EPA·600/1·17-025May 1917 Environmental Health Effects Research Series

SPEECH LEVELS IN, ·VARIOUS NOISEE·NVIRONMENTS, ,"

Office of Health and Ecological EffectsOffice. of Res,arch and Development

U.S. EnYironllle"tal' Protection AgencyWashinl!ton. D.C. 204&0

RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. EnvironmentalProtection Agency, have been grouped into nine series. These nine broad cate­gories were established to facilitate further development and application ot en­vironmental technology. Elimination of traditional grouping was consciouslyplanned to foster technology transfer and a maximum interlace in related fields.The nine series are:

1. Environmental Health Effects Research2. Environmental Protection Technology3 Ecolog ical Research4. Environmental Monitoring5. Socioeconomic Environmental Studies6. Scientific and Technical Assessment Reports (STAR)7. Interagency Energy-Environment Research and Development8. "Special" Reports9. Miscellaneous Reports

This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS RE­SEARCH series. This series describes projects and studies relating to the toler­ances of man for unhealthful substances or conditions. This work is generallyassessed trom a medical viewpoint, including physiological or psychologicalstudies. In addition to toxicology and other medical specialities, study areas in­clude biomedical instrumentation and health research techniques utilizing ani­mals - but always with intended application to human health measures

This document is available to the public through the National Technical Informa­tion Service, Springfield, Virginia 22161.

,

TECHNICAL REPORT DATA(f/L'asc rri'JU ImJ.nrctrOf!S V'i Tlu' ,.1'1 I '.':" Ocri ,,,( (f)'1/!1./( ''-;:g,'

3. REC:i>I.ENT'S Ar:C£:S~I()i"f>l\Ia.1 REPORT NO 12EPA-600/ 1-77-q2_5 ~ , . ~_____I

4, TITL~ AND SUBTITLE 5. REPCFlT DATE

May 1977 issuing date6, PERFORMING ORGAN'ZAT'ON" cobC--Speech Levels in Various Noise Environments

bo":";";':=o-=,,--------'---------------I-:--=-=-='::-:-:------·---,·-7. AUTHOR(SI 8. PERFORMING ORCANIZATION REPOR" NG I

68-01-2466

II. corlT RACTIG RAN,' NO.

Karl S. Pearsons, Ricarda L. Bennett, Sanford Fi~ell--~------+.."Q,.... .",P..,-,OGHAM ELEMENT "D'"".-~----~

1GA085Bolt, Beranek and Newman. Inc.Cancge Park, California 9130~

9. PERFORMING ORGANIZATION NAME AND ADDRESS

: 12"SPONSORING AGENCY NAME AND ADDRESS

Office of Health and Ecological Effects - Wasn., ULOffice of Research and DevelopmentU.S. Environmental Protection A~ency

WaShington. D.C. 20460

1:1, TYPE OF REPORT AND PERIOD COVEREDJ14. SPONSORING AGENCY CODE

EPA/600/l8IS. SUPPLEMENTARY NOTES

16. ABSTRACT-'The goal of this study was to determine average speech levels used by people when

conversing in different levels of background noise. The non-laboratory environ­ments where speech was recorded were: high school classrooms,homes._hospitals.department stores, trains and commercial aircraft,~~esults of speech measurementsat schools confirmed that teachers in typical classroom situations speak at aconsistently higher level (67-78 dB at one meter) than in face-to-face conversation.Further. their vocal effort. increased at the rate of 1 dB/dB increase in backgroundnoise which ranged from 45 to 55 dB. Speech levels recorded in face-to-face con~

versation were lower, averaging 55 dB at 1 meter for ambient l~vels less than 48 dB.As the back9round level increased above 48 dB to 70 dB, people correspondinglyraised their voice levels up to 67 dB at the rate of 0.6 dB/dB as the ambientincreased. For background levels less than 45 dB speech levels ~easured at thelistener's ear - disregarding distance between talkers - ,was also 55. dB. Thelaboratory study of approximately 100 observers for the four varied speech instruc­tions ("speak in a normal, raised, loud, and shout voice") showed an orderly pro­gression in level, and shift in spectral emphasis as voice levels increased. Com­parison of male and female voice levels for the speech categories normal and raisedyielded minimal differences. Background levels to achieve speech intelligibilityare recommended.

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ambient noiseintelligibilityacoustic measurement

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UNCLASSIFIED~cIa~;?{ F

C{E6S f7"i';;"#':;-'--lJAo~_~r:~---EPA Form 2220·1 (9·'3) r -----.--;

L. -I~. u U.S. GOVERNMENT PRINTING OFFICE 1977-757-056/6405 Region No.5-II

SPEECH LEVELS. llJ VARIOUS

NOISE ENVIRONl'lliNTS

by

Karl S. PearsonsRicarda L. Bernett

Sanford FidellBolt, Beranek and Newman, Inc.Canoge Park, California 91305

Contract No. 68 -01-2466

Project Officer

George R. SimonHealth Effects Division

Office of Health and Ecological EffectsWashington, DC 20460

OFFICE OF HEALTH AND ECOIDGICAL EFFECTSOFFICE OF RESEARCH AND DEVELOPMENT

U.S. ENVIRONMENTAL PROTECTION AGENCYWASHllJGTON, DC 20460

ib

EPA-600/1-77-025May 1977

DISClAIMER

'This report has been reviewed by the Health Effects Division,u. S. Environrrental Protection Agency, and approved for publication.Approval for publication does not signify that the contents necessarilyreflect the views and policies of the U. S. Environrrental Protection Agency,nor does mention of trade nameS or col'l'tJrercial nroducts constituteendorsement or recanmendation for use.

ii

ABSTRAcT

Research on speech level measurements was conducted under

laboratory and non-laboratory conditions. The goal of this

study was to determine average spee~h levels used by people

when conversing in different levels of background noise.

The non-laboratory or real-life environments where speech was

recorded were: high school classrooms, homes, hospitals, d~­

partment stores, trains and commercial aircraft. Briefly, the

results of speech measurements at schools confirmed that

teachers in typical classroom situations speak at a consistently

higher level (67-78 dB at one meter) than in face-to-face

conversation. Further, their vocal effort increased at the

rate of 1 dB/dB increase in background noise which ranged from

45 to 55 dB.

The speech levels recorded in face-to-face conversation were

lower, averaging 55 dB at 1 meter for ambient levels less than

48 dB. But, as the background level increased above 48 dB to

70 dB, people correspondingly raised their voice levels up to

67 dB at the rate of 0.6 dB/dB as the ambient increased. It

was also noted that for background levels less than 45 dB,

speech levels measured at the listener's ear - disregarding

distance between talkers - was also 55 dB.

The laboratory po~t1on of the study was conducted in an anechoic

chamber. The analysis of approximately 100 observers for four

varied speech instructions ("Speak in a normaZ, ~aised, Zoud,

and shout voice") showed an orderly progression in level, and

iii

shift in spectral emphasis as voice levels increased. A

comparison of male and female voice levels for the speech

categories normal and raised yielded minimal differences,

thus negating conclusions by other researchers that background

levels shouJd be lowered to accommodate female speech.

This report concludes with recommended background levels to

achieve speech intelligibility for the various environments

investigated in this study.

iv

TABLE OF CONTENTS

ABSTRACTSFIGURESACKNOWLEDSEMENr

iiivi

viii

I.

II.

INTRODUcrION•.•.....•.....•••...•...••............•....

CONCLUSIONS AND RECOMMENDATIONS; •.••..••••.•••.•.•.••.

1

3

A. Conclusions. . . . • . . . . . • . • . . . • . . . • . • . . . . . . . . . • •. • . . . . 3B. Recorrrnendations... . . 5

III. BACKGROUND••••• ; •••••••••••• '••••••••••••••• ; • • • • • • • • • • 9

IV. RECORDING PROCEDURE................................... 12

A. Classroom. '. . . • . • . . . . . • . . . • . • . • . . . • • . . . . • . . . . . . . • . . . 12B. Individual Face-to-Face Cornmunication. .•..••••..... 14C. Anechoic Chamber Measurements...................... 15

v.

VI.

ANALYSIS PROCEIJJRE ••••••••••••••••••••••••••••••••••••

MEASUFD1ENT SITE DESCRIPTION•••••••.•.• ; ; .•••••.•••.•.

.16

17

A. Scl1oo1s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17B. Hc:rn.es .......••.............•.........•.•.•.. I.' .... ,". , 17c. Hospitals.......................................... 17D. Public Places...................................... 18E. Transportation Vehicles. ~ '. 18

VII. RESlJLTS. • • • . • • • • • . • . • • • • • • • • • . • . • . • • • • • • • • • • • • • • • . • • • • • 19

A. Scl1oo1s ~ ". . 19B. Homes................................................ 23C. fbspitals '. ~ _.,.' 29D. Public Places............... . . . • . • . • •• . • • • • • . . • • . • . • 29E. Transportation Vehicles............................. 29F. .Anechoic Chamber .•• ~ ••• '. • • . • . . • • • • . • • • • • • . . • • • • • . • . • 29

.vIII. DISCUSSION•... , .....•.•.• , .....••...•.•.....•••. ,. •••. . 43

A. Lecturing in Schools.... . . . • • . . • . . • . . . . • . . . • . • • . . . . . 43B. Conversing in Various Envircnrrents.......... .•. . .. . . 45C. Speech MeaS1.lI"elTents in an Anechoic Chamber .•....... ;., 54

REFERENCESAPPENDICES

v

6061

LIST OF FIGURES

1. Microphone Locations in Classroom

2. Distribution of Speech Levels in School Produced byTeachers on Several Occasions

3. Speech Levels at 1 Meter Produced by Teachers DuringLectures

4. Speech Intelligibility in Classroom

5. Distribution of Speech Levels at Homes Produced by Peopleon Several Occasions

6. Conversational Speech Levels in Homes Normalized to 1 Meter

7. Distribution of Television Speech Levels at Various Distances

8. Speech Levels Heard from TV as a Function of BackgroundNoise

9. Distribution of Speech Levels in. Hospitals Produced byNurses and Patients on Several Occasions

10. Distribution of Speech Levels in Department. Stores Produced byPeople on Several Occasions

11. Distribution of Speech Levels in Trains and Aircraft Producedby People on Several Occasions

12. Age Distribution of SUbjects Employed for Anechoic ChamberSpeech Measurements

13. Dist~ibution of Speech Levels Produced by Males at FiveVocal Efforts

14. Distribution of Speech Levels Produced by Femal~s at FiveVocal Efforts

·15. Distribution of Speech Levels Produced by Children at FiveVocal Efforts

16. Average Speech Spectra for Males at FiVe Vocal Efforts

vi

LIST OF FIGURES (CONT'D.)

