NAT'L INST. OF STAND & TECH

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i

^^^^ ^o, NBS

\l PUBLICATIONS

' CO NBS SPECIAL PUBLICATION 499

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards
NATIONAL BUREAU OF STANDARDS

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WATIONAli BTJREATJ OP STANDARDS

lilBRARV

^ FEB 8 1978

f9 Noise Criteria for Buildings: R Critical Review

Simone L. Yaniv

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

and

Daniel R. Flynn

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

The work presented in this report has been partially supported by the Environmental Protection Agency;

however, the content and conclusions included are solely the responsibility of the National Bureau of

Standards.

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

U. S NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued January 1978
Library of Congress Cataloging in Publication Data

Yaniv, Simone L. Noise criteria for buildings. (NBS special publication ; 499) Supt.ofDocs.no.: €13.10:499

1. Noise. 2. Soundproofing. 3. Architectural acoustics. I. Flynn, D.

R., joint author. II. Title. III. Series: United States. National Bureau

of Standards. Special publication ; 499. QC100U.57 no. 499 [TD892] 620.2'3 77-18709

National Bureau of Standards Special Publication

Nat. Bur. Stand. (U.S.) Spec. Publ. 499, 82 pages (Jan. 1978) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1978

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402

Stock No. 003-003-01870-8
CONTENTS

Page

1, Introduction 1

2, Assessment of Environmental Noise: Applicability of Various

Rating Schemes to Building Regulations ^

2.1 Rating Schemes Based Upon One Aspect of Human Response . . 3

2.1.1 Loudness 3

2.1.2 Noisiness o 5 2.1.3 Speech Interference 7

2.2 Rating Schemes Based Upon Several Aspects of Human

Response 11

2.2.1 Combined Speech Interference and Loudness 11

2.2.2 Community Response ,.o 16

3, Specification of Noise Isolation in Buildings: Evaluation of

Technical Bases Underlying Current Practices 20

3.1 "Isolation" versus "Insulation" 20

3.2 The Grading Curve for Indoor-to-Indoor Isolation 21

3.2.1 Origin , . o 21

3.2.2 Evidence from Social Surveys 22

3.2.3 Evidence Based Upon Consideration of Loudness

and Noisiness 26

3.2.4 Conclusions Concerning the Grading Curve 37

3.3 Weighted Level Differences 39

4. Isolation Ratings for Buildings: Dependence Upon Indoor Noise

Criteria and Upon Source Spectrum 41

5. Significance of Temporal Variations on Building Noise Rating

Procedures 55

6. Contribution of Outdoor Sources to the Indoor Noise

Environment 58

References 66

iii
LIST OF FIGURES

Page

Figure 1. One-third octave band spectrum, as published, compared

with that computed from spectrum level, as published,

in the current American National Standard for the

calculation of the Articulation Index {32] 12

Figure 2, Noise Criteria curves [52] 14

Figure 3. Speech Communication curves [46] 15

Figure 4. Preferred Noise Criteria curves 151] 18

Figure 5. Percentage of time that a given peak level is exceeded

in radio programs, for various octave bands [92]. ... 27

Figure 6. Required isolation, according to van den Eijk, in

order that peak levels due to a neighbor's radio

not exceed 0 phon for more than the specified

percentage of the time [92] 28

Figure 7, Required isolation, according to van den Eijk, in

order that peak levels due to a neighbor's radio

not exceed 20 phon for more than the specified

percentage of the time [92] . n... 30

Figure 8. Increase in loudness level with increase in number

of octave bands, when each octave band, taken

alone, has the same loudness level. . . . , 31

Figure 9. Noise isolation requirements based on loudness versus

those based on annoyance, both compared with German

Soll-Kurve (see text) 33

Figure 10. Noise isolation required to reduce "standard

household noise" to a level, in the receiving

room, corresponding to an NC-25 contour [96] 35

Figure 11. Comparison among several reference curves used

or proposed for use in rating partitions 38

Figure 12. Noise isolation required in order that the sound in

the receiving room, due to radio programs in the source room, shall not produce, for more than ten

percent of the time, a computed sensation in excess

of that produced by an octave band of noise centered

at 1 kHz and having a sound pressure level of 40 dB

(re 20 yPa) . The several curves correspond to the use of different procedures to rate the noise

environment in the receiving room. 42

iv
Figure 13. Normalized spectra of selected indoor noise sources . . ^3

Figure 14. Normalized spectra of selected outdoor noise sources . . 44

Figure 15. Alternative receiving room spectral shapes used to

derive noise isolation curves for the various noise

sources shown in Figures 13 and 14 (see text) 45

Figure 16. Shape of noise isolation curves required, for

standard household noise, to maintain in the

receiving room the spectral shapes shown in

Figure 15 47

Figure 17. Shape of noise isolation curves required, for average

speech spectrum, to maintain in the receiving room

the spectral shapes shown in Figure 15 48

Figure 18. Shape of noise isolation curves required, for food

blender, to maintain in the receiving room the

spectral shapes shown in Figure 15 49

Figure 19. Shape of noise isolation curves required, for traffic

noise, to maintain in the receiving room the spectral

shapes shown in Figure 15 „ 50

Figure 20. Shape of noise isolation curves required, for train

noise, .to maintain in the receiving room the spectral

shape shown in Figure 15 o 51

Figure 21. Shape of noise isolation curves required, for aircraft

approach, to maintain in the receiving room the

spectral shapes shown in Figure 15 52

Figure 22. Shape of noise isolation curves required, for aircraft

take-off, to maintain in the receiving room the

spectral shapes shown in Figure 15 53

Figure 23. Hourly average A-^eighted level differences required

to maintain an indoor noise environment corresponding

to a PNC-35 contour (approximately an A-weighted

Day-Night Average Level of 45 dB) for the hourly

traffic densities shown in the upper figure (see

text) 56

Figure 24. Daytime (0700-2200 hours) indoor versus outdoor

average A-weighted sound levels (L ) for twelve

sites 59

V
Figure 25. Nighttime (2200-0700 hours) indoor versus outdoor

average A-weighted sound levels (L ) for twelve

sites 60

Figure 26. Evening (1900-2200 hours) indoor versus outdoor

average A-welghted sound levels (L ) for twelve

sites 61

Figure 27. Late night (0100-0500 hours) indoor versus outdoor

average A-weighted sound levels (L ) for twelve

sites 62

LIST OF TABLES

Page

Table 1. Long-term, Root-Mean^Square Speech Levels of Male

Speakers, Corrected to a Distance of One Meter in

Front of the Lips 10

Table 2. Outdoor-to-Indoor Noise Isolation Required (in dB)

to maintain a PNC-35 or an L of 45 dB Indoors

as a Function of Frequency and of Time of Day 57

Table 3. Comparison of Outdoor and Indoor Sound Levels for a Set of 12 Sites Located in Urban Residential Areas

Away from Major Outdoor Noise Sources 63

vi
ABSTRACT

A review is given of existing criteria that could be applied to

rating the noise environment in dwellings, to rating noise isolation

between dwellings, and to rating noise isolation from outside to inside a dwelling. It is concluded that the central problem is to select

appropriate criteria for rating the interior noise environment. Once this

is done, criteria for noise isolation can be derived directly and these in

turn can be used to derive performance requirements for building elements,

such as partitions and exterior walls.

Key words: Building acoustics; building codes; isolation; noise; noise

criteria; rating scheme; sound transmission.

vii

1. INTRODUCTION

The major function of human shelter is to provide a better

environment than that to which people would otherwise be exposed. In

order to enjoy the advantages of an improved environment, most people

spend a large amount of their time indoors. While the majority of

buildings provide adequate protection from heat and cold, wind and rain,

many buildings do not provide a good acoustical environment. Noises heard

indoors are a major aspect of the overall noise problem.

Although noise can be a serious problem in almost any type of

building, the present report is focused primarily upon dwellings. Noise

heard in a dwelling can originate from within that dwelling, from within a neighboring dwelling, or from outdoors. Provision of an acceptable

acoustical environment within a dwelling can be accomplished through

quieting of noise sources, through provision of noise isolation from those

sources, or through a combination of these two approaches. Thus attention

could be directed to any or all of the noise control options shown in the

following table:

1 Quieting

of Sources

Provision of

Noise Isolation

Within one's dwelling

Within a neighboring dwelling

Outdoors

Within a dwelling

Between dwellings

Outdoor-to -indoor

Current regulatory activities are focused primarily on quieting of

outdoor sources. Quieting of indoor sources has been mainly sporadic and

only in response to marketplace economics. However, regulatory actions,

e.g., mandatory labeling requirements for household products, are now

being considered by the U.S. Environmental Protection Agency.

In recent years there has been an increase in the number of building

codes, within the U.S., that specify noise isolation between dwellings.

However, the U.S. is still far behind most European countries in this area

of regulation.

There have been essentially no regulatory actions concerning the

provision of noise Isolation within dwellings

.

Recently, the California Administrative Code incorporated provisions

that effectively specify, for new multifamily dwellings, outdoor-to-indoor

noise isolation in areas having high outdoor noise levels. Other than

this single case, there appear to have been no regulatory requirements on

outdoor-to-indoor noise isolation in the U.S.

1
The noise environment within a dwelling results from sounds

propagating along various paths from various sources. If criteria are established as to what constitutes an acceptable interior noise en- vironment, it is rather straightforward to then derive either criteria for

isolation from a given noise source or criteria for quieting a source so as to be compatible with a given noise isolation. In the present report,

attention is confined to considerations of criteria for rating the

interior noise environment and criteria for rating noise isolation.

Various procedures for rating human response to environmental noise,

and their applicability to building codes, are reviewed in Section 2.

Prior work on rating noise isolation is reviewed in Section 3. The

interactions between noise isolation rating procedures and interior noise

rating procedures are explored further in Section 4. The need to consider

the temporal variation of noise, when specifying noise isolation, is

briefly examined in Section 5. Section 6 includes a brief look at the

relationship between outdoor and indoor noise levels for dwellings that

are not near major outdoor noise sources.

2
2. ASSESSMENT OF ENVIRONMENTAL NOISE: APPLICABILITY OF VARIOUS

RATING SCHEMES TO BUILDING REGULATIONS

People respond to their acoustical environment as a whole and not to

the noise isolation of a particular structure or to the characteristics of

a particular Intruding noise. Thus, noise researchers must find a practical rating scale for assessing the entire interior acoustical

environment from the standpoint of building users. If agreement can be

reached on a scale, the degree of noise isolation needed to achieve a desired environment may be inferred.

People's reactions to noise depends upon the physical nature of the

noise as well as social and economic factors. Even in a given

socio-economic situation, different individuals may react differently to

the same noise. For this reason, ratings of noise are needed which can predict with a reasonable degree of certainty the average response of

groups of people.

2.1 Rating Schemes Based Upon One Aspect of Human Response

Human responses to noise are dependent upon three primary parameters

of the noise: its sound level, its frequency spectrum, and the variations

of both of these quantities with time. For a practical description of the

noise, these three parameters are combined into a "single number" rating

on a psychophysical scale which relates these noise parameters to the

subjective response.

The selection of a particular psychophysical scale depends upon which

aspects of human response are considered important for a given problem

(e.g., loudness, noisiness, interference with speech communication, or interference with sleep). Presently, this selection is based upon

judgment, owing to an incomplete understanding of the basic parameters

affecting human response. Thus, numerous scales exist, reflecting

idiosyncrasies of researchers and the diversion of goals responsible for

development of a particular scale.

