NBSIR 74-606

Consumer Product Noise:

A Basis for Regulation

Pearl G. Weissler, Gerald A. Zerdy and Sally G. Revoile

Sound Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1974

Final Report

Prepared for Consumer Product Safety Commission

Bethesda, Maryland 20014

NBSIR 74-606

CONSUMER PRODUCT NOISE:

A BASIS FOR REGULATIONS

Pearl G. Weissler, Gerald A. Zerdy and Sally G. Revoile

Sound Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1974

Final Report

Prepared for Consumer Product Safety Commission

Bethesda, Maryland 20014

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

ABSTRACT

The Consumer Product Safety Commission is charged with the re- sponsibility for promulgating safety standards to protect the public

against unreasonable risks of injury associated with consumer products.

There is a risk of injury from noisy products, directly by damage to

hearing and indirectly by degradation of essential speech communication.

This report develops criteria relevant to the specification of Safety

Standards for noisy consumer products. Consumer product noise is discussed in relation to the existing body of knowledge regarding noise

induced hearing loss and speech communication. From the EPA Levels

Document, levels of product noise are identified that should protect

against hearing impairment and against speech communication degradation.

Methods of measurement for consumer product noise are described and a bibliography of standards relevant to the regulation of noisy consumer

products is provided. A list of products that are potentially hazardous

to the hearing of the operator is included with typical levels and usage

patterns. The list is based upon reported data and some measurements

made at NBS. Possible discrepancies among noise regulations established

by different governmental agencies are discussed with suggestions for

obtaining uniformity.

Key Words: Consumer products; criteria for safety standards; federal

regulations; hearing impairment; hearing survey; noise

emission; speech communication interference.

TABLE OF CONTENTS

Page

INTRODUCTION 1

CHAPTEE I. THE HEARING MECHANISM AND NOISE-INDUCED HEARING

DAMAGE- 2

CHAPTER II. SPEECH COMMUNICATION AlID CONSUMER PRODUCT

NOISE 10

CHAPTER III. MEASUREMENT PROCEDURES FOR SOUND OUTPUT OF

CONSUMER PRODUCTS 26

CHAPTER IV. NOISE EMISSIONS FROM PRODUCTS: INTENSITY AND

CONSUMER USAGE 31

CHAPTER V. NBS MEASUREMENTS OF THE SOUND OUTPUT OF SOME

CONSUMER PRODUCTS U6

CHAPTER VI. IDENTIFYING SOUND LEVELS FOR CONSUMER PRODUCTS

WITH RESPECT TO HEARING DAMAGE

CHAPTER VII. TOWARD A UNIFIED SET OF NOISE REGULATIONS ... 62

APPENDIX. PUBLISHED STANDARDS RELEVANT TO REGULATION OF

SOUND OUTPUT OF CONSUMER PRODUCTS 66

GLOSSARY 71

INTRODUCTION

The focus of this study at its inception was to obviate conflicts in

regulating sound emissions of consumer products by the Consumer Product

Safety Commission and other agencies of the Federal Government concerned

vith noise. To do this, a basis for such regulation had to be

established. Thus the literature on the effects of noise on man was surveyed. It was not the intent, however, to write just another report

on this subject, since in recent years there has been a proliferation of

such publications on this subject. Rather, it was decided to extract

those effects of noise of greatest relevance to the safety of consumer

products. The two major effects considered are noise-induced hearing

loss and the impairment of speech communication in the presence of noise.

Another important factor in the regulation of consumer products is

the use of proper test methods; i.e., measurement of sound output and

measurement of intelligibility of speech in noise. Some basic physical

and psychophysical principles involved in such tests and specific test

procedures are discussed in this report, again with emphasis on consumer

products. A list of relevant published standards is also included.

A third factor considered as a basis for regulation is a knowledge

of the consumer products themselves their sound output and impact (i.e.,

total number of people using the product and their usage patterns). For

this, use was made of published data as well as measurements made at the

National Bureau of Standards

.

With this scientific basis for regulating noise emissions of con- sumer products for safety, one can resolve the problems of formulating

unified Federal Noise Regulations more intelligently. Suggestions toward

this end are also included in this report. Two important factors,

economic and technological feasibility, were not treated in this report.

1
CHAPTER I THE HEARING MECHANISM AND NOISE-INDUCED HEARING DAMAGE

Some Dimensions of Audition

The sense of hearing enables one to perceive sounds of different

frequencies and intensities. The maximum range of frequencies that can be heard by the human ear varies from about l6 to 20,000 Hz. Within this

range, however, the ear is not equally sensitive to all frequencies (see

Fig. I-l"^). Among the frequencies, different intensities are required to

achieve the threshold of audibility for a sound, i.e., the minimum

intensity that renders it Just barely detectable. For sounds of very

high intensity the ear responds similarly, irrespective of frequency.

The threshold of pain for sound occurs at around ihO dB re 20

micropascals , while the thresholds of feeling and discomfort,

2 respectively, occur about 10 and 20 dB lower.

The Hearing Structure

Anatomical descriptions of the ear differentiate among three

sections: the outer ear, the middle ear, and the inner ear (see Fig.

1-2). The outer ear includes the parts of the ear that are externally

visible: the pinna and the ear canal. The ear canal is terminated

internally by the eardrum that separates the outer and middle ears. The

middle ear is a small air-filled chamber that contains the ossicles - three very small bones connected in a lever-like formation. Two small

muscles partially support the ossicles in the middle ear. The ossicle

formation is attached to the eardrum at one end ajid to the oval window at

the other end. The oval window is a small opening in one wall of the

middle ear that leads to the inner ear. The fluid-filled inner ear contains the sensory structure for hearing, the organ of Corti, as well

as the mechanisms for maintaining equillibrium. The organ of Corti is

located in the cochlea of the inner ear in a fluid- filled, membranous

channel (see Fig. 1-3). The specialized structures of the organ of Corti

include numerous cells with projections of hair at the top. Overhead,

the hairs are embedded in a gelatinoiis structure, the tectorial membrane.

2
3
pinna

1

Figure 1-2. A schematic drawing of the hearing mechanism.

Figure 1-3. A srhenjatlc drawing of a cross section of a spiral of the

cochlea showing the orj^an of Corti.

4
The hair cells make functional contact with nerve endings that comprise

part of the eighth cranial nerve of the central nervous system.

Transmission of Sound to the Inner Ear

Sound is perceived when a listener receives an auditory sensation.

The auditory sensation results from a series of functions in the eax that

normally begin mechanically at the eardrum. The eardrxun is pressure

sensitive and vibrates in response to certain air pressure changes,

namely, sound waves caused by a vibrating surface or air turbulences.

Vibrations of the eardrum cause the ossicles to move in turn, thus transmitting the vibrations to the fluid of the inner ear. (Vibrations may

also be transmitted to the inner ear through the bones of the skull.)

Pressure variations then occur in the inner ear fluid causing a shearing

motion between the tectorial membrane and the hair cells. The mechanical

movement of the hairs is transformed into electrical impulses where the

hair cells contact the neurons of the acoustic nerve. The impulses are then transmitted along the acoustic nerve to the brain.

Injury to the Ear Structure from Loud Noise

3

When a very loud sound (at least 80 dB above threshold of audibility ) produces excessive vibration at the eardrum the muscles that support the

ossicles act involuntarily to restrict the movement of the eardrum and

ossicles. This protective action, called the acoustic reflex, serves to

reduce the vibratory force reaching the inner ear from the loud sound.

However, the reflex action reduces the vibratory force only to a limited

degree and for a limited time. The effective reduction in soimd level is

k on the order of five to ten decibels. After about 15 minutes, the

2

reflex action seems to decrease in magnitude even though the intensity

of the sound is lonchanged. Thus, the acoustic reflex provides only

limited protection to the inner ear and damage can be caused by the

excessive vibratory force from intense sound.

The damage in the inner ear from excessive vibratory force occurs to

the organ of Corti . In the presence of extremely intense sound, such as that from an explosion, immediate structural damage can occur to the

organ of Corti with concurrent hearing impairment. From less intense

5
sound the hair cells and other structures of the organ of Corti seem to

degenerate gradually when the ear is intermittently exposed over

prolonged periods of time. The actual cause of this degeneration is not

known definitely. It has been theorized that mechanical destruction or metabolic changes within the inner ear may be responsible for the hair

cell degeneration. In any case, the destruction is irreversible, sincQ

the specialized cells of the organ of Corti do not regenerate.

Consequently, hearing impairments are irreversible when caused by

permanent damage to the organ of Corti

.

Noise-Induced Hearing Impairments

Most hearing impairments that are caused by noise occur gradually.

The initial exposures to a damaging noise may produce only a temporary

loss of hearing that disappears following cessation of the noise. From

repeated exposures, however, the ear seems to lose the ability to recover

from the temporary loss and a permanent impairment results. At first,

the permanent impairment may not be fully realized because the hearing

damage is usually minor and affects only a limited frequency range.

There may be no more than a slight reduction in hearing sensitivity at

frequencies around UOOO to 6OOO Hz (see Fig. I-U). Even the warning

sensations of hearing damage that may accompany the noise, such as ringing or tickling in the ear, may not seem particularly significant

since they are usually transient. At this point, however, the individual

has already lost some hearing for bird songs, music, and certain speech

sounds. Among the sounds of speech, those often affected earliest are the "s", "f", and "th" as in think. These sounds are comprised of frequencies aroiind iiOOO to 6OOO Hz and contain relatively little speech

energy as well.^ With additional exposure to injurious noise the hearing

damage increases in severity and involves a broader frequency range (see

Fig. I-h) . Generally, the impairment becomes more and more apparent as the individual has increasing difficulty understanding speech.

People vary in susceptibility to hearing damage from noise.

Evidence of the differences in susceptibility is found in studies of

occupational hearing losses. In one study, large differences were shown

6
-10 10

250 500 1000 2000 4000 8000

Frequency in Hz

Figure 1-4. Typical audiometric configurations for noise-induced

hearing impairments representing various durations of occupational

noise exposure.

7
in the severities of hearing impairments among workers exposed to the

same occupational noises for similar periods of time, with little

accompanying exposure to non-occupational noise. Non-occupational noise

exposures are of importance, since the combinations of noises that

workers experience away from the job may increase their total amount of

hearing damage. Non-occupational noises may also be of significance for

people without the hazard of occupational noise exposure. There is

growing concern that the noises encountered in everyday living over a lifetime may be a partial contributory cause to the hearing impairments

7 seen among the elderly. The noise from consumer products may comprise a considerable portion of the noises encountered daily. There is a need to

evaluate the hazard to hearing from noisy consiomer products as well as their possible interference with speech communication. Other effects

from noise, such as annoyance and sleep disturbance, may also be of concern with respect to noisy cons\amer products. However, if consumer

product noise is limited for protection against hearing damage and

impaired speech communication, it is unlikely that other se'rious

physiological effects will be induced.

References

"'"Normal Equal-Loudness Contours for Pure Tones and Normal Threshold of

Hearing Under Free Field Listening Conditions. International Organization

for Standardization R226-1961.

2

H. Davis, "Physics and Psychology of Hearing," in Hearing and Deafness , H. Davis and R. Silverman, Eds. (Holt, Rinehard, 8e Winston, New York,

1963) p. hg.

K. Kryter, The Effects of Noise on Man (Academic Press, New York, 1970).

li G. Bekesy and W. Rosenblith, "The Mechanical Properties of the Ear," in

Handbook of Experimental Psychology , S. S. Stevens, Ed. (John Wiley & Sons, New York, 1951)

•

8
H. Fletcher, Speech and Hearing in Communication (D. Van Nostrand, New

York, 1953) p. 87.

W. Taylor et al., "A study of noise and hearing in Jute weaving," J.

Acoust. Soc. Am. 38, 113-120 (I965).

•7A. Cohen et al. , "Sociocusis - Hearing Loss from Non-occupational Noise

Exposiire," Sound and Vibration 12-20 (19T0).

9
CHAPTER II

SPEECH COMMUNICATION AND CONSUMER PRODUCT NOISE

Many consiimer products are operated in situations where people

communicate. In the presence of a noisy consiimer product asiy conversation that takes place may be disrupted because of the noise. The

disruption or interference in communication from noise is technically

called masking. Masking from the noise of a consumer product can affect

speech communication by changing its message or rendering it partially or completely inaudible.

Experimental Procedures for Measuring the Effect of Noise

on Intelligibility

Information is lacking concerning the effects of noise from consumer

products, in particular, on speech communication. It is possible, however, to deduce these effects from existing information on the masking of

speech in general. Most of our knowledge of the masking of speech by

noise has been obtained experimentally. Investigations have been

conducted in which listeners write or repeat the speech signals they hear

in the presence of masking noise. Generally, in such an experiment,

several different noises are studied individually under controlled test

conditions, using the same listeners to determine the masking effects for

all noises being tested. Because the same listeners participate,

different speech signals have to be presented for each noise under study.

The speech signals used are standardized lists of materials that have

been shown to yield similar results when presented without masking to

normal hearing listeners.

Speech Intelligibility Tests

Different types of speech materials have been developed to determine

the effects of masking noise on speech. These materials include

sentences or phrases, individual words out of context (e.g. Say the word

HILL ) , and nonsense syllables (meaningless fragments of speech or combinations of speech sounds). Tests are available that are composed of one or the other of these types of speech material. The tests include

10
different lists containing equal numbers of the particular speech items

of interest. The intelligibility index for a list is usually reported in

terms of a percentage score computed on the basis of the number of items

identified correctly out of the total number in the list. Tests

consisting of nonsense syllables are called articulation tests. Tests

comprised of single words or sentences are called intelligibility tests.