17. Average Speech Spectra for Females at Five Vocal Efforts

18. Average Speech Spectra for Children at Five Vocal Efforts

19. Differen.ces Between Overall and A-Weighted Sound PressureLevels of Speech

20. Conversing Speech Level as a Function of Background Noisein Several Environments

21. Conversing Speech Level Normalized to One Meter as aFunction of Background Noise in Several Environments

22. Interpersonal Distance 0bserved for Conversations as aFunction of Background Level in Various Environments

23. Articulation Indexes for Conversations in VariousEnvironments

24. Sentence Intelligibility for Conversations in VariousEnvironments

25. Speech Levels for Various Vocal Efforts

A-l Equipment for Measuring Speech and Background Levels inClassrooms

A-2 Microphone Locations in Classroom

A-3 Equipment Setup for Calibration of Miniature Microphone Usedin Conversational Speech Recording

A-4 Speech and Background Analysis System

vii

,,,

ACKNOWLEDGEMENTS

The authors thank Suyeo Tonooka for his diligent assistance

in data collection and ,analysis. Thanks also go to Brian

Curtis for his assistance in recording speech and background

levels and data analysis.

viii

,-

I. I NTRODUCTI ON

Speech communication, although an essential aspect of daily

life, is often degraded by the masking effects of background

noise. EPA has identified various noise levels intended to

guarantee adequate speech communication. These noise levels

were identified on the basis of existing knowledge, rather

than specific research programs. The current research was

undertaken to provide a firmer basis for specifications

of noise levels that insure adequate speech communication in

a variety of real world settings.

To provide information for specifying the noise level in

environments where speech communication may take place, one

needs to know most crucially the distance over which people

choose to communicate, and the speech levels at which people

normally converse. Secondary factors may influence speech

intelligibility as well, notably ~amiliarity of the talker

and listener with the language, the hearing acuity of the

listener, visual cues, the amount of redundancy in the speech

material, and reverberant characteristics of the acoustical

environment. However these secondary factors remained fairly

constant for a given speech ~easurement situation.

The distance between the talker a~d listener is important

primarily when the conversation takes place in an outdoor envi­

ronment, in which speech levels are typical~y reduced 6 dB for

every doubling of distance of separation between the talker

and listener. Indoors, particularly in home environments with

relatively small rooms, the distance between the talKer and

listener is not as critical, since speech leve~s do not

1

decrease in the same fashion as in the outdoor environment.

This is particularly true for distances greater than 1 meter,

since at these distances the listener is in the reverberant

field and speech levels usually remain nearly constant with

distance.

Thus, the principal factor that determines the adequacy of

speech communication is the level produced by the talker.

Most measurements of speech levels have been taken in very

quiet environments (such as anechoic chambers), with a talker

instructed to read from prepared text or word lists. Brown

et al. (1976) have recently shown that even these data can

be highly variable. Since it is important to determine speech

intelligibility in environments other than laboratories,

direct measurements of actual speech levels normally employed

in environments are needed.

The study reported here provides measures of typical speech

levels in homes, schools, hospitals, public places, and trains,

and airplanes. To supplement this information and to make

available detailed information on speech spectra, measurements

were also made of speech levels in an anechoic chamber. Tabu­

lations of one-third octave band statistical distributions of

the speech levels for the anechoic measurements are provided

in the data supplement of this report.

2

II, CON CLUSION SAN D RECOM MEN DA T ION S

A. Conclusions

Several conclusions may be drawn from the data collected and

analyzed in this project.

1) Schools

In the classroom ( lectu,ring) envirunment the teachers' speech

l~veis increased at the rate of 1 dB/dB increase in background

noise for ambient levels of 45 to 55 dB. The teachers'speech

levels at 1 meter ranged from 67 to JB dB.

2) Face-to~Face Communication

a) For background levels less than 45 dB, levels

measured at the listeners ear averaged 55 dB.

b) For background levels less than 48 dB people main­

tained an average voice level of 55 dB when the effects of

distance were normalized to .1 meter.

c) For background levels above 4~up to 70 dB, people

began to raise their voice levels, up to an average of 67 dB,

at the rate of 0.6 dB/dB increase in the ambient level. The speech

levels were normalized t? 1 meter.

d) Distances at which people communicate steadily

decrease with increased background level. In ambient levels up

3

to 45 dB, such as those found in the homes, communication

distances averaged 1 meter. For higher background levels

(above 70 dB) this communication distance decreased to an

average 0.4 meters.

e) High sentence intelligibility of virtually 100%

can be easily achieved when the speech to background ratio is

at least 10 dB. According to the results of this study, this

ratio or better can be maintained with a background level

below 45 dB.

f) Sentence intelligibility of 94%, according to

this study, is possible with a zero speech to background ratio

in an ambient of 70 dB.

3) Anechoic Chamber

The results of the laboratory study indicated that vocal

emphasis shifted from the low frequencies to the high fre­

quencies as the speech categories went from normal to shout.

This trend is evidenced by a 1.6 octave shift in the maximum

one-third octave band from 500 Hz found in the normal voice

spectrum, to 1600 Hz in the shout spectrum.

4

B. Recommendations

1) Schools

The Environmental Protection Agency in the "Levels Document!!

(1947) recommended an indoor level for classrooms not to

exceed Leq (24) of45 dB. This criterion was based on the

consideration of providing an educational environment with a

minimum of speech interference activities. The results from

this study described in this report revealed that the average

background level for occupied classrooms, with no talking during

a test, was an Leq of 45 dB. However, the far more typical

classroom environment consisted of some student-teacher, or

interstudent communication. The ambient level during the normal

classroom activity was 50 dB. Therefore, it is recommended that

for an occupied classroom, the background level could be 50 dB

which would provide 99% sentence intelligibility.

2) Face-to-Face Communication

a) Homes

The 45 dB background level measured in this study for the indoor

residential environment agrees wit0 the recommended criterion in

the EPA !!Levels Document!! (1974). The EPA recommended an indoor

Ldn of 45 dB for speech communication. This would permit vir­

tually 100% sentence intelligibility. The recommended outdoor

Ldn level was set at 55 dB which again corresponded to the

average ambient found in this study for both urban and suburban

environments. This level would permit an average sentence intelli­

gibility of 98% at I meter.

5

b) Hospitals

The hospital interior level set by the "Levels Document" (1974)was Ldn o~ 45 dB. This criterion was based on min~mizing acti­

vity interference and annoyance. The EPA document, however,

failed to stipulate whether this level was based on measu~em~nts

taken in the patients' rooms, or the operating rooms,or the

nurses' stations. The background measurements made for this

study yielded a background of 45 dB for the patients' rooms,

but 52 dB for noise measurements taken at the nurses' station~.

But, even with the higher background levels of 52 dB and a

resulting decrease in the speech to background ratio, the level

was such as to allow 99% sentence intelligibility at I meter.

c) Depaitment Stores

Background leve~s in public places, such as department stores,

were higher than the indoor levels in homes or hospitals. How~

ever, people raised their voice levels to maintain an adequate

speech to noise ratio for communication. For such coinmercial

places as retail stores, restaurants and general office envi~

ronments, a background of 55 dB (EPA 1974, Table D-lO) is an

average level recommended by architects and noise control

engineers as an acceptable noise backgrQund. The sample taken

in department sto~es for this study agrees with the 55 dB level

and will provide. a communication environment to enable ari

average 98% sentence intelligibility at 1 meter.

d) Transportation Vehicles

The noise exposure levels in the trains and airplanes afforded

6

less than desirable sentence intelligibility «95%). The

EPA "Levels Document" (1974) recommended background levels no

higher than Leq = 70 dB over a 24 hour period in order to

protect against hearing loss. The ambient levels measured in

the current study averaged 77 dB. presenting a danger of po­

tential hearing loss and most certainly impeding communication.

It is therefore suggested that a background level of 70 dB

be viewed as a goal for speech communication in both trains

and airplanes. This level would permit sentence intelligibility

of approximately 95% at about 0.5 meter.

3) Future Research

It is further recommended that the Articulation Index calcu­

lation procedure (ANSI. 1969) should be reviewed to incorporate

the new speech spectra information obtained in the anechoic

chamber laboratory study. Additional changes in the standard

would be the inclusion of the new data on differences between

peak and long term rms speech levels.

The data collected in the present study was from participants

with normal hearing. The speech levels that other segments of

the populous use for communication in various environments might

bear some investigation. The elderly, or the hard of hearing at

all ages use public transportation, and in order to facilitate

proper usage of a transportation system such as a com~uter train,

it is vital they be able to communicate adequately. Also it would

be important to determine their speech levels in residential

settings or public environments (such as hospitals or office

buildings) to aid in the development of speech privacy criteria.

7

4) Speech Intelligibility and Annoyance

The results in this study have'been interpreted in terms of

speech leVel (Leq ); with emphasis on the influence of back­

ground noise upon the speech as translated by the Artic~lation

Index and 20rrelated with a percentage of sentence intelli­

gibility. However, no attempt was made to qualify sentence

intelligibility with a subjective evaluation of the b~ckground

level. Thus, a person might be able to communicate at 98%sentence intelligibility but be very annoyed with the kind of

baCkground noise or the ambient level. Such a qualification of

the ambient level might be helpful in analyzing the difference

between 95% sentence intelligibility and 99% intelligibility.

Future research should concentrate on determining a relationship

between the Articulation Index and sentence lntelligibility and

the subjective evaluation of noise.

8

III. BACKGROUND

At first glance, the literature on speech levels seems

reasonably complete. Early studies such as Dunn and White

(1940) established nominal levels observed under controlled

conditions. Subsequent studies, such as those of French

and Steinberg (1947) and Benson and Hirsch (1953) replicated

the early findings with greater numbers of measurements taken

under somewhat wider conditions.

From these studies come much of the data still considered as

"standard" values of speech levels. Par example, the widely

accepted approximation of 60-65 dB (long term rms overall

sound pressure level) at one Qeter for the level of a male

talker reading prepared text aloud with normal vocal effort

dates from these studies. Beranek's early (1947) work on

speech communication, from which later ~easures such as SIL

and PS1L are derived, also is based on these studies.

