

Dampers in ducts cause whistling noises for high-speed flow,

see entry under "dampers". Whistling generated at duch orifices

and dampers can be transmitted through the ductwork.

Use of sound-absorbent lining, flexible connectors and stiffeners

or bracing in ductwork generally alleviates duch problems.
ELECTRICAL EQUIPMENT (See Chapters 3 and 4)

Connnon sources of noise are loose laminations on transformers (which can sometimes be tightened) , sparking (indicated by a hissing,

frying sound), and, occasionally, "singing" of loosely-supported

filaments in lamp bulbs. Sparking can be prevented by tightening

electrical contacts, and by making sure that switch contacts are

' clean. Lamp bulbs that "sing" should be replaced. Loose laminations sometimes develop on the ballasts used with fluorescent

lamps; these should be replaced, preferably with more conserva-

' tively-rated ballasts. Fluorescent lamps yield more light per

watt of power than do incandescent lamps, but they tend to be

noisier than the latter. Noisy wall switches that are likely

to be turned on in the middle of the night - as in bathrooms -

^ can usually be replaced by "silent" mercury switches of the

appropriate rating.

See individual entries for specific electrical appliances.

ELEVATORS (See Chapter 6)

An elevator shaft acts as a speaking tube to transmit sounds from

the drive motors and elevator doors. Proper mounting of the

7 motors and doors can reduce the noise produced. Sound-absorbing

material can be installed in the elevator shaft, though this is

seldom done. Bedrooms should not be placed adjacent to elevator

shafts

.

Especially in tall buildings, where high-speed elevators are used,

the air overpressure and rarefactions caused by the piston

action of the elevator have to be vented somewhere; provision

of alternative vents for this pressure may be feasible, and can prevent the whistling of air past the safety strips on elevator doors.

EXPANSION AND CONTRACTION (See Chapters 3 and 4)

Long sections of sheet metal supported at infrequent intervals along

their major dimensions are likely to make "clacker" type noises

as they expand and contract with temperature. This is a serious

source of noise in air-handling ductwork. Separating the duct

into segments which are supported independently and connected

together with resilient or compliant joints can reduce sound

from this cause considerably. Sheet-metal roofing can be sealed

with mastic placed at frequent intervals where it is laid on the

roof. This can be used to minimize rattling in the wind. Careful attention to the edge of roofing can prevent the rattling

(and tearing) produced when strong gusts of wind penetrate

under the roofing and lift it.
In "vee-groove" roofing, nails should be applied through a spot of

mastic applied at the spring section at the peak of the vee. Motion of the roof relative to the nail will then tend to

clinch the roofing material around the nails.

FANS, EXHAUST

See Chapters 3 & 4. Remember the useful rhyming conditions "slow and

low". Use as slow a fan speed as can be obtained. Exit louvers

should be of easily-cleanable material and massive enough to

prevent rattling. In choosing a kitchen hood filter, give

preference to a longer section of more highly porous material

(i.e., greater thickness); this choice will tend to maintain

smooth air flow. Of course, for ease of cleaning the filter

should be interposed between the hood and the fan.

FAUCETS

For quiet valves see Chapter 4. The greatest nuisance is a dripping faucet with no immediate chance of fixing it (late at

night); simply placing a sponge or a facecloth under the drip

may reduce the sound appreciably. The traditional quick remedy

is to tie a string or shoelace to the faucet so that the drip

is channeled as a miniature stream down the string.

"Singing" of a faucet is almost always a sign of a deteriorating

washer, which should be replaced.

FLOOR NOISES

Squeaking floors and stairways; see Chapter 4. Squeaking

floors often can be silenced by inserting oil in grooves or edges of flooring, renailing, inserting wedges under warped

board, installing additional support or bracing to sagging

floors

.

A curious slapping noise on tiled floors, such as parquet and the

various linoleum, rubber and asphalt tiles can be heard if a

tile becomes loose. The loose unit can be located by walking

briskly across the floor and noting which tile emits the

sound. To prevent tile or linoleum from cracking, apply heat

from hand-type hairdryer or pans of hot water to soften surface.

Even if partly secured, tiles may be partially bent or lifted,

allowing mastic to be inserted under the loose edges. A

weight placed over the tile will hold it in place until the

cement sets.

7-23
GARAGE DOOR (See Chapter 4)

The noise generated by the opening and closing of roll-up type doors

of garages attached to the home can be reduced substantially by

mounting the track on resilient isolators and placing a rubber

gasket at the bottom edge of the door to absorb the impact

shock of closing the door.

GARBAGE COLLECTION (See Chapters A and 5)

Vibration-damped, laminated metal trashcans, which are relatively

quiet are commercially available. Cans made of heavy-gage,

resilient plastic make less noise when dropped or struck than

do ordinary metal cans.

If collection takes place at hours when it interferes with sleep,

there may be a case for community action; see Chapter 10.

GARBAGE DISPOSER

J If possible, select a unit for quiet operation. Sink units feature

J.; resilient mounts, flexible pipe connectors and a sound-insulating

outer shell. Coating the underside of sink basin with vibration

damping compound will improve the noise reduction. Installing

acoustic tile inside cabinet enclosure will reduce noise buildup.

GARDEN TOOLS ^ ^ ^ • ' v

The major noisemakers are lawn mowers and chain saws. Mowers can be

selected for quiet operation. Reel mowers tend to be quieter

(and often somewhat safer) than rotating-blade mowers. Ear

protection should be worn if needed (see Chapter 2 ) , and

attention should be paid to the community's needs for reasonable

quiet.

Since chain saws are hard to shield against noise, they should be

used only where power tools are indispensible , and attention to

adequate rest periods should be stressed.

If it is possible to extend a power cord to the working site,

electrically-operated tools may eliminate a large degree of the

noise.

GRILLS

The ventilator grilles on forced-air heating and cooling systems are

a major source of noise. The most common cause of noise is

excessive air velocity through the grilles and duct; choice of

a more streamline grille with large openings will reduce con- strictions which cause whistling. See Chapter 4.

7-24
GRINDERS

Except when it is directly engaged in grinding, any rotary grinding

tool should be so well-shielded and well balanced that it is

essentially quiet. This can be improved by careful mounting of

the grinder on resilient pads. See Chapter 3. A portable grinder can be operated quietly when set upon a vibrationisolating mount. See Chapter 4.

HEATING SYSTEMS (See Chapter 4)

These are among the major sources of annoyance. See also entries

under fans, steam radiators, furnaces.

One advantage of lowering the thermostat at night during the heating

season is that it minimizes the number of times the heating

system goes into operation during sleeping hours.

Flame noise can be minimized by proper choice of combustion nozzles

and proper adjustment. The quietest system is hot-water heat,

if care is taken to vibration isolate the system from wall and

floor structures by means of resilient mounts throughout the

house. A nois.y impeller can be replaced with a quieter one,

or the rate of flow can be reduced, which will lower the noise

output. Steam systems generate noise through air vents, which

whistle and hiss every time the steam is circulated; a two-pipe

steam system is much to be preferred to the one-pipe steam

system. Steam radiators also "hammer" if water gets trapped in

the circulatory system, a particularly serious fault of the

one-pipe steam system.

Many modern heating systems use forced air circulation because it

permits air conditioning and humidif ication to be supplied

through the same ducts. This is potentially one of the

noisiest systems unless special care is taken in its design

and installation. See entries under fans, ventilation, heating

and air-conditioning equipment.

HEATING SYSTEMS, CENTRAL AND CLOSET INSTALLATIONS

Noise associated with forced-air heating systems is due to a combination of sources, such as mechanical noise of the motor/

blower, blower-blade passage frequency, turbulence, air-flow

noise, combustion or burner noise, thermal expansion and con- traction of ductwork and pulsation and vibration of the ducts.

Substantial reductions in noise output can be made by designing

systems for low-velocity and low pressure operation. Use of

resilient mounts under the motor/blower; resilient hangers,

flexible connectors and acoustic lining in ducts will alleviate

the noise problem.

Closet installations will require in addition soundproof walls, doors

and an acoustic-lined return duct.

7-25
HUM

Most household appliances have some magnetic parts in them, such as the armatures on motors and the reactors in fluorescent lamps.

The magnetic sheets will vibrate against one another, and

generate hum at multiples of the power line frequency. Where

the frames are bolted, as in transformers, tightening the bolts

' may help to eliminate the hum. On reactors for fluorescent

lights, replacement of the "potted" unit may be the only remedy

" available. Radiation of the hum by other parts of the fluorescent

lamp may be decreased by shock-mounting the reactor (ballast);

see Chapters 3 and 4.

HUMIDIFIERS

The noise is largely from the fan or impeller.

Atomizer-type humidif ication may generate a noise from the spray

nozzle, which may be adjusted or replaced with a quieter unit.

