Naval Submarine Medical Research Laboratory 4

NSMRL REPORT 1185 29 April 1993

AD-A264 464

A%.A

";:r STATES

CHARACTERIZING NOISE FIELDS IN SHIPBOARD SPACES

Robert J. Syliester - -

Releasd by 93-11026

P. IC Weathershy, CAPT, MSC, USN "i~ui~ii

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for puhblic release; distribution unlimited
Characterizing noise fields in shipboard spaces

Robert J. Sylvester

Naval Submarine Medical Research Laboratory

Report Number 1185

Naval Sea Systems Command

Program Executive Office Surface Ship ASW Systems

Task No. SSAS-91-77A01 R2

Approved and Released by

P. K. Weathersby

Commanding Officer

Approved for public release; distribution unlimited
SUMMARY PAGE

THE PROBLEM

The problem involves the establishment of a method for characterizing discrete tone sound

fields in reverberant shipboard spaces, in order to asse:zs the noise hazard in these areas and establish criteria for an acceptable noise environment.

THE FINDINGS

Detailed contour sound field maps of a reverberant test chamber insonified with discrete

tones were developed. These maps revealed a significant spread (35.2 dB) in sound pressure

levels from point to point in the sound field. These results demonstrate that measurements taken

with a conventional non-integrating sound level meter could severely under estimate or over estimate the actual noise hazard, depending on the measurement locations chosen. On the other

hand, measurements obtained with an integrating sound level meter were comparable with the

results of the sound field manp. Personal noise dosimetry was also used, but extraneous noise

produced by the subjects affected the results. Therefore, dosimetry was not considered a viable

alternative for measurement of noise hazard.

APPLICATION

These findings contribute to the adoption of a method for characterizing discrete tone sound

fields in ships* spaces.

ADMINISTRATIVE INFORMATION

This research was carried out under a task plan entitled, "Development of acoustic

habitability standards for ships' spaces subjected to intense tones," and was funded by Program

Executive Office Surface Ship ASW Systems Task No. SSAS-91-77AO1R2 dated 14 December

1990, "AN/SQY-1 Frequency Array Testing," Naval Sea Systems Command PMO 424. The

views expressed in this report are those of the authors and do not reflect the official policy or

position of the Department of the Navy, Department of Defense, or the U.S. Government. This

report was approved for publication on 29 April 1993, and designated as NSMRL Report 1185.

ii
ABSTRACT

Three methods of characterizing discrete tone sound fields were tested in a reverberant compartment. Method one uses sound field mapping, method two implements an integrating sound

level meter, and method three uses personal noise dosimetry. Sound field mapping resulted in a

detailed and accurate visual representation of the sound field, but because the procedure is both

complicated and time consuming it is not appropriate for day-to-day analysis of compartments.

The dosimetry measurements were erratic and did not compare well with the sound field mapping measurements. The dosimeters were influenced by the extraneous noise produced by the

activities of the test subjects wearing the dosimeters. Consequently. personal noise dosimetry

cannot be considered a reliable method for characterizing sound fields for the conditions of this

test. An integrating sound level meter combines the accuracy of the sound field maps with the

simplicity of operation of the personal noise dosimeters. A single number was attainable that

was representative of the noise hazard associated with discrete tones in reverberant compartments.

I 've

iii
[Blank Page]

iv
Characterizing Noise Fields in Shipboard Spaces

Introduction When dealing with discrete tones (a sound

wave that is a simple sinusoidal function of

Shipboard personnel are exposed daily to time) the main concein is standing waves.

intense noise from various sources. The Standing waves result from reflections caused

amount of the noise exposure depends on by the walls, floor, ceiling, and other surfaces

various conditions, including the charac- in an enclosed compartment. Standing warc.,

teristics of ship's spaces. The spaces of cur- can be described as the combination of an

rent concern are the ship's berthing areas, outward-traveling wave and a backwardwhich may vary from highly absorptive to traveling wave. The outward-traveling wave

highly reverberant. We consider here only is the original free-field wave that started out

thoroughly reverberant spaces. Sound levels from the source, and the backward-traveling

in reverberant spaces vary substantially with waves are the reflections that are making their

time and measurement location. The severity second, third, fourth, and so on, round trips.

