ASTM E596-96(2002)
(Test Method)Standard Test Method for Laboratory Measurement of Noise Reduction of Sound-Isolating Enclosures
Standard Test Method for Laboratory Measurement of Noise Reduction of Sound-Isolating Enclosures
SCOPE
1.1 This test method covers the reverberation room measurement of the noise reduction of sound-isolating enclosures.
1.2 The noise isolation class may be determined from the noise reduction measured in accordance with this test method.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: E 596 – 96 (Reapproved 2002)
Standard Test Method for
Laboratory Measurement of Noise Reduction of Sound-
Isolating Enclosures
This standard is issued under the fixed designation E 596; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope volume is the part of the space inside the booth where a test
subject’s head is likely to be during audiometric tests.
1.1 This test method covers the reverberation room mea-
surement of the noise reduction of sound-isolating enclosures.
4. Summary of Test Method
1.2 The noise isolation class may be determined from the
4.1 The enclosure to be tested is placed in a reverberation
noise reduction measured in accordance with this test method.
room and prepared for testing. The background noise levels
1.3 This standard does not purport to address all of the
inside the enclosure and in the reverberation room are mea-
safety concerns, if any, associated with its use. It is the
sured in one-third octave bands. After bands of random noise
responsibility of the user of this standard to establish appro-
are produced in the reverberation room, one-third octave band
priate safety and health practices and determine the applica-
sound pressure levels are measured at several points in the
bility of regulatory limitations prior to use.
reverberation room and at appropriate points inside the enclo-
2. Referenced Documents sure. The noise reduction in each one-third octave band is the
difference between the space-averaged sound pressure level in
2.1 ASTM Standards:
the reverberation room and the space-averaged sound pressure
C 423 Test Method for Sound Absorption and Sound Ab-
level inside the enclosure. The noise isolation class (NIC) may
sorption Coefficients by the Reverberation Room Method
be determined from the noise reduction data.
C 634 Terminology Relating to Environmental Acoustics
E 413 Classification for Rating Sound Insulation
5. Significance and Use
2.2 ANSI Standards:
3 5.1 The noise reduction of an enclosure is a property of the
S1.4 Specification for Sound Level Meters
enclosure, the location of the sound source used to measure
S1.11 Specification for Octave-Band and Fractional-
3 noise reduction, and the space in which the enclosure is placed.
Octave-Band Analog and Digital Filters
It is not a property of the enclosure alone, and its measurement
3. Terminology under different conditions can be expected to give different
results. When the noise reduction is measured in accordance
3.1 Definitions and Symbols—Except as noted in 3.2, the
with this test method, the sound source is outside the enclosure
terms and symbols used in this test method are defined in
and the sound field outside the enclosure approximates a
Terminology C 634.
diffuse sound field. Measurements made in accordance with
3.2 Definitions of Terms Specific to This Standard:
this test method can be expected to be reproducible from one
3.2.1 sound-isolating enclosure—any enclosure that com-
laboratory to another.
pletely encloses a space, is intended to provide sound isolation
5.2 The noise reduction measured in accordance with this
for the enclosed space, and can be tested in a reverberation
test method may be used for the following purposes:
room.
5.2.1 To rank the order of sound-isolating enclosures ac-
3.2.2 useful volume of a sound isolating enclosure—the part
cording to noise isolation class, NIC.
of the space inside the enclosure in which the noise reduction
5.2.2 To estimate the highest one-third octave band sound
is of interest. For example, in an audiometric booth, the useful
pressure levels that can occur outside the enclosure without
exceeding specified sound pressure levels inside the enclosure.
This test method is under the jurisdiction of ASTM Committee E33 on
5.2.3 To estimate the one-third octave band sound pressure
Environmental Acoustics and is the direct responsibility of Subcommittee E33.03 on
levels that will occur inside the enclosure with specified sound
Sound Transmission.
pressure levels outside.
Current edition approved Jan. 10, 1996. Published April 1996. Originally
published as E 596 – 77. Last previous edition E 596 – 94a.
