_. Vibration
Mounts

(b)

(ce)

Flex. Connect AINE |

ee

Heavy Wall Housing
New

q
Na

Connectors

Furnace A/O-
Air Conditioner

Vibration Isolators

Acoustic

BASEMENT INSTALLATION

Fig. 2-21. TECHNIQUES FOR THE CONTROL OF NOISE FROM EXISTING ATTIC OR BASEMENT
INSTALLATIONS OF FURNACES AND AIR-CONDITIONING UNITS

possible from the bedroom
areas of your house and
those of your neighbor's
house as well. An ideal
location for the installation
of condenser units would be
in the area between face-to-
face kitchens of adjacent
houses, especially if they
are of rambler-type or one
story construction.

Install the condensing unit
resilient mounts, preferably
on a flat, level concrete
slab that is at least 1 foot
(30. cm) away from the
exterior wall of the house.

Install rubber sleeves or
collars around all piping,
refrigerant lines and
conduits at points of support
or penetration through the
exterior wall of the house,
to prevent the transmission
of compressor vibration to
the building structure.

58

(a)

(e)

(£)

(g)

Va Boot

=
Supply

Acoustic Lining

-2" Concrete Slab

2 Layers Plywood,
Soints Staggered

2 Layers Gypsum BD,
or Gypsum Lath
and Plaster

Lubricate the bearings of the
cooling fan, clean the blades
and balance the unit. You
can balance the fan simply by
spinning it by hand and
marking the bottom blade when
it stops. If the same blade
stops at the bottom following
two or three spins, attach
strips of adhesive tape to

the opposite blade until
balance is restored.

Reduce blower speed, if
possible and clean

protective screen to ensure
adequate air flow. Tighten
and align -fan belts and
pulleys.

Tighten loose parts or panels
to prevent rattling or
vibrational resonance.

Install sound barriers
or partial enclosures around
the condensing unit to shield


NOT THIS

Open Air Discharge

High Pressure Air, Steam or
Vapor Exhaust Lines

= Noisy Flow

Fig. 1-17. SILENCER FOR HIGH PRESSURE EXHAUST LINE

6. Use Vibration
Flexible Couplers

Isolators and

‘Im 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

23

receiver. For example, spring mounts placed
under an appliance or machine may prevent
the floor from vibrating; or an expansion
joint cut along the outer edges of a floor
in a mechanical equipment room may reduce
the amount of vibration transmitted to the
structural frame or walls of a building.
Such measures are illustrated in Figs. 1-18
and 1-19,


EPA is charged by Congress to protect the Nation’s land, air and
water systéms. Under a mandate of national environmental laws
focussed on air and water quality, solid waste management and the
control of toxic substances, pesticides, noise and radiation, the
Agency strives to formulate and implement actions which lead to a
compatible balance between human activities and the ability of
natural systems to support and nurture life.


interruption of water flow; for example, 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 constriction, elbow or tee
connector also may cause hammering of the
Plumbing system.

Hammering can also occur when pipes are
loosely supported on V-shaped wire hangers.
Water surges or pulsations in the pipes may
cause them to bounce or vibrate in the
hangers, or perhaps to swing and strike
against other parts of the building.
Replace the wire hangers with pipe clamps.
Inserting a rubber sleeve around the pipe at
the clamp and fastening it securely to some
solid structure will remedy the 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 occurs at some low

flow velocity setting and diminishes or
disappears at a higher flow setting. For
example, if vibration occurs when a

particular faucet or tap is opened partially
and diminishes when it is fully opened, the
faucet more than likely has some loose or
defective parts.

Pipe vibration frequently is caused by
motor driven pumps which, by virtue of rigid
mechanical coupling, transfer their
vibrational energy 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.

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 and faucet washers. Pitted valve and
washer seats also should be refinished or
replaced.

Flexible connectors should be used in
coupling supply and drain pipes to vibrating
appliances such as pumps, garbage disposers,

67

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 runs 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.

clothes and

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.

Noise Due to Entrapped Air in Pipes

A relatively common noise problem that
is generally confined to newly constructed
buildings is 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, unless they persist
for extended periods. Generally speaking,
the problem eventually corrects itself by
gradual release of the entrapped air through
continued use of the plumbing services.

HOW TO DESIGN A QUIET PLUMBING SYSTEM

If you are planning to build a home
with a quiet plumbing system, you must


Movable Windows
Casement or Double Hung

1/4” Plate
Glass

1/8” Glass

Felt or Rubber
Perim. Gaskets

Fixed Windows
1/4” Plate
Glass
7/16" 3 Ply 7/32” Plate
Laminated Glass
Glass Perim.
Felt or Rubber Acoustic
Perim. Gaskets Lining

Resil.
Channel

Window: Poor

Very Good

‘Wall

I: Poor

Very Good

(£)

(g)

Fig. 3-6. SOUND INSULATION EFFECTIVENESS OF VARIOUS WINDOW-WALL ASSEMBLIES

or cracks should be sealed with
glass fiber wadding and resilient
caulk.

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 mm) thick gypsum
board to the furring or metal
channels. Tape and finish joints
and edges of the gypsum board in
the conventional manner.

Basement Areas

Caulk or weatherstrip
existing windows and install storm
windows.

Weatherstrip existing hinged
or sliding doors and install storm
doors.

Crawl Spaces (see Fig. 3-11)

Install a metal duct vent
attenuator with I-inch (2.5 cm)
thick glass fiber liner at all
air-circulation vents. Seal all
other openings or cracks with

79

glass fiber packing and resilient
caulk.

Install 5/8-inch (16 mm)
thick exterior plywood or
moisture-proofed gypsum board to
the underside of the floor joists.

oy

Wi

WW

WW

WW

AW

Fig. 3-7. HOUSE WITH A CRAWL SPACE AND VENTILATED ATTIC


NOT THIS

Openings Around
Pipes, Conduits, Etc.

o

Input Opening

Output Opening

Open Vent

Cover Skirt

Cover Plates

THIS

Caulk or
Gasket
Seals

Gasket 7

Absorbent
Material

Fig. 1-10. TECHNIQUES FOR REDUCING THE RADIATION OF NOISE FROM OPENINGS IN A MACHINE

effective vibration dampers than

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 which they are
applied.

8. REDUCE NOISE LEAKAGE FROM THE
INTERIOR OF THE APPLIANCE

(See Fig. 1-10)

In many cases machine cabinets can be
made into rather effective soundproof
enclosures through simple design changes,
and the application of some sound absorbing
treatment. Substantial reductions in noise
output may be achieved by adopting some of
the following recommendations, especially if
some of the vibration isolation 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

13

or cabinet should be sealed

with rubber gaskets or a

suitable non-setting caulk.
(4ii) 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 effect an airtight
seal. For example, 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 ventila—
tion purposes should be
equipped with mufflers or
acoustically lined ducts.

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

(b) Apply acoustical materials

(i) Install sound absorbent.
lining on inner surfaces of
cabinets to reduce noise


be provided with storm doors. The
use of storm doors, windows and
weather stripping will also
conserve energy by reducing air
leakage and making it easier to
maintain constant ~indoor
temperatures.

(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
chutes.

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 more than 10 dB for
high-pitched sounds; these measures would
reduce the loudness of the intruding noise
by about 25 to 30 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
soundproofing of existing dwellings may be
costly and impractical, the occupants should
choose those solutions which provide the
most noise reduction 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 the dwelling facing the
noise source.

(2) Install storm windows over the
same windows. Select storm
windows having 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,
soundproof doors provided with
perimeter gaskets and threshold
seals (see Fig. 2-7).

(5) If intruding traffic noise
disturbs your sleep and your bed~
room faces the roadway, choosing
a bedroom which is located on the
opposite side of the house may
reduce the level of intruding
noise about 10 dB. Selecting a
bedroom on the side of the house,
if possible, that is partially
shielded from the noise source
should reduce the level of the
intruding noise about 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.
Such a barrier is most effective
in reducing the level of
high-frequency sounds that travel
in a  beam-like manner. Its
effectiveness for attenuating
low-frequency sounds is limited by
the ease with which such sounds
diffract or bend around a barrier.
At best, only a 5 to 10 4B
reduction of the total sound level
can be expected, but the
attenuation of the high-frequency
sounds may result in an
appreciable reduction in
annoyance. Since the acoustical
efficiency of such’ a barrier may
not be improved by massive
construction, it may as well be
made of relatively light material,
such as l-inch (2.5 cm) thick
boards.

Reducing the Intrusion of Aircraft Noise

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


CHAPTER 2

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 found in industrial
plants. As a consequence, the typical
homeowner or apartment dweller finds it
rather difficult to isolate himself from the
noise. This unfortunate situation is due
primarily to the following factors:

(a) Increasing use of noisy appliances
in virtually all areas of the home.

(b)
homes.
rooms,
screen
freely

The open-space layout of many
Wide doorless passageways between
waist-high partial walls, and open
room dividers permit noise to travel
to all areas of the home.

(c) The poor sound insulation provided
both by the exterior shell of the dwelling

structureborne noise,

(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 2-1 and 2-2 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.

TRANSMISSION OF AIRBORNE AND
STRUCTUREBORNE_NOIS!

The control of noise in the home
involves reducing the travel or transmission
of both airborne noise and
whether generated by
sources 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

and by the partition walls, floors, and noises we encounter daily are of airborne
doors within. origin; for example, the roar of an overhead
~ 2° E>
=~ a
== \) ie lem NN Hoga Aart
H Sag % Sy HM Fh B) Roe
oa) ag r
ome) = )
] SS wan 1 3
a, a i
ye ee x
\ 5 aaa |. ‘
ce G\v7 (ais Lt di) Sear 5
. . _
\~ ws 4 q
= 7
Wl F ~ Nb 8
Srsins “ho
N= g
\Y
c ) (GA :
| an
B or =:
FS
2

Fig. 2-1, COMMON INDOOR SOURCES OF NOISE

31


HEATING SYSTEMS

TABLE 5-3 (Cont'd)

GRINDERS

Except when it is directly
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. (Chapter 1)

engaged in

A portable grinder can be operated
quietly when set upon a
vibration-isolating mount. (Chapter 2)

(Chapter 2, Control of
heating, ventilating and air-condition-
ing system noise)

Most conventional heating: systems
generate noise, some more than others.
For a given system, however, the amount
of noise generated will depend upon the
type of equipment used and method of
installation.

One advantage of lowering the
thermostat at night during the heating
season is that it minimizes the number
of times the. disruptive cycling of 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 noisy 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. Place wedges
under the legs of the radiator opposite
the input end to increase the drainage

angle. This will allow any trapped
water to drain away and thus prevent
water hammering.

Baseboard heating systems can cause

annoyance, especially in the still of
the night, if they are not installed

105

properly. This applies to electrical
as well as hot water systems. The
major causes of the noises are the
expansion and contraction of the heater
assembly, component parts and piping,
and the amplification of such noises by

wall and floor structures in direct
contact with the heating system.
Noises from motors, pumps and

turbulence in the case of hot water
systems, and the low frequency
resonance or humming associated with
the electrical heaters also are sources
of disturbance. Such problems can be
alleviated by structurally isolating
the heaters from walls and floors by
using resilient spacers and leg mounts
made of heat-resistant materials.
Asbestos board backed with pads of
silicone, neoprene or rubber would be
suitable for this purpose, providing
that the asbestos surface supports or
is inserted next to the heater.

Many modern heating systems use forced
air circulation because it permits air
conditioning and humidification 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 blowers, fans,
ventilation, heating and

air-conditioning equipment.

HEATING SYSTEMS, CENTRAL AND CLOSET
INSTALLATIONS (Chapter 2)
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 contraction 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. Placement of resilient
mounts under the motor/blower and use
of resilient hangers, flexible boots
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.


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. 2-7. 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 Appliance Noise

1. Vibration isolate the appliance
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

USE IN ENTRANCE,
‘BEDROOM & BATHROOM
AREAS:

‘SOLID CORE DOOR

DOOR

OPEN
METAL
STRIP

DOOR JAMB GASKETS

TUBE
AUTOMATIC uP GASKET ‘sWeEP
DROP JOINT INST STRIP
WA %

DOOR SILL CLOSURES

prevent the transfer of machine
vibration to the supporting floor.
Pads measuring 1/4 to 1/2 inch (6
to 13mm) in thickness with an
arga of about 2 square inches (13
em’) should provide adequate
vibration isolation for most large
appliances. To prevent screw-type
legs from sinking too deeply in
the pad, place a hard plate on top
of the pad to distribute the load
more uniformly. The legs may
require some adjustment to prevent
rattling against the hard plates.

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 should be

USE IN CLOSET
‘AND STORAGE AREAS

HOLLOW CORE DOOR

RUBBER
TUBE

Fig. 2-7. PROPER INSTALLATION OF SOUND INSULATING DOORS


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 structures from amplifying
the noise. The resilient mounting
will permit the ducts to expand
and contract without binding
against some wall floor
construction.

or

(b) Wrap the ductwork with two or
three layers of building paper
which will act as a vibration
damper. 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.

Install 3/4" (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.

(c)

(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" occurs. The
braces will provide adequate
support of the duct walls and thus
prevent this type of motion.

Air Flow 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 50% may
decrease the output noise level as much as
15 to 24 dB.

Air flow velocities of about 15 feet

63

(4.5 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 air flow 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.

Removal 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 fault 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.


FLANKING NOISE PATHS

FL OPEN PLENUMS OVER WALLS, FALSE CEILINGS
F2 UNBAFFLED DUCT RUNS

3 OUTDOOR PATH, WINDOW TO WINDOW

F4 CONTINUOUS UNBAFFLED INDUCTOR UNITS

5 HALL PATH, OPEN VENTS

F6 HALL PATH, LOUVERED DOORS

FT HALL PATH, OPENINGS UNDER DOORS

FB OPEN TROUGHS IN FLOOR-CEILING STRUCTURE

NOISE LEAKS

LU. POOR SEAL AT CEILING EDGES

12 POOR SEAL AROUND DUCT PENETRATE

13 POOR MORTAR JOINTS, POROUS MASONRY BLK
U4 POOR SEAL AT SIDEWALL, FILLER PANEL ETC.

LS BACK TO BACK CABINETS, POOR WORKMANSHIP
6 HOLES, GAPS AT WALL PENETRATIONS

LT POOR SEAL AT FLOOR EDGES

1B BACK TO BACK ELECTRICAL OUTLETS

L9 HOLES, GAPS AT FLOOR PENETRATIONS:

OTHER POINTS TO CONSIDER, RE: LEAKS ARE (A) BATTEN STRIP A/O POST CONNECTIONS OF PREFABRICATED
WALLS, (B) UNDER FLOOR PIPE OR SERVICE CHASES, (E) RECESSED, SPANNING LIGHT FIXTURES, (D) CEILING
& FLOOR COVER PLATES OF MOVABLE WALLS, (E) UNSUPPORTED A/O UNBACKED WALL BOARD JOINTS (F) EDGES
& BACKING OF BUILT-IN CABINETS & APPLIANCES, (G) PREFABRICATED, HOLLOW METAL, EXTERIOR CURTAIN

WALLS.

Fig. 2-3. COMMON AIRBORNE NOISE TRANSMISSION PATHS IN BUILDINGS

or management will permit such a survey to
be done. However, most owners faced with
noise complaints can be persuaded 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.

34

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:

(1) Stop or reduce the transmission of
airborne sound by installing a
wall or floor structure in its
path. Ideally, the structure
should xeduce the level of


the dwelling, and frequently in adjacent
dwelling units as 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
offensive 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 Plumbing System

Unfortunately, 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 restrained ‘in using the most
effective measure to remedy plumbing noise
problems, that is to vibration isolate the
piping from all large wall and floor sur-
faces which act as sounding boards.
However, he should 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
problen.

66

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, that frequently occurs at
partially opened taps, is associated with
turbulence. It has been suggested that this
noise is due to the combined action of
eddies and collapsing water vapor bubbles.

Although turbulent 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,
especially around constriction in high
pressure systems. Cavitation is associated
with the collapse of vapor bubbles, which
are formed at the constriction 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 can 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-pressure plumbing systems are
inherently noisy, due to the resultant
turbulent flow generated within such
systems. The static pressure of main
water-supply lines of buildings with three
stories or less should be regulated so that
it will not exceed 50 psi (345 kilopascals).
The water pressure in branch lines serving
individual apartment units should not exceed
35 psi (241 kilopascals). 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 plumbing
system is usually caused by the sudden


TABLE 5-3 (Cont'd)
IMPACTOR

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 resilient-mounting of the reactor
ballast; (Chapters 1 and 2)

HUMIDIFIERS

The noise generally is caused by the
fan or impeller. Atomizer-type
humidification 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; (Chapter 2).

HYDRAULIC CONTROLS

The most common cause of trouble is
valve noise, which is discussed under
that entry. Also see Chapter 1.

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. Sound insulating
enclosures can be designed to suppress
such noise.

ICE CRUSHER

See general discussion for kitchen
appliances in Chapter 2.

Like a blender, it can be made quieter
by using a heavy container for the
crushing compartment, and mounting the
crusher on a vibration isolator.

IMPACT NOISE

See Chapters 1 and 2 for general
principles of reduction of impact noise
in machinery, kitchen cabinets, and
floors in homes and apartments.

106

These devices should be operated at
times that do not interfere with sleep
among the neighbors. Shock mounting
helps. One should select an appliance
that is designed for quiet operation.
A hydraulic device can be made quiet
more easily than can a device depending
upon mechanical impacts to compress the
trash. (Chapters 1 and 2)

INCINERATOR CHUTES (Chapters 1 and 2)

JACK

Frequently these are made of relatively
thin sheet metal, which vibrate and
rattle as the trash strikes against the
flexible metal surface. Again,
disposal of trash should be restricted
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.

HAMMER

A few models which feature a sound
insulating jacket and exhaust silencers
are available and should be used.

Workmen should wear hearing protection.
Work with these tools should be
confined to normal waking hours. Avoid
long, continued use of the jack hammer

by interposing adequate recovery
periods.
Use of such noisy equipment may

be a case for community regulation.
Frequently, an additional source
of noise is the compressor supplying
air power to the jack hammer. Com-
pressors with sound insulating en-
closures are available and should
be required.

See discussion undé 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


1. wood floor joists

2. wood subfloor

3. wood finish floor

4, glass fiber blanket, 3 in. thick

5. resilient metal channels
6. gypsum board, 5/8 in. thick
7. acoustical tile

Fig. 2-11, DESIGN OF A SOUND INSULATING CEILING FOR A BASEMENT

RECREATION ROOM

resilient channels with
self-tapping screws.

(4) Provide a  1/4-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 gypsum board
ceiling. As mentioned previously,
the application of the acoustic
tile will not improve the sound
insulation 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 floor and
stairs to absorb both airborne noise and the
impact of foot steps.

44

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
impact 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 during the day. Areas
requiring such privacy are the bedroom,
study, and bathroom areas. Unfortunately,
in most homes and apartments the lack of


& -
+—— 100 t ——

A thick growth of leafy trees
& underbrush reduces noise
about 6 to 7 db./100 ft.
(average over audible freq.
range)
‘Low Freq. Loss: 3-4. db
High Freq. Loss: 10-12 db

pit ce Fy

High Freq, Reduction 3-4 db

Single row of trees is worth-
less as noise barrier. Due to

inter-reflection multi-rows of
trees are more effective.

—_ Nee
— a /
/ a ONAL High

‘ Freq.
} ‘A Low Freq.
4 “Road Cut or “gE

< Embankment

(14

be 24 Spe

5 #
Use Buildings as 2
Noise Barriers

Fig. 4-3, ACOUSTICAL SHIELDING PROVIDED BY LANDSCAPE AND NATURAL AND
MAN-MADE BARRIERS

88


Reducing Resistance In Mechanical Systems
(See Fig. 1-4)

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

should 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 cou-
pling, power 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, resulting in
lower 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 causes uneven wear, resulting
in flat spots which generate vibration
and noise.