By the mid-1950's, some of the limitations of the early work

had been recognized. ~~e first deficiency of the data was

that it was taken under quiet conditions. Normal conversations

are not conducted exclusively in quiet backcround noise envi­

ronments; people converse in noisy places as well. Thus,

studies such as that of Korn (1954) were undertaken to quantify

the relationship between the background noise in which speech

is conducted with actual speech levels. Kor~ fou~d that speech

levels varied by 17.5 dB over a rar.ge of 50 dB in background

noise. He concluded that the best estimate of the rate of

ir.crease of speech levels with background noise levels was

9

0.38 dB/dB. Korn's study had several methodological flaws,

however, which encouraged further research in the area.

Subsequent studies, such as those of Pickett (1958), Webster

and Klumpp (1963), and Gardner (1966) have produced other

estimates of the so-called "Lombard effect" (the tendency

to raise the voice as the background noise increases) (Lombard,

1911) .

A second deficiency was the absence of any real information

on speech levels that people produce when not in controlled

listening conditions. Under what condItions do people vary

their vocal effort from a whisper to a shout? Are certain

speech levels characteristic of cer~aln social settings and

background noise environments? How does speech intelligibility

vary in these circumstances?

Thus, knowledge of speech levels was not wholly adequate

several years ago, when EPA sought to identify noise "levels

requisite to protect the public health and welfare with an

adequate margin of safety". EPA based many of its recommenda­

tions for these health and welfare levels on speech interference

effects, reasoning tnat speech interference was the most

salient effect of noise exposure less intense than that asso­

ciated with hearing damage, yet more intense than that asso­

ciated with sleep interference. The basic phenomena of speech

interference seemed well understood: speech spectra were well

znown; there was general if not detailed agreement on levels

observed in controlled conditions; and several measures of

speech intelligibility were well developed and in general use.

10

Upon closer examination, however, the gaps in the literature

noted above became apparent, The most important lack was

that of informatiari on the statistics of ~istrlbutions of

speech levels encountere~ 1n the real wQrld, beyond liboratbryWc;llis. The present research project was undertaken to pro~

vide more information on speech levelS and thus to createa firmer basis for environmental no~se qriteria necessary for

conversa~i9nal speech. •

11

IV. RECORDING PROCEDURE

Two different procedures were used to make recordings of

speech levels. The first procedure was used for school

classroom measurements, while the second was used in all

other situations for measuring personal (face-to-face)

communication. The main difference between the two proce­

dures was in the number and placement of the microphones.

The classroom situation used three microphones: two placed

at different distances from the teacher, and one (a lavalier

microphone) worn by the teacher. The second procedure

utilized a miniature tape recorder and a single microphone

located at the listener's ear while conversation was taking

place.

A. Classroom

Typical microphone placement used in the classroom situation

is indicated in Figure 1. In general, Position A measured

speech and background levels near the front of the class

approximately 2 meters from the teacher, while Position B

(approximately 7 meters from the teacher) was used to record

speech and background information at the rear of the class.

All microphones including the one worn by the teacher were

connected to a multi-channel tape recorder by long cords.

This arrangement allowed the teacher normal freedom or"move­

ment about the classroom. The speech levels recorded with

the microphone worn by the teacher were converted to equivalent

levels, i.e., those that would have been measured one meter

from the teacher's lips. Both teacher and students were

encouraged to carryon the normal classroom procedures which

12

TEACHER'S MICROPHONE0Norn by Teacher)

BlackboardTeacher's

Desk

DDQDDD D DOSo[J 0DDDDDDO D -0 D

, - ,.

D DD-~ DB D-D D D• • •

pos. B

FIGURE 1. MICROPHONE LOCATIONS IN CLASSROOM

13

included 1) lecturing by the teacher; 2) question and answer

interactions between teacher and class,and 3) study

situations with no speech communication between teacher and

class. Data reduction concehtrated oh speech levels collected

during the teachers' l~ctures. Further detail on the instru­

mentation employed for all measurements is included in

Appendix A.

A speech intelligibility test was given to the students in

the classroom using phonetically balanced word lists. One

of seven 50-word lists waS read by the teacher, who w~s

asked to read them in a customary classroom lecturing voice

to the students. ~he students were asked to write the word

heard on test sheets. The word lists were read in a fixed

cadence, with no repeats. complete instructions and wOrd

lists are included in Appendix B.

B. Indiv'd~al F.te~to~Face Communitat'o~

The procedure employed for all situations, other than schools,

was to record normal cbn~ersation at fixed distances using a

single microphone mounted near the ear on an eyeglass frame

wOrn by a listener. Background measurefuents were made using

the same equipment, but without conversation between the

participants. Several recordings were made to obtain at least 10

seconds bf cQfitinub~S convefsation of the talker alone without

respbnses from the listener.

Because of the m16tophone lo~ation (very ~ear the head)~ it

was expected that the speech levels recorded were somewhat higher

than would have been observed if the microphone had been

i4

placed away from the head. However, the measured speech

levels were representative of those heard by the listener,

and therefore provided reasonable levels for estimating

the listener's intelligibility.

In all cases in the home measurement situations, there was

no difficulty in conversing. This appeared to be true for

most of the speech measurement environments except in the

transportation vehicles where there was some difficulty in

understanding speech. Initially speech measurements were

made at the distance of one meter between the talker and

the listener. However, in later measurement sessions, this

restriction was relaxed, yet people seemed to voluntarily

select this one meter communication distance, at least in

the home environment. For transportation enVironments, this

distance diminished to about 0.5 meter.

C. Anechoic Chamber Measurements

Measurements were made in an anechoic chamber one meter from

the talker to determine speech spectra for men, women and

children. The subjects were asked to repeat from memory

the phrase "Joe took father ' s shoe bench out; she was waiting

at my lawn," for approximately 10 seconds at different vocal

efforts. The stipulated vocal efforts were labeled Normal,

Raised, Loud, and Shout. Complete instructions are reproduced

in Appendix B. In addition, a brief conversation between the

experimenter and the subject was carried on before the formal

test began; this speech was labeled casual conversation.

During the casual conversation phase, the experimenter stood

near the microphone at the one meter distance.

15

v. ANALYSIS PROCEDURE

The analysis was conducted with a one-third octave band real

time analyzer interfaced to a digital computer, as discussed

in Appendix A. All speech samples were at least 10 seconds

in length, which allowed at least 100 samples to be taken

at 0.1 sec. int~rvals. The spectrum analyzer's integration

time was equivalent to "fast" on a sound level meter. Back­

ground noise analyses were completed in a similar fashion.

All speech level and background data are reported in A­

weighted sound pressure levels unless otherwise noted. All

speech levels were corrected as necessary to account for

possible background noise influence. To provide levels of

vocal output at a constant distance, the speech levels were

normalized to equivalent levels at one meter.

16

VI. MEASUREMENT SITE DESCR1PT10N

A. Schools

Measurements were made in two schools. One was located on

a moderately busy street while the other was situated on a

quiet street under the landing path for Los Angeles Inter­

national Airport. Since the noise from aircraft was lower

than expected and since no background noise measurements

included aircraft noise, the schools are referred to as I

and II to avoid misinterpretation. Measurements were made

in a total of 20 classrooms. Classrooms typically were

occupied by 23 students. Windows in the classrooms were

usually closed during the normal classroom activities.

B. Homes

Speech background measurements were made both inside and

outside 25 homes. Some of the homes were located on qUiet

suburban streets and others were situated in areas of high

traffic noise exposure. None of the homes were located under

an airport landing path. Outdoor measurements were made in

the backyard or patio areas not directly facing the street.

C. Hospitals

Measurements were made at 23 hospital locations in four medium

sized hospitals. Speech and background measurements were made

while conversing with patients in their rooms, and also while

talking with on-duty nurses at nurses' stations.

17

D. Public Places

Speech background noise measurements were made at 19 loca­

tions in 7 large department stores while talking with on­

duty sales personnel.

E. Transportation Vehicles

Recordings of speech and background levels were made while

conversing with 11 passengers on the Bay Area Rapid Transit

System (BART) in San Francisco. Speech level recordings of

12 passengers in 5 different commercial aircraft were also

made. ~he measurenent of speech and background levels for

each passenger was made while the plane was cruising at

its normal speed and altitude. Aircraft included Boeing

707s, Boeing 7278, Douglas DC-9s, a Lockheed L-lOll, and a

Lockheed Electra.

18

Ii

II

\I

I

\

\

\

I

'~I. RESULTS

A. Schools

A summary of the speech levels measured in the schools is

shown in histogram form in Figure 2. The speech and back­

ground levels are given in A-weighted sound pressure level

which was used exclusively in this report unless otherwise

noted. The figure summarizes levels measured in the twenty

classrooms at the two different schools, as well as at the

three different microphone locations in the classroom repre­

sented by Positions A and B, and the teacherfs microphone.

The histograms indicate considerable variation in speech

levels measured in different classrooms. The speech levels

at school II for all microphone locations were higher on the

average by 5 dB than those found in school I. Higher back­

ground levels (average 3 dB) were also noted for school II

over school I. An analysis of the speech to background noise

ratio for all microphone locations revealed that the teachers

at both schools maintained about the same ratio. The average

speech level was 15 dB higher than the background for school I

and 16 dB for school II.

Figure 3 summarizes all of the teachers' speech levels measured

with the teacher's microphone and normalized to one meter from

the teacher's lips. The results i~dicate that the teachers'

speech level in the range of 67 to 78 dB in the classrqom in­

creased at the same rate (1 dB/dB) as the background noise, over

a range of 45 to 55 dB.

Figure 4 displays the results of the speech intelligibility tests

administered in the classrooms. Articulation Indices (AI) based

upon samples of the teacher's speech during class lectures were

19

School I

One Meter From Teacher Position A Position B10 r r--1 10 r- IO

'"CD-c-E0

V'l

.....5r I I 51- 50 r--1 -

L-

CD..0

E:::>

Z o I I I .1 I I o I I ,. I 0I I I I ,55 60 65 70 75 80 50 55 60 65 70 75 45 50 55 60 65 70

Leg of Speech in dB

l\Ja

School II

One Meter From Teacher Position A Position BlOr lOr 10

'"CD-a.E0

V'l

.....5 ~ 5r 50 , i ,......,

L-

CD...0

E:::>

Z0 1 I I .' I I o I I I I" I II 1- 0

55 60 65 70 75 80 50 55 60 65 70 75 45 50 55 60 65 70 75

Leg of Speech in dB

FIGURE 2. DISTRIBUTION OF SPEECH LEVELS IN SCHOOL PRODUCED BY TEACHERSON SEVERAL OCCASIONS

80,.-----------------------•

75

co""0

t;;.-~ 70ul1>Q}

0..V')

..... •0

IT 65 r :;:;; .76l1)

....J

• School 1

• School n

60

6055504540

55 '"- ........ .....L. .J- .l...- .-I

35

Leq of Background noise In dB

FIGURE 3. SPEECH LEVELS AT 1 METER PRODUCED BYTEACHERS DURING LECTURES

21

k"~CO~ oCl

V l"'cO L>

/ 6. 6.