Some Factors Affecting the Intelligibility of Speech

The intelligibility of speech materials . If different intelligibility tests are spoken by the same talker in the presence of a given

masking noise, the masking effect will vary in relation to the intelligibility of the speech materials comprising the tests. A fundamental

factor contributing to the intelligibility of different types of speech

materials is the verbal context of the materials. Verbal context is re- lated to the structure and constraints of language, called redundancy,

that allow us to infer what will be said on the basis of what we have

already heard. The greater the verbal context in a speech signal, the

more likely it will be understood. Consequently, a speech test comprised

of sentences is more intelligible than a test containing isolated words,

when both tests are administered in the same amount of noise.

There are other factors inherent in speech materials, themselves,

that will affect their intelligibility when spoken. Some speech sounds are easier to recognize than others. Consequently, the intelligibility

of a word will be influenced by the sounds comprising that word. Among

one- and two-syllable words, intelligibility increases with the number of

speech sounds. Two-syllable words are nore intelligible than one-syllable

words: Also, familiar words are more intelligible than unfamiliar words.

The intelligibility of talkers . If the same intelligibility test is

spoken by different talkers in the presence of a given masking noise, the

masking effect will vary in relation to the intelligibility of the

talkers. People may differ widely in the intelligibility of their

speech. In one study, the same intelligibility test was spoken by 12

different talkers under the same noise conditions.''" The scores that

resulted ranged from hU percent to 85 percent. In a related

11
investigation, the speech characteristics of talkers were studied to

2 determine the aspects important for intelligibility. Other than

acoustical characteristics, aspects shown to contribute to speech

intelligibility in noise were the strength and precision of the

consonants and the dialect.

Intelligibility in relation to the acoustical characteristics of

speech . In the presence of noise, the intensity level of speech is

generally the most important acoustical characteristic contributing to

intelligibility. The intensity of speech varies in relation to vocal

effort and the distance of the listener from the speaker. From a loud

shout to normal conversational speech, intensity level varies about l8

dB. Approximately three feet from the speaker a shout is around 85 dB

sound pressure level (SPL), quiet speech is about U5 dB SPL, and average

conversational speech is approximately 65 dB SPL.^ Among people there

are rather large differences in conversational levels. Conversational

speech varied from 55 to 75 dB SPL when measured at the location of a

1+ telephone microphone for a large number of talkers. Outdoors, the

intensity of speech at different distances from talkers can be estimated

on the basis of the inverse square law. As the distance from the talker

doubles, the level of speech decreases by about 6 dB.

5 In a quiet environment, speech can be understood at about 25 dB SPL

and remains intelligible when amplified through an intensity range up to

and including 130 dB SPL.^ When speech intensity changes with different

amounts of vocal effort in the presence of noise, intelligibility is

greater at speech intensities representing normal or loud speech (about

50 to 80 dB SPL) than for speech spoken with less or more force, eis in a weak voice {-kO dB SPL) or maximum shouting (90-105 dB SPL). Additional

acoustical characteristics of speech found important for intelligibility

in noise are the fundamental frequency and the peaJc pressures of the

2

voice. These characteristics in combination with intensity were shown

to contribute to the "noise-penetrating quality" of speech.

12
The spectrum of speech can be varied significantly without decreasing intelligibility. Measurements of the normal speech spectrum over a period of time show that speech energy occurs between 50 and 10,000 Hz.

Most of the long-term speech energy occurs at frequencies below 1000 Hz.

The area of the spectrum between 200 and 7000 Hz is of greatest imporg tance for speech-intelligibility in noise. In quiet, it is possible to

eliminate frequencies of the speech spectrum either above or below 1900

9 Hz without reducing the intelligibility of ordinary conversation.

Speech Intelligibility in Relation to the Acoustical

Characteristics of Noise

The acoustical characteristics of noise that affect speech intelligibility are intensity, spectrum, and temporal continuity. By far,

however, the most important characteristic is intensity. Other characteristics of noise are irrelevant to speech intelligibility if there

are large differences between the intensity of the noise and the speech.

Extensive investigations have been conducted to determine the masking effects of different noise intensities on speech intelligibility.

Most of these studies were concerned with the interference of noise with

speech over communications systems. The results reported often identified the minimum speech-to-noise ratios (S/N) that permitted accurate

speech perception under certain conditions. In a study using white

noise, listeners understood connected discourse with reasonable accuracy

at a S/N of +6 dB for a wide range of conditions.''"^ However, speech can be detected in the presence of white noise at a S/N of -l8 dB.'^''" The effect of the spectriun of noise on speech intelligibility has

also been studied. The effects of a broad-band noise and narrow bands of

noise at different levels were compared in one study. ''"'^ Over a frequency range from 135 to i+000 Hz, eight different noise bands of varying

levels were tested. The three bands of noise below 1000 Hz were found to

be more effective maskers than those above 1000 Hz at S/N of > -6 dB with

the speech at 95 dB SPL. However, a 20-UoOO Hz broad-band noise produced

more masking than any of the narrow bands. These findings led to the

conclusion that a wide band noise from about 20 to hOOO Hz, with most of

13
its energy concentrated at frequencies below 1000 Hz, should be more

deleterious to speech intelligibility than narrower bands of noise within

the frequency range of the wide band. In general, however, the spectrum

of the noise is of little concern for speech intelligibility, if the S/N

is 20-30 dB.^°

The effect of the temporal continuity of noise on speech intelligibility has been shown in experiments with intermittent noises. Noises

at different S/N were interrupted from 0.1 to 10,000 times per second at

12

a noise-time fraction of 0.5 • At a S/N of +9 dB one-syllable words at

90 dB were >90^ intelligible for all interruption rates. At a 0 dB S/N,

intelligibility ranged between 65 and 90 percent for all interruptions.

For -9 and -l8 dB S/N, interruption rates between 2 and 30 per second

yielded the highest intelligibility - from about 65 to 80 percent.

Noises interrupted at rates > 100 times per second produced a masking

effect similar to that of continuous noise.

Speech Intelligibility in the Presence of Consumer

Product Noise

How is the information above relevant to speech interference from

consumer product noise? The same factors affecting speech

intelligibility under experimental conditions will be operative also in

practical situations. For consumer products, the practical situation of

greatest concern is, perhaps, the communication of a warning in the

presence of a noisy product. To generalize for Just a few factors of

speech intelligibility, we can predict that a phrase of warning will be

more intelligible than a word of warning. A shouted warning will be less

intelligible than a warning in a loud voice. Irrespective of the vocal

effort, the warning will probably not be detected if the product noise

level is l8 dB greater than the level of the warning

.

Many other examples of the effect of product noise on speech could

be generalized. It would be more meaningful, however, to evaluate

directly the expected effect of a given product noise on speech intelligibility. There are at least three means of approach for evaluating the

14
effects on speech cominunication of the noise from a consumer product,

(l) The product noise level may be compared to one of various nomographs

or tables (see Fig. II- 1 and Table II-l) that shov the estimated quality

of communication expected for different levels of noise (p. l8) . (2)

Procedures may be used for calculating the effects of a given noise on speech communication (p. l8). (3) Intelligibility tests may be conducted

in the presence of a product noise (p. 19)- Among these approaches there

are differences in complexity as well as differences in the acciaracy with

which each approach predicts interference with speech communication.

Moreover, one approach may be more appropriate than another for use with

a particiilar noise measurement, or in relation to a particular

communication situation that may occur in the presence of a noisy

consumer product. However, these approaches are not mutually exclusive

for estimating the effects of a consumer product noise on speech

communication. Rather, they may be considered as successive steps in a process that seeks to identify noisy consumer products for which speech

interference is highly probable. In this process the essential first

step is the measurement of the product noise.

Noise Measurements

The noise level of the consumer product should be known relative to

the ear of the operator, or at that point closest to the product where a conversation might logically be heard by a listener. At these locations

the measurements of product noise should be obtained in a controlled

environment (see Chapter III) that simulates the usual situation

encountered during normal product use. Product noises should be measured in A-weighted sound pressure or sound pressure at contiguous frequency bands since A-weighted noise

measurements can be used with nomographs (see Fig.il-l) that show the

effects of noise on speech. Also, measurements of noise at certain

frequency bands across the spectrum are necessary for procedures that

calculate the speech interference of the noise. Measurements of spectrum

are important also for noises that are unusual, particularly those that

have greater energy in the low frequencies. A-weighted measurements are

less appropriate for noises that have a preponderance of low frequency

15
energy. The A-weighted frequency network of a sound level meter

approximates the sensitivity of the human ear to different frequencies.

The ear is less sensitive to frequencies below 1000 Hz than above.

Consequently, A- weighted noise measurements do not fully represent the

contribution of frequencies below 1000 Hz to the measured noise level.

This characteristic of A-weighted measurements is of concern in relation

to the masking effectiveness of noises of different frequencies. As

discussed earlier, noises with greater energy below 1000 Hz are more

effective speech maskers than noises with greater energy above 1000 Hz.''"^ The noise emissions of nearly all of the consumer products measured at

NBS seemed to have most of their sound energy in the middle and high

frequency range (see Chapter V).

Maximum product noise levels for no speech interference . In the

13 Environmental Protection Agency (EPA) "Levels" document, levels of

background noise are discussed that should cause no interference with

13 speech communication. These levels may be appropriate as maximum levels

for consumer product noise that will not interfere with speech

communication. An A-weighted steady sound level of dB was indicated

as the maximum level indoors that would permit 100% intelligibility of

sentences spoken with a normal voice when the talker and listener were

separated by >1.1 meters in a room with a reverberant field. For

outdoors a level of 66 dB was cited as the maximum A-weighted sound level

that would allow 93% sentence intelligibility with a normal voice when

the talker and listener were separated by one meter. Consumer products

emitting noises at or below these levels when used in the environments

specified should not interfere with speech communication. Products with

noise emissions above these levels shoiild be evaluated next relative to

the probability of speech communication occuring during the operation of

the product.

Conditions of Product Use

It is reasonable to assume that speech communication might be

attempted in the presence of any noisy consumer product. Communication

may be a necessity in situations where two people work together using a

16
noisy product. In the use of a bench saw, for example, one person may- operate the saw while another holds the article heing sawed.

Communication may also occ\ir between two people who are uninvolved with

the operation of a product but are in the noise vicinity of the product.

For example, a conversation might take place in a kitchen -vrtiere a dishwasher is operating. To evaluate the communication probability in

the presence of a noisy consumer product considerations of importance

are: (l) the expected duration of use for the product, (b) the necessity

of an operator for product use, and (c) the likelihood of a two-person

team using the product.

In addition to communication probability the product should be evaluated in relation to the possibility of an injury occurring diiring its

use. The operations of some products render them potentially hazaj"dous

.

An injury could more easily occur from an interference in the comm\inication of a warning during the operation of a noisy product that is also

hazardous. Both injury and communication probabilities should be con- sidered in deciding how extensively to evaluate the effects on speech

interference from the noise of a consumer product.

Communication Situations

When communication occurs in the presence of a noisy product there

are three possible situations that can exist among the talker, the

listener, and the product noise. (l) The listener and talker may be the

same distance from the product, hence the noise level is likely to be the

same for both. (2) The talker may be closer to the product, thus the

noise will be greater for the talker than the listener. (3) The listener

may be closer to the product, therefore the noise will be greater for the

listener than the talker. In each of these situations communication

could be disrupted from a product noise of sufficient intensity.

However, the latter situation seems to have the greatest potential for

interference with communication. When the noise is less intense for the

talker than the listener, the talker may raise his voice only in relation

to the noise level at his location. Although ostensibly intelligible to

the talker, the speech signal is masked at the location of the listener

IT
where the noise level is greater. These communication situations are discussed below in relation to the approaches for evaluating the effects

of a product noise on speech communication.

Nomographs and Tables for Estimating the Effect of Noise on

Speech Communication

Recent information for estimating the speech interference from noise

13 ih

appears in documents published by the EPA. ' As part of that information, nomographs and tables (see Fig. II-l and Table II-l for examples)

are presented from which it is possible to estimate for a given level of

noise either: (a) percent intelligibility, (b) the distance between the

talker and listener that allows at least 95% intelligibility, or (c) the

quality of communication at various distances between the talker and the

listener. However, certain characteristics of this information limit its

applicability for estimating speech interference from consvimer product

noises. First, the noise levels specified are based on A-weighted sound

pressure. For this reason, the information is most appropriately used to

estimate speech interference for product noise levels measured in

A-weighted soimd pressure. Second, the information was developed, for

the most part, from extrapolations of experimental data on face to face

communications in noise during which talkers and listeners were surrounded by ambient noise. "'"^ For estimating speech interference from

product noise, then, it would seem that the EPA information best lends

itself to the communication situation in which the product noise is the

same level for both the talker ajid the listener. However, other

communication situations may be compared to nomographs to obtain rough

estimates of the expected interference from a given noise level.

Procedures for Calculating the Effect of Consumer Product Noise

on Speech Communication

' For any communication situation, irrespective of the relative

product noise levels for the talker and listener, procedures may be used

to calculate the expected amount of speech interference. These

procedures require sound pressure measurements of noise at particular

frequency bands, hence they are particularly applicable to product noises

18
for which spectriun measurements are important. The procedures yield a more accurate prediction of the noise effect on speech than estimates

obtained from information based on A-weighted noise measurements.