Reducing Resistance In Air or Fluid Flow
Systems (See Fig. 1-5)

The key advice to effective noise

NOISY DESIGN

lo Ragged Joints
FRR sy _ CELI ITIL REEL
OEE “eo N a

Small iG Fast Turbulent Fi Flow
Diam. — =
lox we CaN a Sa ee
=>
Fr we eae LE
* Rough Surfaces

Lubricate at points A.
Align between points ‘A’~‘A’.
Polish surfaces at Points B.
Counterbalance at points C.

Fig, 1-4.

REDUCING FRICTION OF ROTATING AND SLIDING
PARTS TO DECREASE NOISE RADIATION

control in such systems is
"streamline the flow". This holds true
regardless of whether one is concerned with
air flow in ducts or vacuum cleaners, 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
turbulent 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

QUIET DESIGN

x shy Smooth Joints

EVER UR LERLLELYY

|

Large |
Diam.

L

Slow Streamline Flow ————>-—

soxrrtee SSE
= smooth Surfaces

Fig. 1-5a. DESIGN OF QUIET FLOW SYSTEMS

6


CHAPTER 2

NOISE CONTROL AT HOME... ......

TRANSMISSION OF AIRBORNE AND STRUCTUREBORNE NOISE.
SOUNDING BOARD EFFECT. ......
FLANKING NOISE TRANSMISSION .. . .
GENERAL SOLUTIONS FOR NOISE CONTROL IN THE HOME. .
SOUND ABSORPTION VERSUS SOUND INSULATION. . .

KITCHEN NOISE ........

Install Doors... eee
Control Appliance Noise .

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
ll.
12.

Vibration Isolate the Appliance from the Floor. .....
Isolate the Appliance from the Wall .
Isolate the Appliance from the Cabinet Enclosure. see
Isolate the Cabinet Enclosure from the Wall

Isolate Small Appliances.

Cushion Impact Noise in the Cabinets. . .
Apply Vibration Damping Material. ....

Install Acoustical Lining

Install Exhaust Fans on Rubber Mounts oe

Install Acoustic Ceiling

Install Carpet or Foam~Backed Resilient

Quieting of Large Appliances. ... .

RECREATION OR PLAYROOMS .... .
CORRIDORS, HALLS, STAIRCASES . . .

IMPROVING THE PRIVACY OF YOUR BEDROOM, STUDY AND

IMPROVING THE SOUND INSULATION OF WALLS. ......
IMPROVING THE SOUND INSULATION OF FLOOR-CEILING CONSTRUCTIONS. ra
CONTROL OF FLOOR SQUEAKING ... .
CONTROL OF STAIR SQUEAKING . .. .
CONTROL OF HEATING, VENTILATING AND AIR-CONDITIONING
CONTROL OF DUCT NOISE. ......

FURNACE COMBUSTION NOISE. ....-+.+++-+-+e-
STEAM HEAT NOISE... . we ee eee
NOISE FROM BASEBOARD HEATING SYSTEMS wee ee ee

CONTROL OF PLUMBING NOISE. ....
CONTROL OF NOISE FROM RAIN GUTTERS AND SPouTs. ry

CHAPTER 3

HOW TO INSULATE YOUR HOME AGAINST OUTDOOR NOISE. .

Reducing the Instrusion of Neighborhood Noise
Reducing the Intrusion of Traffic Noise . . .
Reducing the Intrusion of Aircraft Noise. . .

iv

BATH AREAS. oe

SYSTEM NOISE.

Page

73

73
74
74


10.

Fig. 2-9.

When replacement of a ceiling or
hood exhaust fan is due, remember
that squirrel-cage type fans are
less noisy than propeller blade
units, as illustrated in Fig. 3-2.

The ideal solution to avoid
bathroom exhaust fan noise is
to install a squirrel- cage
fan on rubber mounts at the
discharge or outdoor end of
the duct instead of at the intake
end in the 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 noise-
less operation.

Install acoustic ceiling

The installation of an acoustic
ceiling in the kitchen area will

41

ll.

12.

‘MOUNT ARM,

‘SUPPORT BRACKET

RUBBER GASKET

PROPER INSTALLATION OF AN EXHAUST FAN

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.
Install carpet or foam-backed
resilient tile

Installation of foam~backed tile
or an indoor/outdoor type
carpeting, which is stain
resistant, is an effective way of
reducing impact noise caused by
footsteps and dropped objects.

Quieting of large appliances

The application of basic
noise-control principles in the
early design stages of large

appliances would eliminate much of
the noise and disturbance such


CHAPTER 3

HOW TO INSULATE YOUR HOME AGAINST OUTDOOR NOISE

As we know from experience, residential
areas that formerly were quiet and peaceful
in time 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
tranquility of quiet communities and
suburban areas that often are encircled or
flanked by the roadway. In some cases,
local neighborhood noise caused by traffic,
lawn mowers, chain saws, barking dogs, or
perhaps children at play 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 apart-
ment occupants living in residential areas
near airports. The development of medium
jet airports into international airports
handling much larger and noisier aircraft
has resulted in more serious 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, formerly
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. 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.

Generally speaking, most single-family
houses are an assemblage of light-frame

73

interior partitions enclosed and supported
by a light-frame exterior shell. If this
shell were continuous and formed an
air-tight seal around the enclosed space, it
would provide at best a limited amount of
sound insulation. Such construction
typically has a sound transmission class
rating of about STC 30-35. However, this
shell usually contains several windows and
doors. With their customary air and noise
leaks, the windows and doors may reduce the
STC rating of the exterior shell of the
house to a value as low as STC 20. However,
there are ways of preventing this reduction,
and of improving the sound insulation of the
house.

Reducing the Intrusion of Neighborhood Noise

If you have a home in a noisy
neighborhood and are disturbed by the
intrusion of outdoor noise, 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 make
it easier to reduce 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. It is
still more beneficial to install
storm windows, properly sealed, on
all existing windows. This will
provide additional insulation
against low-pitched 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 doors also should


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,
see Case C)

B—Ventilated Attic Space

ce er ene Install new ceiling of 5/8”

>. gypsum board on 1” x 3”
te furring below existing

2] ceiling

C—Flat Roof

Fig. 3-10. ROOF AND CEILING MODIFICATIONS

82


SEPA

United States
Environmental Protection
Agency

Office of Noise October 1978
Abatement and Control
Washington DC 20460

Quieting
in the
Home |



RAIN GUTTERS AND SPOUTS

A major noise source is the turbulent

flow and irritating dripping of
rainwater in the gutters and
downspouts. (Chapter 2)

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 at base of downspout 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. (Chapter 2, 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 MUSIC

Just possibly, this term may become
obsolete before this Guide is
published, 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.

If you must have a rock and roll
session at your house, and if you must

110

ROOF

TABLE 5-3 (Cont'd)

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.

NOISE

"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. Also see entries
under expansion and contraction.

ROTOR TILLERS

The noise generated by a rotor tiller
is comparable to that from a power lawn
mower; see entries under LAWN MOWERS.

SANDERS

SAWS:

Since most noise is generated at the
contact between the sander 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
well-ventilated areas, preferably

treated with sound-absorbing baffles or
acoustic tile ceilings.

BAND, CHAIN AND CIRCHLAR

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.


WAN DUEW

TABLE OF CONTENTS

CHAPTER 1
BASIC PRINCIPLES OF NOISE REDUCTION... ...... 46

SOURCE-PATH-RECEIVER CONCEPT... 1... 2.22 ee

NOISE CONTROL AT THE SOURCE .... 1... eee eee
Select Quiet Equipment ..........2--4-

REQUIKEMENTS FOR QUIET OPERATION... ..... 2 ee
1. Reduce Impact or Impulsive Forces ......
2. Reduce Speed in Machines, and Flow Velocities

in Fluid Systems .......-2-2-+ 2 eee
Balance Rotating Parts. ......-+-+-+--
Reduce Frictional Resistance. ........

Isolate Vibrating Elements Within the Machine .

Reduce Radiating Area... .....-e eee
Apply Vibration Damping Materials ......
Reduce Noise Leakage From the Interior of the

and Pressures

Appliance

Choose Quieter Machinery When Replacing Appliances. . .

NOISE CONTROL IN THE TRANSMISSION PATH ...... 2...

FACTORS AFFECTING TRAVEL OF SOUND. ...... -

1. Absorption: Soaking Up Sound. ......

2. Sound Reflection: Bouncing of Sound. ... .

3. Reverberation: Multiple Reflection of Sound. . .

4. Diffraction: Bending or Squeezing of Sound .
“QUIETING' IN THE PATH... 2... 2 ee ee ee eee

1. Separate the Noise Source and Receiver As Much As

2. Use Sound Absorbing Materials ........

3. Use Sound Barriers and Deflectors ..... .

4. Use Acoustical Lining... .....-2..--

5. Use Mufflers, Silencers or Snubbers .....

6. Use Vibration Isolators and Flexible Couplers

7. Use Enclosures . 2... 2 ee ee ee eee

PROTECT THE RECEIVER . 2 1 ee ee ee ee ee ee ee

USE EAR PROTECTORS . . . - ee ee ee ee ee ee ee
ALTER WORK SCHEDULE. . . 2... 2 eee ee ee ee ee
IS THERE AN ACOUSTICAL PERFUME?. ... 2... 2. eee

iii

Possible.

Page

25

25
25
28


TABLE 5-3 (Cont'd)

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 2 on control of plumbing noise
and Chapter 1 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 3 for reducing the
intrusion of outdoor noise into the
home. See Chapter 1 relative to
detection of sirens.

SNOWMOBILES

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. Asa
precautionary measure, ear protection
should be worn, particularly during
periods of extended or prolonged use.

SOLENOIDS

Many automatic household machines such

111

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.

SONIC BOOMS, SHOCK WAVES

Also see entries under THUNDER.

Depending on the distances involved, by
the time a sonic boom or shock wave
reaches your house, it usually will
have lost some energy by spreading, air
absorption, and perhaps reflection off
natural or man-made barriers.

Building structures that are adequately
sound-insulated against aircraft or
traffic noise will also do well against
sonic booms; but due to _ their
suddenness and infrequency, sonic booms
produce startle and short-term
interference that are more like that
caused by aircraft flyover noise.
Community action may be required to
resolve the problem of sonic boom
disturbances caused by supersonic
aircraft flyovers and the shock waves
caused by “blade slap" associated with
helicopter flights.

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. (Chapter 2).

In apartment buildings, staircases that
are sealed off with fire-proof 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 effect a gradual
reduction in pressure will lower noise


still it makes noise! You should then
operate the unit at times which will cause
the least amount of disturbance to you and
especially your neighbor. Waiting until
later on Saturday and Sunday mornings to
operate your lawn mower and power saw won't
reduce their noise levels, but it may reduce
the intensity of your neighbor's complaint.
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 amount of continuous exposure
to high noise levels. In terms of hearing
protection, it is preferable to schedule 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
landscaping 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 should avoid finishing
intensely noisy jobs in continuous or overly
prolonged runs, unless, of course, he is
wearing ear protectors.

In an industrial plant employing a
large number of people, an. intermittent work
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 minimum 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
background 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 enough to break up the
rhythm of breathing, and this becomes a
source of discomfort.

28

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.
Although lower-pitch masking has a greater
effect on high-pitch sounds, the requirement
that the masker must be in the frequency
range of the tone to be masked is dominant,
as we can recognize from the fact that
orchestral music is heard 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 a limited range 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.
In order to override these levels, the
background sound 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 surroundings 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 simply involves using an
artificially induced noise or the ambient
acoustical environment beneficially for


CHAPTER 5

A TROUBLE-SHOOTING GUIDE

ANALYZING THE PROBLEM:

If you are faced with a noise problem,
examine it first in terms of the three basic
elements: source, path, and receiver. We
have discussed these elements in Chapter 3.
Obviously, the ideal solution is to reduce
the noise output of the source, itself,
since this will benefit both the operator of
the noisy equipment and bystanders or other
people in the vicinity.

If attempts to reduce the noise output
of the source have proved only marginally
successful, it may be feasible to alter the
transmission path so that less noise reaches
the listener. Acoustical absorbers and
noise barriers may be used to attenuate the
moise before it can reach noise-sensitive
areas. Unfortunately, such measures do not
provide much relief for the operator of the
noisy equipment, who usually is immersed in
the direct noise field from the machine.
His only remedy is to wear ear protectors,
and to minimize the duration of each
exposure to noise.

Suppose you find yourself the unwilling
receiver. In the first place, do not risk
your hearing unnecessarily while waiting

hopefully for something to be done. The
most important action is to determine
whether the noise can be hazardous to

your hearing. This you can do simply by
using your ears, and making a few observa
tions. Follow this simple rule of thumb; IF
THE NOISE LEVEL IN YOUR SURROUNDINGS IS SO
HIGH THAT YOU HAVE TO SHOUT TO -CONVERSE
WITH A PERSON NEARBY, CONTINUED DAILY
EXPOSURE AT THIS LEVEL FOR MANY HOURS MIGHT
ENDANGER YOUR HEARING. However, to be on the
safe side, a closer estimate of the noise
level in the area is required. You can
estimate the noise level from the limiting
distances over which intelligible conversa—
tion is possible, and the vocal effort
required to maintain it.

Figure 5-1 shows the empirical
relationship that has been found between the
distance over which spoken words can be
recognized and the typical sound level of
the environment, as one would read it ona
sound level meter using the A-weighting
scale. As an example of the use of the
graph in Figure 5-1: Suppose you are talking
to a person at a customary distance of about
5 feet (1.5 m) from him. If you can carry

91

on your conversation ~ with no unusual
effort to hear him or no feeling that you
need to raise your voice to a higher level
then it's likely that the sound level
does not exceed 67 dB(A) where you are
standing [point (1), Fig. 5-1]. Suppose now
you are at a lively cocktail party which
gradually becomes so noisy that you have to
raise your voice to converse and have

trouble understanding your neighbor [this
condition is at point (2)] -- the noise
level at this location would be

approximately 75 dB(A).

If by chance you were to find yourself
in an industrial plant so noisy that you
must shout to be understood at a distance of
5 feet (1.5 m), [point (3)] the noise
level would be about 90 dB(A). The current
national standard on occupational noise
restricts an employee's exposure to 90 dB(A)
as an eight hour time-weighted average.
From your own experience you can judge the
advantages of maintaining environmental
noise below this level.

To use Fig. 5-l as a guide for
estimating the level of noise in any indoor
or outdoor environment, start a conversation
at a normal voice level with a companion,
and then back away. Arrange to signal to
one another the moment you feel that extra
effort is involved, either in speaking or
listening. At this point, if both of you
have normal binaural hearing, the distance
between you can be noted on the horizontal
scale of the graph. From the solid line on
the graph you can read off the effective
A-weighted sound level in decibels along the
vertical scale. This chart applies to tests
conducted ina fairly reverberant space;
only a very long echo time, as found ina
large convention hall or church, will lead
you to overestimate the sound level by
compellirg you to override the echoes of
your own voice.

To trouble-shoot noise problems in the
home, first listen carefully to the noise
for distinctive clues or characteristics
that might identify the cause or source of
noise. If the source is well known to you,
you can recognize how the transmission has
altered its sound where you are, and thus
can tell whether it is reaching you by air
or through the structure. Airborne sounds
usually arrive with their high-pitched


CHAPTER 4

SELECTING A QUIET HOME OR APARTMENT
(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 determine
how quiet it will be. However, you should
be careful to consider all factors before
making your move, be cause the desirability
of living in a quiet community may be offset
by some disadvantages. For example, it might
take you twice as long to drive to work or
mid-city attractions from the new location
than it does from your present one.

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 noise
producers 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

15 mites—f s—

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. 20014.

Sites near large commercial,
international or military airports
should be avoided if possible.
Residential 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 (24 to 32 km)
away from the airport before the
noise from jet aircraft fly-overs
would be relatively unnoticeable
to the occupants. (See 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 4 miles (5
to 6 km) fromthe flight path
before the noise would drop to a
tolerable level at the building
location.

+5 fun |

Yr

Airport

5

LY

Fig. 4-1. TO AVOID AIRCRAFT NOISE DISTURBANCE, SELECT HOMES OR APARTMENTS OUTSIDE SHADED AREA

85


Cabinet

Machine
Chassis

. Install motors, pumps, fans, etc. on most massive part of the machine.

. Install such components on resilient mounts or vibration isolators.

. Use belt drive or roller drive systems in place of gear trains.

. Use flexible hoses and wiring instead of rigid piping and stiff wiring.

}. Apply vibration damping materials to surfaces undergoing most vibration.

. Install acoustical lining to reduce noise buildup inside machine.

. Minimize mechanical contact between the cabinet and the machine chassis.

. Seal openings at the base and other parts of the cabinet to prevent noise leakage.

OPNOTNERWN>

Fig. 1-7. TECHNIQUES TO REDUCE THE GENERATION OF AIRBORNE AND
STRUCTURE-BORNE NOISE IN MACHINES AND APPLIANCES

10


a ae
=

A

Z
ME OO OE Be prea or
SSS SEES

55. aes
SSS

[EGEEZLEZE
SSIS

oN

SS
>}

Insert cross brace

Insert additional joist

Butt long straight board against
subfloor and nail to joist

Toe-nail with ring nails
Apply mineral oil in grooves
Tighten wood screws

Drill clearance hole for screw

Bene
Noo

Fig. 2-19, CAUSES AND REMEDIES FOR SQUEAKING FLOORS

53


TABLE 5-2

GENERAL NOISE ABATEMENT TECHNIQUES (Arranged in Order of Effectiveness)

Procedure

Reduction in
Sound level, dB

Estimated Decrease in
Loudness

Relative Reduction in
Sound Power

Break up
resonances.

Reduce flow
velocity to half.

Break pure tones
into random spec~
trum, same power.

Reduce dominant
frequency by a
factor of two, as
by halving fan
speed.

Reduce radiating
surface area by a
factor of two.

Increase mass of
sound barrier by
a factor of two.

Double distance
from a source of
sound.

Install sound-
absorbent
materials.

Increase dominant
frequency by a
factor of two.

20 dB or more

18 dB

May be negligible
as read on a
sound level meter

6 dB

6 dB

6 dB

Up to 6 dB
(small source),
up to 3 dB

(line source).

Up to 6 dB,
mostly at high
frequencies.

Up to 6 dB.

Almost 75%, possibly more.
Resonances yield pure tones
perceived as louder than
mixed sounds of equal total
intensity.

Almost 73%

Depending upon composition,
loudness may be reduced
more than 50%. (Equivalént
to about 15 dB SPL.)

Lowered dominant pitch re-
duces loudness equivalent
of additional 6 dB SPL.
Total loudness can be
reduced about 50%.

Noticeable reduction in
loudness (about 25%).

Noticeable reduction in
loudness (about 252%).

Loudness reduction up to
25%.

Noticeable reduction in
echoes and high-frequency
noise, usually noticeable
effect on loudness.

Can reduce audibility for
sounds if original is above
6 kHz. Higher-frequency
sounds are more readily
absorbed by air and weakened
or deflected by barriers.

A last resort.

98

99% or more.

Almost 97%

None

Reduces sound radia~
tion efficiency by a
factor of about four.

Reduces sound radia-
tion efficiency by a
factor of about four.

Reduces sound radia~
tion efficiency by a
factor of about four.

Reduces sound power to
1/4, if sound source
is small and in open
space; to 1/2 if long
line source; by nil {£
large source or echo-
ing space.

Usually reduces sound
power to as little as
1/4.