of the variation in sound level depends on the The addition of these outward and backwardamount and position of reflective and absorp- traveling waves in some places, and cancellative materials, as well as their effective rough- tion in others, cause distinct patterns of

ness, porosity, flexibility, and in some cases sound pressure level; maxima in some places,

their resonant properties. Parallel surfaces minima in others (Harris,1991; Hassall,

(ceiling, floor, and walls) actually enhance Zaveri, 1988).

standing waves by minimizing the distance between reflections. Even the positioning of fur- Broad-band noise may be considered to be

niture and people cause the sound field to comprised of many frequency components.

vary, making it difficult to characterize it. Each frequency component exhibits a particular standing wave pattern that may be

Assessing the noise exposure in these measured using suitable narrow-band analysis.

areas, and establishing criteria for an accept- However, with broad-band analysis, a sumable noise environment, demand the adoption ming effect takes place across the spectrum so

of a method for characterizing the noise level, that the difference between sound pressure

This method should provide a numerical maxima and minima is reduced substantially.

evaluation of the noise (preferably in terms of With continuous broad-band noise having no

a single number) that will bear a meaningful pronounced discrete frequency components,

relation to the amount of interference caused useful analyses of ships* spaces can be made

° by the noise. In order to determine the poten- using simple sound level meters. When dealtially adverse effects of noise on shipboard ing with intermittent discrete tones, as is our

personnel, three methods of characterizing the present concern, the averaging effect is minisound field for discrete tones in reverberant mal and a great variation in sound level can

spaces were tested. Method one uses sound occur throughout the compartment. This

field mapping, method two implements a effect is worsened when working in highly

hand held integrating sound level meter, and reverberant compartments. In such situations,

the third method uses personal noise simple sound level meters produce exceedingdosimeters.

I
ly erratic estimates of the auditory hazard of cated. Figure 2 shows a photograph of the

tones. bcrthing area and the location of the speakers.

Twenty Owi-202 speakers were evenly

Method spaced around the perimeter of the room at a

height of 2.4 m to center, and two coaxial

Exp•sure chamber and noise stimulus. speakers in infinite baffles occupied opposite

Experiments were conducted on the effects of comers of the room to simulate shipboard

24-hour exposures to pure tones on Navy noise by enhancing the lower frequencies.

personnel. The ineasufemeats reported below Each speaker was driven by a separate

were taken from these habitability experi- amplifier. The amplifier outputs were adments to establish exposure levels. justed to produce a uniform near-field sound

pressure level from each of the individual

A schematic of the testing chamber used speakers.

for the measurements is shown in Figure 1.

Six beds occupied two thirds of the chamber, The stimuli were generated by a Hewlett

and three tables were located in the areas indi- Packard 325A universal source generator

TOP VIEW

ILA

AjA

* 2Z $tr- •am

S.

SIDE VIEW

Figure 1. Schematic of exposure chamber: Top View and Side View

2
9u;

Figure 2. ExpoNure chamber.

controlled by a computer. The signal from the were standing, sitting, and sleeping, at ear

generator was fed through a Rockland 75 IA level for an average male (5"9"). All measureprogrammable elliptic filter and Crown D-75 ments were recorded on a Bruel & Kjaer

amplifiers before reaching the 20 Owi-202 (B&K) type 2133 real-time spectrum anal- zer.

speakers.

