A rectangular reverberation chamber was designed, constructed and calibrated for the experimental measurement of the sound power level (acoustic power) of a dog. Calibration of the chamber consisted of comparing the acoustic power measured for a random noise source in the chamber with that for the identical source in a free field environment. Data from dogs indicate that barking noise can be modeled as a square wave pattern with short duration and peak sound power levels in the 500 Hz octave band. A-weighted sound pressure levels of up to 114.7 dBA were absorbed, indicating a potential concern for both animals and man chronically exposed to such environments

Besch, E. L.

Ingley, H. A.

Sierens, S. E.

English

NASA Technical Reports Server

sN79-19024
A
Paper No. 15
METHODOLOGY FOR ESTIMATING DOG NOISE IN
, AN ANIMAL HOUSING FACILITY
S. E. Sierens,M.E., H. A. Ingle¥, Ph.D., and E. L. Beth, Ph.D.,
Univemi_ of F_rida, Gam_ville, Florida 32611
ABSTRACT
: A rectangular reverberation chamber was
designed, constructed and calibrated for the
experimental measurement of the sound power
level (acoustic power) of a dog. Calibration
of the chamber consisted of comparing the
ac,,ustic power measured for a random noise
source in the chamber with that for the
identical source in a free field envirou-
mellt. Data _rom dogs indicate that barking
noise can be modeled as a square wave pattern
with short duration and peak souna power levels
in the 500 Hz octave band. A-we,ghted sound
pressure levels of up to 114.7 dBA were
absorbed, indicating a potential concern for
bot animals and man chronzcally exposed to
suc environments.
['_TkuDUCTION
Although noise has been recognized as an impor--
rant parameter for the research animal bioenvironment
(1,2,3), little scientific evidence is available from
which exposure levels for anzmals may be specified (4).
Previous recommendations on acceptable noise levels for
animals (3) were based on animal exposures to a minimum
noise inte-sity for 40 hours per wee_. Dog barking
a_pears to be a primary cause of high noise in an
animal facility (2,5), but no apparent attempts have
been made to qdantJtate th_ dog as a noise sourc_ or
to characterize the dog's sound power levels. Further,
_i_tle information is av.:ilable concerning permissible
noise exposures of humans in animal facilities or
weather existing levels exceeded those specified by
OSHA (6). Such information not only would be useful
in estimating noise levels but also would allow for
appropriate acou_Lic designs in existin_ or new
facilities. The_e consideratlons lea to the research
_ reported here.
.-SZCED;;J; ' .. ._ ELANK NOT F|L_2_
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MATERIALS AND METHODS
Reverberation Chamber ,
Based on preliminary measurements in a typical
animal facility which indicated noise levels associat_
with barking dogs were predominantly in the frequency -
range of 250 Hz to 4 KHz, a lower limitin_ frequency of
250 Hz was selected for the reverberation chamber
design (7). The dimensions of the chamber were
: selected based on two criteria:
1) the interior volume of the chamber should
: be greater than or equal to 4_ 3, where
_ is the corresponding wavelength for
the lower limiting frequency (8);
2) the chamber dimensions of length, width, ,
and height should possess ratios of 1.0;
: 1.259; 1.587, respectively (8).
The chamber (Fig. 1) was constructed of wood with
' a glazed tile interior wall finish. The glazed tile
provided a hard, reflective interior surface necessary
to produce a diffuse sound field within the chamber.
To further enhance this diffuse quality of the
chamber, irregular geometric shapes were constructed
on several of the walls. The walls were also splayed
so that no two walls were parallel. The final chamber
interior surface area (S) was 31.73 m2 (341.5 it2);
the volume (V) was found to be 9.82 m2 (346.8 ft 2 ).
Chamber Calibration
The schematic (Fig. 2) identifies instrumentation
used in chamber calibration. Eight microphone posi-
tions were monitored for each of ten speaker locations
in the chamber to provide data from which to select an
optimum source and microphone position. A noise
generator (Bruel and Kjaer, Type 1402), a 100 w_tt
amplifier and a sound driver provided the random noise
source. A microphone (General Radio, Type 1560-P6)
and magnetic data recorder (General Radio, Type 1525-A)
were used to monitor the noise levels in the chamber.
All data were analyzed on an audio frequency spectro-
meter (Bruel and Kjaer, Type 2112) and graphic ]eve!