Since the spray noise is relatively high in pitch, acoustic

baffles may help; see Chapter 4.

HYDRAULIC CONTROLS

The most common cause of trouble is valve noise, which is discussed

under that entry. Also see Chapter 3.

As a rule, hydraulic and pneumatic controls are simple and rugged,

but generally more noisy than electrical controls, with which

they can sometimes be replaced.

ICE CRUSHER

See general discussion for kitchen appliances in Chapter 4.

Like a blender, it can be made quieter by using a heavy container

for the crushing compartment, and mounting the crusher on a shock-absorbing surface.

IMPACT NOISE .

See Chapters 3 and 4 , for general principles of reduction of

impact noise in machinery, kitchen cabinets, and floors in

homes and apartments.

IMPACTOR

These devices should be operated at times that do not interfere

with sleep among the neighbors. Shock mounting helps, as does

care in selecting an appliance that is designed upon good

> ' acoustic principles. A hydraulic device can be made quiet more

easily than can a device depending upon mechanical impacts to

compress the trash. See Chapters 3 and 4.
INCINERATOR CHUTES (See Chapters 3 and 4)

Frequently these are made of relatively thin sheet metal, and the

sound made is rattling of the trash against the flexible metal

surface. Again, reason suggests that this is something not to

be used during normal sleeping hours.

The metal chute should be structurally isolated from the building

walls by means of resilient mounts. The exterior surfaces of

the chute should be coated with a vibration damping compound

to reduce the^ drumming resonance of the chutes caused by the

impact of trash or refuse.

JACK HAMMER

Workmen should wear hearing protection. Work with these implements

should be confined to normal waking hours. Avoid long, con- tinued use of the jack hammer, allowing recovery periods. See

Chapter 2.

These may be a case for community regulation; see Chapter 10.

Frequently, an additional source of noise is the compressor

supplying air power to the jack hammer. Adequate muffling is

available, and should be required.

See discussion under compressors and compressed air line in this

index.

KITCHEN APPLIANCES

With the exception of washers and dryers, most kitchen appliances

are used for brief periods of time. However, several

appliances may be in use simultaneously such as clothes washer,

dryer, dishwasher, garbage disposer, etc., which can generate

a rather high level of noise.

For methods of selecting appliances and proper installation see Chapter 4.

KNIFE SHARPENER

Place the appliance on a soft resilient pad to isolate it from the

kitchen counter top or working surface. See Chapter 4.

LAUNDRY ROOMS

The principal sources of noise are clothes dryers and clothes

washers; refer to these entries. These rooms tend to have

hard surfaces and are likely to be very reverberant. Noise

buildup can be reduced by installing sound absorbing material

such as perforated metal tiles backed with glass-fiber pads,

which will withstand the moisture. Resilient mounts should

be placed under all machines; see Chapters 4 and 6.

7-27
For gas-operated dryers and water heaters, consider using an exterior-opening duct to draw outside air for combustion,

'-j This will reduce radiation of combustion and burner noise.

LAWN EDGERS

These tend to be as noisy as gasoline engine-operated lawnmowers

but have a high-speed blade, which emits a somewhat louder and

more irritating high-pitched noise. This is a case for

selecting a quieter appliance. Ear plugs should be worn; they

are especially effective against high-pitched noise.

LAWN MOWERS

Rotary Power Type: Select model with low noise rating, preferably

with under-deck exhaust. Replace the conventional muffler

with a new, somewhat more expensive, but highly effective

model. Sharpen cutting edges of blade and balance blade.

Tune engine and reduce speed; tighten loose and rattling parts.

The above measures should provide about a 6-dB or about a 25-

percent reduction in loudness. Generally speaking, noise

i levels at the user's position frequently exceed 90 dB(A), although this does not pose a hearing hazard because of the brief

; J use of the mower, once every week or two. However, it may

prove very hazardous to workers whose daily occupation is the

mowing of lawns, park lands or the grounds of large institutions.

Parents should consider this point very carefully before allowing

their children to mow lawns to earn money on weekends or during summer vacations. In any event, ear protection should be worn

by all workers exposed to such noise for extended periods. Refer

to Chapter 2 for a discussion regarding noise-induced hearing

damage. Re 11- type power mowers, because of their smaller radiating surface, are somewhat less noisy than the rotary type.

Properly designed electric-motor type mowers generally are the

least noisy. Mower manufacturers can make substantial reductions in the noise out of their machines by adopting the following recommendations.

(a) Install the most effective, not the cheapest, muffler

available.

(b) Vibration isolate engine from the mower deck.

(c) Except for the cutting edge, design a blade with

rounded comers and a serrated or feathered trailing edge.

(d) Underdeck should be designed for smooth streamline

air flow passage ways devoid of any obstacles or sharp corners.

(e) Coat the deck of the mower with a laminated composite

virbation damping or undercoating material.

(f) Enclose engine compartment in a sound-insulating

jacket or cover.
LAWN THATCHERS

Fortunately, these are used infrequently on any given lawn. The

noise problems are common to those of lawn mowers and edgers

,

i.e. the motive power for them is a potent source of noise.

Select units with well-muffled engines. See related entries.

The operator should wear ear protection.

LEAF BLOWERS

Choose a model with a well-muffled engine, large air-inlet apeture,

a squirrel-cage blower, and a streamlined discharge nozzle.

Select attachment hoses that have smooth inner surfaces.

Operate blower at slowest speed that will perform the chore.

LEAF SWEEPERS AND MULCHERS

Select machinery with well-muffled engines. Leaf sweepers are available in two types - the vacuum sweeper and the rotating

brush types. Requirements for quiet operation of the vacuumtype sweeper are similar to those for a leaf blower. Canvas

hoppers should be selected rather than metal to absorb the

noise produced by the impacts of stones, acorns or debris.

Metal hoppers should be coated with a vibration damping

compound. The cutting and blowing action of a mulcher also

can be reduced somewhat by coating the inside surfaces of the

metal housing with vibration damping material.

LIGHT SWITCHES

Silent light and thermostat mercury-type switches are available.

Rotary-disc type switches also are relatively quiet in operation compared to the spring-operated type switches.

MASKING NOISE

See discussion under "acoustic perfume." '

MECHANICAL EQUIPMENT

See individual entries in this section and in Chapter 3 for methods

of reducing the noise output of various types of machinery and

mechanical equipment.

MOTORS

On electrical motors, unbalanced loads and worn bearings are potent

sources of vibration and thumping noises; dry bearings screech.

7-29
Stray electromagnetic field from motors can set steel housings into

vibration; replacing steel housings by brass or other non- magnetic material may alleviate this noise problem.

Motors should be set up on resilient mounts' and vibration isolators.

MOTORBOATS

Relatively quiet outboard motors are available. They come equipped

with vibration isolating mounts, sound insulating jackets, and

under-water exhaust systems. Inboard motors with basically the same features can be installed in an acoustically-lined, soundinsulated enclosure to provide a greater amount of noise re- duction. Electrical, battery-powered motors which operate

quietly are available for light use, such as trolling or fishing. In addition they do not pollute the water.

MOTORCYCLES

Quiet mufflers are available. Except for delayed adolescence, there

is no reason to use a poorly-muffled vehicle. With a properly

, designed muffler, power from the engine will be more smoothly

developed, and greater fuel efficiency can be expected.

MUFFLERS

In general, these are sound-absorbing chambers placed on the exhaust

of internal combustion engines to prevent the discharge of

noise from the combustion process. As a temporary measure,

additional muffler action can be improvised by lining a largediameter metal can with a pad of glass fiber and inserting a slotted, smaller-diameter can. This double wall muffler should

be attached to the end of the exhaust pipe.

To work properly, a muffler must be designed for a given noise

spectrum, sealed carefully to the exhaust pipe, and must itself

have substantial, non-rattling walls, and snd sound baffles.

MUSIC . . -

Unwanted music becomes noise. Two rival sources of music generate

cacophony. Rock bands approach sound levels hazardous to

hearing (see Chapter 2). Similar levels can occur with some "Hi-Fi" systems.

Avoid places that feature such loud music. Warn your children about

the hearing hazard. See Chapter, 4, Recreation Rooms, for

methods of sound-proofing rooms against loud noise or music.
NAIL GUNS

Relatively quiet models are now commercially available. Avoid prolonged use of the device on a daily basis unless hearing protection is worn.

NEEDLE VALVES

The characteristic noise emitted by a needle valve is a high-pitched

hiss. Examine valve and replace it if it is defective. Vibration isolate valve and associated piping from large radiating

surfaces by means of resilient pads or sleeves. Enclose valve

in glass fiber padding with an outer jacket of leaded vinyl.

OFFICE EQUIPMENT

See Chapter 8 for methods of quieting office machines and equipment.

OUTBOARD MOTORS

See discussion under MOTORBOATS.