The "dose-response" relationship between the various noise

environments encountered in buildings and the responses of building

occupants must also be quantitatively established. A scale describing

this dose-response relationship could be used to establish a criterion for

noises that are judged undesirable or unacceptable.

2.1.1 Loudness

Much research conducted within the last 50 years has focused upon

combining the frequency content and overall sound level of the noise into

a metric related to the perceived magnitude (e.g. , loudness) of the noise.

Although investigators disagree as to the details of the function

relating the loudness experienced and the sound level of the noise, there

appears to be a general consensus regarding the form of the function.

Loudness is generally thought to grow as a power function of sound

3
pressure level [1-3]— . In practical terms, each time a sound level is

increased by 10 dB, the loudness experienced increases by approximately a factor of two.

Furthermore, the human ear is not equally sensitive to sounds of

different frequencies. The relative sensitivity of the ear at various

frequencies has usually been studied by determining the sound pressure

level required for a given sound to give rise to the same loudness

sensation as that produced by a reference sound at a prescribed sound

level. Data from these studies are typically shown as a series of

equal-loudness contours which indicate the intensities at which sounds of

different frequencies produce similar loudness experiences.

Equal loudness contours have been determined in the laboratory under

well-controlled conditions for pure tones [4-8] and for bands of noise

19] . Traditionally, contours have been developed with a reference sound

which has been either a 1000 Hz tone or a noise band centered at 1000 Hz.

Results of studies of the kind described show that a person is most

sensitive to sounds at frequencies between approximately 500 and 6000 Hz.

That is, for a very broad-band noise the middle region of the audible

frequency range contributes most to the sensation of loudness. However,

results also demonstrate that as the sound pressure level of a sound

increases from moderate to high levels, the relative contributions of low

and high frequencies to the loudness perception increase until they equal

that of mid-frequencies at very intense sound levels.

In order to compensate for the differential frequency sensitivity of

human hearing, sound level meters are designed to weight the overall spectrum of the noise in such a way as to approximate the measured

loudness-versus-frequency response of the ear. That is, when a sound is

passed through the various networks of the sound level meter, each

frequency region in the noise contributes to the total reading by an amount approximately corresponding to the subjective weighting of that

frequency.

To take into account the findings that the frequency response of

hearing varies with the overall sound level of the noise, three electronic

networks are included in most meters. The A, B, and C networks were originally intended to represent the response of the ear to low, moderate

and high intensities, respectively. However, over the years it has become

apparent that the A-weighted sound level is a relatively good predictor of

human response to broad-spectrum environmental noise [10-11] at all

levels. For this reason, the A-weighted level is emerging now as the most

widely used network when measurements are made with a sound level meter.

—^Numbers in brackets refer to the literature references at the end of

this report.

4
The A-weighted sound level is only an approximate predictor of human

response. For this reason, various investigators have attempted to

improve the accuracy of prediction by using more detailed computation

schemes. These schemes have become increasingly complex as more

parameters relating to human response became known from further investigations ,

Generally, refined schemes are based on a segmentation of the sound

pressure spectrum of a noise into a series of contiguous frequency bands

by means of electrical networks to analyze the distribution of sound

energy over the audible frequency range. From data thus obtained,

"loudness level" can be estimated by first assigning to each frequency

band a loudness index designed to represent the potential contribution to

the perceived loudness of the band. This index is then corrected by

applying a weighting factor to account for the fact that bands with higher

loudness indices may inhibit (or mask) the contributions of other bands.

The weighted loudness indices are summed to estimate the overall loudness

of the noise. A number of variants to this general approach are now

available [12-21].

All of these procedures are complex. It is doubtful, therefore, that

they would be practical for incorporation into building codes. Moreover,

in most investigations comparing the A-weighted sound level performance to

the more complicated schemes, it is found that the A-weighted sound level

performs essentially as well as the more complicated methods in rating the

noise environment with respect to human reactions [10-11, 22-24].

2.1.2 Noisiness

Kryter [25-29] has indicated that in many noise control problems it

is not how loud a sound is that concerns us most, but rather how noisy and

unwanted it is. Inherent in this statement is the assumption that

loudness and noisiness are two distinguishable, although related,

attributes of the human response to noise.

Kryter *s findings were chiefly the outcome of a series of laboratory

investigations of subjective response to aircraft noises. In these

studies, ratings based on jury judgments of propeller and jet aircraft

noises were compared to ratings based upon computed loudness levels.

These comparisons indicated that the computed loudness consistently

underestimated the noisiness or unwantedness of jet aircraft noise.

In another series of investigations by Kryter, loudness contours and

noisiness contours for bands of noise and for pure tones were established,

and then compared. These contours were determined by requiring subjects

to equate (in terms of both loudness and noisiness) bands of noise and

pure tones to a standard stimulus (typically an octave band of noise

centered at 1000 Hz) . The results of these studies indicated that

subjects gave different responses depending upon whether they were

matching the experimental stimuli for equal loudness or equal annoyance.

5
For example, at some frequencies perceived noisiness contours were as much

as 5 to 10 dB lower than corresponding loudness contours. Kryter

concluded that these findings were indicative of the fact that annoyance

and loudness are indeed two distinct attributes of human response.

Stevens [14] maintained that there was no conclusive evidence of a significant difference between loudness and noisiness as far as frequency

weighting is concerned.

Kryter 's findings led to the development of a new scale for assessing

noise called Perceived Noise Level (PNL) . This method is basically

modeled after Steven's methodology [16] for calculating loudness. Thus,

as in the computational procedures for loudness, the band levels are measured, then weighted indices are applied, and results summed up to

arrive at a single number index. However, instead of assigning loudness

indices to each measured band level, a perceived noisiness index is

assigned. The unit of perceived noisiness is the noy and values are obtained from contours of equal perceived "noisiness"

.

Since it was originally proposed, the PNL methodology has been

further altered to account for discrete frequency components of tones

associated with aircraft noises as well as for the fact that, everything

else being equal, aircraft flyovers of long duration are more annoying

than flyovers of short duration [27, 29]. These developments are embodied

in a rating procedure known as the Effective Perceived Noise Level (EPNL)

[26].

In the computations of noisiness, the same assumptions and

mathematical derivations were utilized as in the scales based on loudness.

The only exception, as noted above, is that the loudness concept is

replaced by that of annoyance. Furthermore, as in the development of

methods based on loudness, those based on annoyance were chiefly derived

from laboratory investigations with relatively few types of sounds.

Very recently, the "D-weighting network" has been standardized [30]

for use in sound level meter measurements of aircraft noise. The

D-weighting network has a frequency response that approximates the shape

of the inverted 40 noy contour (which corresponds to a Perceived Noise

Level of approximately 93 dB) . Sound level meters do not sum contributions from different frequency regions in the same manner as is

called for in the procedure for computation of the Perceived Noise Level.

However, readings from a sound level meter using a D-weighting network

generally agree (within a known additive correction) reasonably well with

calculated Perceived Noise Levels, at least for sounds that lie in the

range of, say, 80 to 100 dB SPL. Because of the high levels for which the

D-weighting is intended, and because at present its use is normally

restricted to outdoor aircraft noise measurements, it will not be

considered further in this report as a candidate for use in building noise

criteria.

6
2.1.3 Speech Interference

One of the most widely recognized effects of noise is the

interference with auditory communication. Speech interference is one of

the most annoying consequences of noise; thus there has been considerable

interest in developing procedures to rate the acoustical environment in

terms of its potential for interfering with speech.

The determination of criteria based on speech communication may

include consideration of three factors:

(1) the vocal sound level, as a function of frequency and time,

exerted by various speakers under various conditions;

(2) the degree of speech recognition in the presence of various

types of noise; and

(3) the definition of acceptable speech communication for both

speaker and listener.

Speech can be analyzed into a finite number of sounds which differ

from one another in terms of their total sound levels duration of build-up

and decay, and the distribution of sound level with respect to frequency.

For example, the vowels as a group carry relatively large amounts of

energy, distributed into harmonics of the fundamental frequency of the

voice. These harmonics have distinguishable frequency regions which

differ for each vowel. The consonants, on the other hand, carry much less

energy, but the little energy that they do carry is found in higher

frequency regions and over shorter durations than for the vowels.

The frequency range of speech extends from 100 to 6000 Hz. However,

most of the information contained in speech is carried by the consonants,

which, because they carry little energy, are easily masked.

As one speaks, the various basic sounds are combined into orderly

sequences of phonemes to form syllables, which themselves are arranged

into words and sentences. The result is an acoustical signal which

undergoes rapid fluctuations with respect to sound level and frequency.

In order for a listener to understand speech he must be able not only to

detect the various sounds, but also to integrate and recognize the

constantly shifting patterns.

When noise is present, some of the sounds and their shifting patterns

are lost, and the speech becomes more difficult to interpret. As a result, speech intelligibility deteriorates in proportion to the sound

level and bandwidth of the noise relative to those of the speech signal.

Observations such as the above were the basis for the Articulation

Index, developed by French and Steinberg [31] as a means of estimating

speech intelligibility from a knowledge of speech and noise spectra. This

index represents a measure of the portion of speech which is available to

the listener when communication occurs in a noisy system. In effect the

7
Articulation Index takes into account the sound level differential (i.e.,

signal-to-noise ratio) between speech and noise in 20 contiguous bands

extending from 200 to 6000 Hz which, under optimal conditions, would

contribute equal amounts to the Articulation Index.

The assumptions underlying the Articulation Index can be summarized

as follows:

e the total variation in intensity levels of successive speech

sounds is constant throughout each frequency region and roughly

equal to 30 dB;

• the relative occurrences of intervals of different intensities

are roughly identical for each frequency region;

• average (1/8-second) peak levels of single speech phonemes

exceed the long-term average of the speech levels by about 12 dB

for 10 percent of the time.

The Articulation Index, as originally proposed, requires frequency

analysis in bands that are not readily measurable by available

instrumentation. The standardized version [32] of the Articulation Index

includes alternate procedures based on one-third octave or octave-band

spectra.

The Articulation Index is based upon, and has been principally

validated against, intelligibility tests involving adult male talkers and

trained listeners 133]. Thus, the method cannot be assumed to apply to

situations involving female talkers or children. Moreover, it estimates

speech intelligibility in the presence of steady-state noise and contains

provisions for predicting the effect of noise having a definite duty

cycle. It does not purport to estimate the intelligibility of speech in

the presence of fluctuating noise levels. Therefore, the Articulation

Index must be used with caution in estimating speech interference in

ordinary home and work situations. Finally, the complexity of the

calculation procedure required to obtain the Articulation Index limits its

usefulness for the measurement and monitoring of noise levels on a routine

basis

.

The Speech Interference Level (SIL) , which is being proposed as an American National Standard, is a simple numerical method for estimating

the speech-interfering aspects of noise based on physical measurements of

the noise. Unlike the Articulation Index, SIL does not include specific

consideration of the level and spectrum of the speech. Rather it employs

a table or a nomograph for estimating, in terms of general voice level and

distance between communicators, the noise levels which will seriously

restrict speech communication.