Articulation Index (Al) . Although somewhat complicated to derive,

the AI generally provides the most accurate prediction of the effect of

noise on speech. -Indirectly, the AI represents the percent intelligibility that may be expected for given noise and speech levels. Briefly, the

AI is computed from the difference between the average known or estimated

speech level and the average measured noise level of interest for 20 frequency bands throughout the spectrum of speech. The AI can be calculated

for both steady and intermittent noises. A description of the method for

computing the AI is presented in a standard and additional discussions

15 IT

of the AI are available elsewhere. ' Other less complicated but also

less precise methods for deriving the AI are based on one-third octave or octave band measurements.

Speech Interference Level (SIL) . A simpler thoiagh generally less

accurate procedure for calculating the effects of noise on speech is the

3 15 IT l8

SIL. ' ' ' The derived SIL value is an average of the levels of the

noise measured in either three or four octave bands across the lower-mid

speech spectrum. The derived SIL value must be compared to a table of

speech interference levels to determine the voice level required for

barely reliable conversation at various distances between the listener

and talker.

Intelligibility Tests for Estimating the Effects of

Consumer Product Noise on Speech Communication

If conducted under carefully controlled and relevant conditions,

speech intelligibility tests should provide the most accurate information

concerning the effects of consumer product noise on speech comm^onication.

19 A standard has been written for the measurement of word intelligibility

and a plethora of literature is available concerning speech intelligi-

>,-T+ A ^ 20-2U bility and its measurement

.

In measuring the effect of a product noise on speech, probably the

most reliable results will be obtained through the use of commercially

19
available recorded speech intelligibility tests comprised of lists

equated in difficulty. Various intelligibility tests have been recorded

for experimental purposes and for clinical use in hearing testing. One

of the earliest tests, the Phonetically Balanced (PB) 50 Word Lists,

developed at Harvard, is comprised of 20 different lists of 50 words

each. All of the lists appear in the American National Standard on word

l8 intelligibility. Eight of these lists have been recorded and are distributed by Technisonic Studios, 1201 South Brentwood Bldg., Eichmond

Heights, Missouri. Another intelligibility test prepared by this firm is

the CID Auditory Test W-22 that includes six randomizations of four

different lists of 50 words each. A more recent recording of an intelligibility word test is the Northwestern University Auditory Test

No. 6 (Northwestern University, 2299 Sheridan Road, Auditory Reseeirch

Lab., Evanston, Illinois 6020l). It is composed of four randomizations

of four different lists of 50 words each.

For the three tests mentioned above, a listener receiving the tests

is required only to repeat or write each stimulus word he hears. A

different type of response is required in another recorded

intelligibility test. A listener receiving the Modified Rhyme Test must

circle the stimulus word he hears from a group of six printed words. The

test includes six different lists of 50 words each and was developed at

the Stanford Research Institute, Menlo Park, California.

Recently, a revised version of the CID Sentence Lists were recorded

at the Biocommunications Laboratory, University of Maryland, College

Park, Maryland. The test is composed of ten different lists of sentences

that were originally developed at the Central Institute for the Deaf.

Each list consists of 10 sentences that the listener repeats during

presentation of the test.

Discussions of the relative merits and shortcomings of these tests

25-29

may be found in the literature.

20
Summary

Cons\jmer products vith A-weighted noise levels greater than dB

indoors and 66 dB outdoors may interfere with speech communication. The

amount of speech interference from a given product noise level may be (l)

estimated from a nomograph, (2) calculated using the Articulation Index

or Speech Interference procedures, or (3) determined from the results of

intelligibility tests presented in the presence of the product noise.

References

^M. Abrams et al.. The problem of selecting and training personnel for

communication in intense noise. OSRO Report 98? , Psycho-Acoustic Lab.,

Harvard U. (PB 19785), 19^2.

2

M. Abrams et al.. Speech in noise: A study of factors determining its

intelligibility. OSRD Report 1+023, Psycho-Acoustic Lab., Harvard U.

(PB 19805), 19^1+.

oL. Beranek, Acoustics (McGraw-Hill, New York, 195^)'

^P. Denes and E. Pinson, The Speech Chain (Bell Telephone Labs., I963).

^J. Licklider and G. Miller, "The Perception of Speech," in Handbook of

Experimental Psychology , S. S. Stevens, Ed. (Wiley & Sons, New York,

1951).

^S. Pollack and J. Pickett, "Effects of noise and filtering on speech

intelligibility at high levels," J. Acoust. Soc. Am. 22, 1328-1329 (1957).

J. Pickett, "Effects of vocal force on the intelligibility of speech

sounds," J. Acoust. Soc. Am. 28, 902-905 (1956).

g

J. Licklider and N. Guttman, "Masking of speech by line spectrum

interference," J. Acoust. Soc. Am. 22., 287-296 (1957).

21
^G. Miller, Language and Communication (McGraw-Hill, New York, 1951).

"''^G. Miller, "intelligibility of speech: Types of interference" in

Transmission and Reception of Sounds Under Combat Conditions . Summary

report of Div. IT, NDRC, Vol. 8 (19^6).

"'"^J. Hawkins and S. Stevens, "The masking of pure tones and of speech

by white noise," J. Acoust. Soc. Am. 22, 6-13 (1950).

12

G. Miller and J. Licklider, "The intelligibility of interrupted

speech," J. Acoust. Soc. Am. 22, 16T-1T3 (1950).

13Information on Levels of Environmental Noise Requisite to Protect

Public Health and Welfsire with an Adequate Margin of Safety, Doc. No.

550/9-tU-OOU (197^^).

li;Effects of Noise on People, Doc. No. NTID300.T, Environmental

Protection Agency (l97l).

15

J. Webster, Effects of noise on speech intelligibility in Noise as a Public Health Hazard , ASHA Report No. ^4 (1969).

"^^Methods for the Calculation of the Articulation Index. S3. 5-1969

»

American National Standards Institute.

^'''k. Kryter, The Effects of Noise on Man (Academic Press, New York, 1970).

18

K. Pearsons and R. Bennett, Handbook of Noise Ratings, Natl. Aeronau.

and Space Admin., Report No. NASA CR-2376 (197*+).

^Monosyllabic Word Intelligibility. S3.2-I960, American National

Standards Institute.

20

J. Egan, "Articulation testing methods," Laryngoscope 955-991 (19^8).

21

I. Hirsh, "Perception of Speech" in Sensorineural Hearing Processes and

Disorders, B. Graham, Ed. (Little, Brown & Co., Boston, I967).

22
22

R. Campbell, "Discrimination test word difficulty," J. Speech Hearing

Res. 8, 13-22 (1965).

23

I. Hirsh et al., "intelligibility of different speech materials," J.

Acoust. Soc. Am. 26, 530-538 (1959).

A. House et al., Articulation testing methods: consonantal

differentiation with a closed response sit," J. Acoust. Soc. Am. 31 , 158-166 (1965).

2S

-^B. Elpern, "Differences in difficulty among the CID W-22 auditory

tests," Laryngoscope 70^, I56O-I565 (1960).

26

E. Kruel et al. , "A proposed clinical test of speech discrimination,"

J. Speech Hearing Res. 11, 536-552 (1968).

27

E. Elkins, "Evaluation of modified rhyme test results from impaired

and normal hearing listeners," J. Speech Hearing Res. lU, 589-595 (l9Tl).

28

T. Tillman and R. Carhart , "An expanded test for speech discrimination

utilizing CNC monosyllabic words (N.U. Auditory Test No. 6)," SAM-TR-66-55

,

June 1966. (Available to qualified requesters from Defense Documentation

Center .

)

29

E. Elkins, "Normal listener performance on the revised CID Sentence

Lists." Presented at the annual convention of the Amer. Speech and

Hearing Assoc., Detroit, 1973.

23
0 5 10 15 20 25 30

TALKER TO LISTENER DISTANCE IN FEET

Figure II-l. Speech comniunication quality in relation to

the A-weighted sound level of noise (dBA) and

the distance between the talker and the listener.

24
TABLE II-l. Steady A-weighted noise levels that allow courarunication

with 95 percent sentence intelligibility over various distances out13

doors for different voice levels

Voice Level Commvmication Distance (meters)

1 2 3 k •?

Normal Voice (dB) 72 66 60 56 5U 52

Raised Voice (dB) 78 72 66 62 60 58

25
CHAPTER III

MEASUREMENT PROCEDURES FOR SOUKD OUTPUT OF CONSUMER PRODUCTS

Introduction; Piirpose for Measuring Sound Output

There axe many considerations that affect the measvirement of the

output of a sound source. One has to know what characteristics of

sound to measure, the proper conditions for such a measurement and the

type of equipment to use. The purpose for making the measurement, as well as knowledge of the science of acoustics and electronics, are all

relevant to good measurement.

For consumer products, measurement of sound output for the purpose

of insuring safety is of prime importance. Exposure to loud noise can cause permanent hearing dajnage and affect one's physiological

well-being. Also, noise can mask other signals, making it difficult

for the operator of a noisy product to communicate with another person.

Effective communication is essential in a dangerous task such as cutting a tree where one person operates a power saw and another guides

the tree with a rope. Good communication may not be possible because

of the noise output of the saw. These effects of sound on man are discussed in more detail in Chapters I and II.

Considerations of safety help specify which characteristics of

sound should be measiired. Not only is the overall sound level of

importance, but also other characteristics such as frequency

composition and whether the noise is on-going or impulsive have to be

considered.

For hearing damage from on-going noise, the A-weighted sound level

should be measured, while for impulsive noise, measurement of the peak

pressure level is appropriate. For speech communication, both the

A-weighted sound level and the frequency composition of the interfering

noise are important although it might be more direct to perform

specific articulation tests such as described in Chapter II.

26
There are many other reasons for making a measurement of the sound

output of a consumer product. A manufacturer might be interested in

quality control or in comparison of the noise output of a product vith

one of a new design or in rating a product with respect to noisiness

.

One might wish to obtain information on the exposure of the users to

sound in order to develop a regulation or to check for compliance with an existing regulation or acoustical criterion.

As with safety, all of these objectives determine which qualities of

sound shoiild be measured. To some degree they also determine the

measurement strategy. That is, the objectives determine whether a standard measurement procedure for a large class of sound sources should

be used or whether a procedure specific for the product in question is

more suitable.

Some Principles of Measurement of Sound Output

and Their Relation to Standard Procedures

The sound output of a soiorce is a function of its environment. In

general, the soiind pressure level one would measure from a sound source depends upon the location of the microphone and its relation to the

sotu:ce and the environment. Not only is the distance from the source a factor, but reflections from all nearby surfaces (groiind, buildings,

etc., when outdoors, and walls, furniture, etc., when indoors) as well as the total volume enclosing the source, affect the resultant sound

pressure level. Thus in order to make repeatable and meaningful

measurements of sound level the environment must be specified.

One standard environment used for determining the sound power

radiated by small sources of steady noise is the reverberation room. This is a room designed to have special acoustical properties. It has

hard, reflecting walls, floor and ceiling, with low absorption of soiind

in the frequency range of interest. There is a meajis, such as rotating

vanes, to break up the so^lnd pattern. The room is large enoiigh to

permit measurement of sound level in the reverberant sound field.

27
beyond the direct soiind field of the noise source. These and other

properties and a procedure for qualifying a reverberation room are described in MS SI. 21-1972, "Methods for the determination of sound

power levels of small sovirces in reverberation rooms." This test

procedvire could be used for quality control of product noise emissions

and for information regarding the new design of a product for reduced

noise output. The directionality of the signal is lost, however, in a reverberant room. Another standard environment used for the determination of the

sound power radiated by a source of sound is the anechoic chamber.

This is a room designed to approximate the conditions of a free field

where sound from a source radiates outward and is never reflected back.

The surfaces of the room are highly absorbent to sound in the frequency

range of interest. The room is large enovigh so that the microphones

can be placed in the far radiation field of the sound source without

being too close to the room surfaces . The properties of the anechoic

room and the determination of sound power in a free field are described

in section 3.3 of MS SI. 2-1962, "Physical Measurement of Soxmd."

In an anechoic chamber, an array of 20 microphones are distributed

uniformly over the surface of a sphere enclosing the sound source. From the sound pressiire levels at each microphone position, Lp, the

mean-square sound pressure level in decibels, tp, and ^ the sound power

level can be calculated. As with the reverberation room measurement,

the determination of sound power in an anechoic room is useful in

design of low-noise products. In addition the directivity index (Dl)

of the source can be calculated.

DI = Lp - Lp

.

The directivity index of a sound source is a measure of how much

the actual sound pressure level in a given direction and distance from

the source exceeds that sound pressure level that would have emanated

from the same source radiating the same total sound energy equally in

28
all directions. A knowledge of the directionality of the sound output

of a product with respect to the operator position is of value in

assessing the hazards of its noise emissions.

However, if the purpose for measuring the sound output of a product is to determine exposure to the operator then the actual sound

levels produced in its "natural" environment are of paramount

importance. It is possible to utilize the sound power output of a source to predict the sound pressure at a particular location in a particular environment; however, there are instances where it is

preferable to express noise emission in terms of sound pressure under

specified measurement conditions rather than in terms of sound power.