May be none. Likeli-
hood of efficient
sound radiation
increased, but can
reduce sound trans-
mitted through enclos-
ures or barriers by a
factor of four.


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 community 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 duration of the noise
involved.) Moreover, some studies have
shown that people do not become accustomed
to noise intrusion as time goes on, but
remain intolerant.

If you are one of many home owners who
now find themselves constantly exposed to
intense and highly disturbing aircraft
noise, you should consider carefully the
following four basic facts before you decide
on any course of action to resolve the
problen.

(1) The cost of
existing home
aircraft noise
high.

soundproofing an
against intense
is exceedingly

(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 in the near future through
the. development of quieter
aircraft or changes in aircraft
landing or takeoff flight
procedures, In fact, the noise
environment near a large airport
generally tends to grow worse in
time, with the continuing
expansion in aircraft size and
flight operations. .

75

The most effective solution may be
to move to a more quiet area, even
though it might entail some
financial loss in the sale or
rental of your home.

(4)

The following is a discussion of the
various sound insulating modifications that
may be used to reduce the intrusion of
intense aircraft noise into the home.
Figures 3-1 through 3-11 illustrate the
structural details of such modifications.

Major Sound Insulating Modifications:

Incorporate the noise-reduction
recommendations given above
relative to reducing the intrusion
of neighborhood and traffic noise.

(a)

(b) Windows

Windows are the weakest
acoustical barrier in the exterior
shell or walls of most homes.

Ordinary locked, double-hung
windows generally provide an
average noise reduction of about
18 dB; the addition of a storm
window, as illustrated in Fig.
5-1, will increase the sound
insulation to about 24 dB.
Caulking of both sets of windows
improves the sound insulation
about 3 4B 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,
well-sealed, double pane windows
throughout the house.

As illustrated in Figs. 3-2
and 3-3, the window installation
then would consist of two 1/4-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 within the
framing with acoustic tile or
other sound absorbent material.

This double-window
installation when properly sealed
would increase the sound
insulation to approximately 37 dB.


(2)

VIBRATION

EQUIP.
VIBRATION

IMPACT OR EQUIPMENT INDUCED
VIBRATION IS TRANSMITTED.
VIA STRUCTURAL PATHS THROUGH
OUT BLOG. & RADIATED AS AIRBORNE
NOISE BY WALL & FLOOR ASSEMBLIES

"AIR BORNE NOISE RADIATION

a

Fig, 2-4. COMMON STRUCTURE-BORNE NOISE AND VIBRATION PATHS

IN BUILDINGS

intruding sound sufficiently to
make it inaudible, or at least
unnoticeable in areas where
privacy is desired. The sound
insulating effectiveness of a
single wall is dependent on
weight; there is a gain of about 5
dB in sound insulation or
transmission loss for each
doubling of the mass 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
insulation than a single wall.

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

35

carpet with felt or rubber padding
will be adequate. A floor of
light-frame construction might
Tequire not only carpeting, but
also 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.

Techniques for the control of airborne and
structureborne noise transmission through
wall and floor structures are illustrated in
Fig. 2-5.


As we recognize from daily experience,
the sound transmission loss differs for
sounds of various frequencies. The
low-frequency sounds of a passing truck
travel through a wall structure much more
readily than do the high-frequency sounds
generated by chirping birds. In order to
cope with this variation in a practical way,
a frequency-weighted single number rating,
called the sound transmission class (STC)
was developed. The STC rating of a building
structure is derived in a prescribed manner
from the sound transmission loss values
measured in sixteen frequency bands spaced
between 125 and 4000 Hz. The higher the STC
rating of a partition, the greater is its
effectiveness as a sound insulator. Table
2-1 shows the performance of various wall
structures with different STC ratings
described in terms of their approximate
effectiveness against intruding speech.

Due to conventional building materials
and construction, most interior walls within
a typical home or apartment would have STC
ratings between 30 and 35. The first five
entries in the bibliography at the end of
this Guide contain architectural
illustrations of various wall and floor
structures covering a wide range of STC
ratings.

Many walls, especially party walis
separating apartment units, are particularly
vulnerable 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.

The sound insulation of many such walls
can be improved simply by eliminating the
noise leaks and flanking paths.

(a) Sealing holes and cracks: (see
Fig. 2-14)

All holes or openings around
plumbing fixtures, piping and
drain pipes should be enlarged
slightly to provide a clearance
around the pipe. The opening
should then be filled with a fiber
glass packing and sealed
completely with a resilient caulk.
This same treatment should be used
in openings around ducts, grilles
and electrical outlets.

TABLE 2-1
SOUND TRANSMISSION CLASS (STC) FOR VARIOUS WALL STRUCTURES

Wall Structure

1/4" wood panels nailed on each side of 2x4 studs
3/8" gypsum wallboard nailed to one side of 2x4 studs

5/8" gypsum wallboard nailed to both sides of 2x4 studs

Two layers of 5/8" gypsum wallboard nailed to both

sides of 2x4 studs

Iwo sets of 2x3 studs staggered 8" on centers fastened
to 2x4 base and head plates with two layers of 5/8"
gypsum wallboard nailed on the outer edge of each set

2x4 wood studs with resilient channels nailed
horizontally to both sides with 5/8" gypsum wallboard
screwed to channels on each side

stc
Rating Privacy Afforded
25. Normal speech easily
understood
30 Normal speech audible
but not intelligible
35 Loud speech audible
and fairly
understandable
40 Loud speech audible
but not intelligible
45 Loud speech barely
audible
of studs
50 Shouting barely
audible
55 Shouting not audible

3-5/8" metal studs with 3" layer of glass fiber blanket
stapled between studs. ‘Two layers of 5/8" gypsum wall-
board attached to each side of studs.

47


Pad
Carpet
Resilient metal channels

Ponsa

Existing floor-ceiling structure

5. Wood furring
6. Glass fiber pad
7. Gypsum ceiling board

Fig. 2-18. METHOD OF INCREASING THE AIRBORNE AND IMPACT SOUND INSULATION
OF AN EXISTING FLOOR-CEILING STRUCTURE

(e) Provide a 1/4" (6 mm) clearance
around the perimeter edge of the
wallboard ceiling to avoid contact
with the walls, and fill the gap

with a resilient, non-setting
caulk.
This ceiling assembly should not only

eliminate the airborne noise transmission,
but should make 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 SQUEARING (See Fig. 2-19)

Squeaking floors cause considerable
irritation because they generally produce
high-pitched noises to which the person with
average hearing is highly sensitive.
Although 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,

52

strips or sections of both sub-flooring and
finish floor also cause squeaking. 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, 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 subfloor
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 causing the
squeaking under foot.


()

1. Caulk

2. Lead Wrap 4. Electrical Outlets

3. Glass Fiber Packing

5. Wall
6. Ceiling

7. Floor
8. Pipe

Fig. 2-14, SEALING COMMON NOISE LEAKS IN EXISTING WALLS

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
thorough job.

Sealing leaks behind back-to-back
outlets and cabinets: (see Fig.
2-15)

If you hear your neighbor's noise
coming through an electrical
outlet, remove the cover plate and
examine the opening. rt
necessary, remove your outlet box,

48

pack glass fiber wadding around
your neighbor's outlet, and insert
a 1/16-inch (1 wm) thick sheet of
lead to form an airtight barrier
wall. Reinstall your outlet box,
fill the remaining voids with the
glass fiber and caulk and replace
the cover plate.

If the party wall is of wood stud
construction, you may be able to
rewire and install your outlet in
the adjoifiing 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


(4)

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.
Details of these modifications are
illustrated in Figs. 3-4 and 3-5.

Exterior Walls

Generally speaking, exterior
walls constructed of poured
concrete, 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 the 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 generally consist of
wood studding faced on the inside
with gypsum board and on the
outside with insulation board and

wood, metal or stucco siding.
Such walls are inherently
incapable of providing adequate
sound insulation against

moderately high levels of noise,

much less against the intense
levels of aircraft noise
intrusion. Such walls would have

to be capped on the outside with a

78

Caulk any open joints around
door frame

I|__—_— 1-3/4" thick solid — core door

‘At head and jambs — install closed

cell polyurethane foam compression
gasket or interlocking cloth-lined
‘weather strip to close joints around

both doors

.|___ At double doors, install resilient
vinyl of neoprene gaskets

At threshold, install either
resilient bumper strip or
automatic drop — seal

~

Fig. 3.5, DETAILS OF DOOR MODIFICATIONS

(e)

4-inch (10 cm) thick wall of brick
veneer before the aircraft noise
could be reduced to a tolerable
level inside the house, as
illustrated in Fig. 3-2. Figure
3-6 illustrates the details and
sound insulating effectiveness of
other window-wall constructions.

Roof and
(see Figs.

Ceiling Modifications
3-7, 3-8, 3-9 and 3-10)

Ventilated attic space

If the attic is to be used as
a walk-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 vent
attenuator, as illustrated in Fig.
3-11, at all air-circulation vents
in the attic. All other openings


(b)

(ce)

Select building sites that face
wide open spaces such as parks,
golf courses, rivers, lakes and
seashores. Such areas usually are

very quiet, especially at night.

Choose a building site that is
located as far as possible or is
acoustically shielded from a major
source of noise by other
buildings, natural landscaping or
wooded areas, as illustrated in
Figs. 4-3 and 4-4.

SELECTING A QUIET APARTMENT UNIT WITHIN
"THE BUILDING

Unless the building manager can

demonstrate that the apartment units
will provide an adequate degree of

insulation against
noise

the intrusion of
from other areas within the

building and noise of outdoor origin,
the renter should take the following

precautionary

measures to ensure

freedom from such disturbances.

(a)

(b)

Select apartment units that are
remote from elevators, mechanical
equipment rooms, laundry rooms,
indoor garages, or roof-mounted
ventilation equipment, such as
chiller pumps, compressors or
cooling towers. Rarely are such
powerful noise sources properly
enclosed in sound~insulating
structures or vibration-isolated
from the building structure. 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
develop into an acoustically
intolerable environment.

Apartments that overlook parking
lots, thoroughfares or through
streets, playgrounds and swimming
pools may be noisy during parts of
the~day unless carefully sealed
against noise. Noises caused by
automobile operation such as
starting of engines and door
slamming, particularly during the

89

(c)

early morning hours, can be a
source of annoyance. Likewise,
the voices or shouting of children
at play throughout the day and
evening may be disturbing. If
possible, give preference to an
apartment unit on the quiet side
of the building; that is, one
which faces away from such noise
sources.

Consider the surroundings of
apartments that face U-shaped
courtyards. Such areas tend to be
reverberant and can be noisy,
particularly if they are used as
recreation or play areas or face
main highways or traffic arteries.

NOT THIS THIS

Fig. 44, ORIENTATION OF APARTMENT BUILDINGS FOR
OPTIMUM ACOUSTICAL SHIELDING


FLEXIBLE
CONNECTOI

devices cause. This, of course,
is an engineer's responsibility,
and should have been incorporated
in the design. The consumer can
encourage such practices by giving
preference to quiet appliances.
Existing appliances can be quieted
to some degree by applying the
noise control measures illustrated
in Fig. 2-10, and listed below.

(a) Install ribbed neoprene or
soft rubber pads under the
legs of the units.

(b) Adjust screw-leveling legs to
prevent units from wobbling.

(c) Tighten all loose parts and
panels to prevent them from
rattling.

£5

“AIR LOCKS TO REDUCE
WATER HAMMERING.

EUS BRADY ch BSE BERS Fa

(d)

(e)

Install soft rubber gaskets
around pipe openings and
along the perimeter edges of
doors, of washing machines,
dryers, and dishwashers to
prevent noise leakage from
inside the machines.

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
materials on the inside

surfaces. This will tend to
suppress the vibration and

+ reduce the noise output.

(£)

Apply glass fiber board on
the interior surfaces of the

USE RUBBER PADS AND GASKETS
TO VIBRATION ISOLATE
‘APPLIANCE FROM CABINET

PERIMETER
{o-RUBBER
GASKET

ADs

VIBRATION
ISOLATOR

Fig. 2-10. PROPER INSTALLATION OF APPLIANCES FOR QUIET OPERATION

42


TABLE 5-3 (Cont'd)

obstacles in the air stream that have
sharp or ragged edges or narrow
restrictions.

Turbulence is strongly dependent on
flow velocity. A slight reduction in
flow velocity will often result in a
noticeable decrease in noise radiation,
particularly in the high frequency
range.

See Chapter 1 on design of quiet flow
systems and Chapter 2, Control of
Plumbing Noise.

WINDOW RATTLE

If window panes rattle, look for breaks
in the putty. If the entire frame
rattles, check the adjustment of
springs or weatherstripping.
Double-hung windows in aluminum guides

can have the guide spacings adjusted
for good fit. Wind noise and rattling
in casement windows are more difficult
to prevent because such windows 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
weatherstripping.

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.

115


QUIETING IN THE HOME

Reprinted From

National Bureau Of Standards
Handbook 119

Quieting: A Practical Guide
to Noise Control

by
Raymond D. Berendt, Edith Corliss, Morris Ojalvo

U.S. Environmental Protection Agency
Office of Noise Abatement and Control (AW471)
Washington, D.C. 20460


LEAF

LEAF

TABLE 5-3 (Cont'd)

BLOWERS

Choose a model with a well-muffled
engine, large air-inlet aperture, 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.

SWEEPERS AND MULCHERS

Select machinery with well-muffled
engines. Leaf sweepers are available
in two types - the vacuum and the
rotating brush types. Requirements for
quiet operation of the vacuum-type 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
noise of a mulcher also can be reduced
somewhat by coating the inside surfaces
of the metal housing with vibration
damping material.

LIGHT SWITCHES

Silent mercury-type light switches and
thermostats are available. Rotary-disc
type switches also are relatively quiet
in operation compared to the
spring-operated type switches.

MASKING NOISE

See discussion under "Is There An
Acoustical Perfume?" at end of Chapter
3.

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, eliminate

loads and replace worn
prevent vibration; and
oil dry bearings to

unbalanced

bearings to
thumping noises;
eliminate screech.

Motors should be installed on resilient
mounts and vibration isolators.

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.

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,
sound-insulated enclosure to provide a
greater amount of noise reduction.
Electrical, battery-powered motors
which operate quietly are available for
light use, such as trolling or fishing.

MOTORCYCLES

In addition they do not pollute the
water.
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, mufflers 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
large-diameter metal can with a pad of
glass fiber and inserting a slotted,
smaller-diameter can. This double wall
muffler should then 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 sound baffles.

MUSIC

108

Unwanted music becomes noise. Two
rival sources of music generate
cacophony. Rock bands approach sound
levels hazardous to hearing. (Chapter
2) Similar levels can occur with some
"Wi-Fi" systems.


(c)

This problem can best be
alleviated by decreasing the
rotational speed of the pump or
replacing it with a slow-speed
model.

Pumps and drive 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 pump vibration to
the pipe system.

Installing a surge 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)

(b)

(c)

The major source of noise is the
expansion and contraction of the
heater assembly and component
parts and the amplification of the
noise by wall and floor structures
in direct contact with the heating
system.

Another source of annoyance is a
low frequency resonance of the
heater assembly, which sounds like
the low-pitched hum of a
transformer.

Some installations have individual
thermostat controls in each room.
The clicking of a thermostat in
the still of the night can be
extremely irritating, particularly
if a person is trying to sleep.

Remedies

(a)

(b)

To alleviate the noise of
expansion and contraction of the
heater assembly, use the method
discussed above for hot water
heaters.

In a typical installation, the
low-pitched humming noise
generally is radiated at amplified

(c)

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 made of folded
sheet-metal strips to the long
marrow panels of the heater
assembly will further suppress the
low-pitched humming noise or
resonance.

If your thermostat is excessively
noisy, remove the cover plate to
determine what type of unit was
installed. 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
structure. 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 tape to damp
the vibration. Place lead or
tape on the back of the cover
plate.

CONTROL OF PLUMBING NOISE

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


Caulk

Wood
Furring

A IN |
WA - corer Resilient Channel
\

Wallboard

|
1/2" epun a S
Caulk

iS

Sound Absorptive

Material

\ on XX

Existing
Wall

\

Caulk

Fig. 2-17. METHOD OF OBTAINING A SUBSTANTIAL INCREASE IN SOUND INSULATION FROM AN

EXISTING WALL

(4) Attach 1/2" (13 mm) thick gypsum
wallboard to the metal channels
with self-tapping screws.

(e) Provide a 1/4" (6 mm) clearance
around the perimeter edge of the
wallboard to avoid restraining
contact witn adjoining surfaces of
the room; fill the clearance gap
with a resilient non-setting
caulk.

IMPROVING THE SOUND
FLOOR-CEILING CONSTRUCTIONS

INSULATION OF

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 sound and footstep or impact noise to
non-disturbing levels.

Tf 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.

51

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. 2-18 would be
constructed as follows:

(a) Attach wood furring members,
spaced 16" (40 cm) on centers to
the existing ceiling.

Nail resilient metal channels
perpendicularly to the furring
members; channels should be spaced
24" (60 cm) apart.

(b)

(c) Fill space between the existing
ceiling and the channels with a
glass fiber blanket.

(4) Gypsum wallboard, 1/2" (13 om)
thick should be fastened with
self-tapping screws to the
resilient channels.


TABLE 5-3 (Cont'd)

Use of sound-absorbent lining, flexible
connectors and stiffeners or bracing in
ductwork generally alleviates such
problems.

ELECTRICAL EQUIPMENT (Chapters 1 and 2)

Common 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 in the ballasts used
with fluorescent lamps; these should be
replaced, preferably with more con-
servatively-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 or rotary switches of the
appropriate rating.

See individual entries for specific
electrical appliances.

ELECTRONIC AIR FILTERS

Homeowners occasionally complain about
the loud, sharp, snapping noises
produced by the electronic air filter
unit installed in their heating and
air-conditioning system. Dus
particles passing through the ionizing
cell of the filter are given an intense
electrical charge and are collected by
highly-charged electrical plates.
Abnormally large dust particles
occasionally short across the
electrical plates and cause arcing,
which produces the objectionable
snapping noise. The installation of
acoustical lining or sound silencers in
supply and return ducts for the purpose
of attenuating mechanical equipment
noise will alleviate the electronic
filter noise problem as well.

ELEVATORS (Chapter 4)

An elevator shaft acts as a speaking
tube to transmit sounds from the drive
motors and elevator doors. Proper

103

mounting of the 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 adjacent to elevator shafts
unless storage areas are placed in the
intervening spaces.

Especially in tall buildings, where
high-speed elevators are used, the air
overpressure and rarefactions caused by
the piston action of the elevator cab
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 élevator doors.

EXPANSION AND CONTRACTION (Chapters 1 and 2)

Long sections of sheet metal supported
at widely separated points are likely
to make "clacker" type noises as they
expand and contract with temperature.
This is a serious source of noise in
ventilation 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 (Chapters 1 and 2)

Remember the useful rhyming conditions
"slow and low". Use as slow a fan
speed as can be obtained. Exit louvers
should be made of easily-cleanable
material and massive enough to prevent
rattling. In choosing a kitchen hood
filter, give preference to one that is
long, wide and made of thick highly
porous material; this choice will tend
to maintain smooth air flow. Of


cy
Pump Connector Expansion Joint in sll

Flexible Pipe
Connectors

Duct

Multiple Arch

Flexible

Flexible
Hose

Fig. 1-18. VARIOUS TYPES OF FLEXIBLE CONNECTORS

24


than somewhere else in the room. The upper
corner locations also protect the
ligh-weight fragile material from damage.

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 apartment 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

require the addition of either a floating
floor or a resiliently suspended gypsum
board ceiling to the existing floor-ceiling
construction.

3. ‘Use Sound Barriers and Deflectors
Placing barriers, screens, or
deflectors. in the noise path can be an

20

%05.