5.3 The noise reduction measured in accordance with this
Annual Book of ASTM Standards, Vol 04.06.
test method may not estimate accurately the isolation that the
Available from American National Standards Institute, 25 W. 43rd St., 4th
enclosure will provide when it is used to isolate a noise source
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 596
inside it from the space outside. The user should be cautious
where:
when using noise reductions measured by this test method to
L = adjusted signal level, dB,
a
evaluate enclosures used to enclose noise sources. L = level of combined signal and background noise, dB,
c
and
5.4 Sound-isolating enclosures are frequently made from
L = level of background noise, dB.
prefabricated modular panels. The noise reduction measured b
If the difference between the level of the test signal and the
by this test method applies to the complete enclosure and not
background noise level is not at least 5 dB, then subtract 2 dB
to individual panels from which it is made and cannot be used
from the level of the combined signal and background noise
to infer the sound transmission loss of the individual panels.
and use this adjusted level. When the difference between the
5.5 Specifications for sound-isolating enclosures may in-
signal level and the background noise level is less than 5 dB,
clude reference to noise reduction and noise isolation class
the measurements provide only an estimate of the lower limit
measured in accordance with this test method.
of the noise reduction of the enclosure. Identify such limited
measurements in the test report.
6. Reverberation Room
6.2.2 Structureborne noise within the reverberation room
6.1 Sound Diffusion—The sound field in the reverberation
structure can excite the enclosure to be tested and cause the
room shall closely approximate a diffuse field when the
sound pressure level within the enclosure to be higher than
enclosure to be tested is in place for testing. In general, the
would be measured due to the test signal alone. Therefore, the
requirements for the reverberation room are those listed in the
reverberation room floor should be adequately isolated against
section dealing with Reverberation Room of Test Method
structureborne vibrations which are propagated into the rever-
C 423. These requirements include:
beration room from the outside.
6.1.1 The effective room volume (actual room volume
NOTE 2—When the background noise inside the enclosure is the same
minus the volume occupied by the enclosure) should not be
as the background noise in the reverberation room, it is likely that either
less than 200 m .
the vibration isolation (if any) between the enclosure and the reverberation
room floor is ineffective or the measured background noise is the internal
NOTE 1—Experience and experimental data have shown that as long as
noise of the measuring instruments.
the requirements of 9.1.2 and 9.5 are satisfied, the room volume is not
critical.
6.3 Construction—In accordance with 6.1.2, the reverbera-
tion room should be constructed of materials that have low
6.1.2 The sound absorption in the reverberation room shall
sound absorption coefficients. Normally, when a reverberation
be made as low as possible in order to achieve the best possible
room is to be used to measure sound absorption, sound power
simulation to an ideal diffuse field and in order to keep the
level, or sound transmission loss, it must be constructed using
region dominated by the direct field of the source as small as
materials and design details that will provide needed sound
possible. Within the frequency range described below the
insulation against outside noise sources. If a reverberation
sound absorption of the reverberation room should be no
room is to be constructed solely for testing sound-isolating
greater than the following:
enclosures in accordance with this test method, the sound
2/3
A 5 V /3 (1)
isolation requirements are not so critical, and lighter materials
may be used as long as the requirements of 6.1 and 6.2 are met.
where:
V = room volume, m , and
7. Measuring Instrumentation
A = room sound absorption in metric sabins.
1/3
For frequencies below f = 2000/V (where the number 2000 7.1 The minimum instrumentation required for this test
is an empirical constant with the units seconds per metre), method is:
somewhat higher absorption may be desirable to accommodate
7.1.1 A microphone and amplifier that satisfy the require-
other test requirements (for example, ANSI S1.32, ISO 3741); ments of ANSI S1.4 for Type 1 or better sound level meters
in any case, the absorption should be no greater than three
with the exception that A and B-weighting networks are not
times the value given by Eq 1. For frequencies above 2000 Hz, required.
atmospheric absorption may make it impossible to avoid a
NOTE 3—A flat characteristic is desirable and, when available, should
slightly higher value of sound absorption.
be used in place of the C-weighting network.