The map generated for the horizontal plane

For the habitabiliiv experiments, the at standing height encompassed the entire

stimuli consisted of six discrete tones (720, room (Figure 3). The measurements were

800, 880, 960, 1040, 1120 Hz) presented at taken at regularly spaced points within the

the same amplitude. Each tone was presented room using a predefined grid (80 cm X 80

for a duration of I s with 50 ms rise and fall cm). A more detailed map was generated for

times to eliminate transients. The tones were the map at the sitting level, which used a 30)

presented in pseudorandom sets of six con- cm X 50 cm grid in order to find the absolute

tiguous tones. The six tone sets were repeated maximum and minimum sound pressure

every 23 s (20% duty cycle). The six permuta- levels produced by the standing wave pattions were continuously cycled through for an tems. The third map (sleeping level) used a

exposure period of 24 hrs. 60 cm X 100 cm grid.

Sound Field Mapping. Sound field maps A map was generated for each tone (720.

were generated for three horizontal planes in the 800, 880, 960, 1040, and 112-0 Hz), as well as

exposure area (Figure 3). The three heights used a

3
STANDING LEVEL: [FIG. ( 51

SITTING LEVEL : ( [FIG. 6]

SLEEPING LEVEL: [FIG. 7]

Figure 3. Each level depicts the location of a horizontal plane. The sound field

maps shown in figures 5, 6, and 7 were generated from measurements taken in

each of the three planes above. The map corresponding to each level is

indicated in brackets.

1.8

UJ

2 1.6

Q 1.4

D 1.2

C,,

0

az.. I

x

U. Boom

a,, 800m - -I

z 400m -

S200m

Cm 0 T

: 63 125 250 500 1K 2K 4K 8K 16K

uJx 1/3 OCTAVE FREQUENCY BANDS (Hz)

Figure 4. Reverberation times of exposure chamber (1/3-octave bands).

4
frequency sweep from 720-1120 Hz. The B&K mapping program (CPLOT) wa u-,tcd ti

stimuli were generated in the same manner as linearly interpolate between each measuredescribed above for the testing of subjects. ment point. The results were presented in thu

Each measurement was stored using the B&K tbrm of contour maps depicting the sound

type 2133 spectrum analyzer with third octave pressure levels throughout the compartment in

analysis, linear averaging, and A-weighting. a specified horizontal plane (Figures 5.6. 7.

To obtain an accurate reading for each frequency, each tone was presented for 4 s rather Hand held Sound Level Meter. In this

than the 1-s pulse used for testing subjects. A measurement situation, the widelv fluctuaiinig

2-s sample was taken, programmed to trigger display of a traditional non-integrating sound

after a 1-s delay. The 1-s delay allowed the level meter makes it extremely difficult to

sound level in the room to reach a steady determine the correct sound level. Therefolre.

state. The measurement data were transferred an integrating sound level meter was used.

from the input memory to the buffer memory. These instruments summate noise energv on a

After the 4-s tone, a 1-s delay allowed for relatively long term basis and divide the value

complete decay of the noise before the next obtained by the elapsed time. thus, providing

tone was presented. Reverberation measure- an equivalent sound pressure level (Leq). In

ments of the chamber show that 1 s is suffi- addition, the meter stores the maximum and

cient time for the noise level to reach its minimum SPL recorded during the measureambient level. It can be seen from Figure 4 ment time.

(1/3 octave reverberation times of the exposure chamber) that the reverberation time for Leq, which is equivalent to La,. is the

the frequencies of concern is approximately sound pressure level averaged over the meas800 ms. A total of 2233 measurements were urement period. It can be considered as the

taken for 319 different locations in the sound continuous steady sound pressure level which

field. would have the same total acoustic energy as

the real fluctuating noise over the same time

The measurements taken tbr the frequency period. Thus, the Leq is in fact the RMS

sweep were 30 s in duration. The frequency sound level with the measurement duration

sweep (720 - 1120 Hz) was 10 s in duration. used as the averaging time.

The analyzer was programmed to trigger after

1 s. Unlike the discrete tones, the signal was Leq is given as:

continually fluctuating and a steady state condition was not produced, but the delay was 4q L:(T

necessary to eliminate transients from the eq =Lay 10 log T P

speakers and to allow the sound field to

saturate before the instrument began sam- T measurement duration.

pling. Another 1-s delay after the noise

source was turned off allowed the signal to pt = sound pressure.

decay before another measurement was taken. po = reference sound pressure of 20 rtPa.