Fig. 1-14b. REDUCTION IN NOISE LEVEL WITH DISTANCE FROM A LINE SOURCE

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 machine, which has a fundamental
frequency of about 3000 Hz, can be reduced
in the shadow of a barrier which measures
about 5 feet (1.5 m) ona side by at least
10 dB. Low-pitched noise, however, might be
reduced by only 4 or 5 dB. Figure 1-15
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
sound insulation of the exterior shell.
Windows and doors are common leaks for both
sound and heat. Properly fitted and sealed
storm windows and doors will cut down the


TABLE 5-3 (Cont'd)

washer, dryer, dishwasher, garbage
disposer, etc., which jointly can
generate a rather high level of noise.

For methods of selecting and installing
appliances for quiet operation, see
Chapter 2.

KNIFE SHARPENER

Place the appliance on a soft resilient
pad to isolate it from the kitchen

counter top or working surface.
(Chapter 2)

LAUNDRY ROOMS
The principal sources of noise are
clothes dryers and clothes, washers;

refer to these entries. The 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 and
flexible connectors should be used on
all machines; (Chapters 2 and 4).

For gas-operated dryers and water
heaters, consider using an
exterior-opening duct to draw outside
air for combustion. This will reduce
the level of combustion and burner
noise radiated indoors.

EDGERS

These tend to be as noisy as
gasoline-powered lawnmowers but have a
high-speed blade, which emits a
somewhat louder and more irritating
high-pitched noise. Some models are
noisier than others. Be selective in
choosing a quiet unit. Ear plugs

should be worn; they are especially
effective against high-pitched noise.

MOWERS

Rotary Power e: 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 the blade and balance the 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
107

LAWN

levels at the user's position
frequently exceed 90 dB(A), although
this does not pose a hearing hazard
because of the brief 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

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.
Reel-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

before allowing

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 lightest, muffler available.

(b) Vibration isolate engine from the
mower deck.

(c) Except for the cutting edge, the
blade should have rounded corners
and a serrated or feathered
trailing edge.

(4) Underdeck should have smooth
streamline air flow passageways
devoid of any obstacles or sharp
corners.

(e) Construct the deck of laminated
sheet metal with a viscoelastic
core to suppress deck vibration.

(£) Enclose engine compartment in a
sound-insulating jacket or cover.

THATCHERS

Fortunately, these are used

infrequently on any given lawn. The

noise problems are common to those of
lawn mowers and edgers, i.ce., the
engine is the main source of noise.
Select units with well-muffled engines.
The operator should wear ear
protection. See related entries.


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 and structureborne
noise simultaneously. Sources usually
considered to be strictly airborne noise
generators may produce a substantial amount
of structureborne noise and vibration if
they are fastened rigidly to wall and floor
structures. For example, a loudspeaker
built 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 air-

borne noise; however, when the unit is
mounted in a conventional manner a
combination of both structureborne and

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 ow 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.

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 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.

33

The chief flanking transmission paths
of airborne noise between two adjacent rooms

usually involve common corridors,
ventilation grilles, duct 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 be noise leaks,
particularly along the ceiling, floor and
side edges of the partition wall. Also,
noise leaks may occur 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. 2-3 airborne noise
may travel from one room to another over a
number of different paths, some of which are
not only complicated but often hidden from
view.

Flanking transmission paths of
structureborne noise, as illustrated in Fig.
2-4, 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.

A good rule to follow is to conduct an
inspection of the apartment 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


multiplying its speed (number of
revolutions per minute), by the
number of blower blades and
dividing the product by 60.
(b) Noise Resulting from Air Flow and
Turbulence: 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)
generates a considerable amount of
turbulence. However, the highly
turbulent air flow that usually
occurs at the discharge port of
the blower is the predominant
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 oa
consequence, the wall and floor
structures are set into vibration
and radiate the noise with
increased intensity throughout the
dwelling.

Central Air Return Duct: The
installation of the central return
duct of a typical home size unit
has two serious shortcomings.
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

(4)

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
approximately 1 inch (2.5 cm) at
the bottom to provide passage of
the return air and thus complete
the circulation. Unfortunately,
the large air gaps under the doors
are extremely efficient flanking
noise paths which allow the noise
to intrude into bedroom or other
Tooms where privacy is most
desired.

If you are planning to build a home,
insist that the builder installs both supply
and return ducts in all bedroom and study

57

areas and selects quiet heating and air
conditioning equipment. Equipment should be
selected on the basis of low noise output.
A few progressive manufacturers provide
sound power ratings of most types and sizes
of equipment they market. Such ratings,
which frequently contain sound power levels
in various frequency bands under different
load conditions, are 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, belt-
driven blowers are substantially
less noisy than small-diameter,
high-speed motor-coupled blowers.
(4) 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,
install equipment that is designed
to meet the building's heating and
cooling requirements, instead of
installing smaller units which
must labor continuously at maximum
speed in order to meet the
building's minimal demands.

Although the above advice may be useful
to the potential homebuilder, it
unfortunately offers no comfort to the
tenants who have a noisy heating and
air-conditioning system in their home or
apartment.

If you have a noisy heating and
ventilation system, check the following
possible causes of the noise and respective
remedies.

Remedies: (see Fig. 2-21)
Compressor:
(a) If necessary, relocate

the condenser unit as far as


TABLE 5-3 (Cont'd)

sound absorbent and vibration damping
materials within the housing or
canister. In canister-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 constriction 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 1 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, consider
the following measures: isolate the
valve from the rest of the system by
mechanically flexible couplings; avoid
rigid clamping of plumbing systems to
such sounding boards as floors and
walis; run the piping through
sound-treated ducts.

See Chapter 2, Control of Plumbing
Noise.

VEHICLE NOISE
See entries under Traffic Noise and
under individual types of vehicles,
such as trucks, trains, etc.

VENTILATION SYSTEMS
See Chapter 2, Control of Heating,
Ventilating, and Air-Conditioning
Noise.

VIBRATION
See discussions in Chapters 1 and 2
relative to vibration isolation and
control of structure-borne noise.

WALLS

See Chapter 2, Improving the Sound
Insulation of Walls.

WATER COOLERS

These have major noise sources in the
refrigerdtion equipment and in the
plumbing connections. See entries
under Compressor, Plumbing Noise,
Refrigerators, and Valves.

See Chapter 2, Quieting of Large
Appliances.

WASHING MACHINES

See entries under Plumbing Noise,
Valves, Solenoids, and Drain Pipes.
See Chapter 2, Quieting of Large
Appliances.

WATER NOISES

See Chapter 2, Control of Plumbing
Noise.

WATER HAMMER

See Chapter 2, Control of Plumbing
Noise.

Water is a heavy fluid; when its flow
is suddenly interrupted, its inertia
will produce a sharp.rise in pressure
at the shutoff valve. Sudden starting
or stopping of 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 sharply intermittent flow of water,
can be a potent source of water hammer.
This can be 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.

Hammering can also occur when piping
systems are loosely supported on "V"
shaped wire hangers. Placing a rubber
sleeve around the pipe and clamping it
to. some solid structure will resolve
the problem.

WHISTLING NOISES

114

Turbulence generated by high-speed air
flow past the edge of an obstacle
produces a whistling tone.

Such noises often occur in ducts,
dampers, ventilation grilles, on the
blades of fans, and usually around


Caulk Any Open Joints
Around Frame

Storm Sash Installed With

L 2” Minimum Air lspace
Head Between Glazing
TM.
i .
Jamb =
Sill

Fig. 3-1. DETAILS OF A DOUBLE-HUNG WINDOW WITH A STORM SASH

76


NOT THIS

TIML,

VIBRATION ISOLATION

ACOUSTICAL ABSORBING MATERIAL

BAFFLE

Looe

ENCLOSURE OF ABSORBING MATERIAL,

Ce

Courtesy of General Radio Company

100

BAND LEVEL-db
&

BAND LEVEL-db _
g88sags8

BAND LEVEL-db
2
CJ

OCTAVE —BAND ANALYSIS
OF NOISE

ORIGINAL . —

~~

20

75 180 300 600 1200 2400 4800
150 300 600 1200 2400 4800 9600
FREQUENCY BAND

~~ ORIGINAL
MODIFIED
20 75 150 390 600 1200 2400 4800
75 150 300 600 [200 2400 4800 9600
FREQUENCY BAND

40
30
20
5
100
2%
a
5
ae MODIFIED
S70
ret)
60
20
a rs
“0
30
20 75 150 300 600 1200 2400 4800
75 150 300 600 1200 2400 4800 9600
FREQUENCY BAND

Fig. 1-20, EFFECTIVENESS OF VARIOUS NOISE REDUCTION TECHNIQUES

26


A.

TABLE 5-1

COMMON NOISE COMPLAINTS, LIKELY CAUSES AND SOLUTIONS

Complaint

"This room is
noisy"

"It is difficult
to concentrate”

"It's stuffy and
oppressive in
here"

"You can hear
voices, but they
are unintellig-
ible"

"I hear whistling
noise"

Probable Causes

Noisy appliances, ventila-
tion system

Room is excessively re-
verberant; if the sound of
a person's handclap per-
sists longer than a second,
the room requires acoustic
treatment.

Outdoor noise intrusion

If conversation at an ordi-
nary distance of 3-5 ft
(1-1.5 m) is difficult, the
ambient noise level is too
high [greater than 70 dB(A)].
Excessive noise may be due
to causes described above.

If there is adequate venti-
lation, the room is acous-
tically "dead." There is
too much absorption, i.e.,
excessive drapery, rugs and
pads and upholstered
furniture.

The sound transmission
through a partition or
ductwork, and ventilation
noise in the mid-frequency
range.

High-pitched sound usually
is generated by ventilators
and grilles; worn or defec~
tive washers, and valve
seals in plumbing, heating
and refrigerant systems.
High-velocity gas flow
through furnace burner jets
or nozzles causes similar
noises.

96

Remedies

Reduce noise output of source: in-
stall vibration mounts; isolate source
in sound-insulating enclosure. Ven-
tilation noise: reduce blower speed;
install acoustic lining and flexible
connectors in ducts.

Install sound absorbing materials,
e.g., carpets and pads, drapery, up-
holstered furniture, acoustical ceil-
ing. Total surface area of absorbent
material should be at least one-fourth
of total roém surface area.

Install gaskets around existing win-
dows and doors; install storm windows
and doors; replace hollow core or
paneled entrance doors with solid core
doors.

If the remedies outlined above do not
alleviate the problem, install a pre-
fabricated, sound-insulated engineer's
booth or field office enclosure.

Remove at least 50% of all sound ab-
sorbent material such as drapery,
thick carpet and padding; or replace
existing furnishings with lighter-
weight material.

Caulk or seal all visible cracks at
ceiling and floor edges of party wall.
Remove cover plates of all electrical
outlets in party walls to check for
back-to-back installation; in such
cases pack cavities with glass fiber
wadding and seal with a resilient
caulk. If additional sound attenua-
tion is required, acoustical modifica-
tion of the party wall may be
necessary (see text).

Set dampers at most quiet setting;
place ear at grille, if noise is loud-
er remove grille. _If noise vanishes
with grille remo » reduce blower
speed or install new grille with
larger and more streamlined openings
and deflectors. Reduce pressure in
plumbing system and isolate pipes and
valves from supporting wall and floor
structures with resilient sleeves or
collars. Replace worn or defective
faucet washers or valve seals.


NOISY DESIGN QUIET DESIGN

Pe

Simple Layout
Complicated Layout
Fig. 1-5b. DESIGN OF QUIET FLOW SYSTEMS
operation will employ the following pipe system with a minimum of branches,
features: turns, fittings and connectors is
substantially less noisy than a
Low_flow velocities: Low flow complicated layout.
velocities avoid turbulence, one of the
main causes of noise. Flow velocities Long-radius turns: Changes in flow
should be of the order of 8 to 10 feet direction should be made gradually and
per second (3 m/sec) in domestic smoothly. It has been suggested that
forced-air heating and ventilation turns should be made with a curve
systems and plumbing systems for quiet radius equal to about five times the
operation. pipe diameter or major cross sectional

dimension of the duct.
Smooth boundary surfaces: Duct or pipe

systems with smooth interior walls, Flared sections: Flaring of intake and
edges, and joints generate less exhaust openings, particularly in a
turbulence and noise than systems with duct system, tends to reduce flow
rough or jagged walls or joints. velocities at these locations, often
with substantial reductions in noise
Simple layout: A well-designed duct or output,
NOISY DESIGN QUIET DESIGN
hy ¢| Calming Chamber
Ye Flexible [~ _— |
Sleeve —~
) 4
fr Store Duce N¢ ey
Jy oO 2=Iha HME Round
| [Boond MG ~~ Nee a Corner
re) Bess) | awa) WSL Aa
4 Square Corner High Speed ae
Blower
Turbulent Flow Smooth Flow

Fig. 1-5c. DESIGN OF QUIET FLOW SYSTEMS

7


Sf,

~

aN

Leds

g

4” airspace between glazing

1/4” glass installed with neoprene
“U" gasket or glazing compound

Gasketing or weather strip to
close joints around both windows

Brick or concrete block veneer
installed outside existing walt

Fig. 3-2. INSTALLATION OF BRICK VENEER AND DOUBLE
1/4-INCH WINDOW GLAZING

(c)

Exterior Doors

If the remaining 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 equipped with gaskets or
replaced with soundproof doors.

77

' cos ot 4” Air Space Between Glazing
Head

1/4” Glass in Neoprene Gasket

Continuous Edge Gasket
‘Around Sash

3/16" Diameter Vent Holes
(2 per Sash) With Glass
Fiber Plug

sill
Step B — 1/4” Glass in Separate
Sash

‘Added to Form 4” Air space
Between the Two Windows

Fig. 33. DETAILS OF DOUBLE 1/4.1INCH WINDOW GLAZING

_—- 1-3/4" Solid — Core Door

Storm Door

instal gasket or weatherscip

to close joints on all sides
around both doors

Fig. 34, DOOR MODIFICATIONS.


Install 1/2” thick exterior plywood
or moisture-proofed gypsum board
to underside of joists

| ——-———. Vent to crawl space

A-—Added Floor Construction

Install sound attenuator tightly to

inside of screened openings.
ae See isometric detail
4

B—Vent Attenuators

Galvanized steel duct fully lined
with 1” thick glass fiber duct liner
in proportions shown

2D Hl

Fig. 3-11. CRAWL SPACE MODIFICATIONS

83


a)

b)

c)

a)

Reduce weight, size or height of
fall of impacting mass.

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.

Whenever practical, one of the
impact heads or surfaces should be
made of non-metallic material to
reduce "resonance or ringing" of
the heads. Figure 1-1 shows the
application of measures a, b, and
c.

Substitute the application of a
small impact force over a long
time period for a large force over

NOT THIS

Impacting

a Masses

Metallic
Head

Metal Surfaces

BW

Use Non-

a short period to achieve the same
result.

e) Smooth out acceleration of moving
parts; apply accelerating forces
gradually. Avoid high peak
acceleration or jerky motion.

£) 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

Reduce Mass

Insert resilient

material at points

_.of Fall A or B to cushion
——~- B_ the impact.

WK
RAN A

Fig. 1-1. METHODS OF REDUCING IMPACT FORCES TO LOWER NOISE RADIATION


TABLE 5-3 (Cont'd)

THUNDER

The noise from thunder is very
low-pitched if the thunder arises from
a lightning stroke at a fair distance
from the listener. Methods used for
excluding traffic noise, such as solid
walls and well-sealed windows and
massive roof structures also will
reduce the intensity of the sound from
thunder inside your house.

TOILETS

See Chapter 2 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

TOYS

See entries for individual tools such
as Saws, Sanders, Grinders, etc.

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

The regulations, unfortunately, do not
protect against the use of noisy toys
in reverberant areas, rooms with hard,
reflecting surfaces that will permit
the noise to build up. It is a good
idea to restrict the use of noisy toys
to out-of-doors, where reverberation
and noise buildup are less likely to
occur.

Musical instruments, such as trumpets,
should not be put into the hands of
children who might carelessly blow them

113

near 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 prank. This loss,
though less visible, is a very serious
problem.

TRANSFORMERS:

A transformer carrying a fairly large
amount of power can be a 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

For methods of reducing the intrusion
of traffic noise into your living
quarters, see Chapter 3.

TRAIN NOISE

Airborne noise from a train can be
treated like traffic noise. (Chapters
3 and 4). Also, see entry under
RAILROAD.

For selection of quiet accomodations
while travelling in trains.

TRUCK NOISE

For control of tire noise.

For protection of dwellings from truck
noise, see Chapters 3 and 4.

VACUUM CLEANERS

Relatively quiet models are now
available. Such cleaners feature
streamlined blower and air passage
design, vibration isolation of the
motor from the housing, and use of


Sliding glass door — add
second door with 8”
minimum air space

7 a < i between, and gasket
Replace mail slot in f b | . ASA 4
door or wall with : 7 edges with drag strip
surface-mounted :

mail box

Fig. 3-9. HOUSE WITH SLAB ON GRADE AND A FLAT ROOF

81


NAIL

TABLE 5-3 (Cont'd)

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.

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.

PIPES

See Chapter 1 for design of quiet flow
systems, and Chapter 2 for control of
plumbing noise.

PLUMBING NOISE

See Chapter 2, 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.

109

PUMPS

Sump pumps and automatic-leveling water
pumps are serious noise offenders,
particularly if a large quantity of
water is drawn late at night.
Vibration isolate the pump from the
building and connect it to the plumbing
via flexible tubing. Seal connectors
carefully for maximum pumping
efficiency ( briefest operating time).

Pumps for compressed air systems are
exceptionally noisy devices. See
entries under compressors and jack
hammers.

See Chapter 1, Section 3 and Chapter 2,
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
condensed from cool steam blocks the
access of new steam in the pipes which
causes intermittent hammering). Select
a hot-water 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 2 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 ata
comfortable conversational level.

RAILROAD

A railroad is a source of vibration as
well as airborne noise. Select
dwellings that are at least one mile,
preferably two miles, from a railroad
line. See Chapter 4, "Selecting a
quiet home or apartment site."

If you live near a railroad see Chapter
3. for recommendations regarding
insulating your house against outdoor
noise.


sound and vibration. Transistor radios,
electric shavers and food blenders are
convenient sources of mid-frequency sounds.

Toy whistles and alarm clocks may be
used for the generation of high-frequency
sounds. Golf balls and walking canes can be
used to generate fairly repeatable impact
type noise when dropped from a constant
height. The noise and vibration generated
by all these sources cover a useful range of
the frequency spectrum with an adequate
intensity level for most investigations.

With the noise sources at hand, you now
need a few simple noise-leak detectors and
vibration sensors. Several devices that can
perform these functions also can be found in
most households. Appliances such as flash-
lights, hand mirrors, hairdryers, vacuum
cleaners with crevice tool attachments, long
thin knife blades, and even strips of thin
stiff paper can be used quite effectively to
locate simple noise leaks even without the
noise source.

If you suspect noise leakage through a
partition wall, try the following test.
With a long thin knife blade or a strip of
thin flat sheet metal, probe along the base
of the wall and try to insert the blade
under the wall. If you find places where
the blade penetrates a few inches under the
wall, it is highly probable that noise
leakage occurs at these locations. Mark the
locations and repeat the test on the other
side of the wall. Similar penetration of
the knife blade would be a _ positive
indication of noise leakage, most likely
caused by either warped flooring or wall
base-plates. To eliminate such noise leaks
you could remove the base board molding on
both sides of the wall and lay a continuous
bead of resilient type caulk between the
bottom edge of the wall and the floor, on
each side. The molding may be reinstalled
over the caulking.