V 6.

I 6.

/ Co

J

/ o School I t:J.

6. School TI,

If.--~ 1000 PB w~rds

/V

/ Note: These relations are approximate.They depend upon type of material

Vand ski II of ta Ikers and listeners. -

I I ,I I I I I

100

" 8000..",L-Q)

"c::>~ 60..uQ)L-L-0

U

'""L-0~ 40.....0..CGIUL-GI

a..20

oo 0.4 0.6Articulation Index

0.8 1.0

FIGURE 4. SPEECH INTELLIGIBILITY IN CLASSROOM

22

calculated and compared in Figure 4 to the percentage of

correctly understood phonetically balanced words recited to

the students during the intelligibility test. AI scores

represent the percentage of speech material available to the

listener; i.e., that which is not masked by background noise.

The AI calculation uses the differences in one-third octave

band levels between the speech and the backgroynd noise. This

result is then weighted according to a procedur~ specified by

ANSI (1969).

The results for school I are in good agreement with the

relationship of percent correct versus Articulation Inde.x given

in the Articulation Index Calculation Standard (ANSI, 1969),

represented by the curve in Figure 4. The average percent of

words correct for school I is 91%. However, the results for

school II were in minimal agreement with this curve and the

average percent correct was only 77%.

B. Homes

Figure 5 shows the results of speech level measurements made

in the homes. Speech samples were recorded both inside and

outside homes which were located in suburban and urban areas.

As indicated by the histograms, the average difference between

the speech levels recorded inside the homes in the suburban

or urban areas was 2 dB; whereas the difference in the observers'

speech levels recorded outside the homes for the same areas was

10 dB. The higher speech levels were associated with the mea­

surements in the urban areas.

As anticipated, higher background levels were found both inside

and outside the homes in the urban areas. The average noise

exposure level in the urban areas was 55 dB. This was 10 dB

23

I INSIDE I

I URBAN I

( OUTSIDE I

5

o I I I I I ... I "

45 50 55 60 65 . 70 75

10

75

Leq of Speech in dB

70656055

10on(ll

-a.E0

VI

......50

...QJ

...!l

E:J

Z0

45 50

20

75706055

Leq of Speech in

FIGURE 5. DISTRIBUTION OF SPEECH LEVELS AT HOMES PRODUCEDBY PE,O PLEO N S t: V ERA L 0 C CAS ION S

50o '-I I • I I , ,

45

I\)15~

onQJ-a.E0

Vl

...... lOl- I I 100

...

ISUBURBAN IQJ

5~ I rSl...!l

E:J

Z5

higher than the average ambient in the suburban areas

with 45 dB. A comparison of speech levels to background noise

suggested that people maintain about a 5-8 dB speech to noise

ratio when conversing outside their homes and a 9-14 dB speech

to noise ratio when talking inside their homes. Thus, the

intelligibility was maintained at a higher level inside rather

than outside the homes.

Figure 6 illustrates the effects of background noise on

speech level measured in the home. As the background noise

level increased above a certain level (approximately 45 dB),

in the homes, speech levels for the most part increased also.

The lines connecting the points indicate that the same observer

was recorded both inside and outside the home. The actual levels

were then normalized to reflect what the speech level would have

been if measured at 1 meter. As indicated by the horizontal

lines in Figure 6 for background noise levels below 45 dB,

speech levels measured either inside or outside the home remained

the same. In some cases they remained the same up to a, background

level of 50 dB. However, in general, above a 45 dB background

level the observers tended to raise their voice levels. Speech

level tended to increase with background level above 45 dB,

by about 0.5 dB for every 1 dB increase in background level.

Measurements were also made of television speech levels. The

recordings were made with the microphone locat~d at the observer's

ear. Figure 7 shows a histogram of thoie levels with an average

of 61 dB. The observers were told to adjust the television volume

to their preferred listening level depending upon the distance

they chose to sit from the television set. The average distance

of observers from a television was 3 meters. A plot of television

speech levels as a function of background noise is shown in Figure

8. This figure indicates that people increase the volume on the

television 0.7 dB for every 1 dB increase in background level.

25

75 , i

70

65co--0

I::.-.r.uQ) 60 1-. \ •tilQ..

Vl

I"\) ......0\ 0

0-

55 Ltil .\Y<'- - 7"--lHOMES

• IN SIDE

• OUTSIDE

50

706540,I III I45 , I

35

FIGURE 6. CONVERSATIONAL SPEECH LEVELS IN HOMES NORMALIZEDTO 1 METER

-----------------

/

TELEVISION10

'"Q)

D­Eo

Vl

4­

o...Ql

...Q

E::>

Z

5

O'----I..L-._....l-_-"'::L----a._~45 70

Leq of Speech in dB

FIGURE 7. DISTRI9UTlON OF TELEVISION SPEECH

LEVELS AT VARIOUS [)1~rANCES

27

75

70

65

f§>::·rl 60.g(!)(!)

orG--iory 55S

50

45

./

Vv

••

••V CORRELATION• • COEFFICIENT• / • r = .58

• V • •• • .

~ • • -II'" -

,

•

4035 40 45 50 55 60 65

Leq of Background Noise in dB

FIGURE 8. SPEECH LEVELS HEARD FROM TV AS A fUNCTIONOF BACKGROUND NOISE

28

C. Hospitals

Conversational speech measurements were made for both nurses

and patients in the hospital environment. Figure 9 shows these

results in histogram form. The speech level for the patients

was only 2 dB lower than the speech level for the nurses. At

the nurses' stations there was only a 5 dB speech to noise ratio,

as compared to the 10 dB speech to noise ratio found when

measuring patients' speech in their hospital rooms.

D. Public Places

Speech measurements were also made in department stores. The

histogram for speech level distributions in this environment

is shown in Figure 10. The average speech level, measured at

various distances from the listeners' ear, was 61 dB. The

background level had an average of 54 dE, thus there was a 7 dE

speech to noise ratio.

E. Transportation Vehicles

Speech levels were obtained for two types of transportation:

trains (as represented by the San Francisco BART system), and

conventional aircraft. Histograms of these speech levels are

shown in Figure 11. The average speech level inside aircraft

and trains averaged 75 dB, the average ambient level at 77 dB.

The average distance between speaker and listener for both mea­

surement situations was 0.4 meter.

F. Anechoic Chamber

Speech measurements were also made in a quiet laboratory setting

in an anechoic chamber. Male and female talkers of all ages

29

NURSES PATIENTS

10 10'"IDa.E0

Vl

....... 5 50

~

ID...0

E Mean;:)

Z 0 045 50 60 65 70 45 50 55 60 65

Le q of Speech in dB

FIGURE 9. DISTRIBUTION OF SPEECH LEVELS IN HOSPITALSPRODU~ED BY NURSES AND PATIENTS ON SEVEI<ALOCCASIONS

30

DEPARTMENT STORE

15

."

dl

a.. 10E0

V"J

4-

0

....QJ

5...D

E:l

ZMean

050 55 60 65 70

Le q of Speech in dB

FIGURE 10. DISTRIBUTION OF SPEECH LEVELS IN DEPARTMENTSTORE'S PRODUCED BY PEOPLE ON ~EVERAL

OCCASiONS

31

15 AIRCRAFT 15 TRAIN

VI

V

Q... 10 10E0

Vl

.....0

~

<1l..n 5 5E=>

Z

Mean Mean

0 070 75 80 85 . 90 65 70 75

Leq of Speech in dB

FIGURE 11. DISTRIBUTION OF SPEECH LEVELS IN TRAINS ANDAIRCRAFT PRODUCED BY PEOPLE ON SEVERALOCCASIONS

32

participated in this phase of the study. The range of ages

for approximately 100 talkers was from 6 to 60 years, as shown

in Figure 12. The average age was 24 years. The observers

were grouped as males, females and children (talkers under

age 13).

Histograms for the three groups and for the five different

vocal efforts which were designated casual, normal, raised,

Loud, & shout are shown in Figures 13, 14 and 15. A summary

of the means and standard deviations is found in Table I. For

the categories casual, normaL & raised, there was a small

difference in measured voice level between the males, females

and children. Larger differences in voice levels between male

and female observer groups were found for the loud and shout

categories. As expected, the males produced the highest average

vocal output in the shouting and loud voice categories regis­

tering approximately 5 dB higher than the female group or the

children.

The variability in voice level between talkers increased

with vocal effort. For example, t~e voice level variability

between male speakers for the normal vocal effort was 4 dB.

But the difference between male speakers voice levels was more

pronounced (7 dB) when instructed to recite Joe's Passage at

a shouting voice level. A similar increase in speech level

variability between speake~s was also noted for both the female

and childrens groups.

Figures 16 through 18 show a further analysis of this data in

the plots of the voice spectra for males, females and children.

The complete tabulation of all one-third octave band speech data

recorded in the ane-choic chamber can be found in the Data

33

30 r---....,.......-.....,..----r--~-....,.......-~-.....,..--~-..,.....-__r_-_,

25 t---+---

20

'"....U41

..0:l

ton......