The data stored in the buffer of the B&K This method was implemented with the B&K

2133 were transferred to a IBM Personal Com- 2230 Sound Level Meter (SLM) with a B&K

puter and converted into ASCII code. A

5
EXPOSURE CHAMBER

n 79.2 - 80.0

* 80.0-80.7

* 80.7-81.5

* 81.5-82.2

U 82.2 - 83.0

LOCATION OF MAP

Figure 5. Sound pressure contour map of the reverberation chamber. Elevation: 162 cm (standing level). L q =

82,9 dB, Stimulus: 720-1120 Hz sweep.

6
* 81.8-82.8

* 82.8 - 83.8

* 83.8-84.8

EXPOSURE. CHAMAFR

ti2 U... al

LOCATION OF MAP

Figure 6. Sound pressure contour map of the reverberation chamber. Elevation: 125 cm (sitting level), Lxq

82.1 dB, Stimulus: 720-1120 Hz sweep.

7
EXPOSURE CHAMBER

ELIE 76.2 -77.8

79.1 dh. Stimulus: 720-1l120 Hz1 sweep.
1625 third octave filter to analyze the expo- the dosimeters. Only eight min f d•ata were

sure area. A spatial temporal mea;';urement lost during data storage and reprogramming in

was obtained by performing a 1/3-octave fre- a 24-hr period.

quency analysis with A-weighting while

moving the SLM uniformly thioughout the Each dosimeter was programmed for twv 6-

compartment. The measurement length was hr run times during the day, and a 12-hr run

45 min, and was repeated three times to time during the night. A shorter run time alobtain a Leq representative of the actual noise lows time history statistics to be saved more

dose a subject would receive in that environ- frequently. The dosimeters were configured

ment. The noise stimulus for these measure- using an A-weighting filter.

ments was similar to the discrete tone sequences

described for the habitability experiment. The In addition to the personal dosimeters. two

only difference was that the 23-s delay l- .tween control dosimeters were placed in fixed po'sisequences was omitted. Therefore, the stimulus tions in the exposure room during each 24-hr

was present continuously (100% duty cycle), exposure. The locations were never the same

for any two exposures, resulting in a total of

The SLM simultaneously carries out the 16 different measurement locations. The confollowing measurements: sound pressure level trol dosimeters were programmed with the

(SPL), Maximum SPL, Minimum SPL, and same format as the personal dosimeters.

Leq. Obtaining the Leq, min, and max measurements were of most importance because RESULTS

they are directly comparable with a statistical

analysis of the samples taken with the real- Sound Field Mapping. The data generated

time frequency analyzer (B&K type 2133) using method one (Sound field mapping),

with Sound Field Mapping. with discrete tones showed a significant

spread in sound pressure levels (SPL) from

Personal dosimeter readings. Eight 24-hr point to point. The maximum SPL was

exposures were performed in the experiment. 92.7 dB and the minimum was 57.5 dB. This

Each group was comprised of six subjects', wide range of SPL values demonstrates the

who were allowed to move freely about the significant effect standing waves have in

exposure room. Each subject wore a db-3 100 reverberant compartments. A power average

Metrosonics dosimeter (a device that mea- across all frequencies and measurement locasures the actual noise dose received by a sub- tions was calculated on these same data. resultject by measuring the sound pressure level as ing in an average SPL (or Leq) of 82.7 dB.

a function of time). The dosimeters were

clipped to the subjects belts and the micro- Three maps were generated using the measphones were clipped to their shirt collars urements obtained with the frequency sweep

approximately 10 cm from the ear. for three different planes. The map generated

at 162 cm (standing level) resulted in a power

The results can be displayed as a time his- average of 82.9 dB with a standard deviation

tory of the noise dose on a graph as in Figure across 50 different locations of 0.6 dB