Sometimes you can find a noise leak
simply by looking for a light leak. Ask a
companion with a flashlight to direct a
bright beam of light along the edges of the
wall, while you look for light leakage in a
darkened room on the other side. A small
hand mirror will be useful for looking into
remote corners or otherwise inaccessible
places. Detection of any light leakage
signifies noise leakage. You might want to
judge for yourself the effectiveness of this
particular test. This can best be done at
night. Close the door of a brightly lit
room, such as a bathroom, and look at the
door from an area in total darkness on the

34

other side. If your door is installed ina
typical manner, you might be surprised to
see it framed in a corona or halo of light.
The light coming through the edges of the
closed door traces a path that sounds can
travel just as easily. This demonstrates
quite clearly why many bathrooms provide so
little privacy. However, the absence of a
light leak is not necessarily a sign of an
effective acoustical seal, because sounds
can travel along complicated paths and
corners much too abrupt for light beams.

A test particularly useful for
detection of air and noise leakage around
windows and door frames is to use a
hand-held hair dryer or a vacuum cleaner
with a long narrow crevice tool fitted at
the end of the hose. While your companion
aims the air stream or suction at places
where you suspect noise leaks, you explore
for drafts on the opposite side of the wall.
Wetting your hand or fingers will increase
your sensitivity to the direction from which
the draft is coming.

Another test to determine whether
window or door gaskets are sealing properly,
involves opening the unit, inserting a strip
of paper against the gasket and closing the
unit. If the paper is held tightly or you
feel a noticeable amount of resistance as
you try to withdraw it, the gasket is
functioning properly at that point. This
test must be repeated at intervals along the
entire length of gasketing to determine the
overall performance of the gasket. However,
sound leaks that occur in double-door or
double-window installations with two or more
sets Of gaskets may not always be detected
by this method.

A more reliable test is to operate a
noisy device such as a vacuum cleaner or a
power drill in the offending room and listen
on the other side of the partition wall for
any noise leakage. Although you can use
your ears to locate the noise leaks, you can
make the job much easier by using a sound
probe or detector. A very useful device is
a stethoscope. The child's toy sold in some
“educational kits" is quite adequate for
this purpose. An arm's length of soft
plastic or surgical tubing, one end of which
can be inserted in ypur ear, will work
nearly as well. Ina pinch, you can use a
cardboard tube. The center tube from a roll
of wall paper or a mailing tube of about
that diameter is about the right size to
accomodate one ear, and is long enough to
allow you to move about freely while you
search for the noise leaks. With a small
lump of caulking compound, modeling clay, or


Motor and
(a)
(b)

(ce)

(d)

(e)

(£)

or direct the noise away from
bedroom or other noise
sensitive areas.

Blower:
Lubricate or oil bearings.

Clean blower blades and
balance the unit as described
in item (d) above.

If blower is belt driven,
replace worn or frayed belts,
adjust tension on belt to
prevent belt resonance or
“drumming" and check pulley
alignment.

Mount motor and blower on
resilient isolators, if
possible.

If possible, reduce the
rotational speed of the
blower. A 25% 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.

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" (16 m)
thick plywood base resting on
a 5/8" (16 mm) thick pad of
glass fiber.

A 2-1/2" (6 cm) square, 5/8"
(16 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.

59

(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.

Construction of Central Closet: (see
Fig. 2-22)

(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
on the inside of the closet,
build or install an acoust-
ically lined air transfer
grille between the studding,
as illustrated in Fig. 4-12,
to preserve the required
ventilation and noise
isolation.

(c) Nail resilient channels
horizontally to the studding;
space channels 24" (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


a 2" x 4" brace pressed up against
the subfloor and nailed securely
to the warped joist will provide
adequate support.

(£) Excessive deflection of the
structural 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- beaming with support
columns may be the most expedient
corrective measure.

CONTROL OF STAIR SQUEAKING (See Fig. 2-20)

As -in the case of floor squeaking, the
problem of stair squeaking can be avoided by
using a properly designed structure, good
quality building materials, and proper

construction techniques. As you will
notice, the causes and remedies of the
problem also are similar to those associated
with the problem of floor squeaking.

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).

Renedies:

(a) If the treads are loose, they
should be nailed securely to the
center and side stringers (the

saw-tooth framework that supports
the staircase).

NT

KA

CLEZESN ISN

Ga
N
NN

Ss
GY
1, Tread 7. Wood screws
2. Riser 8. Insert thin wooden
3. Stringer wedges
4. Toe-nail with ring 9. Apply mineral oil
nails at joints
5. Warped treads 10. Insert wooden braces
6. Provide clearance holes 11, Reinforce with metal bracket

Fig. 2-20 TECHNIQUES FOR THE CONTROL OF STAIR SQUEAKING

55


vibrate; this motion
energy in the form
frictional resistance

dissipates the sound
of heat because of
between air molecules

and fibers.

Drapery and carpeting absorb
high-frequency sounds much more effectively
than low. Because of their long
wavelengths, low-frequency 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 frequency 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 sounds bear

to their respective wavelengths.
Unfortunately, materials for absorbing
low-frequency sounds are somewhat

impractical in a house because of their
large size and bulkiness.

Although sound waves generally keep on
traveling in the direction in which they
originally started, high-frequency sounds
tend to follow narrower and more beam-like
paths than do low-frequency sounds. 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.
Low-frequency sounds tend to spread out
uniformly in all directions from the noise
source because of their long wavelengths.

The assumption that sound travels in
straight lines is valid only for wavelengths
that are short compared to the dimensions of
open spaces, rooms or passage ways. Sound
waves traveliin straight lines until they
encounter some obstacle in their path. If
the obstacle is small compared to the
wavelength of the sound, the wave front will
hardly be disrupted.

2.
Sound

Sound Reflection: Bouncing of

When a sound wave strikes a solid flat
surface that is large compared to the
wavelength of sound, the wave is reflected
similar to the way a sunbeam is reflected
from a window pane. As sound waves strike a
flat surface, they rebound at an angle equal
to the one at which they originally struck
the surface, as shown in Fig. 1-12.

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 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 wave or echo is due to the longer
distance it has traveled, and also to the
loss of energy due to absorption by
reflecting surfaces and perhaps the air.

Hard
Surfaces

Fig. 1-12, PROPAGATION OF DIRECT AND REFLECTED SOUND WAVES IN A ROOM

16


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.

If one is disturbed by conversation, TV
sounds, 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.

The sound insulation of an existing
wall may be improved by eliminating such
sound leaks or by laminating another layer
of wallboard, preferably to both sides of
the wall. (See Fig. 2-13.)

IMPROVING THE SOUND INSULATION OF WALLS

A quantitative measure of the sound
insulation provided by a wall or floor

1/4” Gap Filled With
Resilient Caulk ~

structure is the sound transmission loss.
The sound transmission loss is defined as
the number of decibels by which sound power
randomly incident on a partition wall is
reduced in transmission through the wall.
This is illustrated in the left top diagram
of Fig. 2-5, which shows a wall with an STL
value of 30 dB reducing an incident noise
level of 70 dB to a transmitted level of 40
dB, a 30 dB reduction. In this case, the
transmitted noise level is above the
background noise and as a result is audible.
The right diagram shows a 50 dB wall under
the same noise conditions reducing the
transmitted noise to an inaudible level,
i.e., below that of the background noise.
In this instance, the background noise is
said to mask the transmitted noise. In the
first example, the wall would not provide
satisfactory sound insulation whereas in the
second case, adequate insulation would be
achieved under these conditions.

Thus, the satisfactory performance of
the wall in a given situation hinges
primarily on three factors: (1) the sound
level on the source or noisy side; (2) the
sound transmission loss of the wall; and (3)
the background noise level on the receiving
or quiet side of the wall.

Non-setting
Adhesive

1/4” Gap Filled With
Resilient Caulk

Temporai

Existing Wall

Nails
1/2" Thick
Gypsum
Wallboard

Fig. 2-13. IMPROVING THE SOUND INSULATION OF AN.EXISTING WALL


NOT THIS THIS

‘AVOID EXTENDING
‘WALLS TO UNDERSIDE
(OF SUSPENDED CEILING

[EXTEND WAUL TO ROOF
‘OR DIVIDE ATTIC SPACE
‘WITH FUL-HEIGHT BARRIER.

SSS
SSS SSS Han ny

vie Geant SPACE
OR Bas
ATH FU HE HT BARRIER

‘AVOID OPEN

Fig. 2-16. METHODS OF CONTROLLING FLANKING SOUND TRANSMISSION PATHS

50


IN
— = ——
tof 52
oO

aoa

Lf °



Large Vibrating
Surfaces

S

NOT THIS

Q=O

THIS

CvOO

Reduce Size of Part or
Cut Out Excess Material

OR THIS

O-O)

Fig. 1-8. REDUCE THE AREA OF VIBRATING SURFACES TO LOWER NOISE RADIATION

6. REDUCE RADIATING AREA (See Fig.
1-8)

Generally speaking, the larger the
vibrating part or surface, the greater the
noise output. The rule of thumb for quiet
machine design is to minimize the effective
radiating surface areas of the parts without
impairing their operation or structural
strength. This can be done by making parts
smaller, removing excess material, or by
cutting openings, slots or perforations in
the parts. For example, replacing a large
vibrating sheet metal safety guard ona
machine with a guard made of wire mesh or
metal webbing might result in a substantial
reduction in noise, because of the drastic
reduction in surface area of the part.

1

7. APPLY VIBRATION DAMPING MATERIALS
(See Fig. 1-9)

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 and 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


The installation of dry flooring
in damp areas often results in
squeaking floors because the
absorption of moisture by the
flooring causes it to swell or

buckle, especially if no
allowances were made for
expansion.

(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 occurs when either the
depth of the joist is too shallow
or the spacing between joists is
too wide for a given floor span. .-

(d) absence of a sheathing layer: For
reasons of economy, builders no
longer adhere to the long-standing
practice of inserting a layer of
pbuilding paper between the
sub-flooring and the finish
flooring. This omission is common
in current floor construction and
makes floor squeaking caused by
rubbing and sliding contact
between the floor surfaces a much
more serious problem in modern

housing.

Methods of Avoiding Floor
New Construction:

Squeaking in

The problem of floor squeaking can be
avoided by using properly designed floor
structures, good quality materials, and
proper installation techniques. With regard
to floors consisting of wood blocks laid in
mastic over wood or concrete subfloors, the
manufacturer's instructions should be
followed closely relative to the preparation
or priming of the subfloor, application of
the mastic and the laying of the wood
blocks.

In general, floor squeaking can be

minimized by observing the following
construction techniques.
(a) Use straight, true, properly
seasoned flooring materials and
joists.

(b) Build a rigid well-constructed and
properly supported floor system.

(c) Maintain proper moisture content
of flooring prior to installation.

54

(4)

(e)

Insert building paper or felt
between finish and subfloor layers
to eliminate rubbing or sliding
contact.

Employ good nailing techniques,
with emphasis on proper spacing
and angle.

Ways to Remedy Existing Problems:

If you have floors that squeak, the

(a)

(b)

(c)

(4)

(e)

following recommendations should help you
correct the problem.

To locate the problem, have
someone walk over the squeaking
portion of the floor while you
examine the surface closely. If
you hold a flashlight so that its
beam grazes the floor surface, it
is quite easy to see the motion.

If you see no motion on wood block
or strip flooring, the squeaking
may be due to slippage between the
tongues and grooves. Apply
mineral oil sparingly at the seams
between adjacent floorboards to
lubricate the tongues and grooves
where the slippage is taking
place.

Loose or bowed finish flooring may
be securely fastened to sub-
flooring by surface 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.

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.

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,


. Page

CHAPTER 4
SELECTING A QUIET HOME OR APARTMENT . . ~~. ee ee ee eee ee ee ee ee 85
Selecting a Quiet Residential Area. . 1... 2... ee ee eee eee 85
Selecting a Quiet Location Within a Housing or Apartment Development ee 86
Selecting a Quiet Apartment Unit Within the Building ........... 89

CHAPTER 5
A TROUBLE-SHOOTING GUIDE . «wwe ee ew eee ee ee ee ee 91
ANALYZING THE PROBLEM. . . . - ee ee ee ee ee ee ee ee 91
HOW TO LOOK FOR NOISE LEAKS. . . 2 2 1 ee eee eee et te ee ee 93
USE YOUR EARS. .....+ +s. ees er  D 93
USE HOME APPLIANCES AS DIAGNOSTIC TOOLS. wae ee ee rs 93
* COMMON NOISE COMPLAINTS, LIKELY CAUSES AND SOLUTIONS ey 96
GENERAL NOISE ABATEMENT TECHNIQUES . .. . ee 98
INDEXED CATALOG OF SPECIFIC NOISE PROBLEMS AND REMEDIES. eee ee ee ee 99


completely finished to the floor
level on both sides, particularly
in back-to-back tub and/or shower

installations. Failure to surface
the 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, pre-
ferably 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 suggested that the
glass fiber jackets should have a
density of about 6 lb/cu ft (96
kg/m”) and a thickness of at least
3 inches (8 cm). The impervious
covering should, weigh at least 1
1b/sq £t (5 kg/m“).

CONTROL OF NOISE FROM RAIN GUTTERS AND
SPOUTS

4n irritating source of noise,
particularly in the still of the night, is
the turbulent flow of rainwater in gutters
and downspouts during a storm, and the
incessant dripping and plunking of the water
after the storm is over. Rigid attachment
of the downspouts or drain pipes to the
exterior walls of bedroom areas is the chief
cause of the problem. The interior surfaces
of the walls, which perform as sounding
boards, tend to reinforce or amplify the
drain pipe noise. The following measures

should be used to minimize disturbance from
such noise.

vertical
bedroom

Avoid
drainpipes
areas.

installing
outside of

a.

Structurally isolate vertical
drains from the building by
inserting soft rubber or neoprene
sleeves or collars around the
drainpipes where they are clamped
to the wall.

Replace the conventional metal
elbow at the base of the drainpipe
with a soft rubber boot or plastic
hose.
When replacing existing rain
gutters, select units made of
heavy gage metal, with rounded
corners, and coated with vibration
damping material.

Refer to Fig. 2-29 for proper installation
of rain gutters and vertical drainpipes.

——

A Rubber Sleeve
B_ Drain Pipe

C_ Pipe Clamp

D Rubber Boot
E — Sewer Drain

aunt elcnia

71

a

Fig. 2-29. METHODS OF CONTROLLING NOISE FROM
RAIN GUTTERS AND DOWNSPOUTS


Spring Mounts Fiberglass Mounts and Pads
Hangers Hangers
Located Located
at the Clevis Type in the
Ceiling Hanger Rods
(Preferred
Method)
Mounted Unit
Rigid Support

<a

Neoprene Mounts and Pads

Rigid Support

| So
Mounted Unit

Fig. 1-19. VARIOUS TYPES OF VIBRATION ISOLATORS

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 sound. Absorbent lining on the interior
surfaces of the enclosure will reduce the
reverberant buildup of noise within it.
Structural contact between the noise source
and the enclosure must be avoided, or else
the source vibration will be transmitted to
the enclosure walls. and thus short circuit
the isolation. Figures 1-20 and 1-21 show
the design and effectiveness of various
enclosure configurations. Total enclosures
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.

25

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
damage. This can be done by employing some
of the following techniques.

USE EAR PROTECTORS

Molded and pliable earplugs, cup type
protectors, and helmets are commercially
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


CAULK

1/8" CLEARANCE UNDER FLANGE

FLOATING FLOOR
RESILIENT MATERIAL

SUB-FLOOR

‘SOUND INSUL. BD.

RUBBER
SLEEVE

RUBBER SLEEVE OR
GLASS FIBER PACKING

WATER PIPE

WATER PIPES PLY UNDERLAY WATER-AIR TIGHT
WATER-AIR TIGHT al
RUBBER GASKET z.W000 BLK. UBBER GASKET
PLY SUB-FLOOR 2x10 GLASS FIBER
FLOOR SLAB
SPRING
oe PIPE SUPPORT GYPSUM BD.
—
PIPE RUBBER PAD
SUPPORT
Fig. 2-26. METHODS OF INSTALLING PIPES FOR QUIET OPERATION
areas, supply and drain pipes Bath tubs, toilets and shower
should not be installed in walls stalls should be set on under-

separating bathrooms and bedrooms.
Piping should be installed in
partition walls which separate
adjacent bathroom or kitchen
areas. Supply and drain pipes
must be isolated from internal
studding or wall surfaces.

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.

(a)

Install Bathroom Fixtures on
Resilient Bases and Mounts:
(See Figs. 27 and 2-28)

fe)

69

(£)

layments 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.

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


NOT THIS

3 oes, ALIED eT =
ne S|
Noise 2*]]** \ ceiling
Paths Grille
Apt. A |} Apt. B
SOO. TLR MLAP EEE PRET:
Duct
Wall Grille
~
Wall Grille

\
Ceiling
Grille

Nceiling
. Grille
Apt. A Apt. B
CU TET WH ee cA

Duct

Wall Grille
TM=. Metal Splitter

Acoustic Lining

Fig. 2-24, METHODS OF CONTROLLING CROSS TALK AND THE TRANSMISSION OF FLANKING NOISE IN DUCTS

lining 2.5 cm thick.) A comparable degree
of noise reduction for the low-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.
1-16.

If you are disturbed 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.

62

(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 ina
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


Wave Front

—>

New Waves Spread Out
Spherically and Fill Space

New Waves Are of Same
Frequency But Lower Intensity

Fig. 1-13a. DIFFRACTION OF A SOUND WAVE PASSING THROUGH A SMALL HOLE

Wave Front

New Waves Spread
Out Spherically

New Waves Merge With Original
Wave Front and Set Up
Interference Patterns

Fig. 1-13b. DIFFRACTION OF A SOUND WAVE AT THE EDGE OF A WALL

to travel along winding corridors, up
staircases and through duct systems with
surprising ease.

"QUIETING" IN THE PATH
and

1. Separate the Noise Source
Receiver As Much As Possible

In open spaces, sound coming from a
point source, which is defined as one that
radiates sound uniformly in all directions,
tends to spread out in a wave front that is
spherical in shape. The power at any point
away from the source drops in proportion as

18

the surface area of a sphere centered at the
source increases. For each doubling of
distance from the source, the surface area
increases fourfold. Consequently, for each
doubling of the distance, the power drops to
one-fourth or the power level drops by 6 dB.

Any source that ts located at a
distance that is large compared to the size
of the source acts to the observer like a
point source along a direct line between him
and the source, even though the source
itself may be relatively large and may
radiate more sound in some directions than
in others. Thus, a power mower located at a


‘A MASSIVE WALL ISOLATED SURFACE ©

4
\aL.

‘A. CUSHION IMPACT

DOUBLE WALL

. SOUND ABSORBER,

c, _ ISOLATE AND SEAL
IN CAVITY "

PIPING, ETC.

Fig. 2-5. METHODS OF CONTROLLING AIRBORNE AND IMPACT SOUND TRANSMISSION

THROUGH WALLS AND FLOORS

SOUND ABSORPTION. VERSUS 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. These materials have different
properties and are used for different
purposes, which can not be interchanged.
But due to confusion, both materials often
are misused.

Sound absorbing materials such as
acoustical tile, carpets and drapery play an
indispensible part in controlling noise
generated within a room or in reverberant
areas such as lobbies, corridors ‘and
staircases. Although such materials are
highly effective as sound absorbers, they
are relatively poor sound insulators because
of their soft, porous and lightweight
construction. In short, they transmit noise
very easily. To illustrate this point,
imagine a wall constructed solely of
acoustical tile, carpet or drapery material.
Such a wall would provide virtually no

36

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.