PIPES

See Chapter 3 for design of quiet flow systems, and Chapter 4 for

control of plumbing noise.

PLUMBING NOISE

See Chapter 4, Control of Plumbing Noise.

POLISHERS

Quiet models are available. These feature slow-speed, large

diameter rotating discs which can be fitted with brushes or buffing pads.

POWER TOOLS

Variable speed tools like drills and scroll saws are less noisy than

the high speed/torque models. Operate the tool at lowest speed

capable of doing the job. See entries under specific type of

tool.

PUMPS

Sump pumps and automatic-leveling water pumps are serious noise

offenders, particularly if a quantity of water is drawn late

at night. Vibration isolate the pinnp from the building and

connect it to the plximbing via flexible tubing. Seal connectors

carefully for maximum pumping efficiency (briefest operating

time)

.

7-31
Pumps for compressed air systems are exceptionally noisy devices.

See Chapter 3, Section 5 and Chapter 4, Control of Plumbing Noise.

RADIATORS

Steam radiators are inherently noisier than hot-water radiators;

one-pipe steam systems are noisiest because of air-venting

requirements and the frequent onset of vapor lock (water con- densed from cool steam blocks the access of new steam in the

pipes which causes intermi-tent hammering). Select a hotwater system which features large diameter pipes and low

velocity flow. Vibration isolate the impeller pump from the

building structure. Separate the pump from the pipe system

by means of flexible connectors. "Bleed" dissolved air out

of hot-water system at regular intervals to avoid hammering

sounds from trapped air bubbles. See Chapter 4 relative to

steam and hot water heating systems.

RADIO : . ":::) '[ -

' '

Adjust volume control of the radio so that the sound level of

commercials (which usually are about 5 dB higher than program

material) is at a confortable conversational level.

RAILROAD f:'|f--^

A railroad is a source of vibration as wll as airborne noise. Select

dwellings that are at least one mile, preferably two miles, from

a railroad line. See Chapter 6, selecting a quiet home or apartment site.

If you live near a railroad see Chapter 5 for recommendations regarding insulating your house against outdoor noise.

RAIN GUTTERS AND SPOUTS

A major noise source is the turbulent flow and irritating dripping

of rainwater in the gutters and down spouts.

Select rain gutters of heavy gage metal, rounded bends and coated

with vibration damping material. Avoid Installing vertical

drains outside of bedroom areas; isolate drains from the

building structure by using soft rubber sleeves at pipe clamps

and gutter spouts. Replace conventional metal elbow duct at

base of down spout with a soft rubber boot or plastic hose.
REFRIGERATORS

Select units for silent operation. Frost-free refrigerators are operated with numerous fans, all more-or-less contributing to

a noisy kitchen. Any refrigerator will be less noisy if it is

mounted on resilient pads on a solid floor. See Chapter 4,

Kitchen Noise, item 12.

RISERS

Vertical ducts or ventilation risers mounted on the exterior of

buildings frequently are the cause of noise complaints. Such

devices often rattle in windy areas or snap, crackle and pop,

owing to thermal expansion and contraction with outdoor

temperature variation. Further, the outdoor noise of aircraft,

traffic, etc., are easily transmitted by the thin-wall duct and

carried into the building interior. All exterior ductwork

should be of double-wall construction with acoustic lining and

silencers. Risers should be vibration isolated from exterior

walls by means of resilient mounts at all points of support.

ROCK AND ROLL

Just possibly, this term may become obsolete before this publication,

but anyone who has been exposed to amplified music has heard

the noisiest part of "Rock and Roll." The sound levels generated can be high enough to damage the hearing of audience, performers, and bystanders. See Chapter 2.

If you must have a rock-and-roll session at your house, and if you

must play the music so loud that you experience the pleasurably

giddy sensation that high sound levels seem to produce in some

people, the only way to avert noise complaints is to give a block party and invite all the neighbors in.

Obviously, shutting all windows and doors will reduce the amount of

noise escaping outdoors.

ROOFING

"Rain on a tin roof" is a proverbial source of noise. Metal roofing

can be quieted to some extent by mounting it over a layer of

mastic. Slate roofing is strong and relatively quiet, though

liable to breakage by hail and repeated freezing and thawing,

but can only be applied to a roof structure capable of withstanding its great weight. Asbestos roofing is quietest, but

most likely to tear in high winds. Massive roof materials

like lead, copper, and slate serve best as barriers against

exterior noise; sound insulation of the roof of a house is

just as important as it is for the walls.

7-33
ROTOR TILLERS

The noise generated by a rotor tiller is comparable to that from a motor lawn mower; see entries under LAWN MOWERS.

SANDERS

Since most noise is generated at the contact between the disc or belt and the work, little can be done to prevent noise from

being produced. At the factory wear ear protection. Provide

- for adequate rest periods away from the noise. Work in wellventilated areas, preferably treated with sound-absorbing

baffles or acoustic tile ceilings.

SAWS; BAND, CHAIN AND CIRCULAR

Noise reduction at the source is difficult. In the case of chain

saws, a good muffler can make a substantial reduction in noise

output

.

Wear ear protection and provide for adequate rest periods away from

the noise during the working day.

SEWING MACHINES

The reciprocating motion of the machine generates considerable impact noise. Place rubber pads under the legs of the machine

cabinet or under the machine itself if it is a portable tabletop model. Resilient mounting of the machine in the cabinet

will result in a noticeable reduction of noise.

SHAVERS, ELECTRICAL

Motor-driven models are less noisy than vibrator types.

SHOWER STALLS

Shower stall should be mounted on a resilient pad or underlayment.

Plumbing fixtures and drains should likewise be resiliently

mounted. Metal or fiber glass stalls should be coated with

vibration damping materials. See Chapter 4 on control of

plumbing noise and Chapter 3 on vibration damping materials.

SIRENS

Audibility is a natural requirement, useful except for those who live

near an emergency facility such as a fire station or hospital.

Fortunately, the spectral distribution of sirens clusters within

the 500-2000 Hz frequency range, which can be excluded to a considerable degree by closing off living quarters from outside

noise, just as one tries to do for highway noise. See Chapter

5 for reducing the intrusion of outdoor noise into the home.

See Chapter 2 relative to detection of sirens.

7-3A
SNOW MOBILES

Many communities are beginning to regulate the noise emission that

will be tolerated from snow mobiles and other all-terrain

vehicles

.

Select machine on basis of low noise output. Such machines feature

effective mufflers, acoustical lining and vibration damping

treatment. As a precautionary measure, ear protection should

be worn, particularly during periods of extended or prolonged

use.

SOLENOIDS

Many automatic household machines such as dishwashers and washing

machines use electrically-operated solenoids to open and close

input and drain valves. The basic mechanism is a rod of

magnetic material operated by a coil. Usually, a fairly heavy

impact occurs when the solenoid is actuated. Shock-mounting

the device may help to confine the noise to the machine and

its immediate vicinity. Sometimes, a solenoid held back by a spring will vibrate when the slot in which it travels becomes

worn, and replacement will cut down the hum level significantly.

STAIR CASES

The impact from footsteps can be minimized by placing carpets or resilient pads on the treads. Stair halls are often needlessly

"live", and can be quieted considerably by the use of fireproof,

sound- absorbing material on the upper walls.

In apartment buildings, staircases that are sealed off with fireproof doors equipped with quiet closures minimize not only the

fire hazard but, also noise interference.

STEAM AND PRESSURE-REDUCING VALVES

Such valves are exceedingly noisy. Replacing existing valve with a number of smaller units to affect a gradual reduction in

pressure will lower noise output considerably. Enclosing

valves in a gypsum board or plywood box, or duct packed with

fiber glass is an effective means of reducing the noise level.

SWIMMING POOLS

The hard tile surfaces surrounding swimming pools cause the area to

be highly reverberant and thus buildup noise made by persons

at play within the pool. Various types of sound absorbers can be used within indoor pools to reduce echoes, but seldom are. Of course, the water surface is a reflector.

7-35
Pumps and circulating water are additional sources of noise. A

rooftop swimming pool is a nearly insoluble source of noise to

' the residents beneath. Such installations require vibration

isolation of the pool, plumbing and filtration system from

the building structure.

SHOCK WAVES

Also see entries under THUNDER.

By the time these reach your house, they usually will have spread

out, been echoed off many surfaces, and lost some high-frequency

sounds by absorption.

House structures that exclude traffic noise will also do rather well

with shock waves, but in their infrequent occurrence, they

offer problems with startle and short-term interference that

are more like aircraft flyover noise. This involves a community

decision with respect to supersonic aircraft, and also with

helicopters, which generate a minor shock wave in their near

vicinity - "blade slap". See Chapter 9.

STEREO SETS

See entries under MUSIC.

SUMP PUMPS

See discussion under PUMPS.