8, or as an equivalent sound pressure level (Figure 5). The map generated at 125 cm (sitsuch as Leq. Two minutes were required to ting level) resulted in a power average or 82. 1

read the data into the computer and reprogram dB with a standard deviation across 139 dif9
ferent locations of 0.7 dB (Figure 6), and for compared with the data from the other two

60 cm (sleeping level) the power average was planes. Figure 7 demonstraics how the ab79.5 dB with a deviation across 48 different sorptive qualities of the bedding, materials atlocations of 1.6 dB (Figure 7). tenuate the SPL in the areas closest to the

beds. The SPL dropped 3.0 dB above the

The results for the sleeping level show a 2 beds (depicted with white blocks on the condB drop in SPL, and a higher deviation when tour map (Figure 7)). This attenumion caused

(A)

1 2 0 .0 /1 1 1 , A A I ,, a I . i -1 2 0 ý0

8/21

104.0- -1040

V

88 88.0 J :>

W -J u

>

J 7072.0

z z D: {

0 0

56.0 56.0

4001- LAV

40.0I I I I I I I 40.0

10:35;00 II :43-33 12:52:07 14:00:40

TIME (MAGNIFICATION: I 00)

(B)

120.0 - 1 k I a I a a I a a a 1 120.0

1o4.0- 104.D

V -

-J 88.0- 88.0 -JI~

ILltd -J 72.0-

W " 72.0- 72.0 0J

z z 0 M0

56.0- 56.0 n

-- LAV

40.0 1 , , ' ' ' 40.0

I0-46-57 11:55:17 13:03:37 14:1 1;57

TIME (MAGNIFICATION: 1.00)

Figure 8. (A) Dosimeter data showing the sound pressure levels vs. time. The levels were

generated by the subjects' activity and background noise. (B) Sound pressure levels were

generated from a combination of the lone. Stimuli (Leq = 83 dB ) and the subjects' activity.

Noise stimuli present 20% of the time (20% duty cycle): 7 dB must be added to the results alxwe

for comparison with SLM and mapping data (100% duty cycle).

10
the increased variation in levels above and In comparing graphs 8a and 8h, it is dif- around the beds, which accounts for the higher ficult to determine which one was generated

deviation of 1.6 dB at the sleeping level, during the exposure period. This implies that

the subjects were generating random noise at

Hand held Sound Level Meter. The three a level equal to or greater than an L,.,q of 90

45-min continuous measurements taken with dB during the 3.5-hr period. In addition to cxthe integrating sound level meter, resulted in traneous background noise, is the possibility

Leq'S of 82.8, 82.9, and 83.2 dB. The mean for the subjects to obstruct the dosimeters

of these data is 83.0 dB and the standard microphones. The result of such an occurdeviation is 0.17 dB. Comparing the mean rence can be observed in Figure 8a near 1330.

with the power average of all the data

generated for the sound field mapping On the other hand, the results of the conresulted in a difference of only 0.34 dB. trol dosimeters compared more closely with

the results obtained with methods one and

Personal dosimeter readings. Personal two. Figure 9 shows four hours of dosimeter

dosimeter data was collected during the data from a control dosimeter on the same 83

habitability experiment described earlier, dB exposure day.

during which the stimulus was present 20% of

the time (20% duty cycle). Therefore, the It is evident from the graph that the sound

dosimeter results reported below are adjusted pressure levels were more stable with this

by +7 dB for comparison with the sound field measurement. The spikes are decreased in

mapping and integrating SLM results ob- amplitude as well as in number when comtained when the stimulus was present 100% of pared to the subject dosimeter data. Furtherthe time (100% duty cycle), more, the average level (Leq) was 83.6 dB.