Because sound insulators and sound

absorbers are both called "acoustical
treatment", confusion arises between their
proper uses. Improper application of
sound-absorbing treatment to reduce the
transmission of noise between adjoining
areas in an existing building has often been
an expensive and annoying error.

WARNING: Sound-absorbing materials are


(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 through
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
edges of the risers with mineral
oil or silicone spray 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 riser will correct
the squeaking problem.
(e) If the back of the stairs is
accessible, the back edges of the
treads may be nailed to the
risers. Additional bracing also
may be provided by fitting a 2" x
4" brace between the stringers,
pressing it up against the bottom
edge of a riser and nailing it
securely to the stringers.

CONTROL OF HEATING, VENTILATING AND
AIR-CONDITIONING SYSTEM NOISE:

(In Basement, Attic and Central Closet
Installations)

The noise problem associated with
heating, ventilating and air- conditioning
systems is due primarily to the current

trend of installing, in homes and
apartments, small compact units driven by
noisy high-speed, motor-coupled blowers.

The large return grilles, which usually are
coupled with short unlined ducts to the
blower intake port and the open corridors
that serve as centralized air-return ducts,
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 sound attenuation
because of its light-frame construction,
louvered door, and large return grille.
Thus the noise escapes with undiminished
intensity and spreads throughout the home or
apartment.

56

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
Outdoors

(a) Compressor: The noisiest
component of most air conditioning
systems is the condensing system.
It consists of a compressor, motor
and fan encased in a metal cabinet
that is usually installed outside
of the dwelling. As a conse-
quence, it frequently disturbs the
neighbors more than the home
owner, especially if the neighbors
sleep in bedrooms with open
windows that overlook the com-
pressor unit.
(b) The most objectionable noise is
the cyclic operation of the
compressor, in particular the
low-pitched starting groan of the
motor. Blade-frequency noise of
the fan and high-pitched flow
noise add to the annoyance.
Occasionally, a slipping fan belt
will produce a high-pitched
screech, especially as the unit
starts up.

The reflection of the sound waves
between the walls of adjacent
houses builds up the noise level.

(c)

Indoors

(a) Motor and Blower: In a_ typical
installation, the high-speed motor
and blower, which generally are
coupled together, are the main
sources of noise. The mechanical
noises of bearings, brushes and
switches and the siren-like
“blade-frequency" noise of the
blower are transmitted throughout
the dwelling both by air through
the duct passages and by vibration
of the ductwork and supporting

walls or floor structures. The
"blade frequency" noise of the
blower may be determined by


NOT THIS

oe

PRK

sive

THIS

Enclosure
or Barrier

Acoustic Tile” hl
Drapes.
ang h
Carpet \ ft
i — TAA \ = 4

Fig. 1-15. NOISE CONTROL OF THE TRANSMISSION PATH

intrusion of outdoor sounds as well as
reduce heat transfer.

4. Use Acoustical Lining

Noise transmitted through ducts, pipe
chases or electrical channels 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 1” (2.5 cm) thick

acoustical lining are quite possible for
high-pitched sounds. (In metric units, the
reduction is about 10 dB/m for an acoustical
lining 2.5 cm thick.) A comparable degree
of noise reduction for the lower frequency
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.
1-16.

21


90
TT TaN TT a a
‘\ \ Lower Limit for J
— \ Damage, Extended
\ N Exposure
go fj---— _ a
N
_ r ~ \ Shout 7
z \ a
3 79 \ “Raised 4
s Voice” AN
3 i) AN ¢ \
a
2 é N
§ Normal 7
8 Voice
2 60 - Level 4
8
=
w — 4
50 -- 4
g \ 4
40 Fe ee Ge | | LS iti
1.0 (Feet) 5.0 10 20 50 100
(0.3) (1) (Meters) 5) (15)

Limiting Distance for Conversation, “With Ease”

Fig. 5-1. THE “A” WEIGHTED SOUND LEVELS OF SPEECH AT VARIOUS DISTANCES
UNDER ORDINARY CIRCUMSTANCES

components intact; structure-borne sounds
are likely to seem muffled.

Some noise problems are relatively easy
to recognize, especially if both the source
and the noise transmission path are obvious
as in the case of a dishwasher which
operates in the kitchen but transmits much
noise through the air nearby and sends
vibrations along the plumbing system to
other areas of the house. However, most
noise problems are much more subtle and
exasperating to cope with because of the
difficulty in determining let alone

92

locating -~ the noise source or its dominant
transmission paths. Such problems are
particularly difficult in large high-rise
apartment buildings, in which the noises

generated by the numerous types of
equipment, appliances, and occupant
activities occur simultaneously. They

combine and blend, and
offending sources.

thus camouflage the

If noise intrudes into your living
quarters from an adjacent apartment, or
perhaps from one room tp another within your
own dwelling, the following steps should


cabinets to reduce the noise

buildup in these reverberant

enclosures.
(g) The more technically
competent person might try
mounting 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 durable. In addition, the
rooms generally have wide open passageways,
which permit the sound to travel to other
areas.

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 buildup, and
diminish distraction and annoyance.

While such measures will reduce noise
levels in the recreation room, they do
little to keep the noise from spreading to
other areas of the home where a quiet and
relaxing atmosphere may be desired even
during daylight hours. The most effective
measure to decrease the leakage of noise
from rooms with open passageways is to
install sound insulating doors, as was
recommended in the case of the kitchen area.

However, some people, mothers in
particular, might object to having rooms
elosed off for fear that they may not be
able to hear what their children are doing
in other parts of the house. Of course,
when needed, doorways can always be kept
open, but a more practical solution to this
problem is to install an intercommunication
system throughout the house. This
electronic device will enable mothers to

43

hear their children at will anywhere in the
house without compromising the sound
isolation that other members of the family
might enjoy.

Noise in recreation rooms caused by
playing such popular games as darts, table
tennis, and billiards 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 return chutes
with rubber or cork tile. Such treatment
will cushion the impacts and muffle the
resultant noise and distraction.

Earphones or headsets can be used when
anyone wishes to listen to a sound system,
radio or television set without disturbing
other members of the household. This use,
of course, does open the possibility that
the listener unwittingly can turn the sound
volume up to levels hazardous to his
hearing. Some limit should be set, either
by an attenuation pad inserted at the
earphone outlet (which can be installed by a
serviceman) or by marking a stop position on
the volume control, beyond which it should
not be turned.

Basement Recreation Rooms

In one-story homes, special attention
must be paid to prevent the transmission of
sound 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 and quiet
surroundings are most desired. The
installation of a sound insulating ceiling

assembly will alleviate such problems. A
ceiling assembly which will provide adequate
sound insulation under most circumstances
would consist of the following construction,
as illustrated in Fig. 2-11.

(a) If the floor joists are exposed,
install a 3 inch (7.6 cm) thick
layer of glass fiber insulation
between the joists,

(b) attach metal resilient channels to

the under 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 (16 mm) thick

layer of gypsum board to the


(b)

(c)

(4)

Railroads, Expressways and Indus-
trial Areas: If annoyance or

disturbance from these excessively
noisy sources is to to be avoided,
residential buildings should be
located at a distance of at least
one mile and preferably two miles
(1.6 to 3.2 km) from the sources.

Check With City Zoning or Planning
Authorities

Consult with local city or county
planning authorities regarding
future development plans for the
area. As a result of future
rezoning action, quiet residential
areas frequently are bordered by
industrial parks or huge shopping

malls. Although such business
centers by themselves may not
cause any annoyance, the noise

from the increasing flow of
automobile traffic and shipments
by heavy trucks to and from the
areas, especially at night, may
become a major source of
disturbance for you.

Consult With City or County Trans—
portation 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.

Conduct An On-Site Examination

Conduct several on-site
examinations of the area during
daylight and especially 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, ace 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.

86

(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 APARTMENT DEVELOPMENT

Of course the first thing that you
should do is to select and inspect an
apartment development that advertises
"soundproof" wall and floor construction,
quiet, efficient central airconditioning
systems and fully carpeted interiors,
including entrance foyers, corridors and
hallways.

In addition, it is important to choose
an apartment that has a ventilation system
with air supply and return branch ducts
serving individual rooms, and well-fitted,
solid-core doors with perimeter gaskets and
threshold seals installed in bedroom areas.
Such construction and furnishings are
prerequisites for ensuring a quiet
environment and adequate privacy within a
dwelling unit, as well as minimizing the

intrusion of noise from neighboring
apartment units or other areas in the
building.

If possible, avoid choosing a home or
an apartment unit that has only a single

air-return grille or duct to serve the
entire dwelling area. In order to complete
the circulation, entrance doors to

individual rooms must be undercut about 1
inch (2.5 cm) at the bottom to provide an
air gap for passage of the return air.
Regrettably, such air gaps also create a
series of flanking paths throughout the
dwelling, which virtually nullify any sound
insulation that partition walls and doors
separating rooms could provide. If, in
addition, the return grille is undersized,
the air-flow velocity at the face of the
grille must be made fairly high in order to

maintain adequate ventilation. This,
unfortunately, may generate a considerable
amount of high-pitched noise. As a

consequence, the occupants of such dwellings
frequently complain not only about the lack
of privacy, but also of interference to
sleep caused by the grille noise intruding
into the bedroom area.

A particularly serious problem that
often occurs in apartment buildings is
caused by a ventilation system in which a


NOT THIS THIS
Floor Floor
NT pecoeea 10)
\ N 0 ee Acoustic natin soist
\ oustic
Isolation Lining Pads
‘Support Bracket ‘Support Bracket

Bracket ‘Y

Duct
Flexing

Acoustic
Lining

Fig. 2-23. METHODS OF REDUCING NOISE DUE TO AIR FLOW AND VIBRATION IN DUCT SYSTEMS

Cross Talk

Metal ducts act like speaking tubes on
a ship. Noise from one room may be carried
to another room through an unlined duct
serving both rooms. For example, the
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 units, 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
from the thin-wall duct in the adjoining
apartment. Noise transmission from one room

61

to another may also occur by way of openings

and holes around poorly sealed duct
penetrations through wall and floor
structures.

Such noise transmission paths by-pass
the sound insulating effectiveness of the

intervening party walls and floor
structures.

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, it is
possible to obtain noise reductions for
high-pitched sounds of the order of 2 to 3
4B per linear foot for 1" (2.5 cm) thick
acoustical lining. (In metric units, the
reduction is about 10 dB/m for an acoustical


common air return is installed in the
corridor outside the dwelling units. The
entrance doorways of all apartment units
must then be undercut to permit the venting
of the return air. Obviously, the privacy
between adjacent apartments is seriously
breached in such cases.

The only remedy the tenant himself has
is to close the gap at the bottom of each
door in his dwelling with a threshold plate
equipped with a tubular gasket. He must
then install in the wall or ceiling of each
room an acoustically lined air-transfer duct
to vent the air into the adjacent hall or

corridor. Both door thresholds and
air-transfer ducts are commercially
available. Techniques for sealing door

thresholds and installing air-transfer ducts
are discussed in Chapter 2 and illustrated
in Figures 2-7 and 2-12, respectively.

Although the intrusion of outdoor noise
is prevalent in dwellings in urban
locations, it can occur in dwellings in

i

a7 / hie 2
Avoid building sites at intersec-
tions of major traffic arteries.
Such sites are extremely noisy

due to accelerating, decelerating,
and braking vehicles.

SNL

Building sites in open areas are
Jess noisy than sites in congested
building areas.

Avoid hollows or depressions.
They are generally noisier than
flat open land.

supposedly quiet suburban and even rural
areas. While an occasional jet aircraft
flyover or a passing truck may cause some
disturbance in such areas, many problems
arise from a neighbor's air conditioning
unit, barking dogs or bird calls. If the
intrusion of such noise is bothersome to
you, give preference to buildings that have
fixed or well-sealed windows that are
thermally insulated or feature double-pane
construction. Buildings with single pane
windows protected by well-fitted storm
windows also would provide an adequate
degree of insulation against such noise.
The intrusion of outdoor noise may be
minimized even further by observing the
following suggestions relative to selecting
the building site.

(a) Avoid building sites that front on
main traffic arteries or bus
routes. Early morning traffic
noise may be a _ source of

annoyance, as illustrated in Fig.
4-2.

Avoid building sites on the crests
of hilly traffic arteries. Such
sites are very noisy due to low
gear acceleration noise.

Traffic arteries between tall
buildings are quite noisy. Avoid
building sites opposite tall build-
ings in such cases.

WIND DIRECTION

Upwind building site is less noisy
than a downwind site.

Fig. 4-2, EXAMPLES OF APARTMENT SITES THAT SHOULD BE AVOIDED


Install Double Wall for
Optimum Sound Isolation

Avoid Structural

Contact Between we
Walls

Spring

Isolate Source Mount

From Enclosure

Acoustical Lining
Reduces Noise
Buildup

Solid Wall Construction

Install Lined Ducts if
Ventillation or Cooling
is Needed

Airtight Seal Needed
to Preserve Isolation

Fig. 1-21. DESIGN OF AN EFFECTIVE SOUND ISOLATING ENCLOSURE REQUIRING AIR

CIRCULATION FOR COOLING

masking or overriding annoying intruding
sounds. 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
pure-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.

Many examples of sources of masking noise
are given in the literature; the most
commonly mentioned being vehicular traffic
and heating and air conditioning equipment.
Unfortunately neither is suitable. Traffic
noise is seldom steady, and the heating or
air- conditioning equipment is cyclic.

29

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 reception rooms or
offices of dectors, 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.
Physicians have reported, for example, that
it becomes difficult to interpret the sounds
from a stethoscope if the surrounding sound
levels exceed 45 dB.


(d) Water pressure in individual home,
office, or apartment plumbing
systems should be limited to 35
pounds per square inch (241
kilopascals) and flow velocities
of the order of 6 ft/sec (2 m/sec)
for quiet operation. A competent

plumber can perform these
adjustments.
(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
to 1/2 to1/4 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 low level of noise which
usually is unnoticeable in most
residential or office areas. Ina
given system, reduction of air
flow velocity can be achieved by
operating at lower motor or blower
speeds, installing a greater
number of ventilating grilles, or
by increasing the cross-sectional
area of the existing grilles.

Your heating and air-conditioning
contractor can make these
adjustments and modifications.

3. BALANCE ROTATING PARTS

One of the main sources of machinery
noise is structural vibration caused by the
rotation of poorly balanced parts such as
fans, fly wheels, pulleys, cams, shafts,
etc. Measures used to correct this con-
dition involve the addition of counter
weights to the rotating unit or the removal
of some weight from the unit as indicated in
Fig. 1-3. 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 blowers driven
by a single belt, an unbalanced load may be
applied if the blower pulley can move out of
direct alignment with the motor pulley;
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.

(a) Static Unbalance

(b) Dynamic Unbalance

Black blocks are heavy parts of rotor that cause vibration. White blocks are locations where
counterweights must be placed to eliminate the vibration.

Fig. 1-3. EFFECTS OF STATIC AND DYNAMIC UNBALANCE ON ROTOR OPERATION

4, REDUCE FRICTIONAL RESISTANCE

Reducing friction between rotating,
sliding or moving parts in mechanical
systems frequently results in smoother
yperation 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.


privacy in these areas is obvious. This
arises from the use of the following
building constructions and practices:

(a) thin, veneer, hollow-core doors,

(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.

The common practice of installing a
forced-air ventilation system in some
central closet location is responsible for
the lack of privacy in homes and apartments.
Since such a system often uses a central
hall or corridor as the main air return
duct, all other rooms bordering on this hall
must vent the return air through open air
spaces under the doors.

Acoustic Lining

Unfortunately, such_

air paths become sound paths that nullify
any privacy ordinarily provided by walls and
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 room.
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, as illustrated in Fig.
2-12. Such ducts are commercially
available.

For quiet operation: Use large
size grille, 6ft. length of acoustic
lining in each duct run, rounded
duct corners and stream-lined
deflectors or wide-mesh grille
face. Avoid sharp edges.

IN WALL

ON WALL

Fig. 2-12. DESIGN AND INSTALLATION OF A QUIET AIR RETURN DUCT

45


circulation

systems lessens turbulence

resulting in decreased noise radiation.

(a)

(b)

For quiet operation, fans,
impellers, rotors, turbines,
blowers, etc., should be operated

at the lowest bladetip speeds that
will still meet job needs.

Use large-diameter low-speed fans
rather than small-diameter

(ce)

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

Centrifugal squirrel-cage type
fans, sometimes used in furnaces
or on exhaust ducts, are less
noisy than vane axial or propeller
type fans, all other factors being
equal. The two types of fans are
illustrated in Fig. 1-2.

Squirrel Cage or
Centrifugal Fans

Propeller or
Vaneaxial Fans

Fig. 1-2. FOR A GIVEN MASS FLOW, SQUIRREL CAGE FANS GENERALLY ARE LESS NOISY

THAN PROPELLER TYPE FANS


used in the installation of food
waste disposers, and of dish or
clothes washers to avoid the
transfer of machine vibration to
the walls containing the plumbing
outlets or fixtures. Otherwise,
the vibrating walls acting like
sounding boards would tend to
amplify the machine noise.

Isolate the appliance from cabinet
enclosure

Appliances such as dishwashers,
disposers, compactors, etc., which
are built into or enclosed by
counter~type wall cabinets, should
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
1/4 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 of soft rubber to
prevent the transfer of vibration
to the countertop.

As a temporary measure, folded
towels placed under 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 units.
Otherwise, the appliances might
tend to overheat with prolonged
use.

A soft rubber sleeve-type gasket
inserted between the mounting
flange of a waste disposer and a
sink basin will tend to prevent
the sink from vibrating and thus
amplifying the disposer noise.
Figure 2-8 illustrates the proper
installation of a disposer for
quiet operation.

Isolate the cabinet enclosure from
wall

cabinets with
tend to

Countertop wall
built-in appliances

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 behind the cabinet to
avoid rigid contact with the wall.
This will eliminate the tendency
of the wall to act as a sounding
board. Such gaskets will also
reduce impact noise radiation
caused by the stocking of cabinet
shelves and the closing of drawers
and cabinet doors.

Isolate small appliances

Busan

A-— Rubber Gasket F — Ring Plate K — Ring Clamp
B— Sink G — Disp’I-Flange L— Metal Cover

C — Acoustic Mat’l H — Steel Washer M — Glasswool

D — Cabinet | — Rubber Washer —N — Disp’I-Housing
E—MasticCoat  J—Nut O — Rubber Sleeve

P — Rubber Hose

Fig. 2-8. DESIGN AND INSTALLATION OF A

GARBAGE DISPOSER FOR QUIET
OPERATION


3. Reverberation: Multiple
Reflection of Sound
However, in a reverberant space of

small dimensions, the reflected and direct
sound waves tend to merge to produce a scund
that is louder than the direct sound alone.
If successive reflections follow one another
within a time interval of less than 35
milliseconds, the ordinary person perceives
no echo. This corresponds to a_ spacing
between successive reflections of less than
about 35 feet (10m). This type of sound
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 reinforce 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.

Have you ever noticed upon entering a
bare, unfurnished room how much louder your
voice appears to be? The merging of the
reflected waves builds up the sound 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, would 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 materials
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 sound
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

17

reverberant, and requires acoustic
treatment.

Although excessive reverberation of
sounds in most instances is a problem

associated with the interior of buildings or
rooms, it can occur as well out of doors,
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 apart-
ment 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 should
not front on a traffic artery.

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
shown in Figs. 1-13a, 1-13b. This action is
known as diffraction. Diffraction occurs
when sound waves strike the edge of a solid
barrier. This edge acts asa 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
3/4 inch (13-19 mm) 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
amount 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 permit sound


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
are available:

(a) liquid mastics which are applied
with a spray gun and harden into
relatively solid materials, the
most common being automobile
“undercoating";

(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 surface.

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.

