ASTM E596-96
(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
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 subject’s head is likely to be during audiometric tests.
1.1 This test method covers the reverberation room mea-
4. Summary of Test Method
surement of the noise reduction of sound-isolating enclosures.
4.1 The enclosure to be tested is placed in a reverberation
1.2 The noise isolation class may be determined from the
room and prepared for testing. The background noise levels
noise reduction measured in accordance with this test method.
inside the enclosure and in the reverberation room are mea-
1.3 This standard does not purport to address all of the
sured in one-third octave bands. After bands of random noise
safety concerns, if any, associated with its use. It is the
are produced in the reverberation room, one-third octave band
responsibility of the user of this standard to establish appro-
sound pressure levels are measured at several points in the
priate safety and health practices and determine the applica-
reverberation room and at appropriate points inside the enclo-
bility of regulatory limitations prior to use.
sure. The noise reduction in each one-third octave band is the
2. Referenced Documents difference between the space-averaged sound pressure level in
the reverberation room and the space-averaged sound pressure
2.1 ASTM Standards:
level inside the enclosure. The noise isolation class (NIC) may
C 423 Test Method for Sound Absorption and Sound Ab-
be determined from the noise reduction data.
sorption Coefficients by the Reverberation Room Method
C 634 Terminology Relating to Environmental Acoustics
5. Significance and Use
E 413 Classification for Rating Sound Insulation
5.1 The noise reduction of an enclosure is a property of the
2.2 ANSI Standards:
3 enclosure, the location of the sound source used to measure
S1.4 Specification for Sound Level Meters
noise reduction, and the space in which the enclosure is placed.
S1.11 Specification for Octave-Band and Fractional-
3 It is not a property of the enclosure alone, and its measurement
Octave-Band Analog and Digital Filters
under different conditions can be expected to give different
3. Terminology results. When the noise reduction is measured in accordance
with this test method, the sound source is outside the enclosure
3.1 Definitions and Symbols—Except as noted in 3.2, the
and the sound field outside the enclosure approximates a
terms and symbols used in this test method are defined in
diffuse sound field. Measurements made in accordance with
Terminology C 634.
this test method can be expected to be reproducible from one
3.2 Definitions of Terms Specific to This Standard:
laboratory to another.
3.2.1 sound-isolating enclosure—any enclosure that com-
5.2 The noise reduction measured in accordance with this
pletely encloses a space, is intended to provide sound isolation
test method may be used for the following purposes:
for the enclosed space, and can be tested in a reverberation
5.2.1 To rank the order of sound-isolating enclosures ac-
room.
cording to noise isolation class, NIC.
3.2.2 useful volume of a sound isolating enclosure—the part
5.2.2 To estimate the highest one-third octave band sound
of the space inside the enclosure in which the noise reduction
pressure levels that can occur outside the enclosure without
is of interest. For example, in an audiometric booth, the useful
exceeding specified sound pressure levels inside the enclosure.
volume is the part of the space inside the booth where a test
5.2.3 To estimate the one-third octave band sound pressure
levels that will occur inside the enclosure with specified sound
This test method is under the jurisdiction of ASTM Committee E-33 on
pressure levels outside.
Environmental Acoustics and is the direct responsibility of Subcommittee E33.03 on
5.3 The noise reduction measured in accordance with this
Sound Transmission.
test method may not estimate accurately the isolation that the
Current edition approved Jan. 10, 1996. Published April 1996. Originally
published as E 596 – 77. Last previous edition E 596 – 94a.
enclosure will provide when it is used to isolate a noise source
Annual Book of ASTM Standards, Vol 04.06.
inside it from the space outside. The user should be cautious
Available from American National Standards Institute, 11 W. 42nd St., 13th
when using noise reductions measured by this test method to
Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, 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
evaluate enclosures used to enclose noise sources.
L 5 level of combined signal and background noise, dB,
c
5.4 Sound-isolating enclosures are frequently made from
and
prefabricated modular panels. The noise reduction measured
L 5 level of background noise, dB.
b
by this test method applies to the complete enclosure and not
If the difference between the level of the test signal and the
to individual panels from which it is made and cannot be used
background noise level is not at least 5 dB, then subtract 2 dB
to infer the sound transmission loss of the individual panels.
from the level of the combined signal and background noise
5.5 Specifications for sound-isolating enclosures may in- and use this adjusted level. When the difference between the
clude reference to noise reduction and noise isolation class
signal level and the background noise level is less than 5 dB,
measured in accordance with this test method. the measurements provide only an estimate of the lower limit
of the noise reduction of the enclosure. Identify such limited
6. Reverberation Room
measurements in the test report.