Personal dosimeter data resulted in 6-hr Even though the results of the control

L[eq readings ranging from 91.6 dB to 99.5 dosimeter in Figure 9 appears to yield an acdB, and the control dosimeter data resulted in curate measurement, Leq results from the

12-hr [eq measurements ranging from 88.3 other 15 control dosimeter measurements

dB to 95.6 dB. Figure 8a shows the dosimeter ranged from 88.3 dB to 95.6 dB. This wide

data for a period during which the noise range in values was dependent on the location

stimuli were not present. Figure 8b shows of the dosimeters during the eight exposures.

dosimeter data from the same subject on a Because the dosimeter microphone remained

sperate occasion. During this dosimeter read- in the same location throughout the measureing, noise stimuli were present at an Leq of 83 ment time, it is not as accurate as the temporaldB (determined by a B&K 2133 integrating spatial measurements obtained with the

SLM). Therefore, the sound pressure level integrating SLM.

readings in Figure 8a represent the noise

generated by the subjects' activity and con- Discussion

tributions from background noise, and the

readings in Figure 8b represent the noise Method one (sound field mapping) demongenerated by the subjects and the tone stimuli. strates the difficulties in characterizing the

sound field in reverberant compartments

when dealing with discrete tones. The 2233

11
120.0- . ' ' , , , ' , ' -120.0 -

8/22

1100- 110.0

S100.0- 100.0 m

ILJ

z z _J -J Z a 90.0- fz-90.0 a

0 0

0 80.08

- LAV

70.0- 70.0

10-49:00 12:06:53 13:24:47 14:42:40

TIME (MAGNIFICATION: 1.00)

Figure 9. Control dosimeter data for a four hour period, during which the tone stimuli was

present at a SPL of 83 dB.

samples recorded show a 35.2 dB spread in mented with an integrating SLM. An integratsound pressure levels throughout the chamber. ing SLM is less expensive and much simpler

This result demonstrates the impracticability to operate than a real-time analyzer. Additionof describing the noise hazard in this type of ally, the results of this experiment show the

environment. If only a few data points were Leq readings taken with the SLM (B&K type

used, the results could grossly misrepresent 2230) compare well with the power average

the noise hazard. It would be impossible to obtained from the sound field mapping data,

characterize the noise field, and the noise

hazard, by taking only a few random measure- Results from the personal dosimeters were

ments. significantly different from the levels obtained with Sound Field Mapping and an InThe sound field maps in Figures 5, 6 and 7 tegrating SLM. The measurements of sound

give accurate and detailed results, but because exposure were influenced by the subjects*

this method is time consuming, requires ex- movements and speech.

pensive equipment, and requires relatively

complicated procedures, it cannot be con- The scraping of the microphone against

sidered an appropriate method for day-to-day materials created extraneous noise, causing

analysis of compartments. On the other hand, the dosimeters to record artificially high

the results of sound field maps can be used to levels. These effects were caused by the subjudge the accuracy of other methods avail- jects behavior and by the location of the

able. One such method available is imple- microphone. Therefore, the circumstances of

12
this particular experiment resulted in a high

degree of variability in personal dosimeter

data. This is demonstrated by the dosimeter

results in Figures 8a and 8b. The data

recorded on a dosimeter during a nonexposure day is shown in Figure 8a, and data

recorded during an 83 dB exposure day is

shown in Figure 8b.

The mean of the data recorded on the nonexposure day was actually slightly higher than

the mean of the data recorded on the exposure

day. These results indicate that dosimeters

cannot be considered a reliable method for

characterizing sound fields in reverberant

compartments at sound pressure levels of 83

dB or lower. At higher sound pressure levels

the extraneous noise produced by human activity would have a lessened effect, and the

data recorded on dosimeters would be more

meaningful.

The results obtained with the integrating

SLM not only compared well with the sound

field maps, but its simplicity of operation, and

relatively low cost, make it an attractive alternative to sound field mapping. Even though

an integrating SLM is simple to operate, it is

important that the particular measurement

situation be carefully examined before measurements are taken. The location and type of

sound source, as well as the objects and materials located in the compartment will determine how to obtain a uniform measurment.

References

Harris, C. M. (1991). Handbook of acoustical

measurements and noise control. New

York: McGraw-Hill.