In general, sound pressure is appropriate if the operator's (listener's)

location is well defined and the transmission to the operator (listener)

does not differ much among typical applications.

Also for many sources, including mobile sources and stationary

sources powered by internal combustion engines, a confined space is not

a suitable test environment due to the difficulty in providing for

operating loads, heat loads and exhaust emissions. Domestic and international standards exist which define test environments for such sources. For example, ISO Recommendation R362 , Measurement of Noise Emitted by

Vehicles, describes a test site and procedure suitable for moving vehicles.

Acoustical considerations of the site such as area, reflections from

objects, sound absorption by ground, etc. are discussed. This is necessary

so that the sound level emitted by a product at one test site will be the same as at another test site. The more closely the acoustical requirements

are specified and met, the greater the test data will agree. For the test

procedure the mode of operation of the vehicle (load, speed and acceleration,

etc.) are specified.

Developing a Test Procedure for a Specific Product

In developing a test procedure for a specific product, insofar as practical, an existing ANSI or ISO procedure should be used or adapted.

The acoustical properties of a typical or standard environment should

be specified. Tests should be performed under varying conditions of

use including one producing maximum noise. If installation is

29
required, the mounting should be specified. Directionality of the

source should be checked. Sound levels at the operator's ear position

should be measured and if good communication is essential, at the ear

of the second operator or co-worker.

The quality of the measuring equipment and its calibration affects

the accuracy of the sound measurement. Here again, as far as possible

equipment that meets ANSI and/or ISO-IEC requirements should be used.

The overall accuracy of the measurements should be specified.

Particularly helpful is ISO Recommendation RU95 "General Requirements

for the Prepeiration of Test Codes for Measxiring the Noise Emitted by

Machines"

.

The appendix at the end of this report contains a list of

standards relevant to the measurement of sound output of consiuner

products.

Bibliography

E. D. Biirnett, E.L.R. Corliss and R. D. Berendt , "Magnetic Recording

of Acoustic Data on Audiofrequency Tape," U.S. Dept. of Commerce, NBS

Technical Note Tl8, April 1972. This is particularly useful vhen

recording sound output for future analysis or for speech communication

tests

D. R. Flynn, W. A. Leasure, Jr., A. I. Rubin and M. A. Cadoff, "Noise

Measurements for Regulatory Purposes," National Bureau of Standards,

Washington, D.C. 2023^, Report in draft form.

30
CHAPTER IV

NOISE EMISSIONS FROM PRODUCTS: INTENSITY AND CONSUMER USAGE

Dr. Vern 0. Knudsen, an eminent acoustician, has claimed that "the

loudest noises to which we are exposed have increased some 20 decibels in

the past 20 years.""'" A growing population has expressed its demands in

the marketplace for more and more powerful appliances, tools, and

vehicles. The increasing number of noisy consumer products in use has

contributed to the overall growth in the level of environmental noise to

which most of us have been exposed.

In accord with its mission to protect consumers against imreasonable

risk of injury from hazardous products, the Consumer Product Safety

Commission has undertaken the evaluation of the potential hazards associated with the noise emissions of consumer products. Product noise

emissions could prove to be hazardous to the user in a variety of ways.

The noise from a device could prevent the user from hearing (i.e., mask)

an auditory warning signal such as a shout or a horn or siren. Likewise,

a noisy product may prevent the user from detecting a mechanical malfunction. A noisy device might distract the operator from the demands of the

task which he is performing or it may, with time, increase the operator's

level of fatigue or irritability. Any of the above conditions may predispose the operator to respond inappropriately if a crisis situation

should arise and an accident coiild follow. Furthermore, the use of products emitting intense levels of noise may lead to temporary or even permanent loss of hearing. The debilitating effects of such hearing

losses may, in turn, increase even further the users' susceptibility to

accidents res\ilting from auditory failure.

The specific hazards of noisy products are disciassed in greater

detail elsewhere in this report. The present chapter will exajnine the

general scope of the problem of noisy products in terms of their impact

upon the popiilation of consumers. The noise impact of a product can be

considered a joint function of the intensity level of its noise emissions

and the extent to which the user population is exposed to it. Extent of

31
usage is determined from the usage pattern associated with a given

product. At a minimum, a usage pattern describes how many people on the

average use a particular product, how frequently and for how long.

Although there is controversy about how intensity level and amount of

usage should be combined mathematically in order to express noise impact

on the individual (the measure, L seems to be in current favor - see eq

Chapter VI ), it is clear that the hazards associated with a product

increase as both intensity and amount of usage increase. The magnitude

of noise-induced hearing loss becomes greater as the intensity level of

the noise to which the ear has been habitually exposed increases and also

2 as the duration of exposure to the noise increases. Furthermore, the

capability of a noise to mask a warning signal increases directly with

3 its intensity. Finally, the number of people risking either hearing

damage or an accident from a noisy product is likely to increeise in

direct proportion to the number of people who own or use the product.

In order to assess noise impact on the consumer, an extensive list

of potentially noisy products was compiled. This list of products was developed using an updated version of the categories ajid products listed

in the Consumer Product Safety Index of the National Commission on

k

Product Safety. The selection procedure was editorial; that is, the

investigators simply included any item which we felt produced substantial

amounts of noise. In the case of meuiy of these products, data on noise

emissions were not available. This compilation is presented in Tables

IV-la & b. Concurrently, the technical literature was searched for

reported levels of noise emissions from consumer products. The outcome

of this literature search is presented with the list of products given in

Table IV-la. The range of reported A-weighted sound pressure levels

measured at the operator's approximate ear position is given in Table

IV-la for those products for which data were available. The average of

the reported levels is also given along with the sample size if these

were determinable. In some cases the product noise measurements were

reported in octave-band sound pressure levels and the A-weighted level

was calculated. A bibliography listing the sources of the reported

product noise measurements is appended at the end of the chapter.

32
Noise levels for consumer products reported in the literature tend

to concentrate on about a dozen common household items (e.g., air con- ditioners, dishwashers, vacuum cleaners, garbage disposals). Reported

levels on the more esoteric items (e.g., staple-guns, shredder-baggers,

electric ice crushers) are much less common. The most extensive lists of

product noise levels were found in a report prepared by Bolt Beranek and

Newman for the Environmental Protection Agency ("Noise from Construction

Equipment and Operations, Building Equipment, and Home Appliances' )

, and

in a report prepared by the Environmental Design Department of the

University of Wisconsin for the Koss Corporation ("The Auditory

Environment in the Home."^). The Bolt Beranek and Newman (BB&N) report

presents average A-weighted sound levels for thirty different appliances

and eleven shop tools obtained from the literature and from their own

measiirements . The Koss report gives A-weighted sound levels which the

investigators measured for Ul products (presumably, only a single item

was measured in each product category in the Koss study). It is

interesting to note that the noise levels for those 21 products appearing

in both of the above reports differed on the average by about 10 dB.

It is difficult to get a clear and consistent picture of product

noise levels by examining those reported in the literature. As stated

previously, most studies deal with only a handful of the most common

products. Furthermore, measurements from the different studies are hard

to compare since few of the studies provide enough information to

evaluate the measured levels properly. Such information should ideally

specify the number of products sampled, power ratings of the sampled

products, mode of product installation and operation, exact distance at

which measurements were made along with other details of the test

procedure and the acoustic environment.

The BB&N report cited above was perhaps the most useful single source of information about product noise levels. The authors of this

report also emphasized the scarcity of reliable product noise data in the

open literature. Consequently, they chose to supplement their tabulation

33
of noise levels from the literature with noise measurements which they

themselves conducted. The authors of the BB&N report describe their test

procedures in greater detail than is generally the case in other studies.

They also provide octave or 1/3 octave-band sound pressure levels for some of the products whose A-weighted sound level was measured. Brief

descriptions of the sound generating characteristics of some products are also provided.

The data on product noise levels tabulated in the BB&N report have

been updated by us and are incorporated in Table IV-la (see p. 39)'

Product noise levels reported in those studies from our literature search

which were not cited in the BB8eN report (which was completed in 1971)

were added to the tabulation. In addition the A-weighted sound levels

for l6 different products which were measured by us at the National

Bvireau of Standards are also included in the updated tabulation. Our

product noise measurements are presented and discussed more fully in

Chapter V of the present report.

Although published information on product noise levels is scarce,

limited in extent, and often difficxilt to compare and interpret, data on product usage patterns which wo\ild allow precise assessment of noise impact were not found. To our knowledge, the BB&N report is the only

survey or article on product noise which utilizes statistics on consumer

product usage. About the best that could be done was to follow up the

sources of information cited in their report for more recent statistics

of greater relevance to product usage patterns . None of interest were

fotind. Other pertinent sources of statistical information were also

queried without success. Since we could not improve upon the usage statistics provided by the

BB&N report, our discussion of the noise impact of consvmier products is

based entirely on the BB&N usage data. They cite the following as sources of information:

3k:
New York State College of Human Ecology, Cornell University (both

published and unpublished data gathered as part of a 1296-household survey of Syracuse, New York).

Department of Agriculture information based on studies of home

activities (a long-term interest, which is now being continued

under the Agriculture Research Service Division of the Department

of Agriculture).

Potomac Electric Power Company (an informal survey conducted by

their Home Services Department; note: a representative of the

company told us that the original source of the data was probably

the Electrical Energy Institute in New York.)

Manufacturer's industry information.

In addition to the sources of information on product usage cited

in the BB&N report, we foiind the following sources potentially

valuable altho\agh we did not incorporate them in our own analysis:

The 1970 U.S. Census of Population and Housing; series HC Sl-6

June, 1972 (provides information on the availability of

appliances in a 5^ sajnple of 66 million households).

Merchandiaing Week Magazine (supplies market penetration data

for many products - it is more up-to-date than the census information but is biased in ways that can be misleading).

To supplement the data from the sources which they used, the

investigators of the BB&N report conducted their own survey based on

20 households (unfortunately, little information is given on the

details of how the survey was conducted) . Information from these

sources was condensed into two composite statistics to describe the

usage pattern for a variety of products:

(1) the estimated number of people (in millions) in the united

States exposed to a product's noise emissions, and

(2) the estimated average duration of exposure (in hours) to a product in a household for one week.

Admittedly, such statistics are gross overgeneralizations ; there is no such thing as a "typical" household. Households vary greatly in

the niimber of their members, the number of appliances owned, and in

the personal habits of the members. Thus, any analysis of product

noise impact which is based on such generalized statistics should be

interpreted cautiously as an "order-of-magnitude" type of estimate.

35
Unfort\inately , given the quality of information on product noise

levels and usage statistics currently available, such estimates are about the best that can be achieved in assessing the impact of

product noise emissions.

A list of products which we considered as having a high level of

noise impact upon the consumer is presented in Table IV-2. An

A-weighted sound press\ire level of TO dB was chosen as a tentative

and somewhat arbitrary lower limit or criterion level. Only products

whose reported range of A-weighted sound levels exceeded TO dB were considered as potential high- impact products. A cutoff level of TO

dB was felt to be reasonably conservative with respect to protection

of hearing (see Chapter VI). Other information suggests that with an A-weighted sound level not exceeding TO dB (outdoors), communication

is possible with a very loud voice up to a distance of about T ft and

3 that a shout can be recognized up to a distance of about 15 ft.

Thus, within a limit of TO dB, disruption of auditory warning signeils

would probably not be excessively severe. This projection, however,

is a generalization and should, of course, be put to erapiricaJL test

for particular products used in specific situations (see Chapter II).

If a product whose range of noise levels exceeded TO dB also appeared to have a substantial amount of consumer usage associated with

it, then it was included in Table IV-2. Two features of the data in

Table IV-2 are especially notable. The first is that the range of

reported noise levels within a given product category can be quite

wide. This might suggest the possibility that a few of the many

manufacturers of a certain product may be responsible for most of the

noisy models. It also implies that a product category generally

considered as "quiet" may nonetheless harbor some models having

hazardous noise emissions. Finally, reported noise levels are representative only of products in their normal condition. The noise

from some products can be totally innocuous when operating normally,

yet hazardous when the product malfunctions.

36
A second important feature of the data in Table IV-2 is that very

fev of the products for which usage statistics are given and which have

reported noise levels exceeding TO dB are also in use for more than an hour per week in the average household. This might lead to the

conclusion that the noise impact from most products is inconsequential

for the typical cojisumer. However, many noisy products are often used in

atypical patterns. Household appliances and tools are frequently used

for occupational purposes. A home seamstress or a gardener or a handyman

woTild generally use such tools and appliances far in excess of the amount

of time which is representative for the average householder. Since these

individuals are self-employed, they would not be subject to the noisesafety regulations of the Occupational Safety and Health Administration

(OSHA). A similar case can be drawn for products which can be used for

hobbies and recreational purposes such as workshop tools, sewing

machines, snowmobiles, motorcycles and the like. Thus, many of the

products found in Table IV-2 are items which can be used for recreational

and occupational purposes.

In sTommary, it should be recognized that generalized usa^e

statistics such as those presented above are inherently misleading and

any evaluation of noise impact which is based upon them will not fiilly

insure adeq\mte protection for all consumers. A few closing comments are in order regarding usage patterns for

consximer products. The discussion thus far has assumed that a particular

product is used by itself. This assumption is patently unrealistic for

most products. Any complete analysis of product noise impact wo\iId

ideally include Joint product usage patterns as well as combined noise

spectra. Of more importance, however, is the fact that although the

duration of exposure to the noise from products may be relatively small

for most consumers , it must be combined in some manner with the exposure

to noise which is inctirred through one's occupation and the general

environment. This matter will be discussed more thoroughly in Chapter

VI.