Originally, the Speech Interference Level, SIL, was defined [34] as the arithmetic average of the sound pressure levels in the three octave

bands: 600 to 1200, 1200 to 2400, and 2400 to 4800 Hz. In terms of the

8
new, or preferred, band-center frequencies [35] several definitions have

been considered, two of which are worthy of note: (1) the

"preferred-frequency speech interference level", PSIL, which is the mean

level of the octave band levels centered on 500, 1000, and 2000 Hz, and

(2) the speech interference level, SIL(0.5^4), defined as the mean level

of the octave band levels centered on 500, 1000, 2000 and 4000 Hz. This

latter is the version being considered for adoption as an American

National Standard.

For steady-state noises, either version of the Speech Interference

Level is a reasonable predictor of the relative ranking of noises with

respect to their speech-interfering properties. That is, two noises which

are equally-interfering with speech communication will have very similar

Speech Interference Level ratings (typically within 5 dB) . Speech

Interference Level can be used for rough, quantitative estimation of

monosyllabic word intelligibility in the presence of continuous, random

noise. However this procedure is not appropriate for noise spectra with

considerably more energy at high frequencies than at low frequency, or when any of the following conditions exist: (1) the level of the noise is

not of a continuous-in-time, steady-state nature; (2) the frequency

spectrum of the noise is not constant with time; and (3) the speech and

noise are subject to perceptible echo or reverberation.

Webster and Klumpp 124] have developed charts which can be used to

estimate the voice level and maximum allowable distance between talker and

listener for satisfactory face-to-face communication as limited by ambient

noise levels having various values of Speech Interference Level. For many

types of noise, the Speech Interference Level can be approximated by the

A-weighted sound level [10] . Because the A-welghted sound level can be

read directly from a sound level meter, it is an easier measure to obtain

than SIL.

While both the Articulation Index and the Speech Interference Level

can be extremely useful, there is a need to develop predictive techniques

for speech interference with male and female speakers, both adult and

child, and untrained listeners in real situations, rather than in the

laboratory. Consideration should also be given to the additional problems

for listeners suffering from impaired hearing. Statistical predictors

that take into consideration the speech-interference aspects of

fluctuating noises, such as those produced by traffic, are also needed.

The data base regarding speech levels embodied in the speech interference schemes comes from a very limited set of measurements. The total

number of talkers on which present criteria are based is surprisingly

small (total 35 subjects). In addition, most of the data relate to male

speakers and none are available on children's speech.

Crandall and McKenzie [36] used 5 male speakers; Dunn and White [37]

studied the speech of 6 males and 5 females; Rudmose, Clark, Carlson,

Eisenstein and Walker [38] used 7 males; Stevens, Egan and Miller [39]

9
studied speech from 1 male and 1 female speaker; Benson and Hirsh [40]

used 5 males and 5 females; and Pickett and Pollack [41] used 5 males.

Other speech data found in the literature are traceable to the works

already mentioned.

One of the most consistent findings among the studies noted above is

the great variability among speakers. For example, Dunn and White report

sound power level differences among speakers of the same sex of the order

of 18 dB in some frequency regions, while Rudmose et a^-- report differences of the order of 10 dB. However, as observed by Galloway [42],

when the data contained in the various papers are analyzed in terms of

band levels relative to overall levels, the variability of any given band

is reduced to about 4-5 dB. Thus, one may conclude that while speakers

vary as to their power output, the various band levels relative to the

overall level are fairly stable from one study to the next. However, the

total speech power output is an important determinant of the amount of

sound energy available to the listener for interpretation.

There are some discrepancies among the data of various researchers in

terms of both the level of speech and the form of the spectrum during

"normal conversational speech." For example, Dunn and White report a concentration of energy in the 500 Hz region in male speech; this does not

appear in the Benson and Hirsh data and is somewhat ambiguous in the

Rudmose et al. data.

In addition, Dunn and White report 66 dB (re 20 yPa) as the normal

conversational level of speech at one meter for male subjects. This

figure agrees well with the data of Rudmose e^ al . , in which a value of 68

dB is reported (when computed from their reported sound power level) but

disagrees with the value of 57 dB reported by Benson and Hirsh.

The reported overall long-term, root-mean-square sound pressure level

of normal male speech has varied among studies and among individual

speakers within a given study, as indicated by the results shown in Table

1.

Table 1. Long-Term, Root -Mean-Square Speech Levels of Male Speakers,

Corrected to a Distance of One Meter in Front of the Lips

Investigators Sound pressure level, re 20 yPa, dB

Mean of Subjects Max Subject Min subject

Dunn and White [37] 66 70 60

Rudmose et al. [38] 68 72 60

Benson and Hirsh [40] 57 57 56

i

10
Since the total niimber of subjects on which the data are based is

very small, and the variations among subjects are very large, it is

impossible to assess the significance of the differences found among the

various studies, both with respect to actual value and to spectral shape.

In addition, some inconsistencies appear to be present in the speech

spectra given in the American standard for computing the Articulation

Index [32]. Specifically, if one uses the spectrum level (i.e., the level

corresponding to a 1-Hz bandwidth) given in that standard for use in

conjunction with the "20-band method" to compute the equivalent 1/3-octave

band spectrum, differences ranging from 2-5 dB between the 20-band and the

third-octave spectra exist at frequencies above 1000 Hz as shown in Figure

1. Since both spectra are derived from the same data, and since both are purported to represent voice level during normal conversational speech,

there should not be any difference between the two spectra.

An additional problem is associated with the speech data upon which

all speech criteria rest. As observed by Galloway [42], in the development of the Articulation Index and other methodologies, only the data of

Dunn and White were available to define the statistical distribution of

speech level. Furthermore, since the Dunn and White data appeared to

suggest that the statistical distribution of speech levels was similar in

all bands for both male and female speakers, only the data of the 1000 to

1400 Hz band obtained on male subjects were used in the development of the

Articulation Index. Thus, present speech criteria are traceable to only

one study of the statistical distribution of speech levels done 35 years

ago and rests upon the data obtained on only 6 male subjects in a frequency range between 1000 and 1400 Hz!

Although Kryter [33] provides comparisons of predicted and measured

intelligibility of speech in the presence of widely different noise

spectrum shapes and various signal-to-noise ratios, his data validate the

Articulation Index method only for continuous spectra and for male

speakers. Since it is reasonable to assume that in most households women

and children do talk (some would even say too much) it is unlikely that one could justify a design goal for dwellings on the basis of data that

excludes all such persons

.

2.2 Rating Schemes Based Upon Several Aspects of Human Response

2.2.1 Combined Speech Interference and Loudness

In an effort to "bridge the gap" between schemes developed chiefly

from laboratory investigations and the real life situations associated

with the experience gained by the consultant working in the field, Beranek

[43] proposed the Noise Criteria Curves (JSIC) which embody considerations

of both loudness and interference of noise with speech communication. The

Noise Criteria curves represent, as far as is known to the present

writers, the first attempt to arrive at criteria based upon both

laboratory data and consulting experience gained in the field.

11
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published

one-third

octave band

spectrum

one-third octave band

spectrum computed

from 20 band spectrum

1 1

63 125 250 500 1,000 2,000 4,000 8,000

ONE-THIRD OCTAVE BAND CENTER FREQUENCY, Hz

Figure 1. One-third octave "band spectrum, as published, compared with

that computed from spectrum level, as published, in the

current American National Standard for the calculation of

the Articulation Index [32].

12
The Noise Criterion Curves (NC) , introduced in 1957, specify the

maximum noise levels that can be present in each octave band of noise to

meet a specific NC criterion. These criterion curves were in turn derived

from another set of curves, the Speech Communication Curves (SC) [44-45].

The Noise Criteria Curves and Speech Communication Curves are reproduced

in Figures 2 and 3, respectively.

The SC curves are generally similar in contour to the NC curves, but

are approximately parallel to one another at a separation of about 10 dB

in most of the frequency range. At low frequencies the SC curves have

steeper slopes than do the NC curves. Although Beranek [45] did attempt

to describe the actual process by which the SC curves were modified to

become the NC curves, the process is not clear, as pointed out by Schultz

[46.]. It can only be conjectured that the reason for the change was that

the NC curves conformed better to the loudness contours, and, therefore,

may have been thought to be in closer correspondence to the hearing

mechanism.

The data on which the SC and NC curves were based included an extensive research study of attitudes and opinions of office workers

regarding noise and its effects on their ability to perform work and to

communicate by speech. The opinions were obtained through the use of

rating scales. These were then correlated with various physical measures

of the noises present in the offices studied. The respondents in these

studies were chosen among office workers at a large Air Force Base and

among office workers in several commercial office buildings where noise

problems existed and were corrected in response to occupant complaints

[45,47].

The office studies revealed that occupants were conscious of the

ambient noise levels and their effects on speech communication. It was

also found that low frequency sounds were annoying even when they were not

sufficiently intense to mask speech sounds. The two important parameters

that emerged as particularly useful in assessing the way in which people

rate acoustic spaces in office buildings were the Speech Interference

Level (SIL) and the Loudness Level (LL) . Furthermore, results indicated

that acceptable conditions were achieved when the SIL values did not

exceed 40 dB and the noise spectrum was maintained within a shape that

yielded a LL that was 22 units above the values of the SIL. The SC curves were derived using these findings.

In subsequent work, the NC curves were presented together with a table delineating the NC values compatible with conducting various

activities in buildings such as churches, hospitals, and homes [47]. The

precise computational procedure by which these values were derived are

unclear. The NC curves do, however, correspond closely to other criteria

presented by Knudsen and Harris in terms of A-weighted sound levels [48]

.

The NC curves have received widespread acceptance both in the United

States and in Europe. They are often used in stating design goals for

13
OLD OCTAVE-BAND LIMITING FREQUENCIES, Hz

63 125 250 500 1,000 2,000 4,000 8,000

PREFERRED OCTAVE BAND CENTER FREQUENCIES, Hz

Figure 2. Noise Criteria curves [52].

14
15
buildings. Rather similar curves, the Noise Rating Curves (NR) have been

standardized internationally [50].

Recently it has been demonstrated that if one deliberately generates

a spectrum that conforms to the NC curve, the sound heard does not appear

natural. It is unpleasant because it is perceived as being both "hissy"

and "rumbly" [50]. These observations suggest that the effect of the low

frequencies and high frequencies upon human response are underestimated by

the NC curves. As a result of these findings, a new set of curves, the

Preferred Noise Criterion (PNC) curves have been proposed as a replacement

for the NC curves [50-51]. This new set of curves, shown in Figure 4,

calls for lower spectrum levels at both high and low frequencies than do

the original NC curves

.

The early studies of Beranek were conducted because of auditory

environments which had produced complaints. The purpose of developing the

noise criterion contours was merely to lower the rate of complaints to

"tolerable" levels. This goal is quite different from a design goal based

upon optimal conditions.

Moreover, all of the data upon which the NC methodology was based

came from investigations of office noises. Although the methodology has

been extended to other types of buildings, including dwellings, no evidence has been set forth indicating that requirements for quiet in the

home are identical to those for offices. Consequently, unanswered

questions remain regarding the validity of extending this particular

approach to the problem of noise in dwellings.

Another important drawback to the NC methodology is that the

available data are based upon continuous noise spectra. They do not

account for the time variation of noises, which may prove to be one of the

most important parameters in the subjective assessment of interior spaces.