SINGLE LAYER

Apply damping material first to

most cases this will be thinnest
surface.

at tat Composite
surface with strongest vibration. In Layer

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 surface where the most
flexing, bending or motion occurs.
These usually are the thinnest
sections.

(b) For a single layer of damping
material, 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

Vibrating Surface

Mastic coating should be 2 to 3
times as thick as the vibrating
surface for maximum effectiveness.

Vibrating Surface

Mastic Layer

For effective vibration damping,
each layer should be about 1/3 as
thick as the vibrating surface.

Fig. 1-9. REDUCING VIBRATION WITH DAMPING MATERIALS

12


CHAPTER 1

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 structurally 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 - pre-
ferably backed with a copy of the certifying
laboratory's test report. Some appliances
and equipment feature or advertise
noise-control design or construction - look
for descriptive terms such as "sound
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 guard
because such descriptive phrases as "whisper
quiet" may be more poetical than absolute,
or perhaps an expression of hope rather than
reality.

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 differentials, and power ratings
all affect noise output. By looking for
equipment displaying "slower and "lower"
operation characteristics you can be assured
of relatively quieter operation. For
example, large slow-speed fans are
substantially 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


TABLE 5-3 (Cont'd)

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.

STEREO SETS

See entries under MUSIC and, for cabi-
Met resonances, under CABINETS.

SUMP PUMPS

See discussion under PUMPS.

SWIMMING POOLS

The hard tile surfaces surrounding an
indoor swimming pool and the water
surface of the pool cause the area to
be highly reverberant and thus build up
the noise made by persons at play
within the pool. Various types of
sound absorbers that are moisture
resistant can be used within the pool
area to reduce the noise level, but
seldom are.

Pumps and circulation systems which are
additional sources of noise should be
structurally isolated by means of
resilient mounting and flexible
connectors to minimize noise buildup.
A rooftop swimming pool is a nearly
intolerable source of noise to the
residents beneath. Such installations
require vibration isolation of the
pool, and the plumbing and filtration
system from the building structure.

TELEPHONE

If you are disturbed by the noise of a
ringing telephone, select desk type
telephones in preference to
wall-mounted models. Owing to the
sounding board action of the wall, the
wall-mounted telephone tends to be
considerably noisier than the desk type
unit. For this reason, one should
refrain from having wall-mounted
telephones installed in bedroom areas
or on party walls separating dwelling
units.

Most telephones are equipped with a
volume control to adjust the noise
level of the bell. Place phone on soft
rubber pad.

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

112

flashing light. This is done routinely
by the telephone company for
hard-of-hearing clients, and is
available in most systems.

If you are hard-of-hearing, and the
telephone is in a noisy environment,
you can improve your chances of héaring
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.

TELEVISION SETS

Neise complaints involving television
sets are like those concerning "Hi-Fi"
sound systems and rock bands; the sound
levels at which they are played are
objectionable to the neighbors. In
apartment buildings, TV noise
disturbance can be reduced by
requesting tenants to locate their sets
away from party walls, place resilient
pads under the legs of the cabinet or
stand, and set the volume control at a
lower level.

Another source of objectionable noise
is the high-pitched tone radiated by a
poorly-adjusted TV set. Persons with
normal hearing can find this noise
quite bothersome; however, it can be
removed by having the set readjusted by
a repair man.

Occasionally, a high-pitched noise is
radiated from a pulse transformer which
is usually located in the rear of a
television set. The noise, which
generally is directional, can often be
reduced by installing fireproof
acoustical tile on the wall directly
Behind the TV set.

TELEVISION ANTENNA

The television antenna acting like a
vibrating reed can generate a moaning
or mournful sound on windy days, if it
is mounted on the roof or attached to
the chimey of a house. This problem
can be corrected by bracing the antenna
with guy wires or tie rods, or by
installing the antenna in the attic
area where it would be sheltered from
the wind.

THERMOSTATS

See discussion under LIGHT SWITCHES.


incorporate the following design elements in
the early stages of your building plan.

(a)

Vibration Isolate all Plumbing
Systems: (see Figs. 2-25 and
2-26)

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.

Entrapped Air
Compressed By
Water Pressure

“—~ Install In Each
Long Run Of Piping

(b) Use a Simple Plumbing Layout:

(c)

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.

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

Glass Wool Blanket

= =. 5
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Air Lock

Te

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2

SRN

SEER

SD

Bs

Between Studs
Staggered-Stud
bs Dry Or Plaster
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‘Cover Plate
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Finish Floor ary
Plywood Ly Baseboard
Sound Toe Mold
Dead Bd. bec Caulk
Air Chamber ‘Sub Floor
C4 2x6 Split Base
Plate
L,-Wire Hanger
Rubber Sleeve “\@ypsum Board

Fig. 2-25. TECHNIQUES FOR CONTROLLING NOISE IN PLUMBING SYSTEMS


Metal Duct

Glass Fiber

Inner Metal Duct

Glass Fiber
Board Liner

: Silencer Honey-Comb
Glass Fiber

Sinusoid Glass Fiber

Fig. 1-16. VARIOUS TYPES OF ACOUSTICAL DUCT LINING, BAFFLES AND SILENCERS

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

22

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 are discharged into
the open air as illustrated in Fig. 1-17.


NOISY DESIGN

Turbulence Caused by Rectangular Devices

QUIET DESIGN
a Flare End
LSS

Remove or Streamline Objects in Flow Path

Fig. 1-5d. DESIGN OF QUIET FLOW SYSTEMS

Streamline transition in flow path:
Changes in flow path dimensions or

cross-sectional areas should be made
gradually and smoothly with tapered or
flared transition sections to avoid
turbulence. A good rule of thumb is to
keep the cross-sectional area of the
flow path as large and as uniform as
possible throughout the system.

Remove unnecessary obstacles: 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
structural supports, deflectors, and
control dampers, should be made as
small and as streamlined as possible to
smooth out the flow patterns.

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

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 component 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, as illustrated
in Fig. 1-6, will cause the panel to vibrate
and produce greater noise output.

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 mounting of the
vibrating component on the most massive and
structurally rigid part of the machine. All
attachments or connections to the vibrating
part in the form of pipes, conduits, 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 oor hangers may also be
required to avoid bypassing of the isolated
system. In addition to these measures 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 mounts 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. 1-7.


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27


TABLE 5-3 (Cont'd)

Housing or base: choose heavy metal CHAIN SAW

instead of light plastic bases.
Select quiet unit with adequate power.

Mounting: place on resilient pads. (Chapters 1, 2, and 3)
Use as a vibration source for Wear ear protection.
troubleshooting noise problems ;
(Chapter 5). CHILDREN, VOICES AND PLAY NOISES (Chapters 2
and 3)
BLOWERS
Avoid play in reverberant spaces;
Choose slow-speed, large-diameter fan reduce noise buildup by sound-absorbent
with wide blades or squirrel-cage treatment of playrooms and classrooms,
design; prefer belt-drive to direct close off sleeping quarters with
gotoe drive. (Chapters 1 and 2) well-fitted windows, gasketed doors;
treat ventilation ducts with
BOWLING ALLEY (Chapters 1 and 2) sound-absorbing lining.

Reduce noise buildup and reverberation CLOCKS, Alarm (Chapter 2)
by sound-absorbent treatment of walls

and ceiling. Avoid areas where Give preference to the types of alarms
conversation can be done only by that chime or turn on radios, if you
shouting. live in a multiple dwelling. Place

alarm clock on a soft padded surface.
Alley must be vibration-isolated from Be especially careful not to set the

alarm on a surface which joins or
touches, the party wall between your
apartment and the adjacent one, or on a
BUSES wall adjoining another sleeping room.

building structure by means of
resilient mounting.

Avoid residences near major bus routes. CLOTHES DRYER AND WASHER (Chapter 2)

Engines should be well tuned, well

. Chapter 4 Select units with low-noise ratings.
naffled. (Chapter 4) Vent clothes dryer where noise will
Tire tread design should be selected give minimum disturbance. Isolate

laundry room as much as possible from

for quiet running. other living space.

Brakes should be adjusted and properly

maintained to avoid squealing. Install units on resilient pads or

mounts; use flexible connectors in
water and electrical supply line;
install air chambers in water supply
line.

Choose seats near center
CABINETS

-, Use sound-absorbing and vibration
Cheneer 2) core, well-demped door. damping materials on inside surfaces.

Apply mastic to inner panels. COMBUSTION NOISE - FURNACE (Chapter 2)

(Chapters 1 and 2) Have fuel-nozzle adjusted for minimum

noise (this can be done with no loss of
burning efficiency). Separate furnace
from rest of residence with
ine shelves and backs of cabinets with Toom
re on rubber tile to absorb impact fireproof partition, “if possible. Air
noise. (Chapter 2) intake in most residential furnaces is
. direct from surrounding air space;
replacement with duct from outdoors can
reduce noise radiation to rest of
house; it also might reduce need for
. id 2
seoneing on sete chapter 3) humidifying heated air in the house.

Tighten loose strike plates.

CAN OPENER

Flexible connector and sound-absorbing
100


help you to analyze and to alleviate the

problem.
HOW TO LOOK FOR NOISE LEAKS:

In a high percentage of cases, the main
cause of noise transmission problems within
homes or apartments, or between adjacent
dwelling units, is an airborne sound
transmission path or leak. Look for holes,
cracks or openings around pipe and duct
penetrations, plumbing fixtures, ventilation
grilles, back-to-back cabinets, and doors.
Carefully examine the ceiling edges and
corners of walls for cracks caused by
building settlement. Even hairline cracks
will permit passage of a considerable amount
of noise.

For problems involving the intrusion of
outside noise, check the effectiveness of
gaskets or weather-stripping around the
windows and exterior doors. However, the
places that most frequently are overlooked,
but are sources of serious noise leakage,
are concealed behind the thin molding that
frames doorways and windows. In
conventional building practices the openings
cut for the installation of pre-assembled
door and window units are much larger than
need be. These openings, which rarely are
adequately sealed for acoustical or thermal
purposes, present a direct noise
transmission path. Sometimes, air spaces
between door jambs and the wood door-stops
which hold the gaskets, by-pass the gaskets
and thus cause the noise leaks. In other
cases, large holes in exterior cinder block
walls may be hidden from view by thin veneer
paneling. Although a visual examination of
a room should be conducted to detect the
more obvious noise leaks, it can not be
fully relied upon to locate those hidden
from view.

USE YOUR EARS:

When used properly,
highly versatile instruments. Not only can
they identify noise sources, but they can
locate noise leaks and trace transmission
paths, as well.

your ears are

If you have trouble detecting a noise

leak, cupping your hands and placing them
behind your ears will increase’ the
sensitivity of your ears and enhance your

sense of sound localization. If, with your
hands cupped behind your ears, you turn your
head from side to side, you should find
yourself able to locate more precisely the
direction from which the sound or noise is

93

High-frequency sounds, which tend
to be propagated in a beam, can be located
rather easily this way. If the sound is
very high-pitched, sealing one ear with your
hand or finger tip and listening with the
other ear as you turn your head may enable
you to “home in” on the sound much more
rapidly. Any path along which the noise
grows louder will usually lead you to the
area where the noise enters the room.

coming.

Having located the point of entry, you
need next to determine how the noise enters
the room. Is it transmitted through an air
leak such as a crack, hole or an opening in
a wall, or by structural vibration of
pbuilding components such as a wall, or by
both? One way of making this determination
is to conduct a "talk test" with a companion
located on the cther side of the wall. If
the sound of his voice comes through the
wall loud and clear, it is quite evident
that there is a serious air leak in the
wall. On the other hand, if you can hear
him talking but the sound is garbled and you
cannot understand what he is saying, the
sound most probably is being transmitted
structurally through the wall. The
high-frequency sounds of speech, such as
those characterizing the consonants which
make speech intelligible, do not pass
reaéily through wall or floor structures.

Another test permits you to estimate
whether noise is being transmitted through a
wall by way of air leaks or by way of
structural vibration. Plug one of your ears
with your fingertip and press the opposite
ear tightly against the wall. Compare the
loudness of the sound you hear while your
ear is sealed against the wall with what you
hear as you withdraw your ear from the wall.
If the sound you hear with your ear pressed
against the wall is louder, the sound is
most likely travelling a structural path
through the wall. However, if the sound is
no softer when you withdraw your ear, the
sound is probably reaching you through an
air leak.

USE HOME APPLIANCES AS DIAGNOSTIC TOOLS:

Generally speaking, the task of
resolving a noise problem often requires
devices for generating sounds and vibrations
of relatively high intensities.
Fortunately, the average household contains
a number of rather common appliances that
can be used for such purposes. For example,
vacuum cleaners equipped with rug beaters or
power drills with drill bits placed slightly
off-center are excellent sources of airborne


NOT THIS

Radiating
Surface

THIS

| Separate
Direct Contact
Flexible
Connector
=
Direct P =
Contact ump
Resilient
Mount
? 3

Fig. 1-6, ISOLATE LARGE RADIATING SURFACES FROM VIBRATING PARTS


TABLE 5-3

INDEXED CATALOG OF SPECIFIC NOISE PROBLEMS AND REMEDIES

AIR CONDITIONER, Central (Chapter 4)

Compressor: Select unit with low noise
rating; mount on _ resilient pads

preferably on a concrete block located
away from bedroom area.

Ducts: Treat ducts and dampers with
sound-absorbent material; design ducts
for large-volume, slow-speed air-flow
in preference to small-volume, high-
speed flow.

Fan: Choose slow-speed, large-diameter
units. Isolate fan housing from
ductwork with flexible _ sleeves.
Install fan on resilient mounts.

Grilles, Diffusers and Convectors: Se~
lect streamline mits with smooth,

wide openings and low-spread discharge.

Motor: Choose slow-speed unit with
symmetrical belt drive. Use resilient
mounts. :

AIR CONDITIONER, Room or Window (Chapter 2)

Air Filter: If the air filter in the
unit becomes clogged with dust,
condensate may freeze on expander

tubing and thus further restrict the
air flow. This may cause whistling
noise. Clean filters weekly during
season to retain free air flow.

Compressor: Select a unit with
adequate power capacity to do the job.

Fan: Select a large
squirrel-cage belt driven fan.

diameter,

Gasket: Install perimeter gasket of
soft rubber to isolate unit from wall
or window structure.

Mounting: Mount on resilient pads.
Thermostat: Adjust unit to minimize

starting and stopping noise which can
be more troublesome than the noise of
steady running.

AIRCRAFT NOISE

Note alignment of main runways and
flight patterns of commercial or
military airports.

Methods cf avoiding: (Chapter 3)

Recommended dwelling locations:
(Chapter 4)
Sound insulation requirements of
dwellings: (Chapter 3)

AIR HAMMERS

Select units with exhaust silencer and
sound insulating jacket. | Choose
minimum stroke needed to perform work.
(Chapter 2)

APPLIANCES (Chapters 1 and 2)

Choose units
where given.

with low-noise rating

Install properly: Use vibration mounts
or resilient pads, flexible connectors,
vibration damping coatings, and
perimeter gaskets to isolate units from
cabinet enclosures.

See entries under individual appliances
by type.

BIRDS (Chapter 3)

Reducing noise intrusion: Caulk or
gasket existing windows; install storm

BLENDERS

99

windows. This will also conserve
energy by minimizing temperature
variation in the home.

Select unit with low-noise rating;
(Chapter 2)

Container: select glass rather than
plastic.


TABLE 5-3 (Cont'd)

course, for ease of cleaning the filter
should be interposed between the hood
and the fan.

FAUCETS (Chapter 2)

One of the greatest nuisances late at
night is a dripping faucet with no
immediate chance of fixing it. 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. A more effective solution
is to replace the worn washer that is
causing the drip.

“Singing" of a faucet is almost always
a sign of a deteriorating washer, which
should be replaced.

FLOOR NOISES (Chapter 2)

Squeaking floors and stairways;
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
the tile or linoleum from cracking,
apply heat from a hand-type hairdryer
or pan of hot water to soften the
surface. Even if partly secured, tiles
may be lifted enough to allow mastic to
be inserted under the loose edges. A
weight placed over the tile will hold
it in place until the mastic sets.

FURNACES (See entry under heating systems)

GARAGE DOOR (Chapter 2)

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 (Chapters 2 and 3)

Vibration-damped, laminated metal trash
cans, which are relatively quiet when
handled, 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.

GARBAGE DISPOSER (Chapter 2)

If possible, select a unit for quiet
operation. Such units feature
resilient mounts, flexible pipe
connectors and a sound-insulating outer
shell. Coating the underside of the
sink basin with vibration damping
compound will improve the noise
reduction. Installing acoustic tile
inside the cabinet enclosure will
reduce noise buildup.

GARDEN APPLIANCES (See entries under

individual appliances by type) 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 and
attention should be paid to the
community's needs for reasonable
quiet,

Since chain saws are difficult to
silence, they should be used only at
times when neighbors will not be
disturbed; adequate rest periods should
be taken by the operator.

If it is possible to
cord to the working site,
electrically-operated tools may
eliminate a large degree of the noise.

extend a power

GRILLES

104

The ventilator grilles on forced-air
heating and cooling systems frequently
are a major source of high-pitched
noise. The most common cause of noise
is high-velocity air flowing through
the grilles; choice of a more
streamline grille with larger openings
will reduce the whistling noise.
(Chapter 2)


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
high-velocity gas flow through the fuel
nozzle or burner jets.

The most expedient way of dealing with
this problem is to have a heating engineer
adjust the fuel pressure or install nozzles
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 vapor 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 Heatii ‘stems

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.

64

Hot Water Baseboard Heaters

Causes of Noise

(a)

(b)
(c)

The noise produced by such heaters
generally is caused by:

the expansion and contraction of
pipes, heater components and
housing,

water flow and turbulence, and

pump and motor vibration.

Remedies

(a)

(b)

Heaters and associated piping
generally creak at joints, con-
nections and points of support or
contact with building structures
during expansion and contraction
due to temperature variation.
When the units are rigidly
connected to walls and floors,
these structures behave like
sounding boards and amplify 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 taken to
isolate the heater units from the
walls and floors using
heat-resistant resilient spacers
and leg mounts.

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 néises.

If the pipes tend to sing a
high-pitched tone, this is an
indication that there is
high-velocity, turbulent flow in
the system, which generally is
caused by using an oversize, high-
speed pump and undersize piping.


Apt. A Apt. B
ry Wall Continuous To Floor,

A]-— Both Sides (Stag’d Studs)
Basin & Cabinet L- Vent Pipe
Isolated From Wall
Rubber Gasket.
Staggered
Stud Walt
Cabin k
Exterior Plywood Rubber t— Drain Pipe
|—Rubber Sleeve H&C
Water Pipes Rubber
. Sleeves
Split Base
wanes aTile Floor Plate
Bath Tub Shower s <
Installation

3/16” Neoprene Pad

Mounting Bolt

Rubber
In Shear
Resilient
Hanger

Wax Ring

Resilient Pad
In Pipe Hanger

Detail ‘A’

Fig. 2-28. PROPER INSTALLATION OF A TOILET FOR QUIET OPERATION
70


buildup in the reverberant

cavities. (We will discuss
reverberation further in
Section 1 under Factors
Affecting the Travel of
Sound)

(44) Apply vibration damping
material to the inner
surfaces of all vibrating
panels.

9. CHOOSE QUIETER MACHINERY
REPLACING APPLIANCES

WHEN

This advice is, of course, of little
comfort if you find yourself the owner 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 trash
cans for noisy metal cans. Some
laminated metal trash cans have
been made for industrial use; the
new concern with quiet may make
them desirable for ordinary
domestic use.

(c) Use wood or fiberboard cabinets
instead of the noisier metal
units.

(d) Select sliding or folding closet
doors made of wood or laminate
instead of metal doors which are
apt to 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
surfaced hose will reduce this
noise.