150.....dl

..aE:l

Z

10

51----

o6-10 11-1516-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60

Age in Years

FIGURE 12, AGE DISTRIBUTION OF SUBJECTS EMPLOYED FORANECHOIC CHAMBER SPEECH MEASUREMENTS

34

15CASUAL

15 NORMAL15 RAISED

5

10

5

10

5

a...Eo 10

VI

Ql

......o

IVJJE:l

Z

o I I I I. I I I I o , I I I II I I I 0w 40 45 50 55 60 65 45 50 55 60 65 70 50 55 60 65 70 75 80V1

Leg of Speech in dB

LOUD SHO UTlOr 10

Ql-a...E0

VI

......0

5 r I 'I 5.. - -Ql

-0

E:l

Z

"01 I I I I,. , I 0

55 60 65 70 75 80 85 90 60 65 70 75 80 85 90 95 105 100 110

Leg of Speech in dB

FIGURE 13. DISTRIBUTION OF SPEECH LEVELS PRODUCED BY MALES AT FIVE VOCAL EFFORTS

CASUAL NORMAL RAISED

J 0 r lOr r--I 10onQ)

-0-Ec

V)

..... S~ I I Sr- I I 50

L-

Q)

...nE I I Mean~

Z 01 I I * I II I oII I * I L 0

40 45 50 55 60 65 45 50 55 60 65 50 55 60 65 70 75

Leq of Speech in dB

w LOUD SHO UT0\ lOr J aVI

Q),-0-Ec

V)

.....0 sr- I - I n 5...Q)

...nE~

:z01 I '* II II II I I 0

.55 60 65 70 75 80 85 60 65 70 75 80 85 90 95

Leq of Speech in dB

FIGURE 14. DISTRIBUTION OF SPEECH LEVELS PRODUCED BY FEMALES AT FIVE VOCAL EFFORTS

CASUAL NORMAL RAISEDon 10 r 10 r 10Q)-a.Ec

VI

......5 t- 5 l- S0 n n -...

Q)

..D

E I I Mean L- I I Mean:)

Zo I I I I I. I I I I o 'I I I II ! I I 040 45 50 55 60 65 45 50 55 60 65 70 55 60 65 70 75 80

Leq of Speech in dB

w--J

1O~ LOUD 10- SHOUTon(II-0..

Ec

VI

...... 5 L 50

...(II

-r;E:)

?- 01 I I I I I., I I I I I I 0 -- -

55 60 65 70 75 flO 85 90 95 55 60 65 70 75 80 85 90 95

Leq of Speech in dB

FIGURE 15. DISTRIBUTION OF SPEECH LEVELS PRODUCED BY CHILDREN AT FIVE VOCAL EFFORTS

Supplement for thIs report. The speech spectra across observers

were relatively unifor~ in shape for increased vocal efforts;

with a trend towards greater high frequency content at the

higher voice levels. The ~ain difference between male and

female speech spectra can be noted in ?igures 16 and 17, in the

frequencies below 200 Hz. The spectra summarizing the results

for male speakers (Figure 16) show a greater concentration of

vocal energy in the one-third octave bands below 200 Hz. The

speech levels at low frequencies, however, increased only

slightly relative to the increased vocal effort. Furthermore,

for all three groups, the levels at the low frequencies remained

fairly constant.

The relationship between the overall level of speech and A­

weighted sound pressure level was studied because the Articulation

Index calculation procedure utilizes an overall Qeasure of

speech. The difference between the two measures was plotted as a

function of A-weighted sound pressure level for all of the data

collected in the anechoic cha~ber. A plot of these results is

shown in Figure 19. A best fitting second order equation is

provided for these data, as shown in the figure. Note that at

high levels of speech, the average difference between A-level and

overall level of speech is near 0, whereas at the lower levels

(such as those associated with casual conversation) typical

differences of 5 dB occur.

38

88.3 _:..:.-.87.8

ID"'0

Z

-.JW>W-.J

W0:;:)(f) (f)(f)-.JWe:[0:0Q.(f)

oitZo

w ;:)0:'-0 00

(f)-

O:EZo~C\1WW>0:e:[I-00

0a::I:l-I

WZ0

80

70

60

50

40

30

20

-- 0' '''''""I----~- I~ -- 1...- I_

I----- -- -I --

I----- III

r~

Shout I----- ---I---~~ . --

I "I-----.,. I ~ ..

I I Loud_ ~

I-- - ,- .1.L- ~

, .... -• ,",

e-- 1-...... .....I - ..... ...

--I------- I ..-I- I '--

-' ...... '-----j I

" Raised-f--I " " ~ .....- . -- -....- I- I " " -

," roo.... I ,

--- I- o'

\Norm~1f--~\ - I-----..e---- -' " "-r -I .....

...... '"I ", ..... - " - r--- lIoo. 'I .. It.

~ '- ~

_\ Casual-h '- -- r----..... - --'- "-' "f-- -- \1-- '. "- --.... , '"""-l ...1- r-. ..... -

r""'ooOi

I-I-- 1--r- 1"10."-

-

-,I-- 1--- -- +--I-- -

- - +---OA-AL - t--

125 200 315 500 800 1250 2000 3150 - 5000 8000 12,500 20,000160 250 400 630 1000 1600 2500 4000 6300 10,000 16,000

ONE-THIRD OCTAVE BAND CENTER FR~QUENCIES IN Hz (cps)

FIGURE 16. AVERAGE SPEECH SPECTRA FOR MALES AT FIVE VOCAL EFFORTS

1­~

..-~~-+---t- -L--l~-I--+----lr---t-r~- , , -+----If---t- ---1---+--+ - f-- ~ -\ ----.jl---+-+-----ir-I 1--I ,.- __ I"" t-----+---t-- _~

r~~' """

--1---1__ I _-+_.,.,...'_ ~..

, ~ 1'\- Shout -- - _1_-- - 1-- -1---- f-- - - --I--- - ---, _ ___I---

~ - I-- t " -f- --_ ~~ ---t---- - 1----1-_ I- I~ __ I-- ./ _ ._ __~_I-_ --I----- ---~ 1- _ '- _ ~_

--c- 1---- - - I--

-.. - - -~ - --- -- I , - - d- -~ , I 1-- -- --- - 1--- Lou -- ~ _ __- - I- - - - I) ~--+---- ~t--- - - -.... ---L-I-+-:'''-.ot----Ir--r--ri- -I-- -I-- --- f I .............. __ -f--"''4-__01--- ..

r--i~t::t:---:+I-=-t:---+- .1--'--- __.. -1---+...:.H,--t-__-----11---

1--- ---~ , Jr-=-~:-I- I~i-""-i---""""'-- -- J-=:t~.. +=~-.:..::+=i==i=-:tl--::J-~- 7~- ~

- - I '''" ~.... __ ~ Raised f---- \I---j----t---r---, kI ---I -..:... k-f-- -t----f---,f- -t--- 1---- x

~ -+------jr-- -- --.. _ -r __ ~" 1-----'--- -- -- ~ - --f-- ......d----lf--t ~_i---- -1----1-- --- _~-- L-,--t-_ -, -----I----'r~- Normal 1_-=4-r~~~~---1-=.;;;;;~~I--+__1r_~=t==t---=t=l-- r--- '-~, --.- I~ "'" --- - ~ --{ ~ I--.-- -f---

' 1'- ~- ~I------I--- -- ---- -- 1---__ I" f--1---1-- --i' ~ t I - t\- --~~--"'....-!'! -1-- ---:-- _- =:x ~ _1------- -,---\~ _ ,---- - - ---- 10... __ 1---1----- 1-----1-- , -- ~_ ~_ i--- -r""'o.1--- Ii- -- i-, '--'\ _

>--- '1--\-- ~~--I--- r-f-- -) /---1----- - - 1---- - .... --..~ ~;.-- 1-_ ~ _I---1----1-- , 'i---- ---,- ~,- I-- _ ~.~ I" " f--- 1---1-- --- If! _ -- -- f--- f-- -- "" iii' -lil--.... _

1-----4---+-- - ~ 1----- - - J------1~:=t_r~--±---'t___t-- r---.I--- , _ __ '-- __ '\:--/-- --+- - - - I " +----l,-----t-

f--I--- I---I---~':.:Casual=-- .., --.. __I--- 1/j1L--+_+ _1--_ __ _ "- _~ _ _ ~ ~ _+---t---t-- ~---H¥-----;--j -- _ I--- _ _ 1./

,=-t=±=t=~l:l==t==t-I--

1--- ~---+-+------1 -f-----t--+l---+--+--+--1. -+----t----t

OA- AL:=J-

81.5 • _

80

II)

"tJ 70z-...JI.IJ>I.IJ...J en

60I.IJ ...JIX: q::::l 0en enen q:I.IJ Q.

IX: 0Q. IX:o 0 50z i:::lo 0

.l= en N0 0

Z I&J<[ IX:II)

I.IJ 40>q:I--U00IX:- 30:I:I--I

I&JZ0

20/25 200 315 500 800 1250 2000 3150 5000 8000 12,500 20,000

160 250 400 630 1000 1600 2500 4000 6300 10,000 16,000

ONE-THIRD OCTAVE BAND CENTER FREQUENCIES IN Hz (cps)

FIGURE 17. AVERAGE SPEECH SPECTRA FOR FEMALES AT FIVE VOCAL EFFORTS

81.080 .- .----1-=+ I I I

'\

~~=-t=t=--t-+=+-~-=t=t-=~-=t=+=~

.-t--

-~~+-~~=~~-i~±±~-rt~~~Sh~ut~~~1-=-1--1--:== =---1--1-- -~~l= +~+-+--+-+-60 I- 1-- - I -

~I-- I- - _. '-'- -~;-4-- ---. -. --

- --; ..-- -- -f-I'~-f-- -- L_ --'-V--- - --1--1---- -'.~~-f- - --~~..."" - ~....... 1-- Leud----. - ~ --I• r- - - 'rJ'~ v- - -_. -r '- ~

f- - -- -- - f-- -- - - - ~ 1....- I---J. r- ~" '--- ~ --'-- - ,- --- . - -- --f_-- ---- ~,,~--, - ---- -- ---,-- ....

- ----'~~I--f_- - , --- --i~~ --~. --~ --f-- r----i'"-- --I- --50 -- -- f- - - ---,\r - ~ ,... - F~ f- -

- -- -----f- -I.-\- - L~i----'f--- F\R\oised_ ".-f--------~~~- ~--- '-_-- __ I- - - _ 1-__ -...... -- .~ .:..-.-L~ I- _ _ _ -\.l .J .-- _ '

- ---- - I- - -- f f- -- -~~ -~~ ~ f--- '--- -- ---t-'t-- ...... 1-- - -- -

-- - -- I- -- - -- -... I:' - "I', N erma I r-- - "', --J-- --I -- - -~- - -- ~ f-\-- + -- ---~ f- --...... - - -f----"- -_.f-- .- .- _"-~----4 - -- -- -- f_- -_. ...... ---

~ 1 " • 1'\'-- I-- --f_ I- I-- -- - -- --... -- - -~ -_f;-~£~-- - --- ~-=-f_-

-- .-'- I- ~.--- f-- ----- - ',-- ... .-" ....