2.2.2 Community Response

Since the early 1950' s, a number of investigations conducted in

several countries have combined social surveys and physical noise

measurements to assess the effects of environmental noise in residential

areas

.

Although these studies had a similar goal — to arrive at a methodology for relating the human response to environmental noise to the

physical attributes of that noise — a variety of methods has evolved to

interpret the data. These include, for example, the Community Noise

Rating (CNR) , the Noise Exposure Forecast (NEF) , the Community Noise

Equivalent Level (CNEL) , the Noise and Number Index (NNI) , and the Traffic

Noise Index (TNI)

.

16
A priori , It may appear that these ratings are widely different; yet,

they share many attributes. The similarity among ratings Is reflected by

the fact that they are all highly correlated, with a correlation

coefficient of the order of 0.9 [52]. (This high correlation occurs. In

large part, because all of the ratings rise at essentially the same rate

with Increases In sound pressure level.)

Basically, there are two ways of assessing community response to

environmental noise exposure. The first is to examine the action, such as complaints to officials or law suits, taken by individuals, or groups of

individuals, against Identifiable noise sources. The second approach is

to examine the responses made by people Interviewed in social surveys.

The responses of people to questionnaires administered in social

surveys in the United Kingdom [53-56], Sweden 157-60], Austria [61-62],

France {63-66], the Netherlands [67] and the United States [68] reveal

that people exposed to environmental noise In residential areas show an adverse reaction to noise. The adverse general reaction of people to en- vironmental noise is complex and involves a combination of factors. These

Include: Interference with speech communication, interference with sleep,

a, desire for a tranquil environment, and the ability to use telephones,

radios, and televisions satisfactorily. The results of all studies

indicate that in the aggregate the average response of groups of people is

predictable and highly correlated with a number of different measures of

cumulative noise exposure. However, while the average response of people

is predictable, individual responses vary greatly.

Social survey data are in agreement with the general overt responses

of people to noise. Citizens' actions against noise have taken many

forms, ranging from the registration of a complaint to court actions.

Although the rate of complaints has been found to be only a partial

indicator of the number of people annoyed in a community, predictable

relationships exist among rate of reported annoyance, rate of complaints,

and environmental noise levels {69].

As noted above, the surveys have led to a number of different procedures for rating environmental noise. It is not the Intent of this

section to review all of these rating schemes. However, the evolution of one of the families of community noise assessment procedures is given to

illustrate the common elements among rating schemes which appear to be

widely different.

In the United States, the first method proposed for assessing

community reaction to noise was that of Bolt, Rosenblith and Stevens [70],

known as the Composite Noise Rating (CNR) . Originally it was proposed

merely as a scheme for Interpreting community reaction to noise exposure

in eleven case studies of different noise sources. Thus it was derived

from Insights gained from consulting practice and from interpretations of

the limited research data then available.

17
31.5 63 125 250 500 1,000 2,000 4,000 8,000

PREFERRED OCTAVE BAND CENTER FREQUENCIES, Hz

Figure h. Preferred Noise Criteria curves

18
The original Composite Noise Rating specified that the noise was to

be measured and plotted as octave-band sound pressure levels. The

resulting graph would then be compared to a family of curves, which

somewhat resembled loudness contours, plotted for 5 dB intervals in the

region of the mid-frequencies. On the basis of these comparisons, a noise

rank level was assigned to the noise, corresponding to the highest rating

curve into which a measured spectrum intruded. The value thus obtained

was then adjusted by a series of noise corrections based on: noise

spectra, ambient community levels, "intrusiveness" , "impulsiveness",

"repetitiveness" , and previous exposure of the community. Further

corrections were applied to account for the time of day and the period of

year during which the noise intruded.

Each correction factor had the effect of either raising or lowering

the rank level originally obtained. A range of discrete community

responses, as a function of CNR, was also provided for the purpose of

estimating the probable effect of a given noise. These responses were:

"no reaction", "sporadic complaints", "widespread complaints", "threat of

legal action", and "vigorous community reaction".

Since its proposal in 1955, the method has undergone numerous

changes. One was the substitution of the Perceived Noise Level as a means

of determining the noise level rank. Additional refinements were added to

the correction system as more data became available. Finally, a scheme

for computing the effects of a large number of separate events was incorporated into the system. Eventually the method was modified into

what is now the Noise Exposure Forecast 171], which is part of the

procedure utilized by the Federal Aviation Administration for assessing

land use around airports [72],

19
3, SPECIFICATION OF NOISE ISOLATION IN BUILDINGS: EVALUATION OF

TECmiCAL BASES UNDERLYING CURRENT PRACTICES

Scientific attention to noise isolation between dwelling units dates

back to Sabine's work near the turn of the twentieth century. By the late

1930' s, national building codes, primarily in Europe, began to incorporate

requirements for the sound insulation of dwellings. In these codes, the

approach has usually been to specify the acoustical performance which

various interior building elements, such as floor-ceiling assemblies and

party walls, must achieve in order to be acceptable. Social survey data, on the other hand, indicate that the responses of people to indoor noise

levels are somewhat dependent upon the acoustical climate outdoors. For

example, everything else being equal, people who live in noisy areas seem

to be less aware of their neighbors' noises than are people who live in

quiet areas. Yet, none of the national building codes have specified

requirements for outdoor-to-indoor isolation.

In the present section, attention is given to the development of

criteria for noise isolation and the evidence, or lack thereof, in support

of those criteria.

3.1. "Isolation" versus "Insulation"

The large majority of building codes have specified the sound transmission loss, or insulation , to be provided by a particular building

element, such as a wall or a floor-ceiling assembly. However, there is a serious problem with an approach based upon specifying the sound

transmission loss of separate building elements in that reliance is placed

on an isolated structural element regardless of how it may be built or installed and irrespective of the existence of flanking sound transmission

paths. Indeed it is not unusual that a particular set of building

elements may have received an excellent laboratory rating, but be

assembled into a finished product that is poor 173-75]. Consequently, in

recent years there has been an increased recognition [76] of the need to

shift the emphasis in building codes from the sound transmission loss of

individual building elements to the noise isolation , or level difference,

between spaces. Specifications of sound transmission loss should provide

assistance to the building designer in achieving the desired performance,

but the criterion should be the isolation required, rather than the sound

transmission rating, since a specified performance for Individual

structural components may or may not lead to the desired isolation.

In some of the literature reviewed, the distinction between the concepts of isolation , or level difference between rooms, and insulation , or sound transmission loss of a building element, has not been clearly made,

thus resulting in some confusion in comparing the results of different

investigators

.

20
3.2. The Grading Curve for Indoor-to-Indoor Isolation

3.2.1. Origin

Typically, the transmission loss of a partition at each frequency is

measured according to well-defined and prescribed rules [77-78]. The

results of these measurements are then expressed in a graphic form by

plotting the transmission loss as a function of frequency, typically over

a range of 16 to 18 one-third octave bands ranging from approximately 125

to 4000 Hz. While detailed data may be useful in engineering design

applications, in specifying performance criteria for building codes a single number rating of the overall performance of a partition is more

practical, especially for enforcement purposes. Accordingly, various

single-number rating schemes evolved and were adopted in various codes and

standards

,

For some years, requirements for sound insulation were usually stated

in terms of the arithmetic mean of the transmission loss values (expressed

in decibels) over the range between approximately 100 and 3000 Hz [79].

This scheme was soon found to be unsatisfactory. The averaging procedure

allowed for two partitions with very different characteristics to achieve

the same rating. One of them might have good transmission loss throughout

the whole frequency range, while the other might have poor transmission

loss in one region offset by superior transmission loss in another region.

This feature of the rating scheme was recognized and a new approach was developed in the 1950' s. The new approach is to state noise insulation

requirements in terms of the performance relative to a standard reference

curve (or grading curve) ,[80] .

If the transmission losses of a given partition are found to exceed

those of the grading curve at all frequencies, the partition is clearly

acceptable. If the transmission losses at all frequencies are found to be

poorer than those specified in the grading curve, the partition is clearly

unacceptable. Most partitions, however, are neither all "good" nor all

"bad". Rather, in the typical situation the transmission loss may be

better than that embodied in the grading curve at some frequencies while

falling below the requirements at other frequencies. For this reason,

rules had to be devised for making the comparisons between a measured

transmission loss curve and the grading curve to limit unfavorable

deviations to a "reasonable" amount.

In Germany, where the above scheme was first proposed [81] in 1953,

the acoustical performance of a partition is expressed in terms of the

number of decibels by which the grading curve must be either lowered or raised in order that the mean of the unfavorable deviations from the

grading curve does not exceed 2 dB. The resulting number is accompanied

by a positive or negative sign indicating whether the grading curve must

be moved upward or downward. In England, the mean of the unfavorable

deviations (below a different grading curve) is not allowed to exceed 1 dB

[82]. In either case, only the deviations that fall below the grading

curve are used in the computations of the mean of the unfavorable

deviations

.

21
Developments similar to those described for Germany and England have

occurred in various countries. Although the details vary, the approaches

have been similar enough to enable the International Organization for

Standardization (ISO) to arrive at a recommended method for assessing the

relative performance of partitions with respect to their ability to act as sound barriers [83]

.

In the United States a standard method for assessing partition

performance has also been adopted [84] . This method, developed by the

American Society for Testing and Materials (ASTM) , is similar to the ISO

standard. According to the ASTM procedure, the sound transmission loss of

a partition is measured in conformance with a defined procedure at 16

one-third octave frequency bands centered at the frequencies from 125 to

4000 Hz. The results are then plotted as a function of frequency and

compared to a reference curve which is adjusted vertically relative to the

test curve until the following conditions are fulfilled:

• the sum of the deficiencies (that is, deviations below the

reference contour) do not exceed 32 dB

;

• the maximum deficiency at a single test point does not exceed 8

dB.

When both requirements are met, the Sound Transmission Class (STC) of

partition is given by the transmission loss value "corresponding to

the intersection of the reference contour and the 500 Hz ordinate."

Implicit in the American Sound Transmission Class, or the similar

International procedure, are two critical assumptions:

(1) it is known what overall insulation against intrusive noises is

adequate in terms of minimizing adverse human responses

;

C2) it is known how deviations, from the desired performance, at

various frequencies influence human response.

With these assumptions in mind, it is interesting to look at the

experimental evidence behind current practices. A review of the origin of

the grading curve used to judge partitions indicates that the data upon

which it rests are not entirely satisfactory.

3.2.2. Evidence from Social Surveys

Historically, tenant complaints came about at a time when the

building industry was departing from traditional masonry construction

practices and moving toward the use of lightweight, prefabricated

structures. In older constructions, where the rate of tenant complaints was low, dwelling units were often separated by a 25-cm plastered brick

wall whose massiveness was intended primarily to serve as a fire wall.

The smoothed transmission loss curve for this brick wall was taken as the

I

22
criterion against which other structures should be judged. It was only

after this decision was generally agreed upon that a number of

investigations were carried out to provide the data to validate the choice

of this transmission loss curve.

The chief approach taken by numerous investigators to acquire the

necessary validation information was to conduct social surveys to identify

those structures deemed acceptable by the majority of building occupants.