37
References

"^"Environmental Protection Agency Preliminary Summary of Causes

and Sources of Noise" in Noise Control; Hearings before the Subcommittee on Public Health and Environment of the Committee on Interstate and Foreign Commerce, House of Representatives , NinetySecond Congress, First Session (U.S. Government Printing Office,

1971), p. 138.

2

R. Gallo and A. Glorig, "Permanent Threshold Shift Changes

Produced by Noise Exposure and Aging," Amer. Ind. Hyg. Assoc. J. 2^ , 237-2i+5 (I96U).

\j.S. Environmental Protection Agency, "Masking and Speech

Interference" in Public Health and Welfare Criteria for Noise , EPA Document No. 550/9-73-002, (U.S. Government Printing Office,

1973), p. 6-1.

^S. J. Chumas, "Tabulation of Voluntary Standards and Certification

Programs for Consumer Products," National Bureau of Standards

Technical Note 762 (U.S. Government Printing Office, 1973).

^Bolt, Beranek and Newman, "Noise from Construction Equipment

and Operations, Building Equipment, and Home Appliances," (prepared

for the U.S. Environmental Protection Agency) EPA Document No.

NTID300.1 (U.S. Government Printing Office, 1972).

"The Auditory Environment in the Home," a report by the Environmental

Design Department, University of Wisconsin, for Koss Electronics, Inc.,

Milwaukee, Wisconsin.

38
Table IV-la. Consumer products having substantial noise emissions

"With statistics for reported A-weighted sound pressure levels.

Standard

Industrial

Classification

Number^

0823

0321

0629

0215

0213

0127

0126

0217

0511

0306

O21I1

0802

ihOk

0116

1637

0806

0218

1608

0111

O6I+8

A-Weighted Sound

Pressure Level, dB

Product

Air Compressor

Air Conditioner

Alarm Clock,

Electric

Blender

,

Electric

Can Opener,

Electric

Clothes Dryer

Clothes Washing

Machine

Coffee Grinder

Desk Calculator

Dehumidifier

Dishwasher

Drill, Electric

Edger and

Trimmer , Lavm

Electric Broom

Electric Comb

Electric Grinder

Electric Knife

Electric

Toothbrush

Fan

Faucet

References

10

1,^,10,11,15

U,10,ll

1,11

1,11

1,U,11

1,11

12

1

1,^^,11,17

1,11,18

1

18

18

1

1

1

1,11

1

Range

50-70

60-80

62-93

5U-78

52-66

U7-T8

66-79

52-62

5U-85

70-89

78-80

87-97

65-75

U8-55

38-70

Average

9k

68

77

68

58

6k

75

9k

57

66

80

81

82

79

71

52

58

61

Sample

Size

1

55

3

69

7

12

61

3

1

k

k6

7

1

1

2

3

3

3

k2

1

39
Table IV-la (Cont'd)

Standard

Industrial

Classification

Number^ Product References

A-Weighted Sound

Pressure Level, dB

Range Average

Sample

Size

Food Mixer i,U,ll ) 1 r> ft 0 bo 27

rXoor i3Ui 1 er/

Waxer

1 ft d7 1

0208 Freezer 1 I4I 3

0327 Furnace 11 _ 100 1

0237 Garbage Disposal 1,^^,11,17 67-93 79 22

1602 Hair Dryer 1,11,18 59-80 66 7

xC)U± Hair Clipper 1 po 1

0323 Heater, Electric 1 - hi 1

lii27 Hedge Clipper 1 - Qk 1

030U Humidifier 1 Ul-65 53 3

0516 Infant Incubator 5 58 6

02it0 Knife Sharpener 1,11 72-78 75 2

0805 Lathe 11,18 76-80 78 2

lUOl Lawn Mower,

Electri c

1 81-89 85 2

lUOl Lawn Mower

,

Gasoline

2,4,10 OI-9O 90 c

D

1263 Minibike lU 92-96 17

1236 Motorcycle 6 85-110 93 10

1608 Oral Lavage 1 7O-7U 72 2

0208 Refrigerator 1,11 35-52 h3 13

080U Router 1,18 88-103 95 3

0803 Sander, Belt 1,11,18 86-loU 9h \

0803 Sander, Disk 11 93 1

0803 Sander, Orbital 11,18 70-82 76 2

0801 Saw, Band 18 105 1

40
Table IV-la (Cont'd)

Standard

Industrial

Classification

Number^

0801

0801

0801

0801

0801

0801

0112

0808

1601

0611

li+33

1619

1218

06h9

0511

0115

A-Weighted Sound

Pressvire Level, dE

Product

Saw, Chain

Saw, Circxalar

Saw, Jig

Saw, Radial

Saw, Sabre

Saw, Skill

Sewing Machine

Shaper, Electric

Shaver, Electric

Shower

Shredder (Power

Mulcher

)

Siren/Horn,

Snowmobile

Toilet (Flushing)

Typewriter

,

Electric

References

U 9,18

11

11

18

11,18

1,11

18

1

11

18

18

8

1,11

12

Range

96-111

95-98

91-110

100-ioU

Ul-69

103-10i+

103-117

1+6-T6

65-lh

Vacuum Cleaner 1,1+,10,11,1T 62-85

Average

97

68

92

101

102

69

90

60

78

10k

118

109

65

72

Sample

Size

3

1

1

2

2

3

1

11

1

2

1

k

21

Ik

30

See reference k cited in text.

""Numbers entered in this column correspond to the references appended to this

Table

.

41
References to Table IV-la.

1. Bolt, Beranek and Newman, "Noise from Construction Equipment

and Operations, Building Equipment, and Home Appliances," (prepared

for the U.S. Environmental Protection Agency) EPA Docvment No.

NTID300.1 (U.S. Government Printing Office, 1972).

2. W. D. Clark and K. C. Williams, "Rotary power lawn mower

noise," J. Acoust. Soc. Am. 5^, S36~S3T (197^+).

3. A. Cohen, J. Anticaglia and H. H. Jones, "Sociocusis - hearing

loss from non-occupational noise exposure," Sourid & Vibration, pp. 13-

( November, 1970)

h. "Environmental Protection Agency Preliminary Summary of Causes

and Soirrces of Noise" in Noise Control; Hearings before the Subcommittee on Public Health and Environment of the Committee on Interstate and Foreign Commerce, House of Representatives , NinetySecond Congress, First Session, Serial No. 92-30 (U.S. Government

Printing Office, 1971), p. 138.

5. J. C. Farmer and S. A. Falk, Noise Control Report 2_, No. 17,

169 (1973).

6. R. Harrison, "Motorcycle Noise," San Dimas Equipment Development

Center Report, U.S. Department of Agriculture, 197^.

7. R. Harrison, "Development of a Noise Steindard for the Oregon

Dunes National Recreation Area," San Dimas Equipment Development

Report, U.S. Department of Agriculture, 1973.

8. R. Harrison, "Snowmobile Noise," San Dimas Equipment Development

Center Report, U.S. Department of Agricultixre , 1973.

9. P. D. Hart, D. M. O'Brien and D. A. Peroli , "investigation of

noise radiated from a circ\ilar saw," Noise-Con 73 Proceedings

(Inst, of Noise Control Engineering, 1973), pp. U20-U21.

10. M. Hirschorn, "The 90 dBA guideline for noise control engineering

Sound and Vibration, pp. 25-29 (April, 1970).

42
11. "The Auditory Environment in the Home," a report by the

Environmental Design Department, University of Wisconsin, for Koss

Electronics, Inc., Milwaukee, Wisconsin.

12. R. Martin, "Noise measurements on desk calculators and typewriters,

J. Acoust. Soc. Am. 51, 1^3 (1972).

13. E. E. Mikeska, "Noise in the modern home," Noise Control h_t 38

(1958).

Ih. R. P. Oppenheimer, Noise Control Report 2, No. 23, 226 (l9T3).

15. J. R. Schreiner, talk presented before Air-Conditioning-HeatingRefrigeration Exposition of the Air Conditioning and Refrigeration

Institute, Los Angeles, 197^.

16. W. M. Shearer and G. H. Stevens, "Acoustic threshold shift from

power lawnmower noise," Sound and Vibration, p. 29 (October, I968)

.

17. M.C.C. Tsao and R. S. Musa, "Noise control in home appliances,"

Sound and Vibration, p. 31 (March, 1973),

18. Measurements conducted by Pearl G. Weissler and Gerald A. Zerdy

of the Sound Section, National Bureau of Standards, and Thomas Cooper

of the Consumer Product Safety Commission at the National Bureau of

Standards, Wash., D.C.

43
Table IV-lb. Consumer products having substantial noise emissions

for which data were not found.

Standard

Industrial

Classification

Number Product

1202 Bicycle Horn

0606 Electric Generator

0225 Electric Ice Cream Maker

0226 Electric Ice Crusher

0228 Electric Juicer

1611 Electric Manicure

0819 Electric Motor (Separate)

0232 Electric Scissors

1613 Electric Shoe Polisher

0701 Fire Extinguisher

1U05 Garden Tractor

0820 Gasoline Engine (Separate)

0811 Gas Torch

1306 Gasoline Powered Toys

1213 Golf Cart

1237 Guns, Gas, Air, Spring Powered

0108 Ironing Machine

0807 Jointer

1610 Massage Devices, Vibrators

0230 Meat Grinder, Electric

1236 Motor Scooter, Unlicensed

0822 Paint Sprayer

IU12 Pump

OllU Rug Cleaner/Shampooer

IU06 Snow Thrower, Plow

083^+ Stapler, Powered

ikoQ Tiller, Cultivator

1330 Toys, Powered Riding

0252 Trash Compactor

A4
Table IV-2, Consumer products having high noise impact.

Weekly Exposure

Range of Reported Number of Average

A-Weighted Sound Persons ^ Duration

Product Pressure Levels (in dB)

6L (in millions) DC(in hours)

Air Conditioner 50-70 60 3.00

Blender, Electric 62-93 63 0.02

Clothes Washing Machine UT-T8 183 0.50

Dishwasher 5U-85 U7 5-00

Drill, Electric 70-89 9 Fan 38-70 160 10.00

Food Mixer U9-82 163 0.15

Garbage Disposal 67-93 1+6 0.10

Hair Dryer 59-80 9

Lathe 76-80 ? ? Lawn Mower fti 0 oft J.— y 0 9 u. p Minibike 92-96 9 ? Motorcycle 85-110 ? ?

Sander , Powere d 70-lOU 9 9

Saw, Powered 91-110 9 9 Sewing Machine Gh-lU 100 0.25

Shredder 103-lOU 9 9 Snowmobile 103-117 '7.5* 9 Typewriter, Electric 65-7U 9 9 Vacuum Cleaner 62-85 181 1.5

^rom Table la.

^Source: Bolt Beranek and Newman report cited in text, p. 107-

c Source: Bolt Beranek and Newman report cited in text, p. 110.

^Source: International Snowmobile Industry Association.

45
CHAPTER V

NBS MEASUREMENTS OF THE SOUND OUTPUT OF SOME CONSUMER PRODUCTS

Introduction

During the search for reported levels of noise emissions from consiuner products,, described in Chapter IV, the sparsity of available data

became apparent. It was decided to try to fill in some of the gaps with

our own measurements. We were more interested in the order-of-magnitude

of the noise emissions of a variety of product categories rather than the

complete range of sound output of one category of product. Also, meas- urements were made in convenient locations rather than in standard en- vironments such as an anechoic or reverberation room (see Chapter III).

The measurements were made by Pearl G. Weissler and Gerald A. Zerdy of

NBS and Thomas Cooper, a Guest Worker from the Cons\imer Product Safety

Commission.

Apparatus and Procedure for Indoor Measurements

The measurements were made with a sound level meter whose specifications meet those of ANSI SI.U-I97I for a Type I sound level meter. A

commercial acoustic calibrator was used to check the sound level meter at

125, 250, 500, 1000 and 2000 Hz. In addition, the sound output of a sabre saw was measured with this sound level meter and another sound

level meter from a different manufacturer, also a Type I. The results

agreed within 2 dB.

Measurements on all products except the shredders were made in

several different indoor environments; (A) a sound-insulated laboratory

with acoustic tile on walls and ceiling, (B) a small general-purpose shop

with hard walls and high ceiling, (C) a large wood construction shop,

also with hard walls and high ceiling, (D) a small anechoic chamber, (E) a home basement workshop, and (F) in a home bedroom. At E and F the

measurements were taken by Frank R. Breckenridge , at (D) by Edwin D.

Burnett

.

U6
The ambient noise was measured in each room. With the product

turned on, the sound pressvire level was measured near the operator's ear and sometimes in an additional location, except for the freon siren where

no measurements were made at the operator's ear position. Where

applicable, the measurements were made under conditions of load ajid no

load. Both the flat and A-weighting networks were used, and both fast

and slow meter characteristics were used.

Results of Indoor Measurements

The results can be seen in Table V-1. Sound levels for most of

these products, measured with the A-weighting setting are the same as when measured with a linear or "flat" setting. This means most of the

sound energy is in the middle and high frequency range. The lathe,

however, has relatively more low frequency energy.