6.1.3 Diffusing devices such as rotating and stationary
7.1.2 A one-third octave filter set satisfying the require-
diffusing surfaces are useful for creating an adequate approxi-
ments of ANSI S1.11 for a one-third octave band filter set,
mation to a diffuse sound field.
Order 3 or higher, Type 1 or better. The nominal center
6.2 Background Noise:
frequencies of the filters shall be those frequencies that are
6.2.1 The sound pressure level of the background noise
within the frequency range where the noise reduction is to be
inside the enclosure should be at least 10 dB below the level of
measured. This frequency range shall include all of the
the test signal. If the difference between the level of the test
preferred one-third octave bands from 125 to 4000 Hz and may
signal and the background noise level is less than 10 dB and
be extended, if desired.
greater than 5 dB, the adjusted value of the signal level is
7.1.3 A level meter, graphic level recorder, or other device
calculated by:
from which the sound pressure level can be read. The averag-
.1L .1L
c b
L 5 10 log ~10 2 10 ! (2) ing time of the instrumentation shall be sufficient to permit
a
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 596
reading the average sound pressure level with adequate preci- unless the useful volume necessarily includes these regions.
sion (see Section 11).
9.3.2.2 Microphone positions should not approach one an-
7.2 Additional microphone systems may be used. If addi-
other to within a distance of one-half-wavelength at the lowest
tional microphones are used, differences in their responses
frequency of interest.
should be accounted for either by careful calibration or by an
9.3.2.3 For low frequencies it is almost never possible to
appropriate measurement procedure (see 9.6).
select four microphone positions that satisfy the requirement of
9.3.2.2. Whenever this is the case, microphone positions inside
8. Test Signal
the enclosure should be selected to get the best estimate of the
8.1 The test signals shall be bands of random noise at least
space-time average sound pressure level within the useful
one-third octave wide and including every one-third octave
volume, disregarding spatial correlation among positions.
band within the test range. The test range shall include all of
9.3.3 The potential number of statistically independent mi-
the preferred one-third octave bands from 125 to 4000 Hz and
crophone positions N within a space is calculated as
may be extended, if desired.
l
8.2 The signal source shall be placed so that the enclosure to N 5 UV/ (4)
S D
be tested is not in its direct field; the minimum distance from
where UV is the useful volume.
the source to any part of the enclosure shall be:
9.3.3.1 The effective number of independent measurement
1/2
r $ 0.63 A (3)
locations n shall be calculated as follows:
where A is the sound absorption in the reverberation cham-
n 5 N if N independent stationary microphone locations are used,
ber with the enclosure present. Normally, the best practice is to
direct the source into a trihedral corner of the reverberation
5 2pr/~l/2! if rotating microphone traverse of radius r is used,
room. If more than one loudspeaker is used, it is advisable that
5 L/~l/2! if linear microphone traverse of length L is used. (5)
each loudspeaker be driven by an independent noise source.
8.3 The signal level shall be at least 10 dB above the
NOTE 4—A half-wavelength correlation distance is assumed, and the
measured background noise inside the enclosure at each test
number of independent data samples is calculated on this basis. A
frequency.
minimum of four independent data points is required for calculation of the
95 % confidence limits from the table. This is not often possible in small
enclosures at low frequencies. When this is the case, the data should be so
9. Procedure
identified in the report.
9.1 Enclosure Placement—Place the enclosure in the rever-
beration room so that: 9.4 Background Noise—With the sound sources not operat-
9.1.1 No enclosure wall is parallel to a reverberation room ing, measure the background noise levels in the receiving room
wall. at each microphone position or traverse. Corrections shall be
9.1.2 The enclosure is at least one-half wavelength away made unless the background level is more than 10 dB below
from the reverberation room walls and ceiling and any diffus- the combination of signal and background. (The signal is the
ing surfaces at the center frequency of the lowest one-third sound pressure level due to transmission through the test
octave band in which the noise reduction is to be measured. enclosure.) If the background level is between 5 and 10 dB
9.1.3 The enclosure is mounted on the floor in the same way below the combined level, correct the signal level using:
as when it is in normal use. Do not mount the enclosure on
L L
sb b
L 5 10 log 2 (6)
...
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