Subsequently, sound transmission loss measurements were taken, either in

the field or in the laboratory, on these structures. Such surveys were

conducted in England [85-86], Sweden [87-88], Holland [89], and France

[90].

a. The British Surveys

Two surveys 185-86] conducted in England involved both objective

measurements of sound insulation and social surveys of tenant

satisfaction. In the first survey ("Survey 2" in [85]), conducted in

1950, 500 pairs of semi-detached houses were studied. Half of the pairs

of dwellings had 9-in. (23 cm) solid brick party walls while half had

two-layer concrete walls separated by an air cavity. The cavity wall

provided higher transmission loss at high frequencies than did the solid

brick wall. Inhabitants of both types of houses were questioned about the

general conditions in their dwellings and whether they felt that the walls

were providing adequate sound insulation.

The results of this study indicated that the traditional 9-in. brick

wall provided sufficient sound insulation, since tenants of dwellings

separated by such walls did not complain particularly about noise. The

increased sound insulation provided by the cavity wall at high frequencies

did not lead to a perceptible decrease in complaints. Finally, it was determined that people judged their indoor noise environment in a manner

related to their outdoor noise environment. People who lived in "noisy"

areas tended to be less disturbed, and more often unaware, of their

neighbors' noises than people who lived in "quiet" areas.

In 1952/1953 a survey ([86], "Survey 3" in £85]) was made to assess

the subjective response of people living in apartment buildings. In this

survey three groups of apartments were studied. The average transmission

losses (averaged over 100 to 3150 Hz) of the walls were similar for all

apartments and were comparable to that of the traditional brick wall.

However, the party floor-ceiling assemblies had average airborne sound

insulation values of 49, 44, and 39 dB.

The results of this survey indicated that apartment dwellers in

general were more annoyed by their neighbors' noises than were people in

townhouses . In apartments having an average airborne sound transmission

loss of 49 dB, 22 percent of the people were disturbed by noises made by

their neighbors, but were not more disturbed by noise than by other

conditions associated with living in apartments. In apartments with an

23
average transmission loss of 44 dB the incidence of reported disturbance

increased to 36 percent. Moreover, for these people, noise was found to

be the single greatest factor leading to complaints.

Surprisingly enough, the rate of complaints among people living in

apartments having an average transmission loss of only 39 dB was only 21

percent. Close scrutiny of the data, however, revealed that people who

lived in the apartments with the poorest sound insulation were generally

from a lower socio-economic class. Furthermore, this group of people had

been waiting for a long time to move into their apartments , and had

previously been living under much worse conditions. These people did not

complain about any aspect of their dwellings even though they usually

experienced some overcrowding due to the large sizes of their families.

The aforementioned British studies have sometimes been cited in

support of the choice of the brick wall as a sound insulation criterion.

In our opinion, however, the data gathered in these studies do not appear

to provide the desired support for the following reasons:

(1) All of the people interviewed in the two British studies were

relatively low on the socio-economic scale. Since these people

were all living in subsidized housing, their standard of living

and their expectations may have been different from those of

other socio-economic groups.

(2) At the time that these studies were being conducted, England was

only beginning to recover from the effects of World War II and

still suffered a significant housing shortage. Under those

conditions any degree of privacy in housing might have been

acceptable

.

(3) The samples of transmission loss studied covered a limited range

of sound transmission loss. None of the wall structures

provided significantly better insulation than did the classical

brick wall.

(4) In the second study, the three groups of apartments differed

only with respect to the sound insulation of the floor-ceiling

assemblies. It is therefore unclear whether people responded to

airborne noise or to impact noise.

b. The Swedish Surveys

While the British studies were underway, similar but independent

efforts were carried out in Sweden [87-88]. The Swedish studies involved

a set of 500 apartments divided into three groups on the basis of the

sound transmission loss provided by the walls. A physical measurement

program was combined with a social survey study.

24
The data generated in these studies were in good agreement with those

obtained in the British studies. Generally, it was found that the rate of

complaints decreased as the amount of sound insulation increased. When

the average transmission loss was 45 dB, 21 percent of people complained

about their neighbors' noises. The complaint rate dropped to 16 percent

with an increase in the transmission loss to 50 dB , and to 7 percent with

a further increase in the transmission loss to 55 dB. However, as in the

British studies, other non-acoustical factors contributed to people's

judgments of their acoustical environment.

It may appear surprising that the results of the British and Swedish

studies agreed so closely, since the standard of living in Sweden at that

time was considerably better than that of postwar England. However,

Sweden had a chronic and severe housing shortage that might explain the

similarities among the Swedish and the British findings.

c. The Dutch Survey

A study similar to those conducted in England and Sweden was also

carried out in the early 1950's in Holland [89]. This study involved a set of 1200 apartments and 1200 survey respondents. Unlike the previous

studies, the Dutch data failed to reveal a correlation between people's

satisfaction and the sound transmission loss of party walls. The reasons

for the discrepancy between the data obtained in the Dutch survey and

those obtained in the British and Swedish surveys are not clear.

d. The French Survey

A study similar to those conducted in England, Sweden and Holland was more recently performed in France [90], In the French study, six groups

of dwellings were involved and 266 responded surveyed. The dwellings

studied in this investigation were chosen on the basis of their conformity

to the French Construction Standards, which are modeled after the smoothed

transmission loss curve for the standard brick wall. The results of the

French study reveal that, despite the fact that all the dwellings met the

French norm, 40 percent of the people interviewed reported hearing their

next door neighbor's television and radio. Similar results were not found

regarding conversations. On the basis of the French data, it can be

surmised that, while the traditional brick wall may have once provided

adequate isolation for certain noise sources, it may provide insufficient

protection against amplified music, television, and radio sounds (i.e.,

amplified conversation) as well as against modern appliances or household

equipment

.

e. Summary of Social Survey Evaluations

The results of the various social surveys, with the exception of that

performed in Holland, seem to indicate that;

25
tenant satisfaction with acoustical privacy is related to the

degree of sound transmission loss provided by building

elements

;

• everything else being equal, the response of people to indoor

noises is influenced by environmental noise conditions

outdoors;

• while the selection of the acoustical performance of the

traditional brick wall as a design goal for party walls may

have been appropriate at one time, it is perhaps no longer

adequate

.

3.2.3. Evidence Based Upon Consideration of Loudness and Noisiness

Possibly because of the discrepancy between the Dutch survey data and

the British and Swedish survey data, van den Eijk [91], in Holland,

examined a different approach to the problem. His first assumption was

that one could not be annoyed by a noise which one could not hear.

Consequently, if one could specify the statistical distribution of sound

levels for the most annoying noise source, a knowledge of loudness

functions should enable derivation of the insulation required to gyoduce a zero loudness level in a space adjacent to the noise source room.—

Radio sounds had been found in the British survey to be the

predominant source of complaints among apartment dwellers. Van den Eijk

determined the peak levels of radio programs in each of 8 octave bands

having center frequencies from 50 to 6400 Hz. This distribution was derived from data obtained for a radio working continuously through 17

mornings and afternoons. The results were presented as a series of curves showing the peak levels exceeded in each frequency band during various

percentages of time. These results are reproduced in Figure 5.

From the data contained in Figure 5 and from the Fletcher-Munson

equal-loudness contours [4], another series of curves was generated.

These curves were designed to specify the necessary sound transmission

losses in each octave band that would yield a loudness level of 0 phon in

an adjacent room for various percentages of the time. The resulting

values can be seen in Figure 6.

Inspection of Figure 6 reveals that the shape of the curve derived on

the basis of loudness is quite different from the German standard

"Soll-Kurve" (based upon the standard brick wall). Specifically, the curve derived on the basis of loudness drops sharply below 400 Hz and

—Actually, van den Eijk's procedure led to requirements for noise

isolation, or level difference between rooms, and not to the

sound transmission loss, or insulation, of the partition between

them.

26
27
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70 —

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50 —

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20 —

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100 200 400 800 1600 3200

FREQUENCY, Hz

Figure 6. Required isolation, according to van den Eijk, in order that peak

levels due to a neighbor's radio not exceed 0 phon for more than

the specified percentage of the time [92]

.

28
above 3200 Hz whereas that derived from the brick wall does not. In the

range between 400 Hz and 3200 Hz the curve based on loudness is

essentially flat while the other is not. Furthermore, the requirements

based upon a 0 phon loudness level are much stricter than those of either

the German or British standards. To reduce radio noise to this extent,

the sound isolation required could be prohibitively expensive.

Thus, van den Eijk also estimated the isolation required to reduce

the levels he measured for radio programs to a loudness contour of 20

phons in the receiving room. The results of these computations are shown

in Figure 7, together with the requirements embodied in the German

standard (i.e., the Soll-Kurve) . As can be seen in Figure 7, if a 20-phon

loudness contour is used instead of a 0-phon loudness contour, van den

Eijk's derived isolation requirement would more nearly be in agreement

with the Soll-Kurve, insofar as average level is concerned. However, the

differences concerning the shape of the curves remain.

Based upon the previous analysis, van den Eijk concluded that the

most important frequency range for airborne sound insulation is from 400

to 800 Hz, since the insulation required is controlled by the

contributions in this frequency region. He further hypothesized that if

the noise is allowed to intrude next door at a low or moderate level

(e.g., 20-'phon loudness level), it should not be annoying. Van den Eijk

reports that his transmission loss requirement curve is based upon an intrusion of radio programs for 10 percent of the time at a loudness level

of 20 phon. Thus, the Dutch Building Code, which specifies the insulation

required in each octave band between 250 Hz and 2000 Hz, was derived

partially on the basis of allowing radio sounds to intrude next door by

the above amount,

A number of questions are raised by the work of van den Eijk. He

computed the isolation required in order that each octave band, taken

alone, lie on the 20-phon contour. However, if there are a number of

bands, each of which singly produces a loudness level of 20 phon, the

overall estimated loudness level in the receiving room will exceed 20 phon

by an amount which increases with the number of contributing bands.

Specifically, if each octave band taken alone produces a loudness level of

20 phon, it may be reasonable to assume that each band contributes equally

to the loudness level in the receiving room. Accordingly, the incremental

loudness level in the receiving room as a function of the number of bands

present can be estimated using various computational procedures. The

results of these computations are shown in Figure 8 for the

Fletcher-Munson [4], the Stevens' Mark VI [12,13], and the Stevens* Mark

VII [14], loudness calculation procedures. As can be seen in Figure 8,

the overall loudness level for the 8 bands utilized by van den Eijk might

be about 16 to 18 dB above that of each individual band, depending upon

29
80

70

60 -

50 -

40 -

30 -

20 -

10 -

100 200 400 800 1600 3200

FREQUENCY, Hz

Figure 7. Required isolation, according to van den Eijk, in order tnat peatc

levels due to a neighbor's radio not exceed 20 phon for more than

the specified percentage of the time [92].

30
25

NUMBER OF OCTAVE BANDS

Figure 8. Increase In loudness level with increase in number of octave

bands, when each octave band, taken alone, has the same loudness level.