recorder (Brve] and Kjaer, Type 2395). The reverbera-
tion time (T60) of the chamber was determined for
several octave band frequencies.
" Reverberation chamber data were compared with
data from a free field environment to verify the
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1979010842-171
' T l- Plan Viewof Chamber 110"
×
Front View _ ;j__
of Chamber
" 77" 83"
76" _
figureI. CoordinateSystem and ReferenceAxes for Locat"on
of Speakerand Microphone Positions,Reverberant Reid
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1979010842-172
_J" ,
'x
Chamber
I I
Microphone
I __ II I
" ! " I a" I
Noise Amplifier I H°rn
Generator I I
I._ J
IO__OIm m _ l m m mMagneticLaboratory Tape
Recorder_ I
time Graphic ___
Level Frequency
Recorder Spectrometer
_gure 2. Schematicof Instrumentatio_Used
in ReverberationTime _,leasurements
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1979010842-173
reliability of results obtained in the chamber.
Although free field measurements usually provide more
accurate means of determining sound power levels for
a noise source, it is very difficult to use such a
field to determine acoustic power levels for laboratory
animals.
Animals
A male, adult German Shepherd dog was acclimated
to the chamber for a period of 14 days. A microphnne
was placed in the chamber at the optimum position ":
determined during the calibration runs:. The dog was
place4 in one corner of the chamber which appeared to
be a satisfactory location for the sound power level
! determinations. Dog barks were recorded on magnetic
tape for a perlod of 15 minutes.
From analyses of fifty barks recorded during the
test period, peak sound pressure levels, duration
times, and rise times were recorded for each bark.
Using the sound pressure level and room response data,
average sound power levels were calculated for octave
bands centered at 250 Hz, 500 Hz, 1KHz, 2 KHz, 4 KHz,
_ 8 KHz, and 16 KHz.
Calculations
Assuming that the chamber would provide a diffuse
sound field, equation (i) was used to determine sound
Fower levels (PWL) for the sound source placed in the
room:
PWL = SPL + I0 Log V - i0 Log T60 +
S_ .5
I0 Log (I + _-_) - 13 (dB) (I)
where PWL = sound power level, dB, in frequency band
of interest
SPL = average sound pressure level (usually
from several microphone positions), dB,
in frequency band of interest
V = total volume of test room, m 3
T60 = reverberation time of test room in
frequency band of interest, sec.
" S = interior surface area of room, m2
= wavelength of center frequency of test
band, m
The volume (V) and interior surface area (S) were
/ determined from the dimensions of the reverberation
chamber. The reverberation time (T60) and average
?
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1979010842-174
sound pressure level (SPL) were determined
experimentally.
RESULTS
Data (Table I) from several free field environ-
ments compared favorably with data taken in the
reverberation chamber utilizing the same sound power
source operating at identical power settings. In most
comparisons of the free field to reverberant field
measurements ot sound power levels, the percent error
: did not exceed 5_.
Data from the barking dog (Table 2) were consis-
tent and reproducible and the range of sound pressure
levels in any octave band appeared to be less than 20
dB. The dog appears to have the widest range of
sound pressure levels in the lower frequencies with a
decreasing range at increasing frequencies. For
6xample, at ] KHz the range of sound pressure levels
was 13 dB (102 to 115) while at 16 KHz the range was
,. ,. 4 dB (68 to 72). The standard deviations in sound
pressure level varied from 3.7 dB at 2 KHz to 1.3 dB
at 16 XHz. The 95% confidence intervals were
extremely small, ranging from 0.4 dB at 16 KHz to 1.0
: dB at 2 KHz and 4 KHz, due in part to the large sample
size. The sound pressure level in the 500 Hz octave
band was within 0.5 dB of the overall sound pressure
level (All Pass) indicating that the sound pressure
levels in the remaining octave bands contribute little
: to the total sound level. The A-weighted sound pressure
levels measured in the reverberation chamber ranged
from 100-119 dBA, with aD average A-weighted sound
pressure level of 114.7 dBA,
The slope and general pattern of the decay curves
(room response) from an interrupted noise source were
'_ virtually identical to the slope and p_ttern of the
decay portion of the dog barks. Thus, the barking
pattern can be treated as a square wave pattern with