TELEPHONE

Most telephones are equipped with a volume control to adjust the

noise level of the bell.

If you need only to know when there is a call for you, and don't

wish to have an audible signal, you can arrange to have the

ringing signal replaced by a flashing light. This is done

routinely by the telephone company for hard-of-hearlng clients,

and is available in most systems.

If you are hard-of-hearing, and the telephone is in a noisy environ-

' ment , you can improve your chances of hearing the conversation

by having your hearing aid fitted with a telephone pickup coil,

which picks up the electrical signal from the earphone of the

telephone. This will reduce markedly the competition from the room noise.

7-36
TELEVISION

Many problems with television receivers are like those from "Hi-Fi"

sound systems and rock bands; i.e., people play them at a level objectionable to the neighbors. However, another source

of objectionable sounds is the high-pitched noise of a poorlyadjusted television receiver. Persons with normal hearing can

find this noise quite troublesome; however, it can be removed

by having the receiver readjusted.

In apartment buildings TV noise disturbance can be reduced by

requesting tenants to locate their sets away from party walls,

and to place resilient pads under the legs of the cabinet.

THERMOSTATS

See discussion under LIGHT SWITCHES.

TIRE NOISE

See Chapter 9, Automobiles.

TOILETS

See Chapter 4 on control of plumbing noise.

Water flow in the drains is a major source of noise. "Silent

flushing" toilets are available.

Syphon-Jet toilets with flush-tank fixtures equipped with adjustable

flow valves are considerably less noisy than conventional

models. A high-pitched noise which occurs when the flush tank

is being refilled usually is a sign of defective seals. Replacement of the seals eliminates the problem.

TOOLS

See entries for individual tools such as "Saws", "Lawn Mowers",

"Grinders", etc.

TOYS

Toys perform useful functions for children, but their use does not

Justify risking a child's hearing.

Explosive devices such as cap and air pistols are a serious hazard,

now subject to regulation in many states (see Chapters 2 and 10).

The regulations do not protect against the use of noisy toys in rooms with hard, reflecting walls that will permit the noise

to build up. It is likely to be a good idea to restrict noisy

toys to out-of-doors, where the chances of reflections and

reverberation are lessened.

7-37
Musical instruments, such as trumpets, should not be put into the

hands of children who might carelessly blow them in the near vicinity of another child's ear. Noisy firecrackers are banned in many places, primarily as a fire

and explosion hazard, but occasionally a child may be deafened

permanently by another child's pramk. This loss, though less

visible, is a very serious problem.

TRANSFORMERS .C^^L:^

A transformer carrying a fairly large amount of power can be a

. J. serious noise problem. The core of the transformer is made up

of layers of magnetic iron alloys. Occasionally these layers

("laminations") work loose and vibrate with the frequency of

the alternating current passing through the transformer. On

large transformers, there is often a provision for tightening

the bolts holding the laminations together. On cheaper

appliances, such as the fluorescent lamps and high-intensity

lamps, the laminations are "potted" in a tarry mixture, which

may become heated and leak out, permitting the laminations to

vibrate. These must be replaced.

TRAFFIC NOISE - , !

- i^

For reducing invasion of traffic noise into your living quarters,

see Chapter 5, Reducing the Intrusion of Expressway Traffic

Noise

.

TRAIN NOISE .

Airborne noise from a train can be treated like traffic noise, see Chapters 5 and 6.

For selection of quiet accomodations while travelling in trains,

see Chapter 9.

TRUCK NOISE .

'

^ 'O-

. For tire noise, see Chapter 9.

For protection of dwellings from truck noise, see Chapters 5 and 6.

VACUUM CLEANERS .

, ,

'

Relatively quiet models are now available. Such cleaners feature

improved blower and air passage design, vibration isolation

of the motor from the housing, and use of sound absorbent

and vibration damping materials within the housing or cannister.

In cannister-type cleaners, replacing corrugated hoses with

smooth-wall hoses may eliminate pure-tone whistling noises

caused by air flow turbulence in the hose.
VALVES

Quiet valves are now available. Since a valve involves the con- striction of fluid flow, it is always a potential source of

noise.

A smooth flow path for the fluid should be provided at the entrance

and exits of the valve. See Chapter 3 for design of quiet

flow systems. A valve that gradually becomes noisier, generally

has worn gaskets, seals or valve seats. Replacement of the

defective part usually alleviates the noise problem.

Reduction of water or fluid pressure frequently lowers the noise

output substantially.

To prevent valve noise from being carried all over the house, con- sider the following measures: isolate the valve from the

rest of the system by mechanically flexible couplings; avoid

rigid clamping fluid-flow systems to such sound boards as floors and walls; run the piping through sound-treated ducts.

See Chapter A, Control of Plumbing Noise.

VEHICLE NOISE

See entries under Traffic Noise and under individual types of

vehicles, such as automobiles, trains, etc.

VENTILATION SYSTEMS

See Chapter 4, Control of Heating, Ventilating and Air-Conditloning

Noise.

VIBRATION

See discussions in Chapters 3 and 4 relative to vibration isolation

and control of structure-borne noise.

WALLS

See Chapter 4, Improving the Sound Insulation of Walls.

WATER COOLERS

These have major noise sources in the refrigeration equipment and

in the plumbing connections. See entries under Compressor,

Plumbing Noise, Valve Noise, Refrigerators, and Valves.

See Chapter 4, Quieting of Large Appliances, for methods for

shock-mounting appliances.

WASHING MACHINES

See entries under Plumbing Noise, Valves, Solenoids, and Drain

Pipes. See Chapter 4, Quieting of Large Appliances.

7-39
WATER NOISES

r See Chapter 4, Control of Plumbing Noise.

WATER HAMMER

See Chapter 4, Control of Plumbing Noise.

Water is a heavy fluid; when its flow is interrupted, its inertia

will produce a sharp rise in pressure at the shutoff valve.

Starting and stopping the flow of water gives rise to "water

hammer", unless some means of prevention is applied. In

plumbing systems, an air cushion is used to absorb some of

the shock. A defective washer in a tap, by producing a sharpley intermittent flow of water, can be a potent source

of water hammer, easily remedied by putting in a new and

better-fitting washer. Gate valves are more likely to produce water hammer than are needle and globe valves.

Water hammer can also occur when piping systems are poorly

supported on "V" shaped wire hangers. Placing a rubber sleeve

around the pipe and clamping it to some solid structure will

resolve the problem.

WINDOWS V- , vl.}-..>i ^

If loose window panes rattle, look for breaks in the putty. If

the entire frame rattles, check the adjustment of springs or weatherst ripping. Double-hung windows in aluminum guides can have the guide spacings adjusted for good fit. Sliding and

casement windows are harder to quiet because they are harder

to seal or weatherstrip properly.

In a pinch, you can make a temporary stop to window rattling by

forcing a wedge of wood between the panel and the window frame,

or by wedging the space between the panels of double-hung

windows. A more satisfactory and durable repair is to refit

the window sashes and install adequate weatherstripplng.

Storm windows provide acoustic insulation as well as thermal insulation, and in the interest of quiet, can be left on windows

that need not be open.

WHISTLING NOISES

Turbulence generated by air flow past the edge of an obstacle at

high speed generates a whistling note.

This is, of course, made use of in flutes, whistles and pipe

organs, but it occurs where it isn't wanted, in wires, air

ducts, dampers, air-conditioner and heating grilles, and on the blades of fans, usually around obstacles that have sharp

or rugged edges or narrow restrictions.
Turbulence is a very strong function of flow velocity, and lowering

the fluid flow by a relatively small factor can get rid of

many whistling noises immediately.

See Chapter 3 on design of quiet flow systems and Chapter 4, Control

of Plumbing Noise.

7-41

Chapter 8

NOISE CONTROL AT THE OFFICE

Noises at the office often can reach levels high enough to interfere with

a person's ability to do his work. Interference in coimnimication, disruption

in concentration, and invasion of privacy are ajnong the chief complaints.

NOISE SOURCES

The main sources of noise in most offices are:

conversation among workers and on the telephone,

noise from typewriters,

ringing telephones

,

noise from office machinery, such as copiers, teletypers, etc.,

noise from ventilation systems,

and intr\ision of outdoor noise, such as traffic and aircraft.

REDUCING THE NOISE

In order to control the noise the first thing to do is to examine the

office environment. If the wall, ceiling, and floor surfaces are hard and

smooth the space will be excessively reverberant and will tend to ajnplify the

noise to disturbing levels. Installing an acoustical ceiling, draperies, euid

good quality carpeting will lower the noise level approximately 5 to 6 dB (or

approximately 1/k to 1/2 in loudness).

Typewriter noise may be reduced by placing soft rubber pads xmder the

machine to prevent vibration of the desk top. Applying vibration damping

material to the underside of the desk top or typewriter stand, partic\ilarly if

it is made of metal, will tend to reduce the soiinding board effect axid the

visual noise buildup.