31
which computational procedure is used to compute the loudness level.—

Thus the fact that van den Eijk did not sum the estimated loudness of the

individual bands means that the equivalent loudness level in the receiving

room might reach 36 to phon even though the contribution from each band

did not exceed 20 phon.—

Moreover, while it is reasonable to assume that one cannot be annoyed

by a noise that cannot be heard, it is an entirely different matter to assume that one cannot be annoyed by a noise heard at a low or moderate

level (e.g., 36 to 38 phon). It has been argued [25-27,92] that loudness

may not be an adequate predictor of annoyance or "noisiness". Thus, it

might be argued that van den Eijk's requirements may have been derived

through the use of an inappropriate descriptor. To test this possibility van den Eijk's published data and his rationale were used in conjunction

with the 0.16-noy contour [93] rather than the 20-phon contour. (The reason for choosing the 0.16 noy contour was that it also corresponds to a sound pressure level of 20 dB, re 20 Pa, at 1000 Hz.) The curve corresponding to the 0.16 noy contour was compared to the curve derived by van den Eijk for the 20 phon loudness contour. The result is presented in

Figure 9.

Inspection of Figure 9 suggests that the isolation values "required"

on the basis of the Fletcher-Munson loudness differ from those based upon

perceived noisiness, which in the context of Kryter's work is synonymous

with annoyance, both in terms of the frequency range to be considered and

the actual levels required. While the use of the Fletcher-Munson loudness

curve suggests that the isolation required is independent of frequency in

the range between 800 and 1600 Hz, the noisiness curve leads to isolation

requirements that increase as a function of frequency in this range. The

practical implication of this finding is that isolation requirements in

building codes should be specified up to at least the 3200 Hz band, in

contrast to van den Eikj's conclusion that isolation requirements need not

be specified beyond the 800 Hz band. In addition. Figure 9 reveals that

in the range below 400 Hz significantly more isolation is required than is

suggested by van den Eijk's curve.

— Note that the summation procedure of Fletcher and Munson applies

only to pure tones; consequently, in order to estimate the overall

loudness level associated with van den Eijk's spectrum each octave

band was replaced by a single pure tone located at the band center

frequency

.

4/— While loudness calculation procedures may not be accurate in

predicting the growth of loudness as the bandwidth increases

to eight octaves, it seems evident that the loudness will be

considerably greater than that of a single octave band.

32
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Noise isolation requirements based on loudness versus those based

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33
In addition to the problem of using loudness level as a criterion for

generating noise isolation requirements, another difficulty exists.

Inherent in van den Eljk's conclusions is the assumption that a solution

to the problem of a neighbor's radio is a general solution for all noises.

Although in subsequent studies van den Eljk [94] also examined the

isolation required for television programs, isolation that is sufficient

for television or radio programs might not be adequate for noises that

have different spectral shapes. The British surveys clearly demonstrate

that people in dwellings are disturbed by other types of noises — such as the sounds from musical Instruments. These sounds contain energy in

regions other than those between 400 and 3200 Hz. Certainly in a country

where modern stereo systems, household appliances, and home tools are common, requirements based upon the loudness of a neighbor's radio

programs could be misleading. Furthermore, van den Eljk did not take into

account other factors such as the preferred output level for radio or television programs, the location of the radio or television with respect

to the party wall, or the background noise in the receiving room.

Northwood [95] has used an approach somewhat similar to that of van

den Eljk to estimate noise Isolation requirements for party walls. In his

studies he combined the spectra of sounds from television, radio, speech,

and domestic appliances. He also pointed out that this "standard

household noise" must "compete" on the quiet side of the partition with

the existing background noise. In the absence of data on ambient noises

in homes , Northwood assumed a background noise with a spectrum similar in

shape to the NC-25 contour 151] . Isolation requirements were then derived

on the basis of the "standard household noise" Intruding next door and

being heard above this background noise. A curve of isolation as a function of frequency was thus obtained. This curve is reproduced in

Figure 10, where it is compared to the German Soll-Kurve. Northwood

states that the calculated isolation requirement shown in Figure 10

probably corresponds to about a 50 percent probability of intrusion. To

get down to a reasonable value, say 10 percent to 20 percent, would

require that the sound Insulation be raised perhaps 5 dB. Thus, it

appears that the German grading curve ... is about the right shape and

not far from the right level." It might be noted, however, that

Northwood 's isolation requirements fall off at ^yequencies above 1000 Hz,

while those in the German grading curve do not.—

— Note, however, that it is relatively simple to build partitions

with adequate transmission losses at high frequencies, provided

that they are well-sealed. Thus, the shape of the grading curve

at high frequencies may have little practical significance.

34
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CALCULATED

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REQUIREMENT

NC-25

(V2 OCTAVE)

125 250 500 1000 2000 4000

FREQUENCY, Hz

Figure 10. Noise isolation required to reduce "standard household

noise" to a level, in the receiving room, corresponding

to an NC-25 contour [961.

35
Northwood points out that the noise isolation requirements developed

are rather speculative. This is so because:

(1) Data regarding the distribution of indoor noise levels are limited and thus Northwood 's standard household noise may or may

not be representative of typical households.

(2) There are no data regarding the relation between the NC-25

contour and actual household noises, and thus the NC-25 contour

may or may not be a reasonable way to define ambient noise in

dwellings. It is known that spectra that meet NC contours are judged "hissy", "rumbly", and unnatural [46]. Consequently, it

is questionable whether they represent typical background

noises

.

In 1969 Clark [96] carried out a series of psychoacoustic studies

designed to test the validity, from a human response viewpoint, of the

shape of the rating curve embodied in the ISO and ASTM standards as well

as to examine the need for the "8 dB" rule (described in Section 3.2.1).

In one series of experiments, subjects were exposed to three different

"noise" sources — male speech, popular music, and vacuum cleaner noise.

Each source was presented alternatively through one of two filters — one representing the shape of the ASTM rating contour (STC) and the other

being a one^third octave or octave band-pass filter. The stimuli were

presented in a background noise conforming to the spectrum shape and level

of the NC-25 contour. Subjects were asked to adjust the level of the

comparison band of noise until it was judged to be equal in annoyance to

the test noise passing through the "STC filter". The results of these

experiments showed that when subjects equated the "annoyance" of a one-third octave or an octave band of noise to that of the same noise

passing through the "STC" filter, they were in fact approximately tracing

an inverted STC contour. This finding was interpreted as an indication

that the shape of the STC contour is indeed representative of the relative

contributions of the various bands of noise to annoyance.

However, the study may not adequately solve the problem of the shape

of the grading curve for the following reasons

:

• Since the subjects were always judging the one-third or octave

band of noise against an STC contour the results could have been

biased towards the STC contour due to attentional effects.

• Inherent in Clark's experimental design was the assumption that

household ambient noise is adequately represented by an NC-25

contour. This contour may or may not represent appropriate

conditions. The annoyance produced by an intruding noise is

dependent upon the signal-to-noise ratio (i.e., the ratio of

intruding sound to background noise in receiving room) ; thus the

shape of the background noise spectrum may be critical.

36
• The range of sound levels in Clark's study was limited to levels

that were just perceptible above the background noise.

Accordingly, generalization to other situations may be

questionable.

In a second series of experiments, Clark [96] addressed the question

of the importance to human observers of coincidence dips in a transmission

loss curve. The experiment was carried out in a manner similar to the one described previously, but the band-pass filter was replaced with a filter

corresponding to the noise isolation between two rooms. The filter also

simulated coincidence dips, either one-third octave or an octave in width

and 0 to 20 dB in depth. Subjects were asked to adjust the attenuation of

the noise passing through the STC filter until it was as annoying as the same noise passing through the simulated noise isolation filter. The

results of this series of experiments suggest that dips in the noise

isolation are not very important subjectively. Thus, the 8 dB rule

present in the STC rating scheme may not be necessary. However, these

results should also be interpreted cautiously since some of the same uncertainties described above are applicable to this second set of

experiments

3.2.4. Conclusions Concerning the Grading Curve

The previous discussion indicates that, although precise and

well-defined rules exist for rating building elements with respect to

their ability to provide sound insulation, the human response data upon

which these requirements are based are inconclusive.

While the social surveys conducted in England and Sweden appeared, at

least superficially, to demonstrate that the traditional 9- in plastered

brick wall leads to a minimal rate of complaints among residents , the

French survey tends to demonstrate that such walls may not provide

sufficient protection. In addition, since all the surveys reviewed

employed a very limited range of insulation, and since none considered any

structure significantly better with respect to insulation than the 25-cm

brick wall, it is impossible to extrapolate from these surveys how people

would respond to walls with either superior insulation capabilities or different characteristics.

The evidence based upon subjective response (e.g., loudness or annoyance) is even more sketchy, and highly speculative. It is therefore

not surprising that, over the years, numerous reference curves have been

used for rating noise insulation and that, as shown in Figure 11, these

curves vary somewhat with respect to shape, frequency bounds and the

extent of insulation required. Since there is a scarcity of data as to

what constitutes subjectively significant changes in household noise

intrusions, it is difficult to estimate the significance of the

differences observed among the curves

37
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for use in rating partitions.

38
The curves based upon loudness (or annoyance) also imply that the ISO

and ASTM curves may be too stringent at low and high frequencies. While

good transmission loss is easy to achieve at high frequencies (provided

that no large coincidence dip exists), it is both difficult and expensive

to achieve good isolation against low-frequency sounds. Therefore, from a design standpoint, it would be desirable if isolation requirements could

be relaxed at low frequencies , as implied by the curves derived on the

basis of loudness. However, such a recommendation may be premature given

the limited data base.

To conclude, international and national standard curves exist against

which partitions can be judged. However, unresolved questions remain

regarding the shape of the grading curve, the frequency region of concern,

the significance of deviations from the grading curve, the importance of

coincidence dips, and, most importantly, the adequacy of the grading curve

in terms of meeting human requirements. On the basis of current

knowledge, answers to these unresolved questions cannot be given.

3.3. Weighted Level Differences

An increased interest is evident in the single values obtained when

sound levels (e.g. , A-weighted or C-weighted) are measured in both the source and the receiving room. This trend is a reaction to the

substantial data requirements necessary to make measurements of noise

isolation and sound transmission loss in narrow (e.g., one-third octave)

bands

.

In 1965 Gosele [97] and Gosele and Bruckmayer [98] noted that high

correlations exist between partition ratings based on the ISO procedure

(see Section 2) and ratings based on the difference between the A-weighted

sound level in the source room and the A-weighted level in the receiving

room. These observations were confirmed experimentally by Gosele and Koch

[99], Fuchs 1100] and Harman [101]. Similar agreements have also been

noted for outdoor-to-indoor noise reductions by Scholes and Parkins [102].

These observations led Siekman, Yerges and Yerges [103] to propose a simplified field sound transmission test for partitions based on an A-weighted level difference. Quindry and Flynn {104] and Flynn [105] have

also demonstrated a good correlation between ratings based og^level

differences and those derived from the "ASTM/ISO procedures"— . Their

analyses indicate that the best correlations with the Noise Isolation

Class are obtained when C-weighted sound level is used in the source room

and an A-weighted level is used in the receiving room.

— That is, those procedures whereby the grading curve is fitted

to the measured data in accordance wth the American [85] or International [84] standards.

39
Donate 1106], in a study on insulating houses against aircraft noise,

found good agreement between Sound Transmission Class and the difference

between the outdoor and indoor Perceived Noise Levels.

In all of the above investigations, good agreement was observed

between ratings based on weighted level differences and those obtained

using the ISO/ASTM procedure. In addition, there appears to be a consensus among all the above researchers (except Donato) regarding the

desirability of using the A-weighted level in the receiving room. A

similar consensus, however, does not exist with respect to the weighting

function to be used in the source room, since some investigators advocate

the use of an A-weighted level while others advocated the use of the

C-weighted level.