Outdoor Measurements

The noise outputs of two shredders, h and 5 HP, were measured outdoors in two locations with the same sound level meter described above.

The first location (see Figure V-l) was in a driveway leading to a loading platform. With the shredders turned off, the background noise in

the area was measured. Then each shredder in turn was placed Just north

of the loading platform near an industrial disposal with the muffler

facing east and then turned on. Sound level measurements were recorded

near the position of the operator's ear, (with the operator present), at a distance of T-6 m north of the shredder, (position l), and at a distance 7*6 m east of the shredder (position 2). The sound level was measured under conditions of no load and loaded with twigs and thin tree

branches. The sound level meter was alternately set to read the

lanweighted sound pressure level ("flat" scale) and the "A"-weighted sound

pressure level ("A" scale). The A-scale weights the sound pressure level

as a fiinction of frequency somewhat as the ear does . This attenuates

frequencies below 1000 Hz. The meter was set to "fast" response.

hi
Some measurements were also made at a second location (see Figure

V-2) which was in the center of a grass area north of a large building.

The shredders were oriented with the muffler facing the building. Here

position 2 is 7-6 m south of the shredder, between the shredder and the

building.

Results are summarized in Table VI-2. There is no significant difference between the A-weighted sound level measured with the fast or slow

meter response for the no-load condition. Sound levels were slightly

lower in location 2, probably due to sound abosrption by the grass and

the elimination of a large reflecting surface (the industrial disposal)

Just behind the sound source.

kQ
Table V-1. NBS measurements of noise emissions from certain

consumer products.

Sovind Source

SPL, dB

Room A-Weight Flat

Meter

Response

Sabre Saw:

at operator's ear, no load A 110

hanging by string, rear, near switch A 12h

Impulse

Fast

at operator's ear, load B 100 Fast

Sabre Saw (different brand):

at operator ' s ear , no load c 91

91

91 Fast

Slow

Electric Hand Drill, 1/U", I8OO rpm:

at operator's ear, no load A Qh Imp\iJ

Electric Hand Drill (different brand):

at operator's ear, no load C 89-90

89

89-90 Fast

Slow

Circular Saw:

at operator's ear, under load B 95-98 95-98 Slow

CircTilar Saw (different brand, 9"):

at operator's ear, no load E 95 95

Electric Band Saw, 7":

right ear, no load

right ear, wood load

B

B

100

101-105

100

101-105

Fast

Fast

Drill Press

at operator's ear, under load B 72 Fast

Belt Sander:

at operator ' s ear , no load

at operator's left ear, wood load

at operator's right ear, wood load

C

C

C

98

98

9h

97

9U-96

98

95

9U-96

Fast

Slow

Fast

Slow

Fast

Belt Sander (another type):

at operator's ear, no load

at operator's ear, wood load

B

B

102-loU

97-101

102-loU Fast

Orbital Sander:

at operator's ear, wood load C 80-82 81-83 Fast

Router

at operator's ear, no load

at operator ' s ear , wood load

C

C

89

90-95

93

89

93

Fast

Fast

Slow

A9
Table V-1 (Cont'd)

SPL, dB

Meter

Soiind Source Room A-Weight Flat Response

Router (another typej:

at operator's ear, to side, no load B 97 98 Fast

at operator's ear, above, no load B 99-100 99-100 Fast

. at operator's ear, to side, wood load B 100-103 100-103 Fast

at operator's ear, 15" above, vood load B IO2-IOI+ IO2-IOI1 Fast

Skilsaw io-1/2 in.;:

at operator's ear, no load C 93 93 Fast

93 Slow

; at operator's ear, wood load c 98-loU 98-loU Fast

Shaper (with l-l/i|" bit):

at operator's left ear, no load c 85 86 Fast

85 Slow

at operator's right ear, wood load c 90 91 Fast

blow

at operator s right ear , no load p\^ r as u Lathe

:

at operator's ear, no load 1 3-Td 00-01 A A At

r ast

Floor Buffer:

at operator's ear A d5-dT d5-dd T71 J_ Fast

Electric Broom:

at operator's ear, slow speed A Td-TT 76-77 Fast

at onpra tor ' ear. hich SDeed A 81-82 81-82 Fast

Electric Comb:

at operator's ear, while combing A 78 78 Fast

Electric Comb (different brand):

at operator's ear, while combing F 80 80

Hair Dryer

:

near ear, under cap A 78-80 83-85 Fast

Freon Siren:

U5" in front of source B 118 117 Fast

1 m from source D llU Fast

Ambient Noise: A 25 61 Slow

B k3-h6 63-71 Fast

c 3h 68 Fast

D 25 63 Slow

50
•H

COo uo

2S 3a3O

(UCO •HOc s 6

CNCo

09o c o a CO •H o 3 o

0) c

to <U c

(U CO •HM 14-1 O O

00

T3

auo

c4 I >M3

bO

•H

(>4

51
M

0) •a

(Uu

CO o

ijVao 3 0

so

01o

PL.

uo

4-1 3a3O

(UCO •Hoc

ofGi

<u3

CO

fo CMCO

•H i U

a. OS •H u 3 o

(U c

•H o

CO c U o d) •H T3

4J 13

CO 0) 4J U c JC

0) CO o o

CMI >

>-l 3

60

•H

[14

60

pq

52
Table V-2. NBS measurements of shredder noise emissions.

Soiuid So\irce A-Weighted Flat Meter Response

Location 1

Background noise U8-5O 70-75 Fast

onreu.a.er , 4 lur

.

ati operator s ear, no xoau oU QQyy r asL

at operator ' s ear , load Ofi yo ^ (TP r asX

position 1, no load 7ft ftli 04 r as li position 1, load 80-82 85 Fast

position 2, load 87 88 Fast

Shredder, 5 HP:

at operator's ear, no load oft yo r asx

at operator ' s ear , load 1 on r as u position 1, no load fti ox— ft? Oc fto oy r asL

position 1, load fto oy ftft 00—Qlyx r asu position 2, no load ftQ 90 r ast

position 2, load 87-91 93 Fast

Location 2

Shredder, 5 HP:

at operator's ear, no load 96 98-100 Fast

96 Slow

position 2, no load 78 88 Fast

80 Slow

53
CHAPTER VI

IDENTIFYING SOUND LEVELS FOR CONSUMER PRODUCTS

WITH RESPECT TO HEARING DAMAGE

During the course of a day an individual is exposed to many different sources of noise. His noise exposure pattern depends upon

whether he lives in a city or on a farm, whether he travels to work by

subway, bus or car, whether he works in a factory, office or at home,

and whether after work he mows the lawn, retires to his basement

workshop to refinish an old desk or reads a book. If his daily noise

exposure is sufficiently high, then after a niomber of years he may begin

to lose his hearing. Noisy consumer products play a part in this

complicated pattern. It is important for the Consumer Product Safety

Commission to know whether or not a product is contributing

significantly to the degradation of hearing.

In order to gain some insight into the problem of determining which

cons\imer products could be considered safe or luisafe with respect to

noise-induced hearing loss, use was made of the March 197*+ EPA Levels

Document''' and some of its principles were applied to the consumer

products listed in Chapter IV. This EPA Document identifies levels

requisite to protect public health and welfare with an adequate margin

of safety for both activity interference and hearing loss. To define a level which protects the public health, with respect to hearing

conservation, some observations and assumptions had to be made about the

nature of noise and its measurement with respect to its effect on hearing. Some of these EPA assumptions follow.

The A-weighted sound level is widely accepted as an adequate way to assess noise with respect to its potential for causing hearing loss. A

characteristic of much environmental noise is that it is not steady,

making it difficialt to say that a person at a given location is exposed

to so many decibels of noise. In addition, as a person moves from place

to place he is exposed to different levels of noise. His total noise

exposure is related to the whole time-varying pattern of sound levels.

5U
Accordingly, an Equivalent Soxmd Level, L^^, was defined in terms of

that equivalent steady noise level which, in a given period of time,

wovLLd contain the same noise energy as the time-varying noise during the

same period.

2 ^1 ^1 p^

o

where p(t) is the time varying sound press\ire and p^ is a reference

pressiire equal to 20 micropascals

.

This is a particularly useful concept when combined with the Equal

Energy Hypothesis which states that equal amounts of sound energy will

cause equal amounts of noise-induced permanent threshold shift regardless

of the distribution of the energy across time.

An early symptom of noise-induced hearing damage is a change in

hearing level at UOOO Hz, the typical noise-sensitive frequency. A

change in hearing level of less than 5 dB is not considered

significant. Thus, if a noise exposure level could be identified which

causes less than a 5-dB change in hearing level at UOOO Hz in a large

percentage of the exposed population, then the public health would be

protected. In order to do this a considerable amount of data on hearing losses of people with known histories of noise exposure were

examined. By comparing groups of such individuals with similar

non-noise exposed populations, evidence for noise-induced permanent

threshold shift could be inferred.

Much of these data came from industrial environments and thus

initially an eight-hour exposure level was identified which was protective of a large proportion of the population. By application of the

Equal Energy Hypothesis, corrections were made for yearly and daily {2h

hour) dosages. Another correction (+5 dB) was made to allow for the

intermittency of environmental noise eind the final result was rounded

down by l.k dB to allow for uncertainties.

L =10 log

eq

55
Thus available data suggested that for hearing conservation, a level less than or equal to an equivalent sound level of 70 dB over a

2i4-hour day f^eq(2i4) "^^ protects virtually the entire population

against a change in hearing level greater than 5 dB at UOOO Hz.

^gq(2U)

represents the sound energy averaged over a 2l+-hour period and the level

identified represents annual averages of the daily level over a period

of forty years.

Similarly, for more than 99 percent of the people studied the data

suggested that an

^Q(^^2k) °^ ^ will cause no more than a 5-clB shift

in hearing level averaged for the frequencies 500, 1000 and 2000 Hz, and

an

^Q^(^2h)

^ will cause no more than a 10-dB shift averaged for

the frequencies 500, 1000, and 2000 Hz. However, an average 10-dB shift

in the low and middle frequencies is accompanied by a greater hearing

loss in the high frequencies (see Fig. 1-k) . Also, although the data

cover a UO-year span, a large part of the damage due to noise occurs in

the first ten years.

According to the Occupational Safety and Health Act of 1970, protection

against the effects of noise expos\xre for workers is not mandatory \inless the sound level is greater than 90 dB, A-weighted for 8 hours a

2

day. The criterion of 90 dB, A-weighted, comes from data showing the

dependence of hearing impairment on age, experience and noise exposure.

OSHA considered a handicap for speech as a requirement for its

definition of hearing impairment, specifically, a hearing level averaged

for the three frequencies 500, 1000, and 2000 Hz, that is greater than

25 dB. If this level of 90 dB were adjusted to environmental levels, by

correcting for intermittency and by summing energy on a 2h hours/day and

a yearly basis, it would be equivalent to L^^^^i^) ~ 88. i+ dB. This is

close to the EPA identified level of L 86 dB described above.

Thus one can infer from the EPA Levels Document that for determining which consumer products could be considered safe or \msafe

with respect to noise-induced hearing loss, the criterion

^Q^(^2k)

^ "^^ dB is indicative of safe products and L z^, x > 86 dB is indicative of

eq(2U) - those products whose safety may be in question. For all products con- tributing to an

^Q^(^2h)

^ '^^ total noise impact must also be

considered (see Chapter V).

56
To calculate equivalent soiind levels for consumer products

according to the Levels Dociiment , Eq. VI-1 can "be employed. If we

consider an exposure period consisting of two constant sound levels,

and L , where x is the fraction of the time L is on and (l-x) is the

X X

fraction of the time is on, then Eq. VI-1 can be written

^eq = H, ^ 10 log (1-x) + x-lO VI-2

To calculate ^^^^2^) ^ person who drives a snowmobile for ein hour a day and who is exposed for the remainder of the day to an equivalent sound level of Uo dB we substitute

= UO dB,

L = 117 dB, and

X

X = l/2k

into Eq VI-2.

L f ^\ \ = 103 dB is the result.

This means that a noise exposure of one hour at 117 dB (e.g. from

a snowmobile) and 23 hours at Uo dB is equivalent to a noise exposure

of 103 dB for 2k hours. This is true for all backgroiind noise levelg

< 91 dB. For L^^ > 91 dB, L^^^^i^) increases. Similarly if one were to

operate a power tool producing a soiind level of 100 dB (L^ = 100) for

two hours, the equivalent noise expos\ire, Lgq(2U) ^® ®^

^

^

< 77 dB. A convenient solution to Eq. VI-2 for low values of c&n be

found in Table VI-1.

To utilize the EPA identified levels of L x = 70 and L /oi \ = eq(24) eq(24)

86 we solve Eq. VI-2 for L . x

57
= + 10 log

eg

10 - (l-x) VI-3

Now vith Lgq(2li) ~ '^^ ^ ^^'^ with exposure times, x, corresponding to

consumer usage patterns we can identify levels of exposure, L^, for

consumer products that would be safe for use within a limited range of

noise exposure during the rest of the day. Table VI-2 gives examples

of such exposures

.

Similarly, with ^^^(2^) ~ ^ can identify exposures to sound

output of consumer products that, with daily use over many years, for a large percentage of the population would cause no more than a 10-dB

increase in hearing level averaged for 500, 1000 and 2000 Hz, provided

the equivalent soiind level for the rest of the day < 7^ dB. These ex- posures are shown in Table VI-3.