; f_ - ~ Casua 1- -f-c- _ _ _ I- _1_ ,- - 1-------

70~=__BaJ"V

Z....JI&J>I&JJI&J0::

--V) V)V)JwCl:o::UnoV)oel:zo..

J::"

:>0

I-'

00:(/)~

0 2Zoel:NaJ

Ww

~o:....U00a:::J:....I

WZ0

125 200 315 500 800 1250 2000 3150 5000 8000 12,500 20,000160 250 400 630 1000 1600 2500 4000 6300 10,000 16,000

ONE-THIRD OCTAVE BAND CENTER FREQUENCIES IN Hz (cps)

FIGURE 18. AVERAGE SPEECH SPECTRA FOR CHILDREN AT FIVE VOCAL EFFORTS

L

• CASUAL

0 NORMAL

..A. RAISED

6- LOUD

• SHOUT

•

In......•

•

•: ..•

(). t>...rf ••_t:\ _ ~.

· _.rl' ..- •• - •• lI I't> •••" .~. LI • __ •

d __ •• •-- .~

B.•

••• • • 06~ "...~ 0 \0··0 •

a:l ......0"lJ •l:; .IUO .000 ..-- ..QJ 4 o~>Ql .. ..

...J 0I

0'" 0 ; .. 0

<C ~.fiPt .. II- •-a 2

J:::' ...I\J III

,>

0

0

11010090807060504030-2 I I , , , I I I , ,

20

leq of Speech in dB

FIGURE 19. DIFFERENCES BETWEEN OVERALL AND A-WEIGHTED SOUNDPRESSURE LEVELS OF SPEECH

VIII DISCUSSION

A. Lecturing in Schools

The average speech level comp~ted for all teachers (normalized

to 1 meter) was 71 dB. T~is was coopared to the other speech

measurement situations. ~his level was 13 dB greater than

t~e average voice level (normalized to 1 meter) employed either

inside or outside the home. The teachers' voice levels were

also compared with the laboratory study of speech measured in

the anechoic chamber. As ~oted in Table I, the 71 dS average

voice level for the teacters would fal~ between t~e raised and

loud vocal effort.

The increase in background level had a noticeable effect on

the teachers r vocal efforts. The speech level increased with

background level at I dB/dB whereas for all other speech measure­

ment situations the ra~e ~as 0.6 dB/dB (Figure 20). Over one­

quarter (28%) of the teachers sampled spo~e at an average voice

level o~ 75 dB or more. Allor these were teachers measured at

school II. The average lec~uring level at the back of the

classroom (Position B-estimated a~ 7 meters from the teacher) was

also measured for all teachers i~ both schools a~d was 60 dB.

The increase in voice level did ~o~ see~ to help performance in

the word intelligibility test given to the st~dents. ~hus. even

though the teachers' speech levels at school II were on the

average 5 dD higher than that used at school I. the students in

school I achieved 14% bet~er scores on their word intelligibility

test. A possible explanation is that the students in school II

lacked the motivation to adequately perform on this test.

It is important to mention also ~hat although the sites for

the SCh00l were selected as being representative of a traffic

TABLE I

SPEECH LEVELS (dB) AT VARIOUS VOCAL EFFORTS MEASURED IN

AN ANECHOIC CHAMBER* (BACKGROUND LEVEL Leq = 16 dB)

MALE FEMALE CHILDREN AVERAGE

VOICE LEVEL Leq Leq Leq La a (J eq

Casual 52.0 4.0 50.0 4.0 53.0 5.0 52.0

Normal 58.0 4.0 55.0 4.0 58.0 5.0 57.0

Raised 65.0 5·0 63.0 4.0 65.0 7.0 64.0

Loud 76.0 6.0 71. 0 6.0 74.0 9:0 73·0

Shout 89 ..0 7.0 82.0 7·0 82.0 9·0 85.0

*Results were rounded off to the nearest decibel.

44

noise environment and an aircraft-noise environment, the main

source of background noise, particularly in the aircraft

exposed school, was produced by the students themselves in

the classroom.

B. Conversing in Various Environments

The means and standard deviation of the speech levels measured

under non-laboratory conditions are summarized in Table II.

These data reflect speech and background levels measured under

conditions, as judged by the observers, of adequate speech

intelligibility. These conditions take into consideration, among

other variables, the distance between the talker and the listener,

the visual cues and the length of the conversation. Thus, for

conversations recorded in high background noise environments (above

70 dB), such as trains or airplanes, the distance of 0.4 meters

between the participants was shorter than between participants

recorded in quieter environments such as the home where the dis­

tance was approximately 1.0 meter. Communication in the high

ambient environment also necessitated careful attention to the

speakers' phraseology in addition to visual cues to achieve

adequate intelligibility.

The spread in speech levels between talkers and between speech

samples was considered. The average variability of speech levels

computed from the speech samples collected from each talker in

the hone was approximately 2 dB, as compared to an average

standard deviation of 5 dB between talkers for speech measured

in ~he r-o~e. The variability between ta:kers for the :aboratory

condition designated as cQsua~, normal & raised ranged from 4 dB

to 7 dB (Table I). The intertalker variability in speecb- levels

increased even More when the talkers spoke at a shouting level

(ranging from 7 to 9 dB).

45

TABLE II

AVERAGE SPEECH LEVELS IN VARIOUS ENVIRONMENTS l

BackgroundLevels (dB Speech Levels, dB

Pas. A Pas. S1 Me~er 2 Meters 7 Meters

Lea a Lea a Lea a Leq a .-Schools - I 48.0 2 2.0 69.0 4.0 62.0 5.0 57.0 4.0

II 5J .0 2 3·0 73.0 4.0 66.0 5.0 62.0 6.0

Corrected C:onversationTo 1 Meter Distance

Homes -Outside Urban 61. 0 5.0 65.0 4.0 66.0 !J.O

Suburban 48.0 4.0 55.0 5.0 56.0 5.0

Inside Urban 48.0 2.0 57.0 6.0 57.0 6.0Suburban 41. 0 3·0 55·0 5·0 5';>.0 5.0

Hospitals - Nurses 52.0 5·0 56.0 3.0 57.0 Ii. 0 .

Patients 45.0 2.0 56.0 2.0 55.0 1.0

Department Stores 54.0 4.0 58.0 3·0 61. 0 3.0

Trains 74.0 ~.O 66.0 2.0 73.0 3.0

Aircraft 79·0 3·0 68.0 4.0 77.0 4.0

lResults were rounded off to the nearest decibel.

2~easurements were made with typical student activity. Background valuesof classrooms during the phonetically balanced word test and other "quietperiods" were 47 for School I and 43 dB for School II.

1.\6

The measurement of speech levels in face-to-face communication

revealed a corresponding increase in speech level as background

levels rose above 45 dB. Figure 20 summarizes this effect for

all of the speech levels measured in a ~wo-way communication

situation. The points are coded for the type of environmer.t.

While all the speech measurements were not taken at the same

distance for all speakers, the criteria of adequate observer

assessed intelligibility was maintained.

Regression lines were computed for the data plotted in Figure

20. An approxination of the regression line was also drawn.

This approximation falls well within the confidence interval

of the regression lines. The results for this study suggested

that for background levels below 45 d3, the level at the lister.er's

ear remained constant at 55 dB. ~hereafter, the speech level

increased up to approxinately 80 dB at a rate of 0.6 dB/dB in­

crease in background level which ranged from 45 to 81 dB.

By utilizing Table I & II, it was possible to compare the results

from the face-to-face speech rneasurerr.ents to the data collected

under laboratory conditions in the anechoic chamber. Tne casual

conversation measure was conducted in a Danner sinilar to the

face-to-face co~munication situation, only ~n a controlled back­

ground level of 16 dB in the anechoic chamber. The average speech

level measured for all observers under this laboratory condition

was only 3 dB below the speech levels obtained at 1.0 meter in

the suburban home environment. The average speech level obtained

~or observers speaking in a normal voice in the c~anber was 57 dE,

orly 2 da higher ~han the quiet ~ome si~uation.

47

L

•85 11 ------------------­i

SO•••

•

REGRESSION LINE

- -- -- APPROXIMATION

• HOMES

• HOSPITALS.. DEPT STORE

• TRAIN

• AIRCRAFT

75

70co-u

c.--'"u

65

•<l)

<l)

Ja..

V)

4- -. •0

•

.J:="

cr-

•

(X)

'"•

--'

• •• . . . ~••

., ~ . ..t= -7' · •• ••• •

• •• •501- • • •• ••

-. ~.....r ••

~ .,p

•",.

'/'/ .

/"'..~. .

H57570656055504540

I ,I II II I I45 I I

35

Leq of Background Noi'e Level in dB

FIGURE 20. CONVERSING SPEtCH LEVEL AS A FUNCTION OF BACKGROUND NOISEIN SEVERAL ENVIRO~.jMENTS

In Figure 21, a more precise comparison was made between speech

results obtained in the anechoic chamber and those collected

under non-laboratory conditions. The speech levels measured in

the different noise exposure situations were originally recorded

at varying distances, however for this analysis, all results

were adjusted to approximate speech levels measured at 1.0

meter. It was noted from this plot that speech levels used

in the homes and hospital ~nd department stores could be

characterized as casual to normal voice levels, as determined

from the anechoic chamber measurements. People in transportation

interior environments such as trains or aircraft appeared to

speak at what could be compared to raised or loud voice levels

in the laboratory situation.

Three regression lines were calculated for the data plotted

in Figure 21. An approximation of the three regression lines

was also drawn in Figure 21. This simplified relationship

indicated that speech level stayed at about 55 dB when backg~ound

levels were below 48 dB. This is only a 3 dB increased dif­

ference in background level from results in Figure 20, where

speech levels were plotted disregarding distance between speakers.

It is noted in Figure 21 that people started raising their voice

level after 48 dB and continued to do so at the rate of 0.6 dB/dB

increase in the background level. At an ambient of 70 dB, the

speech data appeared to level out at 67 dB which indicated that

most people stopped raising their voice above a 70 dB ambient.