Hassall, J. R., and Zaveri, K. (1988).

Acoustic Noise Measurements (5th ed.)

Naerum, Denmark: Bruel & Kjaer.

13
[Blank Page]

14
UNCLASSIFIED

-LSECUR•Y-TCLASS1FICATTON- OFTHIS PA'•E

Form Approved REPORT DOCUMENTATION PAGE OMB No 074-0188

1a. REPORT SECURITY CLASSIFICATION lb RESTRICTIVE MARKINGS

2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTIONAVAILABIUTY OF THE REPORT

Anproyed for pubiq, release;

2b. DECLASSIFICATIONIDOWNGRADING SCHEDULE dl~tribution uni mnted

4. PERFORMING ORGANIZATION REPORT NUMBER(S) 5, MONITORING ORGANIZATION REPORT NUMBER(S)

" NSMRL Report 1185 NA

6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION

Naval Submarine Medical (IfApp/icable) Naval Medical Research and Development Research Laboratory Command

Sc. ADDRESS (City, State, Zp Code) 7b ADDRESS (City, State. Zp Code)

Box 900, Naval Submarine Base NLON, 8901 Wisconsin Ave.

Groton, CT 06349-5900 Bethesda, MD 20889-5606

8a. NAME OF FUNDING/SPONSORING 8b. OFFICE SYMBOL 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER

ORGANIZATION (IfApplicable) Task No. SSAS-91-77A01R2 dtd 14 Dec 90

Naval Sea System Command PMO 424

Sc. ADDRESS (City, State, Zip Code) 10. SOURCE OF FUNDING NUMBERS

Washington, DC 20362-5101 PROGRAM PROJECT NO. TASKNO. WORK UNIT ELEMENT NO. ACCESSION NO,

_I I DN 242605

11. TITLE (Include Security Classification)

Characterizing noise fields in shipboard spaces

12. PERSONAL AUTHOR(S)

R. J. Sylvester

13a. TYPE OF REPORT 13b. TIME COVERED 14. DATEOFFRIK)STYftbrMOrtDa 15. PAGECOUNT

Interim FROM -_TO 11993 April 29 15

16. SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP Agoustic hibitability standards; intense tones; sound

field mapping; Ship's spaces

19. ABSTRACT (Continue on reverse if necessary and identify by block number)

Three methods of characterizing discrete tone sound fields were tested in a reverberant compartment. Method

one uses sound field mapping, method two implements an integrating sound level meter, and method three uses

personal noise dosimetry. Sound field mapping resulted in a detailed and accurate visual representation of the

sound field, but because the procedure is both complicated and time consuming, it is not appropriate for

day-to-day analysis of compartments. The dosimetry measurements were erratic and did not compare well with

the sound field mapping measuremnts. The dosimeters were influenced by the extraneous noise produced by the

activities of the test subjects wearing the dosimeters. Consequently, personal noise dosimetry cannot be

considered a reliable method for characterizing sound fields for the conditions of this test. An integrating sound

level meter combines the accuracy of the sound field maps with the simplicity of operation of the personal noise

dosimeters. A single number was attainable that was representative of the noise hazard associated with discrete

tones in reverberant compartments.

20. DISTRIBUTION/AVAILABILITY OF ABSTRACT 21, ABSTRACT SECURITY CLASSIFICATION

XiUNCLASSIFIED/UNUMITED __SAME AS REPORT ý-'DTIC USERS UNCLASSIFIED

22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE (Include Area Code) 22c. OFFICE SYMBOL

Susan D. Monty, Publications Office (203) 449-3967

DO Form 1473, JUN 86 Previous editions are obsolete. SECURITY CLASSIFICATION OF THIS PAGE

S/N 0102-LF-014-6603 UNCLASSIFIED
StkUUHFFT' CLDASSIFICAJ ION 01- I HIS PAC~h

DD Form 1473, JUN 86 (Reverse) ..... SECURITY ...................... CLASSIFICATION OF .. THIS PAGE ..