The EPA levels document states "in pleuining community noise abatement, local governments should bear in mind the special needs of those

residents who experience levels higher thein L^^^g^ at 70 on their

jobs." The L^^^^i^) ^ worker exposed to 90 dB for 8 hours, and one of the exposures listed in Table VI-3, equals 88.8 dB.

The effect of noise on hearing is cumulative over the years. To

decide whether a particular product is a potential hazard, its sound

level, usage pattern and additional noise exposure of the person iising

the product have to be considered. As an exajnple, in the winter a person may drive a snowmobile regularly and have an Lgq(2l+) °^ '^^^ In the Slammer he may sleep near a noisy air conditioner (70 dB), mow

his lawn or use a powered tool for one hour (90 dB), and work in a factory (90 dB). His resulting exposure would thus be L^^^^i^) ~ ®^

This is mainly due to the exposure at work. However, if the sound

level at work is low, his L /^i \ would be 77 dB, with the main

eq(2U)

contributions coming from the air conditioner and lawn mower.

58
From Table IV-2, one could find products having noise levels > 100

dB that could conceivably be used nearly every day for an hour. These

products are obviously, by themselves , hazardous (e.g., many powered

tools). There are more noisy products that are not hazaj-ds in

themselves. It is the general level of noisiness of many consumer

products and their variety, prevalence, and impact that constitute the

danger to the hearing of the population. Any product whose sound level

and usage exceed that in Table VI-2 could contribute to degradation of

the hearing of its users. Any product whose sound level and \isage

exceeds those specified in Table VI-3 contributes more seriously to the

degradation of hearing of its users. However, any product whose sound

level is greater than TO dB has the potential to impair hearing if used

over a period of sufficient length. These conclusions are inferred from

the EPA Levels Document.

References

1. U.S. Environmental Protection Agency, "Information on Levels of

Environmental Noise Requisite to Protect Public Health and Welfare

with an Adequate Margin of Safety," 550/9-7^-00^+, March 197^.

2. U.S. Department of Health, Education and Welfare, "Criteria for a Recommended Standard. . .Occupational Exposure to Noise," 1972.

59
Table VI-1. Factors to convert the soiand level of a consumer

product (L^) to the equivalent sound level for 2h ho\irs tLgq(2U)-'

provided that the equivalent exposiare for the remainder of the

day, L^, is at least 12 dB below the derived

^Q(^(^2k)'

Duration of L , ho\irs L -L dB

X eq(2U)'

0.5 IT

1 Ik

2 11

h 8

Table VI-2. Product noise exposures that do not exceed those

protective of the public health and welfare, provided the

equivalent sound level for the remainder of the day < 58 dB.

Increased exposure could cause hearing loss.

Exposure Duration, hours Exposure Sound Level, dB

0.5 87

1 Qh

- 2 81

k 78

60
Table VI-3. Product noise exposures that, with daily use over many

years for a large percentage of the population, woxild cause no more

than a 10-dB increase in hearing level averaged for 500, 1000 and

2000 Hz provided the equivalent sound level for the rest of the day

< dB. Increased exposure could cause more hearing loss.

Exposiire Duration, hours Exposure Sound Level, dB

0.5 103

1 100

2 97

9^

61
CHAPTER VII

TOWARD A UNIFIED SET OF NOISE REGULATIONS

In the Introduction it was pointed out that conflict in the regulation of the soimd output of consumer products could arise because of

different mandates from Congress to the agencies of the Federal Government

concerned with noise. A brief summary of the pertinent parts of these

mandates would serve to clarify the issue.

The purposes of the Consumer Product Safety Act"^ are:

(1) to protect the public against unreasonable risks of injury

associated with consumer products;

(2) to assist consiimers in evaluating the comparative safety of

consumer products;

(3) to develop uniform safety standards for consumer products and

to minimize conflicting state and local regulations; and

(U) to promote research and investigation into the causes and prevention of product-related deaths, illnesses, and injuries.

In Sec. 31 of this Act it says "The Commission shall have no authority under this Act to regulate any risk of injury associated with a consumer product if such risk could be eliminated or reduced to a sufficient extent by actions taken under the Occupational Safety and

Health Act of 1970."

2

The purpose of the Occupational Safety and Health Act of 1970 is

".. to assure as far as possible every working man and woman in the

nation safe and healthful working conditions."

3

As expressed in the Noise Control Act of 1972, it is the policy of

the United States to promote an environment for all Americans free from

noise that jeopardizes their health and welfare. This is to be done by

coordinating Federal effort in noise control, establishing noise emission

standards for products distributed in commerce; and providing information

to the public respecting the noise emission and noise reduction

characteristics of such products. The Environmental Protection Agency

has the main responsibility for implementing this act.

62
Many products used "by consumers could also he used in industry;

e.g., lawn mowers, power tools, snowmobiles. Their noise emissions affect

not only the operator "but also the outdoor environment. The noise

emission of these and other products could he regulated by EPA, OSHA and

CPSC , all from somewhat different points of view. For mobile sources,

EPA at present is primarily concerned with the environment and emphasizes

measiirements of noise levels at 50 ft from the source. However, noise

levels which protect the community at a criterion of 50 ft may still be

unsafe at the operator's ear. The present OSHA regulations deal with

noise exposure in a working environment, usually the result of many noise

sources in the same room. Usually consumers are exposed to one noise

source at a time. Thus, three incompatible standards for a single

product could result from the differing regulatory interests of these

agencies

.

Another type of problem could occur as a result of differing

priorities. Recently, the EPA identified products as major sources of

k

noise. Highest priority was given to sources that contribute to

community noise exposure. So far only two products have been identified;

medium and heavy-duty trucks and portable air compressors. It appears as though CPSC will be in a position to set standards for products of mutual

interest to EPA, much before EPA will be ready to consider them.

Another problem is the procedirre for summing noise exposxires . The

OSHA Act uses a 5-dB r\ile for relating exposure level and time. That is, an exposure of 90 dB (A-weighted) for 5 hours is considered equivalent to

95 dB, A-weighted, for h hours or 100 dB, A-weighted, for 2 hours. This

is in contrast to the Equal Energy Hypothesis which is equivalent to a 3-dB rule for relating exposure level and time. That is, 90 dB,

A-weighted, for 8 hoiirs is considered equivalent to 93 dB, A-weighted,

for h hours.

Resolution of these conflicts requires legal, administrative, and

scientific Judgments.

In order to begin the necessary communication between EPA and CPSC, a letter was written to the Deputy Assistant Administrator for Noise

Control Programs, Office of Noise Abatement and Control, Environmental

63
Protection Agency. This letter stated the interest which the Consumer

Product Safety Commission has in establishing safe noise levels for con- sumer products, and the Commission's concern about a uniform set of noise

standards for the Federal Government, particularly with respect to those

products that both EPA and CPSC would regulate.

As a result, communication at the working technical level was immediately established. This enabled us to keep informed of ONAC's

program and latest publications. A significant portion of this report is

based on information from ONAC's technical publications.

Also, a meeting between CPSC and EPA representatives was recently

held. The areas of standard setting, labeling and state/local interface were identified as ones for high level discussions for the purpose of

developing agreements. Similar future meetings with CPSC, OSHA and EPA

could resolve any OSHA-CPSC overlap.

Of equal importance would be the establishment of a formal procedure

for the regular exchange of information among EPA, OSHA, NIOSH and CPSC

regarding their activities in noise control. This could take the form of

periodically circulating lists of publications, grants and contracts

proposed and awarded, standards under consideration, etc. Duplication

would be avoided and each agency would have the benefit of the others' resources. For example, the EPA has recently awarded a grant for

developing improved criteria for verbal communication in noise. This

procedure has been followed successfully by the Office of Naval Research,

Army Ordnance Research Office, and Air Force Office of Scientific

Research and others in the area of research and development grants and

contracts.

On a scientific basis both EPA and CPSC could be in fundamental

agreement since the critical levels of human exposure to noise reported

here (see Chapters II and VI) come from those published by ONAC.^ In

regulating a mobile source that is used outdoors, measurements should

be made of the sound levels at the operator's ear and at a reference

distance to the side of the vehicle, so that one standard could satisfy

both community and consumer needs.

64
References

1. Consiamer Product Safety Act, Public Law 92-573, 1972.

2. Occupational Safety and Health Act of 1970, Public Law 9I-596.

3. Noise Control Act of 1972, Public Law 92-57^.

h. Identification of Products as Major Sources of Noise, Federal

Register 3^, 22297-22299 June 21, I97U.

5. Information on Levels of Environmental Noise Requisite to Protect

Public Health and Welfare with an Adequate Margin of Safety, U.S.

Environmental Protection Agency, Office of Noise Abatement eind

Control, March, 197^.

65
APPENDIX

PUBLISHED STANDARDS RELEVANT TO REGULATION OF SOUND OUTPUT

OF CONSUMER PRODUCTS

These standards fall into one or more of the following categories:

1. Principles of measurement of noise,

2. Procedure for determining sound power output of stationary

sources

,

3. Principles for preparation of test codes for measurement of

noise emitted by machines,

h. Industrial procedures for determining sound levels produced by

specific types of sound so\irces,

5- Specifications for acoustical measuring equipment, and

6. Procedures for measuring speech intelligibility.

Addresses of the organizations from which these standards can be

obtained appear at the end of the list of standards.

International Organization for Standardization (ISO)

ISO Recommendation R362. Measurement of Noise Emitted by Vehicles

(196M.

ISO Recommendation RU95. General Requirements for the Preparation

of Test Codes for Measuring the Noise Emitted by Machines (1966).

ISO Recommendation R220U. Guide to the Measurement of Acoustical

Noise and Evaluation of Its Effect on Man.

ISO Draft International Standard 2880. Determination of Sound Power

Emitted by Stationary Noise Sources in Reverberation Rooms. Part I: Broad Band Noise Sources.

ISO Draft International Standard 29^6. Determination of Sound Power

Emitted by Stationary Noise Sources in Reverberation Rooms. Part II:

Discrete-Frequency and Narrow-Band Noise Sources.

Draft Proposal for Determination of Sound Power Emitted by Stationary

Noise So\irces . Part V: Sources Operating in Laboratory Anechoic Rooms.

Draft Proposal for Reverberation Room Measurement of Sound From

Heating, Ventilating and Air Conditioning Equipment.

66
Draft Proposal for Determination of Sound Power Emitted by Stationary

Noise Sources. Part III: Engineering Methods Appropriate for Special

Reverberant Rooms

.

Draft Technical Report on Measurement of Noise with Respect to its

Effect on the Intelligibility of Speech.

International Electrotechnical Commission (lEC)

lEC Recommendation, Publication 123. Recommendations for Sound Level

Meters (196I).

lEC Recommendation, Publication 179 • Precision Sound Level Meters

(1965).

American National Standards Institute (ANSI)

AJISI BTl. 1-1972. American National Standard Safety Specifications for

Power Lawn Mowers , Lawn and Garden Tractors and Lawn Tractors

.

ANSI SI. 1-1960 (RI971). American National Standard Acoustical

Terminology.

ANSI SI. 2-1962 (RI971). American National Standard Method for the

Physical Measurement of Sound (Partially Revised by SI. 13-1971 and

by SI. 21-1972).

ANSI SI.U-I971. American National Standard Specification for Sound

Level Meters

.

ANSI SI. 5-1963 (RI97I). American National Standard Recommended

Practices for Loudspeaker Measurements.

ANSI SI. 13-1971. American National Standard Methods for the

Measurement of Sound Pressure Levels. (Partial revision of

SI. 2-1962)

.

ANSI SI. 21-1972. American National Standard Methods for the

Determination of Sound Power Levels of Small Sources in Reverberation

Rooms. (Revision of Section 3.5 of SI.2-I962.)

ANSI S3. 5-1969. American National Standard Methods for the Calciilation of the Articulation Index.

ANSI S3. 17-1972 (DRAFT). American National Standard Methods for

Rating the Sound Power Spectra of Small Stationary Noise Sources.

67
Society of Automotive Engineers (SAE)

SAE Recommended Practice Jl8U. Qualifying A Soiind Data Acquisition

System (1970).

SAE Recommended Practice J192a. Exterior Sound Level for Snowmobiles

(approved 1970, revised Nov. 1973).

SAE Recommended Practice J331. Sound Levels for Motorcycles (1973).

SAE Standard J952b. Sound Levels for Engine Powered Equipment (1969).

SAE Recommended Practice XJIOU6. Exterior Soiind Level Measurement

Procedure for Small Engine Powered Equipment (1973).

American Society of Heating, Refrigerating, and Air-Conditioning Engineers

(ASHRAE)

ASHRAE Standard 36-72. Methods of Testing for Sound Rating Heating,

Refrigerating, and Air-Conditioning Equipment (Supersedes ASHRAE

Standards 36-62, 36A-63, and 36B-63).

Air-Conditioning and Refrigeration Institute (ART)

ARI Standard Stajidard for Sound Rating of Room Fan-Coil AirConditioners (1970).

Air Moving and Conditioning Association (AMCA)

AMCA Standard 3OO-67. Test Code for Sound Rating.

Association of Home Appliance Manufacturers (AHAM)

AHAM Standard No. RAC-2SR. Room Air Conditioner Sound Rating (l97l).

National Machine Topi Builders Association (NMTBA)

NMBTA Technique. Noise Measiorement Techniques (1970).

Power Saw Manufacturers Association (PSMA)

PSMA Standard Nl.1-66. Noise Level.