The noise of ringing telephones may be reduced almost to inaudibility.

There is a control in the base of the telephone that adjusts the ringing

volume. The control can be reset to lower this volxjme. In fact, the bells can

be replaced with flashing lights in most instances.

Office equipment like copiers, teletypes, computers, card punches and

printers often are exces&ivly noisy. If at all possible, such equipment shovild

be installed in a separate room, such as a storage area. Otherwise, they

should be located in an area as far as possible from office personnel.

Acoustically lined barriers or partial enclosvires should be placed around the

machines to confine the noise. Any other noise control measures usuaJLly

8-1
require making modifications to the equipment itself as illustrated in Fig.

8-1. This shovLLd be done when the machine is idle or awaiting repairs, and

preferably by a skilled technician or repair man. In most cases, the machine

noise can be reduced by adopting the following recommendations in the order

listed. This order is chosen on the basis that noise from the major source must be attenuated before reduction of the noise from subsidiary sources will

have any significant effect.

li.. Cover all ports or openings aroiind card piinches, copiers, readers

and printers with 1/k inch (6 mm) thick clear plastic shields edged

with soft rubber gaskets to maJce an airtight seal.

2. Wherever possible, vibration-mount all drive motors and cooling fans on rubber pads, or use rubber grommet-type sleeves on mounting

,"' bolts. ,

3.. Treat all console panels with viscoelastlc-type e.g., gum mastic,

vibration damping material.

Install 3/^ inch (19 mm) thick fiberglass board liners on the inside

surfaces of console paneling to reduce the noise build-up in the

hollow reverberant cavities.

5. Install acoustically lined ducts at intake and discharge sides of

cooling fans . ,

6. , Install resilient pads or vibration isolators under all equipment to

reduce low frequency vibratory transmission to the supporting false

floor.

: ...^ .g. 5 Install acoustically-lined U-shaped partial enclosures around

individual card punches, readers and printers.

,8. V If a choice is available, give preference to many-bladed slow speed

fans and wide ducts in providing for the cooling of equipment.

The above measures shoiild be attempted a step at a time in the order

listed \intil the noise level in the office is reduced to acceptable limits.

However, the most effective way of quieting office equipment is to incorporate

good noise control techniques early in the design stage. In many cases,

objectionable amoiants of noise are generated at the supply and return grilles

of the ventilation systems. This is especially true where such systems are of

the high velocity-high pressure types. If the noise at a grille is highpitched, it is more than likely generated by the high velocity air flow

striking the grille deflectors. A quick test to determine the cause of noise

is to remove the grille. If there is a marked reduction in the noise output

with the grille removed, it is evident that either the grille is at faiilt and

should therefore be replaced with one with better design (that is, more

streamlined and with wider spaced deflectors) or if practicable the air speed

in the duct should be reduced by 10 to 15 percent. A slight reduction in fan

speed will often restilt in a noticeable reduction in noise. If there is no

8-2
appreciable reduction in the noise output without the grille, the noise may be

due to other sources farther back in the duct system. Measures for controlling

noise in ventilation and duct systems are discussed in Chapter k.

EXTRANEOUS NOISE

The intrusion of noise from outside sources such as automotive traffic or aircraft flyovers can be minimized by improving the sound insulation of the

windows, which usually are the weakest acoustical barrier against outdoor

noise. Seal existing windows tightly with non-hardening caulk; if additional

soiind reduction is required, try installing a storm window, preferably encased

in a rubber gasket. See Chapter h for more detailed instructions for minimizing the intrusion of outdoor noise.

PRIVACY BETWEEN OFFICES

If lack of privacy between offices, as for example, between an executive's

office and the outer office, is of major concern, you should examine walls,

doors, and ventilation ducts separating the two spaces to determine their sound

insulating capabilities as well as the presence of noise leaks. In most cases,

the door separating the office areas is the weakest barrier against indoor

noise transmission. More than likely it is a hollow core door, constructed of

thin veneer panels and with an open air space of 1/2 inch (13 mm) or more at

the base. Such a door at best will provide a noise reduction of only 10 to 15

dB. Replacing the door with a solid core, sound proof door with gasket seals

at the top ajid sides and a drop closure at the base will correct the problem.

However, if the partition wall separating the two offices extends only to

the underside of a suspended ceiling, noise from one office can easily travel

through the ceiling plenum over the walls and emerge into the space on the

other side. Measures to correct this problem involve installing an acoustical

barrier of lead sheet and fiber glass blanket in the plenum space immediately

above the wall. Noise leakage at the base of the wall can controlled by

caulking the bottom edge on both sides of the wall with a resilient,

non-setting coii5)ound.

Ventilation ducts serving both spaces shoiild be acoustically lined or equipped with baffles to prevent them from acting as speaking tubes. If

additional sound insulation is required after the above measures have been

adopted then an additional wall or resilient attachment of a layer of gypsum

board to the existing' wall will be required. This would involve attaching

furring strips to the existing wall, fastening resilient metal channels

horizontally across the furring strips, and with self-tapping screws, screwing

the layer of wallboard to the channels.

A relatively simple and moderately effective measure for improving the

privacy between two offices is to locate personnel, desks, office machines,

file cabinets, etc. in both offices as far as possible from the intervening

wall, and especially the door, as illustrated in Fig. 8-2.

8-3
PRIVACY IN OPEN-PLAN OFFICES

In large open-plan offices with many employees, acoustical privacy is

difficult to achieve between the work zones. Where privacy of a confidential

nature is important in various work zones , speech originating in any one zone

must be made either unintelligible or non-distracting when heard in adjacent

zones. In order to achieve satisfactory privacy, a highly sound absorbent

environment throiighout the entire office area is mandatory. This cem best be

done by installing acoustical ceiling with a very high sound absorbent rating,

erecting acoustical beirriers around work zones, introducing an unobtrusive

broadband "masking noise", (similar to the sound of a splashing foiintain or air

diffuser noise) and decorating with carpeting and draperies. The work zones should be situated no less than 15 feet (U.6 m) apart. The factors controlling

privacy in open plan offices are illustrated in Fig. 8-3.

The acoustical ceiling should be installed at a height of 9 feet (a little

less than 3 m) or less. For best results the ceiling should be suspended to

provide a plenum of at least 30 Inches (T6 cm). The ceiling tile or panels

should have a NRC, Noise Reduction Coefficient, of between 0.70 and 0.80. The

NRC ratings usually appear on the labels of the cartons containing the tile.

The acoustical barriers should be at least 5 feet in height, (1.5 m) 8

feet (2.5 m) in length with a sovind absorbing layer 2 to U inches thick (5 to

10 cm) . Acoustical barriers encased in metal frames and faced with fabric are commercially available. Such barriers should be placed directly on the floor

and positioned so that they will shield the employee from any line-of-sight

so\irces of noise or reflecting surfaces. In other words, the barriers should

be arranged so that they break-up all direct paths of sound travel from one work area to another. The larger and taller the barrier the greater is its

effectiveness

.

Soiind systems which produce specially designed "masking" noise are commercially available. Such systems include a number of loudspeakers which

generally are installed above the suspended acoustical ceiling. The level of

masking noise should be high enough to over-ride distracting noise sources in

the office, but yet must be low enough not to interfere with conversation in a given work area. This points out one of the limitations or risks of using

masking noise, even if it specially shaped, to improve speech privacy. If the

level of masking is too high, people will tend to talk louder, in order to

maintain intelligibility. Consequently, their conversation will be more eeisily

understood in other areas. Thus, instead of improvement there is actually a reduction in the degree of privacy provided by the masking.

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Chapter 9

NOISE CONTROL WHILE TRAVELING

Prolonged exposure to noise and vibration, even at moderate levels,

produces a certain amount of fatigue and irritation. This explains why most of

us usually have experienced a feeling of exhaustion and irritability following

a day-long automobile or bus trip or a cross-country Jet plane flight, even though we were supposedly resting comfortably in our seats or simply relaxing

while reading, conversing or watching the scenery roll by.

According to a recent- survey many cars and trucks traveling at expressway

speeds generate such intense infrasonic sound (i.e., sound below the threshold

of human hearing) and such vibration levels within the vehicle that drivers are adversely affected by them. They experience symptoms brought on by stress

including fatigue, irritability, recklessness, euphoria, dizziness emd lowered

efficiency and vigilance.

Noise levels of about 100 dB in the infrasonic range have been measured in

these vehicles, with windows closed. When windows were opened the noise levels

increased to 110-120 dB. Infrasonic sounds, althou^ they cannot be heard, are

felt or sensed as separate pulsations.

An individual person has no control of the noise levels while he is

traveling in public transportation vehicles such as buses, trains, or airplanes. He has at his disposal several techniques, however, which can be used

to make a substantial reduction in noise level in the automobile he drives.