An explanation for the dramatic difference between Figures 20 and

21 in the speech measurements above 70 dB background level, was

that the high levels measured at the listener's ear and plotted

in Figure 20 were due to the short distance between the speaker

and the listener and not necessar~ly increased voice level due to

130, i

•75~ • . ~-

LOUD ~E

• Q). ~OJ

70r • ~~ Q)

"U ~

C -.-- • Q). ~

Q) _ • • E

~ 65 •• •• ~-' , • • RAISED U

~ •• •• uu 0-

\Jl QJ. • • 0QJ ~

o a.. A. • U

~ 60 • •• I .... • • HOME S ~D" • • • • HOSPITALS EQ) •• ..... 0-' • • DEPT STORE NORMAL u'::

• ••_. • • TRAIN -55 ~-. --; -:- --::- ~

•• • AIRCRAFT ::

• ~ • w

• • ~ 0• • REGRESSION LINE CASUAL U

•• • 0

50 J-- •• • • • _ - - APPROXIMATION >

• ••• ••45 I I I

35 40 45 50 55 60 65" 70 75 80 85

Leq of Bockground Noise Level in dB

FIGURE 21. CONVERSING SPEECH LEVEL NORMALIZED TO ONE METER AS A FUNCTION OFBACKGROUND NOISE IN SEVERAL ENVIRONMENTS

increased background level. Therefore in Figure 21 when the

levels were adjusted for the same 1.0 meter distance, 86% of

the speech measurements taken in an ambient environment above

70 dB dropped below the 70 dB speech level.

A plot of the interpersonal communication distance between

speaker and listener as a function of the background level is

seen in Figure 22. As the slope of the line indicates, the

distance between the participants in the quieter environments

such as homes or hospitals was approximately 1.0 meter. The

average background level corresponding to this distance was 43 dB.

When the background level increased to 70 dB such as in the trans­

portation environments, there the distance between the partici­

pants decreased to 0.5 meters.

A sUbjective determination of speech intelligibility was ,not the

sale criterion. Speech intelligibility was also defined objec­

tively by the Articulation Index (ANSI, 1969). The relationship

between AI and background level is seen in Figure 23. The corre­

lation coefficient for the regression line drawn through this data

was r =-0.82. Reading from the slope of the regression line, at

the background level of 40 dB, the AI = 0.82. For an increased

ambient level of 70 dB, the AI = 0.44. Thus, it was observed

that as the background level increased, the Articulation Index

decreased.

The curve plotted in Figure 24 is a translation of the regression

line in Figure 23. This was achieved by converting the Articulation

Indices into speech intelligibility scores taken from the psycho­

metric function which describes the percentage of sentences

51

\-----2.0

I •

•

'l • •1.4 • HOMES•1.3 • • • Hosp"ius1.? .. DEPT (>TO~t• • rr~AIN1.1

• AIRCRAf 1~

1.0 •Q)

~ •c .. ••0,9 •Q)

ur •~ 0.8 •-- •0

~ OJ •Q)

c .. ..Vl

~~

f\.) -- 0.6-'

0.5 ~..

0- ...~ • ... .......... • •• •'"-" .. ...0

'" ~... •Q.

V> •• •..........

O.~ l- ••

••

0.3 1_. •

•I I I I I I I I

35 4() 45 50 55 60 65 /0 75 90 °5 90leg of Background Noi'e levol in dB

FIGURE 27. INTEHPERSONAl DISTANCE OBSERVED FOR CONVERSATIONS AS AFUNCTION OF BACKGROUND LEVEL IN VARIOUS ENVIRONMENTS

i1.0 I ..••••••

•

•

•••

• HOMES

• HOSPITALS

• DEPT STORE

• TRAIN

• AIRCRAFT

•

••••

•

•

•

••

...

•

•

•

•

...

•

...

.... ...•

'\

••

•

•

••

•

•

••

•

•••••

•

•

••

•

•3 J-

.6 t--

. ) J-

.B t--

.41-

•9 .-.

, ......... .

" ." .. ..'-' .. ...... . .

...... ..· """, .. ... . '"", ..,..,~. ," ',.

...... ,"

" ' ...................... ... ....... ~ ...,

...... ,"

.7J-

\JlW

• •.2 I I I I I I I I I • I

3) 40 45 50 55 60 65 70 75 80 85

Leg of Background Noise Level in dB

FIGURE 23. ARTICULATION INDEXES FOR CONVERSATIONS IN VARIOUS ENVIRONMENTS

correctly understood (ANSI, 1969). Thus, for an AI = 0.50

the sentence intelligibility score is 97% and this occurs at a

background of 65 dB. This curve can now be utilized to predict

sentence intelligibility given an ambient level. For example,

at an ambient of 80 dB, the sentence intelligibility score was

81%.

A detailed comparison was made of the Articulation Indices and

sentence intelligibility scores for the speech levels utilized in

the five environmental situations with decidedly different back­

ground levels. As representative of the quiet environments, the

average AI for homes was 0.71 with virtually 100% sentence in­

telligibility; and for hospitals the AI = 0.63 with 99% intelli­

gibility. As the background level increased above 45 dB, the

Articulation Index decreased. ThUS, for department stores the

AI = 0.61 with 98% intelligibility; for trains the AI = 0.44

with 94% sentence intelligibility; and for airplanes the AI =0.38 with 90% intelligibility. Thus, it was apparent that intelli­

gibility was inversely correlated to background levels. However,

the decrease did not impede communication until the background level

was above 70 dB, then the AI dropped two-tenths to AI = 0.44 and

sentence intelligibility was calculated at less than 95%.

C. Speech Measurements in an Anechoic Chamber

Table I pummarizes the results of the anechoic chamber mea­

surements. There was approximately a 30 dB difference between

the average voice levels designated casual and shout. But the

progressive increase in level for the five speech categories

54

lOD

1

I. • -, ~7II.' • .."...,. Ie •• • . • •• • •• .-.• • • • • •

~-• •

• •• •

90r-•

>-. •~

•u

I•

Cl.l •~

~ •0

u 80 •-000~

~

~

I EQUIVALENT REGRESSIONQ)

-0 OF FIGURE 23 (SEE TEXT)<.: 70::>~

Q)

0 I •c:Q)

\Jl~

c:\Jl Cl.l 60

Vl

4-

0.. I • •c:Q)

0"- 50Q)

I"- •

40

30 I I I I I I I I ! I I

35 40 45 50 S5 60 65 70 7S 80 85

l~q of Background Noise Level in dB

FIGURE 24. SENTENCE INTELLIGIBILITY FOR CONVERSATIONS IN VARIOUS ENVIRONMENTS

(casual, normal, raised, loud & shout) ranged from 5 to 12 dB.

The smallest increase was between casual speech and normal

speech; the largest increase was between loud speech and shout.

A comparison of the speech levels in t~e categories of casual,

normal & raised for male and female speakers showed approxi­

mately a 2 dB difference. These results would not support

Beranek's (1954) recommendation that background levels be

lowered by 5 dB to accommodate the voice levels used by female

speakers. The real effect of vocal effort on speech level is

more evident in measurements made for the loud and shout cate­

gories where the difference between male and female speech

levels was 5 and 7 dB respectively.

Figure 25 shows the results of this phase of the speech study and

compares them with an earlier study by Beranek (1954) in wh~ch

the criteria for the Speech Interference Level (STL) were developed.

A comparison of the voice range between normal and shout revealed

that in the current study the difference was 28 dB, but in

Beranek's results the difference was only ~l dB. Both studies

agreed (within 1 d3) on approximately 73 dB for the loud speech

level. nowever, for the other speech categories (normal, raised

& shout) the results from the two studies differed by 3 to 4 dB.

The normal (57 dB) and raised (64 dB) voice levels in this st~dy

were lower than those suggested by Beranek with 61 dB and 67 dB

respectively; while shout was higher by 4 dB.

As Figure 25 indicates the standard deviation between speakers

increased with vocal effort from approximately 4 dB for casual

speaking to 9 dB at the shouting level. This increase in

56

90l1J.....111

~

0

(Bj 80a:l-0

c::

dl 70::>Q)

...J

.s:.:uQ)

Q)

a.. 60V"l

....Shaded Area0

tr Ind ica~es StandardQ) Deviation

...J

50

Casual Normal Raised Loud Shout

VlJCO! Efforts

FIGURE 25. SPEECH LEVELS FOR VARIOUS VOCAL EFFORTS

57

variability between individuals may be attributable to several

factors. One explanation is that while all sUbjects were given

the same instructions for measuring their speech in the anechoic

chamber, the individuals may have differed in their personal

interpretation ·of the five vocal effort descriptors. For example,

it might be more difficult (especially for the children as evi­

denced by the 9 dB standard deviation) to understand how much

vocal effort the experimenter meant when the instructions were to

shout. The subjects seemed better able to uniformly relate to

the instructions to speak in a normal voice, with a resulting de­

crease in inter~ubject variability. Another factor contributing

to the variance between subjects may be related to the difference

in individual capabilities to speak at the various voice levels.

Thus, most subjects were able to maintain level·s within the

speech range of the first three speech categories. However, for

the vocal effort in the Zoud and shout categories, the ,capacities

of the individuals to maintain these levels differed greatly.

Finally, most individuals speak everyday at a speech level which

would be characterized as either casual, normaZ, or raised.

Therefore, when asked to speak at a loud or shout level, they

would be less familiar with what level to maintain and they would

be far less accustomed to exercising lhis leve~ of speech.

The shape of the speech spectra also changed in an orderly fashion,

providing higher level components at high frequencies for increased

voice level. An indication of this trend is the shifting of the

maximum one-third octave ba~d from 500 Hz to 1600 Hz (which is

approximately 1.6 octaves) as the voc.al effort progressed from

normal to shout. The comparison between speech spectra among

males, females and children also indicated similarity, except at

58

the higher speech levels. In all cases, however, the speech

spectrum presented in the Articulation Index standard (ANSI,

1969), contains less irregularities than in the spectrum ob­

tained for the present data.

59

REFERENCES

ANSI, American National Standards Institute, "Methods for theCalculation of the Articulation Index", ANSI S3.5-1969.

Benson, R. W., 1. J. Hirsh, "Some Variables in Audio Spectro­metryl!, J. Acoust. Soc. Am. 25,499-505,1953.

Beranek, Leo L., "Acousticsl!, McGraw-Hill Electrical and ElectronicEngineering Series, 1954.

Brown, W. S., Jr., Thomas Murry & David Hughes, "ComfortableEffort Level: An Experimental Variable", Journal of the AcousticalSociety of America, Vol. 60, No.3, September, 1976.

Dunn, H. K., S. D. White, I!Statistical t>leasurements on Conversa­tional Speech", J. Acoust. Soc. Am. 11, 278-288, 1940.