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
minus the volume occupied by the enclosure) should not be
NOTE 2—When the background noise inside the enclosure is the same
less than 200 m .
as the background noise in the reverberation room, it is likely that either
the vibration isolation (if any) between the enclosure and the reverberation
NOTE 1—Experience and experimental data have shown that as long as
room floor is ineffective or the measured background noise is the internal
the requirements of 9.1.2 and 9.5 are satisfied, the room volume is not
noise of the measuring instruments.
critical.
6.3 Construction—In accordance with 6.1.2, the reverbera-
6.1.2 The sound absorption in the reverberation room shall
tion room should be constructed of materials that have low
be made as low as possible in order to achieve the best possible
sound absorption coefficients. Normally, when a reverberation
simulation to an ideal diffuse field and in order to keep the
room is to be used to measure sound absorption, sound power
region dominated by the direct field of the source as small as
level, or sound transmission loss, it must be constructed using
possible. Within the frequency range described below the
materials and design details that will provide needed sound
sound absorption of the reverberation room should be no
insulation against outside noise sources. If a reverberation
greater than the following:
room is to be constructed solely for testing sound-isolating
2/3
A 5 V /3 (1)
enclosures in accordance with this test method, the sound
isolation requirements are not so critical, and lighter materials
where:
may be used as long as the requirements of 6.1 and 6.2 are met.
V 5 room volume, m , and
A 5 room sound absorption in metric sabins.
7. Measuring Instrumentation
1/3
For frequencies below f 5 2000/V (where the number
7.1 The minimum instrumentation required for this test
2000 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
slightly higher value of sound absorption.
NOTE 3—A flat characteristic is desirable and, when available, should
6.1.3 Diffusing devices such as rotating and stationary
be used in place of the C-weighting network.
diffusing surfaces are useful for creating an adequate approxi-
7.1.2 A one-third octave filter set satisfying the require-
mation to a diffuse sound field.
ments of ANSI S1.11 for a one-third octave band filter set,
6.2 Background Noise:
Order 3 or higher, Type 1 or better. The nominal center
6.2.1 The sound pressure level of the background noise
frequencies of the filters shall be those frequencies that are
inside the enclosure should be at least 10 dB below the level of
within the frequency range where the noise reduction is to be
the test signal. If the difference between the level of the test
measured. This frequency range shall include all of the
signal and the background noise level is less than 10 dB and
preferred one-third octave bands from 125 to 4000 Hz and may
greater than 5 dB, the adjusted value of the signal level is
be extended, if desired.
calculated by:
7.1.3 A level meter, graphic level recorder, or other device
.1L .1L
c b
L 5 10 log 10 2 10 (2)
~ ! from which the sound pressure level can be read. The averag-
a
ing time of the instrumentation shall be sufficient to permit
where:
reading the average sound pressure level with adequate preci-
L 5 adjusted signal level, dB,
a
sion (see Section 11).
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
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
N 5 UV/ (4)
8.2 The signal source shall be placed so that the enclosure to
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
5 2pr/~l/2! if rotating microphone traverse of radius r is used,
direct the source into a trihedral corner of the reverberation
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
minimum of four independent data points is required for calculation of the
frequency.
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-
9.4 Background Noise—With the sound sources not operat-
beration room so that:
ing, measure the background noise levels in the receiving room
9.1.1 No enclosure wall is parallel to a reverberation room
wall. at each microphone position or traverse. Corrections shall be
made unless the background level is more than 10 dB below
9.1.2 The enclosure is at least one-half wavelength away
the combination of signal and background. (The signal is the
from the reverberation room walls and ceiling and any diffus-
sound pressure level due to transmission through the test
ing surfaces at the center frequency of the lowest one-third
enclosure.) If the background level is between 5 and 10 dB
octave band in which the noise reduction is to be measured.
below the combined level, correct the signal level using:
9.1.3 The enclosure is mounted on the floor in the same way
as when it is in normal use. Do not mount the enclosure on
L L
sb b
L 5 10 log 2 (6)
s 10S 10 10D
beams, rails, or vibration isolators unless they are normally
10 10
used with the enclosure.
where:
9.2 Enclosure Preparation:
L 5 the background n
...
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