All the proposals reviewed above were based upon the high correlation

obtained between ratings based on level differences and those based on the

ASTM/ISO methods (and therefore^yraceable to the grading curves contained

in the ASTM and ISO standards).^ In view of the lack of evidence

regarding the validity, from a human response viewpoint, of the ISO and

ASTM rating methods, the observed correlations of these schemes do not, in

themselves, justify the adoption of level-differences in building codes.

With respect to typical household noises , we support the view of

Schultz [107], who thinks it is not necessary to demonstrate high

correlation between level differences and other rating schemes, since an A-weighted level difference has as much independent claim to validity as that of the STC procedures.

—Note that a large portion of the good correlation among rating

schemes arises because of the fact that if a noise isolation (or

sound transmission) versus frequency curve is shifted by X dB

,

all of the ratings also shift by X dB,

40
4. ISOLATION RATINGS FOR BUILDINGS: DEPENDENCE UPON INDOOR NOISE

CRITERIA AND UPON SOURCE SPECTRUM

In the course of the present study, computations were performed to

illustrate how various requirements for rating noise isolation result from

alternate choices of procedures for rating the indoor noise environment.

Further calculations (see Section 3.2.3) were made using a spectrum

(octave band levels that were exceeded ten percent of the time) from van

den Eijk's study [92] of radio programs. Two attributes of human response

and several computational procedures were examined. "Loudness" was computed using the procedures of Fletcher and Munson [4], Stevens' Mark VI

[12,30], and Stevens' Mark VII [14]. "Noisiness" was computed using

Perceived Noisiness, as now standardized [72]. Computations were also

made using the A-weighted sound level.

For each procedure used to rate the noise in the receiving room,

computations were made of the isolation required, as a function of

frequency, for each octave band to contribute equally to the rating of the

noise environment — i.e., so that the contribution to loudness,

"noisiness", or A-weighted level of each octave band would be the same. In order to tie the five schemes together, the isolation was computed for

the "loudness", "noisiness", or A-weighted level in the receiving room

predicted to be judged equivalent to an octave band of noise centered at

1000 Hz and having a sound pressure level of 40 dB re 20 yPa.

The results of these computations are shown in Figure 12. It can be seen that, depending upon the scheme used to rate the noise environment in

the receiving room, curves of isolation versus frequency are derived which

differ with respect to both frequency dependence and the magnitude of

isolation required to yield a noise environment that is "equivalent" to

the 1000 Hz octave band of noise used as a reference sound. Specifically,

if the A-weighted level is used to rate the receiving room spectrum, the

criterion for isolation specifies a much lower level than for either

loudness or noisiness. This occurs because the perceived magnitude of

broad-band noise increases more rapidly with bandwidth than does the

A-weighted sound level.

In order to examine further the effect of the rating scheme (for the

receiving room noise) on the spectral shape of the required isolation

curve, a number of similar computations were carried out for other noise

spectra commonly found indoors and outdoors. The indoor spectra used in

these computations are shown in Figure 13, and the outdoor spectra in

Figure 14. With these spectra, the isolation required was derived so that

each one-third octave band would contribute equally to each of several

rating schemes for the receiving room spectrum. Specifically, the

isolation required in each one-third octave band was computed so that the

shape of the receiving room spectrum would conform to a PNC-35 contour, a

1 sone contour (Mark VII), a 1 noy contour, or an inverted A-weighting

contour (these contours are shown in Figure 15)

.

41
63 125 250 500 1,000 2,000 4,000 8,000

FREQUENCY, Hz

Figure 12, Noise isolation required in order that the sound in the

receiving room, due to radio programs in the source room,

shall not produce, for more than ten percent of the time,

a computed sensation in excess of that produced by an octave band of noise centered at 1 kHz and having a sound

pressure level of 40 dB (re 20 pPa) . The several curves correspond to the use of different procedures to rate

the noise environment in the receiving room.

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In these analyses, only the shapes of the isolation curves were

examined. For this comparison, all of the curves were normalized to a common ordinate value at 1000 Hz. The shapes of the isolation curves needed to

maintain the desired spectral shapes in the receiving room are shown in

Figures 16, 17, and 18 for three different source room noises (Northwood's

household noise, average speech spectriim, and a food blender,

respectively.

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For household noise and speech, the computed requirements for

isolation above approximately 1000 Hz do not increase as rapidly with

frequency as does the actual isolation that can be obtained with typical

party walls commonly found between dwelling units. Thus, unless an unusually severe coincidence dip exists in the noise isolation in the

frequency range above 1000 Hz, the overall rating for the noise isolation

between spaces would be governed by the isolation in the frequency range

from only 125 to 500 Hz approximately.

On the other hand, for a source having a spectrum such as that shown

for the food blender, the overall rating of noise isolation would often be

governed by the performance only between 1600 and 4000 Hz, particularly if

there were a coincidence dip in this region. With the possible exceptions

of food blenders (which typically have a very short duty cycle) and vacuum

cleaners, few indoor noise sources appear to have sufficiently high levels

at frequencies above 1600 Hz to constitute a serious problem in a neighbor's dwelling. Thus, from a practical point of view, ratings for

the noise isolation between dwelling units would usually be governed by

the performance at frequencies below about 1000 Hz.

For source room spectra such as those shown in Figure 13 for

Northwood's household noise and speech, the frequency dependence of the

isolation required (see Figures 16-17) to attain any of the four spectral

shapes in the receiving room (see Figure 15) is generally similar in shape

to the ASTM contour and to the A-weighting contour. Thus for such

spectral shapes it would appear to be reasonable to rate isolation in

terms of the ASTM contour [84] or to rate isolation in terms of A-weighted

level differences [107] .

If the source spectra contained considerably more high-frequency

energy than the spectra of "household noise" and speech, the isolation

ratings might differ significantly, depending upon the grading curve used.

For such sources a choice among various human response criteria (based

upon loudness, noisiness, etc.) could be quite crucial. For example,

deficiencies in high frequency isolation would affect a rating based on the Perceived Noise Level more than it would a rating based upon, say,

A-weighted sound level.

For outdoor spectra the isolation curves derived to maintain the

indoor noise intrusion spectrum along a PNC-35 contour, a 1-noy contour, a

1 sone contour, and an inverted A-weighting contour are shown in Figures

19, 20, 21, and 22 for each of the outdoor spectra shown in Figure 14.

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53
These figures show that when the outdoor noise source has significant

high-frequency components (e.g., a large turbofan aircraft on approach),

the indoor noise spectrum will be dominated by this frequency region. A

rating based upon either loudness level (Mark VII) or noisiness (PNL)

would emphasize this high frequency region more than one based upon either

a PNC contour or an inverted A-weighting contour.

When outdoor noise spectra are similar in shape to typical household

noise (e.g., traffic noises), an inverted A-weighted contour would suggest

noise isolation requirements generally similar to those derived on the

basis of loudness or noisiness. When the outdoor noise source produces

significant low frequency noise (e.g., train noise), the interior noise

contains considerable low-frequency energy, e.g., in the 50 to 125 Hz

region. For such spectra, a rating based upon noisiness would emphasize

these low frequencies more than the other curves considered.

For the present it appears that most outdoor sources of noise will be

regulated in terms of A-weighted levels. Since noise sources having

various frequency distributions will contribute to the interior noise,

ratings of outdoor- to-indoor isolation should take into account

differences among source spectra. For example, isolation requirements

(for the building envelope) based on an A-weighted level difference

measured for traffic noise would be inappropriate for either train or aircraft noise.

54

i
5. SIGNIFICANCE OF TEMPORAL VARIATIONS ON BUILDING NOISE RATING PROCEDURES

Human response to noise is substantially affected by temporal

variation of the sound level and frequency spectrum of the noise. None of

the schemes proposed, or incorporated into building codes, have attempted

to account for this factor. For this reason, regardless of which scale is

utilized to rate the interior environment, consideration must be given to

the need for a cumulative measure of noise which appropriately accounts

for its time variation.

Recently, the Environmental Protection Agency has proposed [69,108]

the Day-Night Average Level (L ) for describing the noise environment,

both outdoors and indoors. AltRough it may be premature to generalize

methods developed from studies of outdoor environments to the assessment

of interior environments, the method does appear promising. For this

reason an initial exploration of some of the implications of L with

respect to outdoor-to-indoor required isolation was conducted. ^Similar

computations could be carried out for various cumulative noise measures

such as the Noise Pollution Level and the Traffic Noise Index.

To perform the analyses described below it was arbitrarily assumed

that a house is located 60 meters away from a freeway, 15 meters away from

a railway and in proximity to an airport, with aircraft overflights at an altitude of 300 meters. One-third octave band Single Event Noise Exposure

Levels were assumed for average passbys of each type of noise source, as were average craffic densities for each hour (see Figure 23). From these

data one-third octave band hourly average noise levels (L ) at the facade

of the dwelling were computed. The results were then utifSzed to derive

the isolation required so that the one-third-octave band hourly average

level inside the dwelling would conform to a PNC-35 contour.

From these detailed spectral data, A-weighted hourly average level

differences were computed. Representative data are presented in Table 3

where it can be seen that the A-weighted level differences (e.g.,

isolation required to maintain PNC-35 indoors) varied from a low of 10 dB

during the quietest hour of the night (0200) , (when there were no trains

or planes) to a high of 30 dB (1300) during the period of high traffic

activity.

The average A-weighted isolation required to maintain a PNC-35 indoor

(or approximately an A-weighted level of 43 dB) throughout the daytime

period (0700-2200 hours) was 27 dB. This isolation requirement dropped to

22 dB for the nighttime period (2200-0700 hours). However, when the

Day-Night Average Level was computed, the 10 dB night penalty caused the

average isolation requirement to exceed 30 dB. This is equivalent to

having required the nighttime interior level to drop to about a PNC-25 (or an A-weighted level of approximately 34 dB) . A summary of these data is

presented in Figure 23 in terms of A-weighted level differences. The

upper part of Figure 23 shows the corresponding traffic densities.

55
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57
6. CONTRIBUTION OF OUTDOOR SOURCES TO THE INDOOR NOISE ENVIRONMENT

In the previous section, indoor noise levels were aosumed to be

entirely due to outdoor sources and the isolation requirements were computed accordingly. However, if indoor noise levels due to indoor sources exceed the selected indoor noise criteria, it might be argued that

less isolation against outdoor sources is needed if they are already

competing with the interior "ambient" noise levels due to, for example,

heating and air conditioning systems, appliances, music, or conversation.

However, unlike most outdoor noise sources many indoor sources are either

totally or partially under the operator's control. For example, while one cannot control the noise emission from a vacuum cleaner one may choose not

to use the device at a particular time. Moreover, one may choose to raise

the level of desired sounds such as speech, radio, television, or stereo,

so that they can readily be heard above the level of sounds intruding from

outdoors. This may lead to the conclusion that the indoor source is

primarily responsible for the interior noise environment while, in fact,

the contribution from the indoor source was partially determined by the

levels intruding from outdoors.