AUTOMOBILES

1. Select A "Quiet" Automobile : The first course of action is to

purchase or rent cars which eire specifically designed to be quiet. As a rule they are considerably less noisy than other cars.

2. Drive at Slower Speeds : Driving at slower speeds results in less wind

noise, engine noise, tremsmission noise, road or tire noise and reduces

the low frequency noise and vibrations described above.

3. Drive with Windows Closed : Driving with car windows closed may reduce

the interior noise level including infrasonic noise, by 10 to 20 dB. The

roar of rush ho\ir traffic is likewise greatly reduced. Unfortunately,

siren noise is equally diminished, therefore the driver has to be

especially alert for approaching emergency vehicles. Turning off the

radio and cooling fan would help to lower the interior noise level and

thus maJce emergency signals more audible.

h. Use Air Ventilators : If air ventilation is required in the car, as on

a hot summer day, the driver should use the car's air conditioning or ventilation system rather than open windows. In the event a car window

must be opened to provide ventilation, opening the rear window -

9-1
preferably farthest from the driver - usually 'exposes him to the least

noise. The worst condition, and unfortunately the one most commonly

chosen by the driver, is to open the windov nearest him. Especially at

expressway speeds, this places his ear virtually vrithin the source of very

intense wind noise and air turbiilence. The common driving habit of

resting an elbow on the window ledge and sticking it out into the wind

stream usually intensifies the noise and vibration levels. It is no wonder that a driver completing a sustained, high-speed trip under these

conditions might feel exhausted, dizzy and short-tempered.

5. Use Slow Fan Speed : With rare exception, air conditioning,

ventilation and defroster fans in most automobiles are excessively noisy

at their high speed settings. Since fan noise is highly related to the

speed of the blades , even small reductions in fan speed often result in

noticeable reductions in noise output. It follows that to minimize noise,

you should try to achieve adequate ventilation for the lowest possible fan

speed.

6. Turn Off the Radio : It is seldom recognized that sustained exposure

to moderately loud radio noise causes some acoustic fatigue. To

demonstrate this fact to those who ordinarily drive with their radios

blaring, may we suggest that they drive home from work some evening with

the radio t\irned off. They might discover to their surprise that they

arrive home less tired. Try it - you might like it!

7. Select Quiet Tires : Some types of passenger car tires are noisier

than others. Some make a singing or whining noise, while other - like

snow tires - produce a low-pitched rumbling or humming noise. Generally

speaking, the noise output of a tire is influenced by tread design. The

buyer has a choice of three basic types of tread designs: continuous rib;

block; and cross-bar, as shown in Fig. 9-1. Tires using the continuoiis

rib pattern are relatively quiet. Furthermore, the buyer should select a continuous rib tire with a randomized or nonsymmetrical design; that is, one in which the design of each individual rib is different and the number

of transverse grooves or slots between each pair of ribs is different.

Such tread designs tend to smooth out pure-tone hum into a less

objectional broadband noise. The noisiest tires are those utilizing the

cross-bar designs; these are generally found on snow tires.

8. Balance Car Wheels ; Automobile wheels or tires even slightly out of

balance can generate a substantial amovint of vibration and low-pitched

noise - often with annoying pure tone htimmlng. Good wheel balance

generally results in a smoother, quieter and less tiring ride. It also

reduces tire wear.

9. Reduce Windshield Wiper Noise : Driving an automobile in rainy weather

can be rather tiresome, but if one is forced to listen to the incessant

noise of a chattering and groaning windshield wiper the trip can be nerve

wracking. Usually, a noticeable increase in wiper noise is a sign that

the rubber in the wiper blades has aged and has become stiffer and harder.

An expedient though temporeiry measure to control such noise is to file the

edges of the wiper blades with an emory board of the type found in most
ladies' handbags. This will remove the hard rubber edges and expose the

' soft resilient rubber underneath; this will result not only in a reduction

of noise but improved wiper action as well. The long term solution, of

course, is to replace worn or dried-out wiper blades as soon as they

become noisy or streaJty.

If it is a question of mechanical noise, lubricating the wiper motor and

linkage mechanism usually will result in somewhat quieter operation. If noisy

operation still persists, look for loose or worn parts, or for rubber motor

moiints or gaskets that have become brittle and hard. Replacement of the

defective parts often will restore quiet operation.

BUSES MD TRAINS

Passengers generally will find that seats in the center of the vehicle

provide the smoothest and quietest ride, as illustrated in Fig. 9-2. In buses,

seats located above the wheels and near the rear engine are the noisiest and

usually have the greates vibratory motion.

AIRPIANES

Generally speaking, seats farthest removed from the windows - for example,

aisle seats and those located near the center of the passenger cabin - are the

quietest and provide the smoothest ride, as shown in Fig. 9-3. Window seats,

as a riile, are noticeably noisier because of the windstream noise and the

closer proximity to the noisy engines. Seats located in the rear or tail

^ section of a jet plane are uaually the noisiest, regardless of whether the

plane has wing-mounted or tail-movmted engines.

SELECTING A "QUIET" MOTEL OR HOTEL

Having once experienced the exasperation and frustration of spending a sleepless night in some noisy motel or hotel, the weary traveler hopes that he

will have better luck in picking "quiet" lodgings in future travels. He can

reduce the element of chance substantially in selecting a "quiet" motel by

observing a few cardinal rules, as illustrated in Fig. 9-U and listed below.

(a) Avoid all motels or hotels within sight of traffic expressways,

railroads or airports. With regard to expressways and railroads, select

motels that are at least 1/2 mile (800 m) away. If you are traveling by

car, you can use the odometer to measure the mileage or distance.

(b) Avoid all motels or hotels located in the path of direct overhead

aircraft flyovers. Unfortunately, finding a motel which is free of annoyance from nighttime Jet flights may be difficult because of the intensity

of the noise and the great distances that are required to attenuate it to

acceptable levels simply by air absorption alone. Ordinarily, the

traveler faced with the problem of determining whether or not Jet aircraft

flying in the vicinity of a given motel might disturb his rest can resolve

it in one of three ways

.

9-3
(i) If he is a trusting soul, he can ask the registration clerk

(• ; whether or not aircraft noise is a source of disturbance at night.

'• (ii) He can conduct a simple "talk test" outside the motel. If it

is possible to converse normally with a person three to five feet

away without difficulty or disruption during a typical aircraft

fly-by, he need not worry.

(iii) He should request a trial demonstration inside a given room

to determine for himself whether or not aircraft noise is audible

; and possibly annoying.

(c) Avoid motels or hotels with window or wall-mounted air conditioners.

Window or wall-mounted air conditioners are inherently and excessively

noisy devices, especially models that are five or more years old. The

noise levels produced by such units will in most cases disturb one's

sleep. Furthermore, the air intake and exhaust ports of such units act as speaking tubes or noise leaks, thereby allowing the transmission of

exterior noise into the room. As a consequence, even if you choose not to

operate the unit because of the noise, you may well be disturbed by the

noise radiating from air conditioners in adjoining rooms or other areas,

not to mention noise associated with the late arrival or early departures

of motel guests.

(d) Avoid motels or hotels with louvered windows or doors. Although open

louvers are often desired for fresh air ventilation, they unfortunately

constitute an open path for the intrusion of outdoor noise. Further,

because of notoriously poor seals, closed louvers provide very little protection from outdoor noise.

(e) Avoid motels of wood frame construction. Unless dwelling units or rooms are spatially separated from each other, such as individual cottages

or cabins, the intrusion of noise generated by the occupants in adjoining

rooms can be a serioiis source of disturbance. Party walls in wood frame

motels rarely, if ever, provide adequate privacy between rooms. In

response to niomerovis complaints from guests about the lack of privacy

between rooms, owners of such motels often install acoustical treatment in

the rooms in a hasty though thoroughly misguided and futile attempt to

correct the problem.

The traveler shoiild not be deceived into believing that the presence of

acoustic tile on the ceiling or walls of a particvilar motel is an automatic

guarantee that the room is "soundproofed". While such treatment effectively

reduces the buildup of noise within the room, it is totally ineffectual in

preventing the intrusion of noise from outdoor sources or from adjoining rooms

or other areas within the building.

Generally speaking, most motel or hotel rooms do not require any

acoustical treatment on ceilings or walls; the ordinary room furnishings of

carpeting, drapery, bedspreads and mattresses and other furniture are good

sound absorbers and prevent the room from becoming too reverberant and noisy.

Have you every wondered why your bedroom is so much more quiet thsji, say» your
kitchen or "bathroom? The sound-absorbing furnishings in the bedroom make the

difference. It also explains why the "Bathroom Baritone" rarely sings in the

bedroom - there his voice would sound weak and flat.