Environmental Protection Agency, "Information on Levels of Envi­ronmental Noise Requisite to Protect Public Health and Welfare withan Adequate Margin of Safety", 550/9~74-004, Environmental ProtectionAgency, Washington, D. C., March 1974.

French, N. R. and J. C. Steinberg, (1947), "Factors Governingthe Intelligibility of Speech Sounds", J. Acoust. Soc. Am. 19, 90-119.

Gardner, Mark B., "Effect of Noise, System Gain, and Assigned Taskon Talking Levels in Loudspeaker Communication", Journal of Acous­tical Society of l America, iQ, No.5, 955-965, 1966.

Klumpp, R. G. and J. C. Webster (1963), "Physical Measurements ofEqually Speech-interfering Navy Noises", J. Acoust. Soc. Amer., 35,1328-1338.

Korn, T. S. (1954), "Effect of Psychological Feedback on Conversa­tional Noise Reduction in Rooms", J. Acoust. Soc. Am., 26, 793-794.

Lombard, E., "Le Signe de L'elevatlon de la volx", Ann. Mal.·Oreil. Larynx, 37, 101-119, (1911).

Pickett, J. M. (1958), "Limits of Direct Speech Communication inNoise", J. Acoust. Soc. Amer., 30, 278-281.

60

APPENDIX A

INSTRUMENTATION EMPLOYED IN SPEECH

MEASURErIJENT AND ANALYSIS

~l

rNST~UMENTATrON APPENDIX A

Block diag:r'Clms are presented in this s~ction of instru­

mentation used to acquire speech level data, calibrate

equipment, and reduce data,

1. pata A~qu1sition

Equipment used to measure speech levBIs in classrooms is

shown in Figure A.l, Data Were recorded on three independe~t

tracks of a standard tape recorder. Pigure A-2 shows the

typical microphone placement wit~in a classrOom_

2. Eq~ipment Calibfation

Calibrat·ion of the teacher's microphone was achieved in'" " "

an anechoic chamber under 90nditi9ns outlined in Figure A~3,

The basic procedure was to place the min~ature microphone

immediatelY adjacent to a standard instrumentation microphone

(a 1" B & K condenser microphone). Output levels producedby

the two microphones 1 meter from a loudspeaker were then com_

pared at a variety of frequencies and levels. A correction

spectrum so developed was incorporated into all subsequent

processing involving data recorded by the miniature microphone.

Calibration of the miniature microphone in the fielq was

accomplished via. a B & K type i.J230 (gi.J dB) caHbrator, for

which an adaptor was specially prepared.

3. Data Analysis

All data reduction was accomplished by SBN's rea+ time

one-third octave band ana:lysis s;ystem, shown in Figul"€ A-4. The

process involved playing magnetic tape recordings .into a tipeotrum

analyzer, procep~ing the frequency ana:lyzeddat q d~gitallY, using

a specially designed computer program, pl,lnching Paper tape for

long term storage, ~nd listing the paper tapes on a line printer.

62

Magnetic TapeRecorder

e+------ID 0 0 0SoundLevelMeter

SoundLevelMeter

SoundLevelMeter

MicrophoneCalibrator

AnnotationMicrophone

Teacher'sMicrophone

MicrophonePre-AmplifierPosition A

Microphone LPre-AmplifierPosition B

fr---'

A'- ~ EQ U rPM EN T FOR MEA 5URI N G 'S PEE C HAN DBA C KG R0 UN DLEvELS IN CLASSROOMS

Teacher's MicrophoneMicrophoneRandom Inc idence CorrectorPre AmplifierPower SupplySound Level MeterMagnetic Tope RecorderPiston Phone CclibratorRandom Incidence Corrector Adaptor

TransDund, Mode I 74-A (M in; mic)B & K 1 Condenser, 1.0 InchB& K, Type UA005SHP r Type 15108BHP, Type 15114AB& K, Type 2205Sony, Model 854-45B & K , Type 4220B& K, Model 152

63

TEACHER'S MICROPHONErNorn by Teacher)

DDQDDD D 005'lJ DDDDDDD- D D D DDDDDDBOOnO•POS.S

BlqckboordT8Clcher's

Desk

FIGURE A-2. MICROPHONE LOCATIONS rN CLASSROOM

64

GraphicLevelRecorder

Drive

SineRandomGenerator

SoundLevelMeter

SoundLevelMeter

PowerAmplifier

r Ref:r:c7Mic:ph:n;- - - ,& Pre - Amplifier

Miniature MicrophoM

A-3 EQUIPMENT SETUP FOR CALIBRATION OF MINIATUREM ICR0 PH0 N E USE DIN CON VERSA T 1'0 N A L· SPEE C HRECORDING

Reference MicrophonePre-Ampl ifier,Sub-M in iature Microphone.

Sovnd Level Meter (SlM)Graph ic leve I RecorderSine Random GeneratorPower Ampl ifierSpeakerPiston Phone Calibrator

B & K, Type 4133, 1/2 InchG-R, Type P42Tronsovnd, Minimic, Model 74-A ,

or BBN, Electret MicropnoneB & K , Type 2205B & K , Type 2305B& K, Type 1024JBl , SE400SJBl , C40B& K , Type 4220

65

6-0Magnetic TapeRecorder

/'-.. Reel-TimeSound One-Third DigitalLevel Octave Computer

~ ""- Band ...Externa I - ow ...Filter ""-

Meter Analyzer.. -

A-4 SPEECH AND BACKGROUND ANALYSIS SYSTEM

Magnetic Tape RecorderSound level Meter (5lM)Edema I Fil terReal Time Third Octave Analyzer

Sony, Model 854-45 or Nagra, Model SNB& K, Type 2203BBNHP, Type 8054A

66

APPE~DIX B

INSTRUCTIONS AND WORD LISTS USED IN CLASSROOMSAND ANECHOIC CHA~BER

67

CLASSROOM INSTRUCTIONS

To the Teacher

Please read the following word list to

your students. Read the words one at a

time and do not repeat the word even if

asked by a student to do so. Read the

words at a normal pace and maintain the

same classroom lecturing voice level

throughout the presentation.

To the Student

Listen carefully to the words the teacher

will read. They will be read only once.

Do not ask the teacher to repeat a word

that you have missed. This is not a

spelling test, nor does it count on your

grade. Pay close attention and do the

best you can.

68

PHONETICALLY BALANCED WORDS READ IN CLASSROOM

LIST 1 LIST 2 LIST 3 LIST 4 LIST 5 LIST 6 LIST 7CANE TANG vIHY FLOAT FEED AS GASPTHERE FATE TURF SAGE GAPE PUN WOODISH SUCH GNAW CLOAK SICK ROUGH THOUGHHID ELSE DROP RACE GREEK NIGH ACTHEAP PIT JAM TICK ROE BEST DWARFPANTS GILL FLUSH TOUCH CHOOSE JAG SCOUTHUNT CHARGE ROUSE HOT TRUE TONGUE SLEDGENO BOUGHT NECK POD PASS HITCH SNIFFBAR CLOUD SOB FRO\'iN BROWSE BOG FLINGPAN MUTE TRIP RACK PUNT ROQl\1S COOKFUSS BEAN DILL BUS SHOVE FOWL DOPECREED SCYTHE THRASH BLONDE HILL REAP GUNBOX VAST DIG PERT BLACK WRITE JUGSTRIFE RIB RATE SHED HIGH iVIFE l'vlUDDIKE PICK FAR KITE RIND CLOTHES PLODNOT HOCK CHECK RAW VASE GAGE FAKEFORD OUR AIR HISS RODE FORGE PHASEEND HIT BEAD FIN PUFF PRHm RASHTHEN JOB SPED SCAB INCH SCAN RJ;CHBASK WISH CAST HOW BRONZE GROPE BUTFRAUD NUT CLASS STRAP SOLVE SUP POUNCESJI'lILE DAB LUSH SLAP BATHE SLOUCH WHIFFDEATH FROG SHOUT PINCH ADD THUS PIGARE LOG BALD OR REAR PRIG ROARBAD SNUFF CAPE STARVE SHINE FLICK SAGPEST BLUSH SIZE NEW SLY BADGE BYSLIP NAB \.JEDGE RUT WRATH CLOTH AMRUB BAIT DECK NEAT LOVE KEPT NINEFEAST BUD HURL DODGE BECK FLOP vJIREDEED RAP \.JHARF SKETCH THICK FALL AIMCLEANSE ["lOOSE LEAVE JlmRGE FLAP ItIASP SHAFTFOLK TRASH CRAVE BATH CHEAT ODE SOUTHNOOK GLOSS VOW COURT \<lINK HULL i10E["lANGE PERK LA1rJ OILS ZONE FEE CHOPSUCH VAJI'lP STAG SHIN ODDS LAG KNITUSE START OAK PECK KID THIGH RAIDCRASH EARL NEST BEAST TRADE CHART SINRIDE CORPSE SIT HEED SCARE '.1AIT CUTPILE SLUDGE CRIJI'lE EEL MAST COB HIf>1RAT TAN tWCK tiJOVE PIPE MASH DOSERAG WAYS FAl'lE EARN GOOD EYES QUIZIS BOUNCE TAKE BUDGE LEND RAISE SIEGEWHEAT NIECE i'iHO SOUR YAWN DEEP COASTRISE AWE TOIL RAVE '.1ATCH SHANK GRADEHIVE THEM PATH BEE THUD RAY FORTGROVE NEED PULSE BUSH TUG GAP CONESTOE QUART FIG TEST CURSE CRIB OFFPLUSH FIVE BARB HATCH 01tlLS PUS PENTCLOVE HIRE PLEASE COURSE NOSE EAT RANGEFERN SEOE ACHE DUPE GRUDGE DAD JllOTE

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INSTRUCTIONS FOR SPEECH MEASUREMENTS IN ANECHOIC CHAMBER

PLEASE MEMORIZE THE FOLLOWING SENTENCE:

"JOE TOOK FATHER'S SHOE BENCH OUT; SHE WASWAITING AT MY LAWN."

1. Speak in a NORMAL VOICE - th~t which you would use ineveryday conversation.

2. Then speak in a RAISED VOICE.

3. Then speak as LOUDLY AS POSSIBLE without straining yourvocal cords.

4. Then speak at a SHOUTING VOICE level.

FOR EACH VOICE LEVEL. REPEAT THE ABOVE SENTENCE UNTIL NOTIFIEDTO STOP.

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