(£) Replace small high-speed floor
fans or exhaust fans with larger,
slower-moving units.

Substitute a belt-driven furnace
blower operated by a
resiliently-mounted motor for a
motor~coupled blower.

(g)

14

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 sound- insulating
box or enclosure.
Selection of the most effective

technique will depend upon various factors
such as the size and type of source,
intensity and frequency range of the noise,
and the nature and type of environment. In
addition one should have a basic under-
standing of the characteristics and behavior
of sound that influence its propagation or
travel through the air.

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. 1-11. The distance
between adjacent peaks of the high pressure
waves is the wavelength of the sound. The
frequency of the sound "f" and its speed of

"c" determine L the wavelength.

travel "c
These three quantities are related by the
equation c = fL. 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 (345 m) per second.
Therefore, the wavelength for a 100 Hz tone
would be approximately 11 feet (3.45 m)
whereas for a 1000 Hz tone it would be about
1.1 feet (34.5 cm). As we shall see, both
frequency and wavelength affect the
propagation of soundin 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


TABLE 5-3 (Cont'd)

lining in air ducts can reduce
transmission of combustion noise from
the furnace to room areas.

COMPACTOR
Vibration isolate the unit from
enclosing cabinet and floor by means of
resilient mounts and gaskets. (Chapter
2)

COMPRESSED AIR LINE
Select quiet blower nozzle; install

silencer on exhaust port; keep tight
couplings. (Chapter 1)

Maintain uniform diameter; avoid abrupt
changes in cross-section. Avoid rigid
connection between pipe and wall, to

prevent "sounding board" effect.
(Chapter 1)

COMPRESSORS

~ Use muffler on air intake to reduce
radiation of whistling noises.
(Chapter 1)
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. (Chapter 1)

CORRIDOR NOISE

Treat corridor floor with carpeting and
the ceiling with sound-absorbent
acoustic tile. Install sound
insulating doors with gaskets to reduce
sound leakage into living areas. Walls
of apartments that are common with
corridor walls should be of sound-
insulating construction. (Chapter 2)

COURTYARD NOISE

Courtyards tend to be reverberant and

noisy.

Seal windows that overlook courtyards
and draw ventilation from other expo-
sures. If necessary, increase weight
of glazing in windowpanes or install
storm windows. (Chapters 3 and 4)

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. See entry under
floor noises, also see Chapter 2.

For creaking door hinges and blinds,
lubricate hinge pins. Weatherstripping
improves the door seal and also
restricts the freedom of the door 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
plenums, crawl spaces,
ducts. (Chapter 2)

in ceiling
and ventilation

Flanking transmission and small
acoustic leaks are common causes of
crosstalk between supposedly isolated

adjoining spaces. (Chapter 2) For
general discussion of "Troubleshooting"
and leak-finding techniques, see
Chapter 5.

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 5. If dampers are remotely
located from the grilles, some
improvement can be obtained by
inserting acoustical lining or sound
silencers in the intervening ductwork.

Some flutter noisé may be generated in
a flexible damper; substitution of more
rigid, heavier, or streamlined dampers
may help.

DIFFUSER NOISE

101

Diffuser outlets in ventilating systems
frequently are sources of whistling or
hissing noise. Reduction of air flow
velocity is the most effective remedy.
Replace existing diffuser with a
large-diameter, low-spread,
better-streamlined unit. Ina pinch,


distance of 100 feet (30m) anda large
noisy factory located at a distance of 1/4
mile (0.4 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 your distance from a point source
you will have succeeded in lowering its
loudness by at least one-half or roughly 12
dB. However, 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 comparable
to its length, the noise level will begin to
drop at the rate of 6 dB for each subsequent
doubling of distance. Figures 1-l4a and
1-14b illustrate how the noise levels drop
as distance increases from both types of
noise sources.

Indoors, the noise level generally
drops only from 3 to 5 dB for each doubling
of distance in the near vicinity of the

source. However, further from the source,
reductions of only 1 or 2 dB occur for each
doubling of distance, due to the reflections
of sound off hard wall and ceiling surfaces.

2. Use Sound Absorbing Materials

Sound absorbing materials such as
acoustic tile, carpets, and drapes placed on
ceiling, floor or wall surfaces can reduce
the noise level. in most rooms by about 5 to
10 dB for high-pitched sounds, but only by 2
or 3 dB for low-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.

If you have a small or limited amount
of sound absorbing material and wish to make
the most effective use of it ina noisy
room, the best place to put it is in the
upper trihedral corners of the room, formed
by the ceiling and two walls. Due to the
process of reflection, the concentration of
sound is greatest in the trihedral corners
of a noisy room. Therefore, the acoustic
material which absorbs a fixed percentage of

the sound energy that strikes its surface
will remove a greater amount of sound
energy when placed in such corners

Fig. 1-148. REDUCTION IN NOISE LEVEL WITH DISTANCE FROM A POINT SOURCE

19


NOT THIS

‘AVOID RECESSED BACK-TO-BACK MOUNTING
‘OF CABINETS IN PARTY WALLS

DISCOURAGE PLACEMENT OF TV SETS
AGAINST PARTY WALLS BY PROVIDING
TV ANTEN. OUTLETS IN NON-PARTY WALLS.
‘AVOID RECESSED BACK-T0-BACK
MOUNTING OF ELECTRICAL OUTLETS

STAGGER OR SURFACE
MOUNT CABINETS

‘SWITCH OR ELECTRICAL OUTLET.
USE QUIET TYPE LIGHT SWITCHES
THROUGHOUT APTS, PARTICULARLY
IN PARTY WALLS.

Fig. 2-15. PROPER INSTALLATION OF CABINETS AND ELECTRICAL OUTLETS IN WALLS

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:

Fig. 2-16)

(see

The chief flanking paths in homes
and in apartment buildings are
open ceiling plenums, attic
spaces, basement areas and crawl
spaces which span freely across
dwelling units or adjacent rooms.
Such areas should be completely
subdivided with full height
partitions or barriers installed
directly above and below the party
walls separating the dwelling
units or rooms in question.

If the above recommendations fail to
improve the sound insulation of the party
wall sufficiently, then modifications to the

49

existing wall must be made. Where only a
moderate degree of sound insulation is
required, laminate a 1/2" (13 m) thick

layer of gypsum wallboard preferably to both
sides of the existing wall with a resilient
non-setting adhesive, as illustrated in Fig.
2-13. In addition, provide a 1/4" (6 mm)
clearance along the perimeter edges of the
wallboard and fill the space with a
non-setting caulk compound.

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. 2-17, would be constructed
as follows:

(a) Fasten wood furring members,
spaced 16" (40 cm) on centers
vertically, to the existing wall.

Nail resilient metal channels
perpendicularly to the furring
members; channels should be spaced
24" (60 cm) apart.

(b)

(c) Fill the space between the
existing wall and the channels

with a glass fiber blanket.


Fr

G.

Complaint

"I hear my
neighbor's TV
and stereo"

"Footstep noises
from the apartment
above annoy me"

TABLE 5-1 (Cont'd)
Probable Causes

Acoustically-weak partition
wall due to inadequate con-
struction, noise leakage
through cracks at floor and
ceiling edges or through
back-to-back electrical out-
lets. Neighbor's TV set may
be too close to party wall.

Rigid, light-frame construc-
tion of floor assembly;
solid concrete floor slab
covered with tile; lack of
carpeting and padding.

97

Remedies

Use same methods as in D above.
Suggest that neighbor place resilient
pads under his TV and stereo sets and
relocate them away from the party
wall.

Suggest that carpet and padding be
installed on the floor above. If
additional footstep isolation is de-
sired, test both ceiling and the
walls in your room with a stethescope
to determine which is radiating most
noise. If noise radiation from ceil-
ing is greater, install a gypsum
board ceiling mounted on resilient
hangers, place fiber glass blanket in
void between ceilings. In some
cases, wall paneling mounted on re—
silient furring members may be re-
quired in addition.


Fig. 2-2. COMMON OUTDOOR SOURCES OF NOISE

jet plane, the blare of an auto horn, voices
of children, or music from stereo sets.
Airborne sound waves are transmitted simply
as pressure fluctuations in the open air, or
in buildings along continuous air passages
such as corridors, doorways, 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 attenuated more easily than
structureborne noise. The sound from your
neighbor's stereo system may cause annoyance
in rooms of your apartment which are
adjacent to his, but rarely in rooms farther
removed unless doors or passageways are
open.

Structureborne 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 surfaces, which behave
somewhat like the sounding board of a piano,
transmit their motion to the surrounding
air, causing pressure 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 structure when it has
been excited into vibration by an airborne
sound wave because the vibrating source is
more efficiently coupled to a structural

32

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
sound 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 a water pipe, produces relatively little
airborne sound; but on the other hand, it
will radiate high-pitched sounds more
efficiently than low-pitched 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 reipforced or amplified. A
piano provides an illustration of this
effect. If we were to remove the sounding
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


Wavelength

Spherical
Spreading

High Pressure

Wavelength

Atmospheric
Pressure

Wavelength

Low Pressure

i ‘Frequency
[Hz]

Fig. 1-11. PROPERTIES OF SOUND WAVES

absorbs sound, especially high-pitched
sounds. That is why we hear only the
low-pitched roar of exhaust noise from 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.

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 and
carpeting 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 80% 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 for the
same amount 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.

When sound waves strike such
materials, 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


BALCONY

b uot Pee ©

LIVING ROOM BEDROOM LIVING ROOM
BATH 1
— I — Tr
DINING ROOM 1
KITCHEN BEDROOM DINING ROOM = — KITCHEN

LIVING ROOM

aaa

DINING ROOM KITCHEN

BEDROOM

SELECTING PROPER LOCATION FOR CLOSET-INSTALLED FURNACE UNIT

CEILING
A USE CAVITY BETWEEN
JNED
KITCHEN AREA HALL AREA Seean ucts el onitte
ORILE DOUBLE OR STAGGERED
STUD WALL vat anen
RUBBER
CLOSET INSTALLATION: RUBBER
vere acoustic
STAGGERED STUD WALL LINING
‘OR MASONRY WALL

RECOMMENDED DESIGN OF CLOSET AND INSTALLATIGN OF FURNACE UNIT

Fig. 2-22. TECHNIQUES FOR THE CONTROL OF NOISE FROM CLOSET-INSTALLED FURNACE

AND AIR-CONDITIONING UNITS

the closet to reduce noise

buildup.
CONTROL OF DUCT NOISE: (see Figs. 2-23 and
2-24)
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 pulley noise,
furnace ignition, flame noise, and the

60

creaking and snapping noise due to the
expansion and contraction of metal parts are
easily transmitted through the ducts to all
areas of the house.

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 duct#ork. Such treatment is
most effective when it is installed in both
supply and return branch ducts serving the
individual rooms, and preferably near 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.


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 cleaners, window air conditioners,
etc. However, large mechanical
installations, such as central heating or
air conditioning systems can only be
properly evaluated in-place.

The following summarizes the features
that the buyer should look for and the steps
he should take in selecting quiet equipment.

(1) low-noise certification,

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

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

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

(5) request an on-site inspection of
mechanical equipment of the type
you are considering, that the
dealer has previously installed,
for the purpose of making your own
evaluation of the noise output.

REQUIREMENTS 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 motor, gear
train, pump, pulleys, cams, bearings,
electrical switches, automatic valves, and
water flow. Reducing the noise output of
such a device usually requires a
considerable amount of study to identify the
major sources of noise and their respective
transmission paths. In other words, it is
important to know whether it is the motor,
gear train or the pump 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 surfaces of the machine
which, in turn, 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 surface vibration, will
have any significant effect. The need for

these investigations increases with
increasing size and complexity 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 design engineer 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 quick-acting cut-off
valves found in washing machines and furnace
humidifiers. The loud "thump" they often
make can be startling, annoying, or in the
case of some furnace controls, they can
disturb 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
impact-produced noise. But application of
even one suggested measure can often reduce
the noise appreciably. A knowledge of the
principles underlying impact-noise reduction
can also assist you in purchasing quieter
equipment.


putty at hand, you can make temporary seals
of any leaks as you find them. This will
make it easier to locate the major or
dominant leaks that must be sealed before
any appreciable reduction of the intruding
noise can be expected. This principle
applies to the radiation of noise from
vibrating surfaces as well.

At times, the noise problem may involve
the transmission of both airborne and
structureborne sound through a building
construction. In such cases, you have to
determine which path is dominant before you
can proceed to the next step with any hope
of success. Remember that your ear, when
pressed tightly against a vibrating surface,
is a sensitive detector of vibration
covering a fairly broad range of
frequencies. Your finger tips are a
sensitive detector of low-frequency
vibration, when held lightly against a
vibrating surface. However, because of its
sensitivity and flexibility, the stethoscope
is even better suited for detecting
structural vibration and sound leaks. As
you probe around the edges of a wall or door
with a stethoscope, a noticeable increase in
the noise level will signify a noise leak at
that location. If you fail to find any
leaks, press your stethoscope against the
wall at several places. A substantial
increase in the noise level upon contact
with the wall surface will indicate that the
noise is coming through the wall as
structural vibration.

If there is no appreciable increase in
the noise level, as detected by the
stethoscope, and the intruding noise is
still noticeable, then you have to examine
other surfaces of the room. It may be
possible that the noise is entering.the room
through the ceiling or the floor. The
surface having the largest vibrating area or
undergoing the most intense vibrational
motion must be quieted before the reduction
of noise from any other vibrating surfaces
will have any significant effect.

A useful thing to remember while
searching for sound leaks is that sound
generally travels through a wall as easily
from one direction as from the opposite one.

95

Since the sound path is reversible it may be
convenient to interchange the positions of
the noise source and the observer in dealing
with noise intrusion problems.

If outdoor noise is entering your room
through a leak in the exterior wall, it is
sometimes easier to locate the leak by
making noise inside the room, and detecting
that noise on the outside. This
arrangement, of course, causes less
disturbance in your neightborhood. Whether
the noise source should be placed indoors or
outdoors will depend on the background noise
levels in each location at the time of the
investigation. The rule of thumb is to
place the listener or investigator in the
location with the lower background noise
level, which generally, but not always, is
indoors. In such cases, power mowers, chain
saws, or motorcycles running at fast idle
make excellent outdoor noise sources. For
safety, such machinery should not be left
running unattended.

the manner in which a
listener describes an irritating noise
problem and the way it affects him might
reveal the probable causes of the problem
and ways of alleviating it. Table 7-1 gives
a capsular description of some of the more
common noise problems, their probable
causes, and the acoustical measures needed
to rectify them.

Quite often,

Table 5-2 outlines, in order of
importance, the strategies and techniques
that one could use in resolving a noise
problem. The table also gives an estimate
of the amount of noise reduction that one
can expect from each technique. This order
is chosen because noise from the major
source must be attenuated before reduction
of noise from subsidiary sources will have
any appreciable effect.

For your convenience in _ solving
specific noise problems, we have compiled in
Table 5-3, at the end of this chapter, an
alphabetized catalog of common noise
sources, practical remedies, and references
to other chapters in the Guide where more
technical background information on noise
abatement and control is presented.


generally light and porous. They should not
be used on the interior surface of one room
with the sole intention of preventing the
transmission of sound to the next room. The
porosity of the material actually
facilitates sound transmission.

KITCHEN NOISE

With rare exception, the kitchen is the
noisiest room in the home. This is due to
its hard sound reflecting surfaces, and the
frequent and oftentimes simultaneous
operation of the various types of very noisy
power-driven appliances 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 interfers 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 can 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

(4) 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.

What 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
illustrated in Fig. 2-6, and described in
greater detail below.

(1) Install solid door with gaskets

(2) Use vibration isolators & mounts

(3) Isolate appliance from cabinet with rubber:
gasket

(4) Insert rubber gaskets behind cabinets and
appliances to avoid wall contact

(5) Place rubber pads under small units, dish racks
and in sink basins

(6) Install rubber or cork tile on backs and shelves
of cabinets
(7) Apply vibration damping material
(8) Install acoustic tile
(9) Install exhaust fan on rubber mounts
(10) Install acoustic ceiling
(11) Install carpet or foam backed tile

Fig. 2-6. RECOMMENDATIONS FOR REDUCING KITCHEN NOISE


TABLE 5-3 (Cont'd)

removing the diffuser altogether and
replacing it with a "spreading plate",
i.e., a panel treated with
sound-absorbing material on the side
toward the duct opening and suspended
2-6 inches below the opening can be
used to diffuse the air flow quietly.
(Chapter 2)

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 connectors
in pipe and drain lines to minimize

vibration conduction. Load dishes so
that they are not free to flap in the
washing stream. Tighten loose
fittings, especially door latches and
shelf supports. Mount unit on

resilient pads and isolate it from
cabinet enclosure with rubber gaskets.
(Chapter 2)

DOG BARKING (Chapter 3)

DOOR

DOOR

Voice your complaint to the owner of
the dog. Dogs that bark persistently
should not be left out in the yard at
night, out of consideration for the
neighbors. Keep your own dog indoors,
he makes a fine burglar or fire alarm
in your house.

Caulk or gasket windows; install storm
windows.

KNOCKER (Chapter 2)

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.

SLAMMING (Chapter 2)

Install door closure dampers on all

exterior doors or spring-loaded
self-closing doors, such as screen
doors. A resilient gasket or

weatherstrip surrounding the door will
reduce the impact 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.

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 which act 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; (Chapter

2). Use heavy-walled pipe such as
ceramic or metal pipe rather than
plastic pipe.

DRILLS, PNEUMATIC
Drills with exhaust silencers and

sound-insulating jackets are available.

Repairs on city streets using
pneumatic drills should not be carried
out during sleeping hours. In many
cities, ordinances forbid such noise
during night hours.

Caulk or gasket existing windows facing
source; install storm windows.

DRUMMING, BELT (Chapter 1)

DUCT

102

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.

NOISE (Chapter 2)

The principle causes of duct noise are
creaking, rubbing. and ‘snapping of
ductwork due to expansion and
contraction. Turbulent flow through
ducts causes roaring sounds.

Dampers in ducts cause whistling noise
for high-speed flow, see entry under
damper noise. Whistling noises
generated at duct openings, branches or
elbows can be transmitted through the
ductwork. Sound conducted through the
ductwork as though it were a speaking
tube can be minimized by installing
sound-absorbing material and sound
baffles.


Sometimes lining the inside
surfaces of an appliance with a
metal or lead foil-backed adhesive
coated tape will damp the vibra-
tion of the case and thus result
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
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 drumhead type amplification of
impact noise by the hollow
reverberant cabinets.

sink

Cushion
cabinets

impact noise in the

Install soft rubber or cork tile
on the shelves and back surfaces
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.

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.

Apply vibration damping material

Sink basins equipped with a food
waste disposer should be under-
coated with a thick layer of a
mastic type vibration damping
material or other types of
vibration dampers as illustrated
in Fig. 1-9. Such treatment will
suppress the vibration of the sink
and resulting noise caused by
operation of the disposer.

40

Damping treatment applied to the
interior surfaces of the metal
cabinets) and tumblers of larger
appliances, especially washing
machines and dryers, would result
in a noticeable reduction of noise
due to cabinet vibration.

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.

Install exhaust fans on rubber
mounts

Most ceiling exhaust systems use
high speed, noisy propeller fans
that are mounted rigidly to the
ducts, which in turn are connected
to the ceiling by means of the fan
grilles. These structural paths
carry the fan vibration to the
ceiling, which acts like a large
sounding board and amplifies the
noise. You can reduce the noise
level noticeably by following this
three-step procedure: Tf
possible, remount the fan on
rubber grommets or resilient
spacers to isolate it from
the duct, as shown in Fig. 2-9.
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 thefmoise 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.