(f) Select motels of brick, concrete or masonry construction. Such

motels generally have reasonably massive party walls and floors, good

quality carpeting and drapery, relatively quiet air conditioning and

ventilation systems, well-fitted solid-core doors, and sealed non-operable

plate glass windows. These features combined tend to provide a quiet,

restful, interior environment free from the intrusion of outdoor noise, or noise from adjoining rooms or other areas within the b\iilding.

SELECTING A "QUIET" ROOM

Select a room on the "Quiet" side of the motel (See Fig. 9-5). Since

buildings are relatively large and massive structures, they can effectively

reflect, block, or deflect (diffract) sound or noise. As a consequence, they

are exceptionally good noise barriers. The larger the building, the greater

its effectiveness as a noise barrier. When a sound wave strikes a building,

some of the soimd energy penetrates into the building and is absorbed; the

remaining energy is reflected or deflected by the building in other directions.

That side of the building receiving the full force of the soiind wave will, of

course, be relatively noisier thaji the opposite or shielded side.

Therefore, when selecting a motel, the traveler should remember that rooms

on the side of a motel that faces a major source of noise, such as an expressway or railroad, may be objectionably noisy; whereas, rooms on the

opposite side in the acoustic shadow of the building may be relatively quiet.

In addition, rooms on the "quiet" side of the motel ordinarily are disturbed less frequently by noise generated on the motel premises, such as noises caused by swimming pool activities, patio peirties, or the traffic

associated with guest registration.

Other tips on selecting a "Quiet" motel or hotel room:

(a) Avoid rooms which are adjacent to or near stairways, elevators, or

areas containing vending machines, cooling towers, fans, or air conditioning

equipment. The noise radiation from such equipment or from people using the

vending machines may be quite distiirbing. See Fig. 9-6.

(b) Avoid rooms located on the ground floor level, if noises from

footsteps, parking lots or plumbing are particularly annoying to you. Rooms

located on the top floor provide the most privacy from such disturbances.

(c) In large hotels in downtown locations, rooms facing an inner courtyard are usually much less noisy than rooms overlooking the street.

9-5
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9-11

Chapter 10

POLITICAL AND LEGAL ACTION - WHEN ALL ELSE FAILS

INTRODUCTION

As an individual you can apply the principles of noise control given in

the previous chapters. By doing so, you can protect yourself from the harmful

and irritating effects of noise from many sources. Yet, there are some sources

of noise which affect you, and over vhich you have no direct control. What can you do in such cases?

What one person did is forcefully described in a pioneering book he wrote

entitled, The Tyranny of Noise* . Robert A. Baron woke up one April morning in

I96U to "a symphony of insanity" opposite the windows of his apartment. A

construction company had started five diesel-driven air compressors to operate

Jackhammers and rock drills being used in a construction project for the New

York City Transit Authority.

Mr. Baron wrote:

"What happened to the residents of ray neighborhood, as I was to

learn, is already happening or will soon happen to millions of hxxman and

animal receivers of noise. The clatter of a Jet or helicopter flight

path; the incessant hum of a thruway; 'temporary* construction sounds; the

miilti-level buzz of a dozen modern kitchen appliances ; conversations of

neighbors in the next apartment; automated office equipment; the roar of

an air conditioner; power lawn mowers, chain saws and mechanized farm

implements - you don't have to live near a subway project to suffer from

noise.

First, naively, Mr. Baron complained to the neighborhood policemsji; then

he contacted the Transit Authority, the contractor, his city councilman, the

Commissioner of Health, a doctor on the Board of Health, the police department,

the governor of the state, the Division of Occupational Health of the U. S.

Public Health Service, and private acoustic consultants. As a result of all

this, he found himself back at the beginning - the noise continued \inabated.

In May I965, Mr. Baron called for a neighborhood meeting at which a hundred people showed up to establish the Upper Sixth Avenue Noise Abatement

Association. Even this organized group lost the battle against noise; but this

led to the formation of a larger group in New York City, named Citizens for a Quiet City, Inc. (CQC), which began operating in January 196?. CQC encouraged

the mayor to authorize a task force on noise control and endorsed the birth of

New York City's Bureau of Noise Abatement. Also, Mr. Baron, as executive vice

president of CQC, was appointed to the Commerce Technical Advisory Board Noise

* Baron, Robert A., The Tyranny of Noise , St. Martin's Press, Inc., New York,

1970.

10-1
Abatement Panel of the U. S. Department of Commerce in I968. A report of the

Board* recommended the establishment of an Office of Noise Abatement and

w Control (ONAC) within the U. S. Environmental Protection Agency (EPA); and,

indeed, legislation enacted in 1970 did establish ONAC as an operating entity

of EPA.

FEDERAL NOISE REGULATION :

' '

The Noise Control Act of 1972 represents the first major Federal legislation in the field of noise control. The Act requires the U. S. Environmental

Protection Agency to develop and publish information concerning noise levels

that may be hazardous, and to set standards defining permissible noise levels

for products that have been identified as major noise sources. These may

include such products as power lawn mowers, mufflers, and room air

conditioners.

Although EPA has primary responsibility for most Federal efforts to control noise, other agencies are also concerned with special areas of noise control.

Department of Transportation : The Federal Aviation Administration (FAA)

sets criteria and standards for controlling aircraft noise. EPA advises the

FAA in fulfilling its responsibilities, while much of the research and experimental testing for aircraft noise abatement is performed for FAA by the National Aeronautics and Space Administration and by the U. S. Air Force. The

Federal Highway Administration, also within the Department of Transportation,

has adopted Noise Control Standards and Procedures for use in planning and

design of highways to assure that measures are taken to hold highway noise to

levels that are compatible with various land uses.

Department of Labor : The Occupational Safety and Health Administration

sets and enforces regvilations under the Occupational Safety and Health Act of

1970, designed to protect the hearing of workers. Authority is limited to

regulation of companies engaged in interstate commerce. Under this Act, the

Department of Health, Education and Welfare performs research to define

occupational noise limits needed to safeguard the hearing of workers. The

Labor Department relies upon results of this research in setting noise

standards . _ , .

Department of Health, Education and Welfare; Department of the Interior:

Under the authority of the Federal Coal Mine Health and Safety Act of I969, the

National Institute for Occupational Safety and Health, Department of Health,

Education and Welfare is responsible for the development of noise standards to

protect the hearing of miners. The enforcement of these standards is the

responsibility of the Mining Enforcement and Safety Administration, Department

of the Interior.

The Department of Housing and Urban Development : The Department of

Housing and Urban Development (HUD) has developed criteria for the sovind

insulation characteristics of walls and floors in row houses, nursing homes,

and multi-family housing units. These criteria must be met by housing of this

type in order to qualify for HUD mortgage insurajice.

w ^"The Noise Around Us: TrTcluding Technical Backup," Report of the Pajiel on Noise Abatement to the Commerce Technical Advisory Board, CTAB-71-1, September
Many other Federal agencies, such as the National Bureau of Standards and

the National Science Foundatioh, are concerned with research in noise control

and abatement in factories, homes, offices, and commercial work areas.

STATE AND LOCAL REGULATION

For almost a century and a half the control of noise by regulation within

the United States has been a matter of concern for city governments. It is

only within the last decade that some states have seriously entered the field

of noise regulation. Over UOO m\inicipalities (representing a combined

population in excess of 60 million people - 30 percent of the U. S. population)

have enacted noise regulations; however, until recently, there has been very

little leadership at the state level except for the enactment of regulations

requiring mufflers on motor vehicles. An up-to-date compilation of various

city and state noise control ordnances is maintained by EPA (Washington, D. C.

20I+6O)

Both local and state noise control laws aj-e usually classed as general

nuisance laws which include a prohibition of "unnecessary," "excessive," or "unreasonable" noise. These criteria are often too subjective to be effectively enforced. When vigorously challenged, this type of noise control law

tends to be struck down by the courts because they are too broadly worded for

objective enforcement. What is "unnecessary" or "unreasonable" for one person

may be "acceptable" to another.

Noise control laws which are based upon performance standards appear to be

far superior to nuisance laws if they are properly written and correctly

applied. Performance standards typically specify the maximum allowable noise

level at a given point; and this requires monitoring equipment and trained

personnel for enforcement.

A promising trend has been the adoption of noise control laws with perfonnance standards (such as specified in the model ordinance prepared by the

National Institute of Municipal Law Officers, Washington, D. C. 20006) and the

establishment of offices of noise abatement to supervise enforcement. The

advantages of such legislation and of establishing a regulatory agency are

several:

1. An Office of Noise Abatement can act as a focal point for activities

in noise control regulation, enforcement, and public education.

2. A staff can be assembled that is specifically trained to respond to

complaints and monitor noise levels.

3. Authority would exist for the Office of Noise Abatement to use initiative in seeking out the worst offenders.

k. An Office of Noise Abatement would have legal authority to advise

zoning commissions on the noise impact of different zoning plans under

consideration.