In order to explore the relative contributions of outdoor and indoor

noise sources to interior noise levels, indoor and outdoor data obtained

in an earlier EPA study [109] were analyzed in further detail. In this

study, indoor and outdoor noise levels were measured simultaneously at 15

sites in urban residential areas, distant from any major outdoor noise

sources (e.g., highway or airport). Although the EPA study included 15

sites, only 12 contained sufficient data for the present analysis. Noise

measurements consisted of continuous monitoring and recording of

A-weighted sound level on digital tape. Frou these data, hourly average

sound levels (L ) were derived for each site, both indoors and outdoors.

These hourly ave^'age levels provide the data for the analyses reported

here

.

Average sound levels were derived for daytime (0700-2200) , nighttime

(2200-0700), evening (1900-2200) and "late" night (0100-0500). The

results of these calculations are presented in Figures 24-27, where each

data point represents a site, and the average indoor sound levels are plotted versus the outdoor levels. The mean sound levels (e.g.,

arithmetic mean of the sound levels for the 12 sites) , and the standard

deviation about that mean, were also computed for each time period. In

addition, the correlation coefficient between indoor and outdoor sound

levels for each time period was determined. The results of these

computations are summarized in Table 3.

Inspection of the entries in Table 3 reveals that at sites removed

from any major outdoor noise source ;

• the correlation between indoor and outdoor sound levels is

weak, (0.3 or less) except during the late night hours, from 1 a.m. to 5 a.m. , when the correlation coefficient is slightly

better (0.54);

58
75

I L I i

I 40 45 50 55 60 65 70

AVERAGE OUTDOOR SOUND LEVEL, dB re 20 ji Pa

Figure 24. Daytime (0700-2200 hours) indoor versus outdoor average

A-weiehted sound levels (L ) for twelve sites.

eq

59
65

1 60

55 —

50

45

uj 40

C3

35

30

40 45 50 55 60 65 70

AVERAGE OUTDOOR SOUND LEVEL, dB re 20 ^Pa

Figure 25. Nighttime (2200-0700 hours) indoor versus outdoor average

A-weighted sound levels (L ) for twelve sites.

eq

60
70

65

o

0) 60

55 —

50 —

LU^ 45

40 —

35

40 45 50 55 60 65

AVERAGE OUTDOOR SOUND LEVEL, dB re 20 ^aPa

70

Figure 26. Evening (1900-2200 hours) indoor versus outdoor average

A-weighted sound levels (L ) for twelve sites.

eq

61
55

50

COO 45

Q 40

35

LU

(D 30

25

20

40 45 50 55 60 65 70

AVERAGE OUTDOOR SOUND LEVEL dB re 20 /iPa

Figure 27. Late night (0100-0500 hours) indoor versus outdoor

average A-weighted sound levels (L ) for twelve sites,

62
Table 3

Comparison of Outdoor and Indoor Sound Levels

for a Set of 12 Sites Located in Urban Residential

Areas Away from Major Outdoor Noise Sources.

Time of DayDaytime

(0700-2200)

Nighttime

(2200-0700)

Evening

(1900-2300)

"Late" Night

(0100-0500) ^dn

Outdoors

mean sound

level, dB 58.3 51.4 57.3 49.7 59.9

standard

deviation,

dB 3.5 4.0 3.5 4.4 3.7

Indoors

mean sound

level, dB 58.5 47.0 58.6 36.9 59.9

standard

deviation

,

dB 7.0 10.4 8.6 6.0 7,7

Indoor/

Outdoor

Correlation

Coefficient 0.1 - 0.3 0.1 0.54 - 0.2

Mean

Difference

between

indoor

and outdoor

levels +0.2 - 4.4 1.3 -12.8 0

63
• despite the noise isolation provided by the building structure,

levels measured indoors were generally higher than those

measured outdoors during the period extending from 7 a.m. to 10

p.m. ;

• only during the late night hours (1 a.m. to 5 a.m.) were the

indoor noise levels markedly lower than those measured outdoors

(i.e., 37 dB versus 50 dB)

;

• at all times the indoor standard deviations about the mean

significantly exceeded those observed outdoors.

The minimum indoor level occurred during the middle of the night

(i.e., 0100-0500) hours, when most people sleep. This level could either

be governed by ' intrusions from outdoors or by noise from heating and air

conditioning systems. During the day and evening, when people are awake

and active, the indoor sound levels (at sites away from major outdoor

sources) appear to be logically due to the activities of the tenants,

including speech, use of television, radios, household appliances, home

tools and the like.

The large standard deviations observed for indoor noise levels during

the day and evening, relative to those associated with outdoor levels,

suggest that people's activities vary considerably from household to

household. The observed differences are likely to depend upon the size of

the families, the age of family members, socio-economic status and other

sociological and psychological variables. During the course of the EPA

study, no data were obtained on these factors.

The results given above must be interpreted with great caution for two

reasons: first, the sample on which the data are based is very small (12

cases) and, second, this sample was drawn from a limited population of

residential locations and intentionally excluded noisy areas such as those

around highways and airports. Nevertheless, the data presented above

suggest that in relatively quiet urban residential areas, where outdoor

A-weighted Day-Night Noise Levels (L^^) range from approximately 52 to 65

dB, indoor sound levels are primarily controlled by the occupants'

activities. Only during the nighttime, when people were asleep, was the

acoustical climate of the home possibly controlled by outdoor intrusions.

The above conclusions were based upon the use of A-weighted average

sound level as the descriptor of the noise environment. It is not clear

whether these conclusions would hold if a descriptor were used that is

greatly influenced by variations in noise level, such as Noise Pollution

Level, or if a frequency weighting were used that assigns more importance

to sound at lower frequencies (which can more easily be transmitted from

outside to inside)

.

64
Regardless of what descriptors are used to characterize the outdoor

and indoor environments, however, Indoor noise levels will also be due to

both Indoor and outdoor sources. The question thus arises as to how one should establish criteria for Indoor noise levels and for the

contributions, to Indoor levels, of outdoor sources.

65
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[65] Lamure, C, and Bacelon, M. , La gene due au bruit de la circulation

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,

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[66] Aubre, D., Auzou, S., and Rap in, J. M. , Etude de la gene due au trafic automobile urbain (Annoyance caused by noise from automobile

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[67] Bitter, C, and Van Wieren, P., A study of the problem of social

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[68] Tracor, Inc., Community reaction to airport noise. Report No. NASA

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[69] Information on levels of environmental noise requisite to protect

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.

[70] Rosenblith, W. A,, Stevens, K. N. , Bolt, R. H. , A community's

reaction to noise: Can it be forecast?. Noise Control 3^, 63 (1955).

[71] Galloway, W. J., and Bishop, D. E. , Noise exposure forecasts:

Evolution, evaluation, extensions and land use interpretations.

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for 1967, 1970, and 1975 operations at selected airports. Report No.

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[73] Blomquist, D. S., Fath , J. M. , and Flynn, D. R. , An investigation of

procedures for field measurement of sound transmission loss

(unpublished), Second Arden House Workshop on Noise Control

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[74] Lang, J. , Differences between acoustical insulation properties

measured in the laboratory and results of measurements in situ , Appl.

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[75[ Higginson, R. F. , A study of measuring techniques for airborne sound

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1972)

.

{76] Schultz, T. J., How noise creeps past the building codes. Noise

Control Engng. j^(l), 4-15 (Summer 1973). Errata, Noise Control

Engng. 4(2), 53 (March-April 1975).

[77] International Organization for Standardization Recommendation for

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178] American Society for Testing and Materials Standard Recommended

Practice for Laboratory Measurement of Airborne Sound Transmission

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[79] Brandt, 0., European experience with sound-insulation requirements,

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[80] Cremer, L. , Der Sinn der Sollkurven (The meaning of the specification

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,

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[83] International Organization for Standardization Recommendation for

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of sound insulation between dwellings (Her Majesty's Stationery

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[86] Gray, P. G. , Cartwright, A., and Parkin, P. H. , Noise in three groups

of flats and different floor insulations (Her Majesty's Stationery

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.

[88] Brandt, 0., and Dalen, I., Is the sound insulation in our dwellings

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1955)

.

[90] Josse, M. , et al.. Etude sociologioque de la satisfaction des

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[91] Van den Eijk, J., My neighbour's radio, Vol. II, Proceedings of the

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D. W. , A controlled experiment on the subjective effects of jet

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Administration, Washington, D, C. , April 1974).

[94] Van den Eijk, J., My neighbour's television. Vol. Ill, Proceedings of

the 6th International Congress on Acoustics, Tokyo, Japan,

E-113-E-116 (Japan, 1968).

[95] Northwood, T. D. , Sound insulation and the apartment dweller, J.

Acous. Soc. Am. 36(4), 725-728 (April 1964).

[96] Clark, D. M. , Subjective study of the sound transmission class system

for rating building partitions, J. Acous. Soc. Am. 4_7(3) , 676-682

(March 1970)

.

[97] Gosele, K. , Zur Bewertung der Schalldammung von Bautellen nach

Sollkurven, Acustica 15(5) , 264-270 (1965).

[98] Gosele, K. , and Bruckmayer, F. , Vorschlag fur eine Kennzeichung der

Luf tschalldammung von Bautellen, Gesundheits-Ingenieur ^6^, 172-175

(1965)

.

[99] Gosele, K. , and Koch, S., Bestimmung der Luf tschalldammung von

Bautellen nach elnen Kurzverfahren, in Vol. 68 of

Berichte aus der Bauforschung (Wllhelm Ernst & Sons, Berlin, Germany,

1970, pp. 87-93).

[100] Fuchs , G. L., Correlation between physical measurements of

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Acustica 21(5), 303-306 (1969).

[101] Harman, D. M. , The role of the dB(A) , Appl. Acous. 2^(2), 101-109

(April 1969)

.

[102] Scholes, W. E. , and Parkin, P. H. , The insulation of houses

against noise from aircraft in flight, Appl. Acous. 1^(1), 37-46

(January 1968).

[103] Seikman, W. , Yerges , J. F. , and Yerges , L. F. , A simplified

field sound transmission test, S)V Sound and Vib. 5^(10), 17-22

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73
[104] Quindry, T. L. , and Flynn, D. R. , On a simplified field

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.

[106] Donato, R. J. , Insulating houses against aircraft noise, J. Acous. Soc. Am. 53(4), 1025-1027 (April 1973).

[107] Schultz, T. J., A-level differences for noise control in

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[108] von Gierke, H. E., Impact characterization of noise including

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74
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC ATION OR REPORT NO. NBS SP-499

2. Gov't Accession

No.

3. Recipient's Acccs.sion No.

4. TITLE AND SUBTITLE

Noise Criteria for Buildings: A Critical Review

5. Publication Date January 1978

6. Performing Organization Code

7. AL'THOR(S)

Simone L. Yaniv and Daniel R. Flynn

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiect/Task/Work Unit No.

n. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Environmental Protection Agency, Office of Noise

Abatement and Control, Washington, D. C. 2O46O; and the

National Bureau of Standards

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-18709

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.)

A review is given of existing criteria that could be applied to

rating the noise environment in dwellings, to rating noise isolation

between dwellings, and to rating noise isolation from outside to inside

a dwelling. It is concluded that the central problem is to select

appropriate criteria for rating the interior noise environment. Once

this is done, criteria for noise isolation can be derived directly

and these in turn can be used to derive performance requirements for

building elements, such as partitions and exterior walls

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)

Building acoustics; building codes; isolation; noise; noise criteria;

rating scheme; sound transmission.

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