PSMA Standard N2.1-67. Noise Octave Band Measurement.

PSMA Safety Specification for Gasoline Powered Chain Saws (Proposed) . Draft #3, November 1973.

68
Military Specifications

MIL-S-3151a, and Notice-1. Sound-Level Measuring and Analyzing

Equipment (196T).

International Snovmobile Industry Association (ISIA)

ISIA Draft Procediire for Measuring Snowmotile Operating Sound Levels

(1973).

U.S. Department of Agriculture, Forest Service, Equipment Development

Center (USDA-FSEDC)

USDA-FSEDC Equipment Development and Test Report 7120-5(197^+), Snowmobile Noise, Appendix II. Proposed Sound Level Standard and Winter

Test Procediire for Snowmobiles.

USDA-FSEDC, Development of a Noise Standard for the Oregon Dunes

National Recreation Area (1973), Appendix I. Proposed Sound Level

Standard and Test Procedure for Dune Buggies.

USDA-FSEDC, Motorcycle Noise (197^), Appendix II. Proposed Sound

Level Standard and Test Procedure for Motorcycles

.

Addresses

American National Standards Institute (ANSI)

IU30 Broadway

New York, New York IOOI8

(for ANSI, ISO and lEC Standards)

Society of Automotive Engineers (SAE)

Two Pennsylvania Plaza

New York, New York 10001

American Society of Heating, Refrigerating and Air-Conditioning Engineers

(ASHRAE)

3I45 East UTth Street

New York, New York 10017

Air-Conditioning and Refrigeration Institute (ARI)

1815 North Fort Meyer Drive

Arlington, Virginia 22209

Air Moving and Conditioning Association (AMCA)

30 West University Drive

Arlington Heights, Illinois 6000ii

69
Association of Home Appliance Manufactiarers (AHAM)

20 North Wacker Drive

Chicago, Illinois 60606

National Machine Tool Builders Association (NNfTBA)

7901 West Park Drive

McLean, Virginia 22101

Power Saw Manufacturers Association (PSMA)

13h 15th Street, N.W.

Washington, D.C. 20005

Military Specifications

Conmanding Officer

Naval Publications and Forms Center

5801 Tabor Avenue

Philadelphia, Pennsylvania 19120

International Snowmobile Industry Association (ISIA)

5205 Leesburg Pike

Falls Chvirch, Virginia 220Ul

U.S. Department of Agriculture, Forest Service

Equipment Development Center

San Dimas, California 91TT3

Reference

Jack M. Fath, Standards on Noise Measurements, Rating Schemes and Definitions

A Compilation, NBS Special Publication 386 (1973), U.S. Dept. of Commerce,

National Bureau of Standards, Washington, D.C. 2023^.

70
GLOSSARY

A-WEIGHTED SOUND LEVEL. See SOUND LEVEL.

ACOUSTIC REFLEX. The involuntary contraction of the muscles (stapedius

and/or tensor tympani) of the middle ear in response to acoustic or mechanical stimuli.

AMBIENT NOISE. The all-encompassing noise associated with a given

environment, being usually a composite of sounds from many soxirces near and far.

ARTICULATION INDEX (AI). A numerically calculated measure of the intelligibility of transmitted or processed speech. It takes into account

the limitations of the transmission path and the background noise. The

articulation index can range in magnitude between 0 and 1.0. If the AI is

less than 0.1, speech intelligibility is generally low. If it is above

0.6, speech intelligibility is generally high. See ANSI 33.5-1969-

BROAD-BAND NOISE. Noise whose energy is distributed over a broad

range of frequency (generally speaking, more than one octave).

BACKGROUND NOISE. The total of all noise interference in a system

used for the production, detection, measurement, or recording of a signal,

independent of the presence of the signal.

CONNECTED (CONTINUOUS) DISCOURSE. Continuous speech usually spoken

with little variation in intensity (or rapidity) and generally presented

by one speaker reading from several paragraphs of written material having

little emotional appeal or interest value.

DECIBEL. One tenth of a bel. Thus, the decibel is a unit of level

when the base of the logarithm is the tenth root of ten, and the queintities concerned are proportional to power.

71
Note 1: Exajnples of quantities that qualify are power (any

form), sound pressure squared, particle velocity squared, sound intensity,

soimd-energy density, voltage squared. Thus the decibel is a unit of

sound-pressure-squared level; it is common practice, however, to shorten

this to sound pressure level because ordinarily no ambiguity results from

so doing.

Note 2: The logarithm to the base the tenth root of 10 is the

same as ten times the logarithm to the base 10: e.g., for a number X*^,

2 2

log^Ql/lO X = 10 log-j^Q X = 20 log^Q. This last relationship is the one ordinarily used to simplify the language in definitions of sound pressure

level , etc

.

DOSE. The summed exposure (to sound) over a period of time.

EQUAL ENERGY HYPOTHESIS. Equal amounts of sound energy will cause

equal amounts of noise induced permanent threshold shift regardless of

the distribution of energy across time.

EQUIVALENT SOUND LEVEL. The level of a constant sound which, in a given situation and time period, has the same sound energy as does a time-varying sound. Technically, equivalent sound level is the level of

the time-weighted, mean square, A-weighted sound pressure. The time interval over which the measurement is taken should always be specified.

HEARING CONSERVATION. Those measures which are taken to reduce the

risk of noise-induced hearing loss.

HEARING LEVEL (HEARING LOSS, HEARING-THRESHOLD LEVEL). The amount,

in decibels, at a specified frequency by which the threshold of audibility

for that ear exceeds a standard audiometric threshold.

INVERSE SQUARE LAW. In a free field (no reflections) the Intensity

of a point source of sound decreases inversely with the square of the

distance from the source.

LEVEL. The logarithm of the ratio of a quantity to a reference

quantity of the same kind. The base of the logarithm, the reference

quantity, and the kind of level must be specified.

72
MASKING. The process by which the threshold of audibility for one soimd is raised by the presence of another (masking) sound. Masking as a generic term refers to the reduction in performance to one sound as a result of the introduction of a second sound. Reduction in performance may

be expressed as a shift in threshold acviity but also, by extension, as reduced speech reception. . .and so forth, whenever the signal to be responded

to is admixed with some other sound in a more or less favorable ratio.

NARROW-BAND NOISE. A relative term describing the pass-band of a filter or the spectral distribution of a noise. Note: The term frequently

implies a bandwidth of 1/3 octave or less (cf. Broad-band noise).

NOISE. Any undesired sound. By extension, noise is any unwanted disturbance within a useful frequency band, such as landesired electric waves

in a transmission channel or device. Noise is an erratic, intermittent,

or statistically random oscillation.

Note 1: If ambiguity exists as to the nature of the noise, a phrase such as "acoustic noise" or "electric noise" should be used.

Note 2: Since the above definitions are not mutually exclusive,

it is usually necessary to depend upon context for the distinction.

NOISE EXPOSURE. The cijmiilative acoustic stimulation reaching the

ear of the person over a specified period of time (e.g., a work shift, a day, a working life, or a lifetime).

NOISE EXPOSURE PATTERN. The various sound intensities and their

durations that may be encountered throughout daily living.

NOISE-INDUCED HEARING LOSS. (Noise-Induced Permanent Threshold

Shift.) The cumulative permanent hearing loss that is due to repeated

exposure to intense noise.

NOISE-TIME FRACTION. The fraction of time that a noise is presented

during a given time period.

OCTAVE. The interval between two sounds having a basic frequency

ratio of two. Note: The interval in octaves, between any two frequencies,

is the logarithm to the base 2 of the frequency ratio.

73
PEAK SOUND PRESSURE. The maximum absolute value of the instantaneous

sound pressure in that interval. Note: In the case of a periodic vave,

if the time interval considered is a complete period, the peak sotmd

pressTire becomes identical with the maximum sound pressure.

PHONETICALLY BALANCED WORD LIST. A list that includes words containing a distribution of speech sounds that approximates the distribution of

the same sounds as they occur in conversational American English.

RANDOM NOISE. An oscillation whose instantaneous magnitude is not

specified for any given instant of time. The instantaneous magnitudes of

a random noise are specified only by probability distribution functions

giving the fraction of the total time that the magnitude, or some sequence

of magnitudes, lies within a specified range. Note: A random noise whose

instantaneous magnitudes occur according to the Gaussiaji distribution is

called "Gaussian random noise."

REVERBERANT FIELD. In an average enclosed room close to the sound

source the sound-pressxire level tends to vary with the distance from the

source as it does under free-field conditions. This region is sometimes

called the near field. Far from the source the sound-pressiire level becomes independent of the directivity and the distance to the source. This

region is called the reverberant or far field. Here the level is determined

by the acoustic power radiated by the source and the acoustic characteristics of the room. The region over which the transition between the

free-field behavior and the reverberant field occurs is determined by the

directivity factor and the room constant.

SOUND. An oscillation in pressure, stress, particle displacement,

particle velocity, etc., in a mediijm with internal forces (e.g., elastic,

viscous), or the superposition of such propagated oscillations. Sovmd is an auditory sensation evoked by the oscillation described above.

SOUND INTENSITY (SOUND-ENERGY FLUX DENSITY) (SOUND-POWER DENSITY).

In a specified direction at a particular point, the average rate of soxind

energy transmitted in the specified direction through a unit area normal

to this direction at the point considered.

7A
Note 1: The sound intensity in any specified direction, a, of

a soirnd field is the soiind-energy flux through a unit area normal to that

direction. This is given by the expression

1 rT a T ^ 0 ^ a

where

r = an integral number of periods or a time long compared to a period

p - the instantaneous sound pressure

y

^ - the component of the instantaneous particle velocity in the direction a

t = time.

Note 2: In the case of a free plane or spherical wave having the

effective so\md pressure, p, the velocity of propagation, c, in a medium

of density, p , the intensity in the direction of propagation is given by:

2

P c

SOUND LEVEL. A weighted sound pressxare level, obtained by the use of

metering characteristics specified in ANS Standard Specification for General

Purpose Sound Level Meters, SI.U-196I. In this report only A-weighted sound

level is used. The ear does not respond equally to frequencies, but is less

sensitive at low and high frequencies than it is at middle or speech-range

frequencies. The A-weighted network weights the sound frequencies approximately as the ear does at medi\am sound pressure levels.

SOUND PRESSURE LEVEL. Sound pressure level, in decibels, of a sound

is 20 times the logarithm to the base 10 of the ratio of the pressure of

this sound to the reference pressure. The reference pressure should be

explicitly stated.

Note 1: The standard reference pressure is 20 micropsiscals per

square meter for sound in gases and is the reference pressure used in this

report

.

75
Note 2: Unless otherwise explicitly stated, it is to be understood that the soiind pressiire is the effective (root-mean-square) sound

pressure.

SPECTRUM. A description of the resolution of a f\inction of time into

components, each of different frequency and (usually) different amplitude

and phase. "Spectrum" is also used to signify a continuous range of com- ponents, usually wide in extent, within which waves have some specified

common characteristic; e.g., "audio-frequency spectrum."

THRESHOLD OF AUDIBILITY. The minimum effective sound pressure level

of a signal that evokes an auditory sensation in a specified fraction of

the trials.

THBESHOLD OF FEELING (or Tickle). The minimiom so\ind pressure level

at the entrance to the external auditory canal which, in a specified fraction of the trials, will stimialate the ear to a point at which there is a sensation of feeling that is different from the sensation of heetring.

'. THRESHOLD OF DISCOMFORT. The minimum effective sound pressure level

of that signal which, in a specified fraction of the trials, will stimulate the ear to a point at which the sensation of feeling becomes

xincomfortable

.

THRESHOLD OF PAIN. The minimum effective sound pressure level of

that signal which, in a specified fraction of the trials, will stimulate

the ear to a point at which the discomfort gives way to definite pain

that is distinct from mere non-noxious feeling of discomfort.

WHITE NOISE. A noise whose spectrum density (or spectrum level) is

substantially independent of frequency over a specified range. Note:

White noise need not be random.

USCOMM NBS DC 76
U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 74-606

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Consumer Product Noise: A Basis for Regulation

5. Publication Date November 1974

6. Performing Organization Code

7. AUTHOR(S)

Pearl G. Weissler, Gerald A. Zerdy, Sally G. Revoile

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 2130113

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

Bethesda, Maryland 20014

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) The Consumer Product Safety Commission is charged with the responsibility for

promulgating safety standards to protect the public against unreasonable risks of

injury associated with consumer products. There is a risk of injury from noisy

products, directly by damage to hearing and indirectly by degradation of essential

speech communication. This report develops criteria relevant to the specification

of Safety Standards for noisy consumer products. Consumer product noise is discussed

in relation to the existing body of knowledge regarding noise induced hearing loss

and speech communication. Levels of product noise are identified that should protect

against hearing impairment and against speech communication degradation. Methods of

measurement for consumer product noise are described and a bibliography of standards

relevant to the regulation of noisy consumer products is provided. A list of products

that are potentially hazardous to the hearing of the operator is included with typical

levels and usage patterns. The list is based upon reported data and some measurements

made at NBS. Possible discrepancies among noise regulations established by different

governmental agencies are discussed with suggestions for obtaining uniformity.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Consumer products; criteria for safety standards; federal regulations; hearing

impairment; hearing survey; noise emission; speech communication interference.

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(THIS REPORT)

21. NO. OF PAGES

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