10-3
The main disadvantage is the cost of such a program. Although this cost

is not high relative to other kinds of pollution controls , it represents yet

another demand on city, county and state budgets.

CORRECTIVE ACTION PROGRAMS

"" To he effective in solving community-vide noise problems the average

citizen must make himself heard — as in Chicago where an organization called

Citizens Against Noise persuaded the City Council to pass an effective antinoise ordinance in 1971; and as in New York City where Robert Baron and

Citizens for a Quiet City, Inc., succeeded in establishing a Bureau of Noise

Abatement.

Obviously, it is first necessary to familiarize yourself with the various

regulations (Federal, state, and local) which affect your "noise environment."

This familiarization need not be a close and detailed reading of all the

applicable laws. At the local level, a telephone call to the police department

and the city or county council is a starting point for determining what laws

exist, if any, relating to noise control and their applicability to your

particular case. The matter of noise in a community could also be brought up

at a local civic association meeting - many voices can be more effective than

one!

At the state level, you may write or call your elected officials in the

legislature to inquire what they are doing about an effective noise control law

in the state. The governor's office should also be contacted. Again, it is a matter of being heard. If enough organizations and private citizens ask

probing questions about noise pollution, elected officials will take notice of

this interest and corrective action will be forthcoming.

Although the activities of many Federal agencies have some bearing on

noise control, it is the U. S. Environmental Protection Agency that taJces the

lead in coordinating these activities and initiating others. Write to the EPA

Office of Public Affairs (Washington, D. C. 20U60) for publications, general

information, and answers to specific questions on noise control. Your voice,

individually and collectively, can be heard at the Federal level through many

channels of communication - by making your concern known to your representative

and two senators in Congress, and to the President of the United States. You

can also exert influence by lu-ging EPA and other Federal agencies to develop

and enforce noise control standards.

A corrective action program, to be effective, must involve powerful

political groups in the community. Since both government and industry

ultimately respond to public demands, the only real solution to the overall

noise problem is a rising public awareness of the dangers of noise and a persistent demand for effective noise control.

10-4
LOCAL NEIGHBORHOOD NOISE PROBLEMS

Some noise problems may be quite local in character and are best solved on

a neighbor-to-neighbor basis. For example, while nuisance laws might be invoked

to engage the police in quieting a neighbor's dog, such tactics may do little to

promote friendly neighborhood relations! Perhaps a better approach to solving

problems of this kind might be to raise the issue of noise at a meeting of yovir

local neighborhood association, or at a block party, attended by yovir neighbors.

You might suggest appointment of a "noise warden" whose duty it would be to

register complaints to those causing a disturbance. If such complaints were

brought to the attention of the offender in a diplomatic way, and perhaps in

indirect fashion through an appointed neighborhood representative, sensibilities

may be spared - and more positive affect achieved!

Note: Persons interested in assuming an activist role in community noise

control will find the following publication especially valuable:

Gatley, W.S., and Frye, E.E., Regulation of Noise in Urban Areas - A Manual Prepared for Public Officials, Managers and Environmental

Engineers , available from the Extension Division, University of

Missouri, Rolla, Missouri 65^01, price $21.00 postpaid. Although

the publication is designed for administrators and professional

engineers, the interested layman would benefit from discussion of

the technical, medical, sociological, political, and legal aspects

of noise and noise control. S\iggestions are given for specific

steps that can be taken to develop a realistic program of noise

regulation at the state and local levels.

10-5

BIBLIOGRAPHY

The following books are reconnnended to the reader for more detailed information on noise control:

"A Guide to Airborne, Impact, and Structure-borne Noise Control in Multifamily Dwellings," FT/TS-24, prepared for the U.S. Dept. of Housing and

Urban Development by R. D. Berendt, G. E. Winzer, and C. B. Burroughs,

National Bureau of Standards, January 1968.

"Solutions to Noise Control Problems in the Construction of Houses,

Apartments, Motels and Hotels," Owens-Coming Fiberglas, December 1963.

"A Study — Insulating Houses from Aircraft Noise," U.S. Dept. of Housing

and Urban Development, HUD TS-19, May 1967.

"Noise Assessment Guidelines," U.S. Dept. of Housing and Urban Development,

TE/NA-171, August 1971.

"Sound, Noise, and Vibration Control," Lyle F. Verges, Van Nostrand

Reinhold Company, New York, 1969.

"Acoustical Designing in Architecture," Vem 0.%Knudsen and Cyril M.

Harris, John Wiley & Sons, Inc., New York, 1950.

"Sound Control Constructions, Principles and Performance," United States

Gypsum, 1972.

"Handbook of Noise Control',' Cyril M. Harris, Ed., McGraw-Hill Book Co.,

Inc. , New York-Toronto-London, 195 7.

"The Tyranny of Noise," Robert Alex Baron, St. Martins Press, New York,

1970.

"Handbook of Noise Measurement," Arnold P. G. Peterson and Ervin E. Gross,

Jr., (Seventh Ed.), General Radio Co., 1972.

"How You can Soundproof your Home," Paul Jensen and Glenn Sweitzer,

Lexington Publishing Co., Lexington, Mass., 1974.

"The Noise Around Us," Including Technical Backup, Commerce Technical

Advisory Board on Noise Abatement, CTAB-71-1, September 1970.

"Regulation of Noise in Urban Areas - A Manual Prepared for Public

Officials, Managers and Environmental Engineers," W. S. Gately and

E. E. Frye, University of Missouri, Rolla, 2nd edition, 1972.

B-1
"Noise from Construction Equipment and Operations, Building Equipment,

and Home Appliances," NTID300.1, U.S. Environmental Protection Agency,

December 31, 1971.

"Effects of Noise on People," NTID300.7, U.S. Environmental Protection

Agency, December 31, 1971.

"A Survey of Studies on the Effects of Noise on Performance and Health

within the Socialist Countries," E. Gullian, Report to the Committee

on Hearing and Bioacoustics (CHABA) , sponsored by the Occupational

Safety and Health Administration (OSHA) , 1974.

"Effects of Noise on Physiological State," Proc. Conf. Noise as a Public Health Hazard (American Speech and Hearing Administration,

G. Jansen, pp. 89-98 (1969).

"Annoyance Reactions from Aircraft Noise Exposure," R. Rylander,

S. Sdrensen, and A. Kajland, J. Sound and Vibration _24, 419-444 (1972),

"Some Effects of Infrasonic Noise in Transportation," M. J. Evans and

W. Tempest, J. Sound and Vibration 22, 19-24 (1972).

"Acceptability Criteria for Noise in Large Offices," E. C. Keighley,

J. Sound and Vibration 11, 83-93 (1970).

"A Laboratory Study of the Nuisance Due to Traffic Noise in a Speech

Environment," C. G. Rice, B. M. Sullivan, J. G. Charles and C. G.

Jordon, J. Sound and Vibration 37, 87-96 (1974).

"Effects of Noise on People," J. D. Miller, J. Acoust. Soc. Am. 56,

729-764 (1974).
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. F^UHLK ATION OR HI I'OK I NO.

NBSIR 75-668

2. Gov't Accession

No.

3. Rci ipicnt 's Accession No.

4. TITLE AND SUBTITLE

Quletlngl A Homeovmer's Practical Guide to Noise Control

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Raymond D. Berendt, Edith L.R. Corliss, Morris S. Ojalvo*

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project /Task/Work Unit No. 2130116

1 I. V-ontract/lirant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

*Guest Worker from the National Science Foundation

16. ABSTRACT (A 200-word or lesa factual summary of most sigfxificartt intormation. If document includes a sl(^nificartt bibliography or literature survey, mention it here.)

This publication Is a guide offering practical solutions for the ordinary noise

problems that a person is likely to meet in his home, while traveling, and at work.

The discussion describes the ways In which sounds are generated, travel to the

listener, and affect his hearing and well being. Recommendations are given for

controlling noise at the source and along its path of travel, and for protecting the

listener. The guide instructs the reader by way of "Warning signs" on ways and

means of determining whether prolonged exposure to a noisy environment may be

hazardous to his hearing. General principles for selecting quiet appliances are

given. The remedies for noise problems deal both with prevention and with selection

of quiet alternatives to existing noise sources. Ways of searching for the sources

of noise and the paths over which they travel to the listener are described. A

detailed index is given for individual noise sources and the solutions to the

problems they present. General ways of looking for inherently quiet homes and travel

accomodations are described. In a final chapter, there are suggestions for enlisting

community help where large external sources of noise must be quieted, such as those

arising from public transportation and public utilities.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper Is. name; separated by semicolons

)

Airborne and structure-borne sounds; annoyance; appliance noise; health and hearing

hazards; household noise; legal and community action; loudness; noise control and

abatement.

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