a very steep rise time (0.1 second) and a duration of
about 0.05 second. These curves - spaced about 1.5
seconds from one another - have peak levels that vary
with the octave band (Table 1).
Figure 3 illustrates the sound power level
frequency distribution for the dog bark, calculated
from equation (1) with appropriate substitutions.
i Data points of octave bands above 500 Hz appear to be
linear with an average _lope of minus 10_1 dB per
octave. The single exception is at 8 KHz where au
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174
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+
I +,,++
+
i.
]9790]0B42-]77
Plot at llg.3 dB _
All Pass---tlO4__
114.7 dBA......... e
110
100 .
Mean Sound ,
Power Level for
Barking Dos, dB
90 "
80 .
¢
70 -
250 500 1000 2000 4000 BOO0 16000
Octave Band Ce.ter Frequency,Hz
Ngure 3. Sound Power Level (PWL) versus _equency for Dog
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1979010842-178
slight deviation from the linear decay is noted. From
250 Hz to 500 Hz the rate of increase was about twice
the rate of decrease from 500 Hz to 16 KHz, or about
J
22.7 dB per octave. Analysis of the three 1/3 octave
bands in the 500 Hz octave band indicates the the
"characteristic frequency" is in the range of 447 to
562 Hz for this particular dog.
: DISCUSSION
Our reverberation chamber appears to have provided
a reliable tool for determining sound power levels for
the laboratory dog. The data obtained from one bark-
ing dog resulted in hzghly reproducible calculations
of sound power levels. However, the generalized use
of these data may have limited value for immediate
appl_,cations for acoustic problems in animal housing
facilities. Barking noise from more breeds needs to
be analyzed. Other does may provide significantly
different sound power level - frequency profiles,
although sound levels are expected to reach the same
' , magnitude as reported here.
I_ order to completely evaluate the effects of
barkin_i dog noise on the animal itself or the humans
involw_d with the animals, further investigations
for establishing the A-weighted noise exposure and
the time pattern of the dog barks will be necessary.
The average A-weighted noise level of 114.7 dBA
reported here is an indication in itself that there
is a potential concern for both man and animals.
Data from Table 2 and Figure 3 may be used to
predict the sound pressure levels in any environment
through the use of standard acoustical relationships
(8). For example, equations similar to equatior (I)
may be rearrange/ to solve for the average sound
pressure level in any given environment if the sound
power level of the noise source and the acoustical
characteristics of the room are known. Further, with
additional sound power level data, noise levels in _n
animal room of known design may be estimated prior to
construction. These data also would be invaluable in
solving noise problems for existing facilities.
ACKNOWLEDGMENT
This research was partially supported by NIH
Grant No. :_R 00942.
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1979010842-179
REFERENCES
J
1. McPherson, C., Why Be Concerned About the
Ventilation Requirements of Experimental Animals,
ASHRAE Transactions, Vol. 81, _art 2, pp, 539-541,
1976.
2. Moreland, A.F., Characteristics of the Animal
Research Bioenvlronment, ASHRAE Transactions, Vol.
81, Part 2, pp. 542-548, 1976.
3. Anthony, A., Criteria for Acoustics in Animal
Housing, Laboratory Animal Care 13, pp. 340-350,
1963.
4. The Design and Function of Laboratory Animal
Houses, A Laboratory Animal Symposia held in
London, 1967, Edited by Hare, R., March 1968.
J.
5. U.S. Department of Health, Education and Welfare,
Guide to the Care and Us£ 0 f Laborator _ Animals,
: DHEW Publication NO. (NIH) 74-2_ 1974, Bethesda,
Maryland.
6. U.S. Department of Labor, Guidelines to the
Department of Labor's Occupational Noise Standards
for Federal Supply Contract, Office of the
Solicitor, Bulletin 334, 1971 (Hey.), Washington,
D.C.
7. Sierens, S.E., The Design, Construction, and
Calibration of an Acoustical Reverberation Chamber
for Measuring Sound Power Levels of Laboratory
Animals, Unpublished Master's Thesis, Department
of Mechanical Engineering, University of Florida,
August, 1976.
8. Beranek, L.L., Noise and Vibration Control, McGraw-
Hill Book Company, New York, 1971.
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1979010842-180


A methodology for estimating dog noise in an animal housing facility

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