ASTM E596-96(2016)
(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
SIGNIFICANCE AND USE
5.1 The noise reduction of an enclosure is a property of the enclosure, the location of the sound source used to measure noise reduction, and the space in which the enclosure is placed. It is not a property of the enclosure alone, and its measurement under different conditions can be expected to give different results. When the noise reduction is measured in accordance with this test method, the sound source is outside the enclosure and the sound field outside the enclosure approximates a diffuse sound field. Measurements made in accordance with this test method can be expected to be reproducible from one laboratory to another.
5.2 The noise reduction measured in accordance with this test method may be used for the following purposes:
5.2.1 To rank the order of sound-isolating enclosures according to noise isolation class, NIC.
5.2.2 To estimate the highest one-third octave band sound pressure levels that can occur outside the enclosure without exceeding specified sound pressure levels inside the enclosure.
5.2.3 To estimate the one-third octave band sound pressure levels that will occur inside the enclosure with specified sound pressure levels outside.
5.3 The noise reduction measured in accordance with this test method may not estimate accurately the isolation that the enclosure will provide when it is used to isolate a noise source inside it from the space outside. The user should be cautious when using noise reductions measured by this test method to evaluate enclosures used to enclose noise sources.
5.4 Sound-isolating enclosures are frequently made from prefabricated modular panels. The noise reduction measured by this test method applies to the complete enclosure and not to individual panels from which it is made and cannot be used to infer the sound transmission loss of the individual panels.
5.5 Specifications for sound-isolating enclosures may include reference to noise reduction and noise isolation class measured in accordance with th...
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.
General Information
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Designation: E596 − 96 (Reapproved 2016)
Standard Test Method for
Laboratory Measurement of Noise Reduction of Sound-
Isolating Enclosures
This standard is issued under the fixed designation E596; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 3.2.1 sound-isolating enclosure—any enclosure that com-
pletely encloses a space, is intended to provide sound isolation
1.1 This test method covers the reverberation room mea-
for the enclosed space, and can be tested in a reverberation
surement of the noise reduction of sound-isolating enclosures.
room.
1.2 The noise isolation class may be determined from the
3.2.2 useful volume of a sound isolating enclosure—the part
noise reduction measured in accordance with this test method.
of the space inside the enclosure in which the noise reduction
1.3 This standard does not purport to address all of the
is of interest. For example, in an audiometric booth, the useful
safety concerns, if any, associated with its use. It is the
volume is the part of the space inside the booth where a test
responsibility of the user of this standard to establish appro-
subject’s head is likely to be during audiometric tests.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4. Summary of Test Method
4.1 The enclosure to be tested is placed in a reverberation
2. Referenced Documents
room and prepared for testing. The background noise levels
2.1 ASTM Standards:
inside the enclosure and in the reverberation room are mea-
C423 Test Method for SoundAbsorption and SoundAbsorp-
sured in one-third octave bands. After bands of random noise
tion Coefficients by the Reverberation Room Method
are produced in the reverberation room, one-third octave band
C634 Terminology Relating to Building and Environmental
sound pressure levels are measured at several points in the
Acoustics
reverberation room and at appropriate points inside the enclo-
E413 Classification for Rating Sound Insulation
sure. The noise reduction in each one-third octave band is the
2.2 ANSI Standards:
difference between the space-averaged sound pressure level in
S1.4 Specification for Sound Level Meters
the reverberation room and the space-averaged sound pressure
S1.11 Specification for Octave-Band and Fractional-Octave-
level inside the enclosure. The noise isolation class (NIC) may
Band Analog and Digital Filters
be determined from the noise reduction data.
3. Terminology
5. Significance and Use
3.1 Definitions and Symbols—Except as noted in 3.2, the
5.1 The noise reduction of an enclosure is a property of the
terms and symbols used in this test method are defined in
enclosure, the location of the sound source used to measure
Terminology C634.
noise reduction, and the space in which the enclosure is placed.
3.2 Definitions of Terms Specific to This Standard:
It is not a property of the enclosure alone, and its measurement
under different conditions can be expected to give different
results. When the noise reduction is measured in accordance
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
with this test method, the sound source is outside the enclosure
and Environmental Acoustics and is the direct responsibility of Subcommittee
and the sound field outside the enclosure approximates a
E33.03 on Sound Transmission.
diffuse sound field. Measurements made in accordance with
Current edition approved April 1, 2016. Published April 2016. Originally
approved in 1977. Last previous edition approved in 2009 as E596 – 96 (2009).
this test method can be expected to be reproducible from one
DOI: 10.1520/E0596-96R16.
laboratory to another.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.2 The noise reduction measured in accordance with this
Standards volume information, refer to the standard’s Document Summary page on
test method may be used for the following purposes:
the ASTM website.
5.2.1 To rank the order of sound-isolating enclosures ac-
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. cording to noise isolation class, NIC.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E596 − 96 (2016)
5.2.2 To estimate the highest one-third octave band sound 6.2 Background Noise:
pressure levels that can occur outside the enclosure without 6.2.1 The sound pressure level of the background noise
exceeding specified sound pressure levels inside the enclosure. inside the enclosure should be at least 10 dB below the level of
5.2.3 To estimate the one-third octave band sound pressure the test signal. If the difference between the level of the test
levels that will occur inside the enclosure with specified sound signal and the background noise level is less than 10 dB and
pressure levels outside. greater than 5 dB, the adjusted value of the signal level is
calculated by:
5.3 The noise reduction measured in accordance with this
.1L .1L
c b
L 5 10log 10 2 10 (2)
test method may not estimate accurately the isolation that the ~ !
a
enclosure will provide when it is used to isolate a noise source
where:
inside it from the space outside. The user should be cautious
L = adjusted signal level, dB,
a
when using noise reductions measured by this test method to
L = level of combined signal and background noise, dB,
c
evaluate enclosures used to enclose noise sources.
and
5.4 Sound-isolating enclosures are frequently made from
L = level of background noise, dB.
b
prefabricated modular panels. The noise reduction measured
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
structure can excite the enclosure to be tested and cause the
6.1 Sound Diffusion—The sound field in the reverberation
sound pressure level within the enclosure to be higher than
room shall closely approximate a diffuse field when the
would be measured due to the test signal alone. Therefore, the
enclosure to be tested is in place for testing. In general, the
reverberation room floor should be adequately isolated against
requirements for the reverberation room are those listed in the
structureborne vibrations which are propagated into the rever-
section dealing with Reverberation Room of Test Method
beration room from the outside.
C423. These requirements include:
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 . thevibrationisolation(ifany)betweentheenclosureandthereverberation
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
6.3 Construction—In accordance with 6.1.2, the reverbera-
critical.
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
bemadeaslowaspossibleinordertoachievethebestpossible
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 of6.1 and 6.2 are met.
where:
V = room volume, m , and
7. Measuring Instrumentation
A = room sound absorption in metric sabins.
7.1 The minimum instrumentation required for this test
1/3
For frequencies below f = 2000⁄V (where the number
method is:
2000isanempiricalconstantwiththeunitssecondspermetre),
7.1.1 A microphone and amplifier that satisfy the require-
somewhat higher absorption may be desirable to accommodate
ments of ANSI S1.4 for Type 1 or better sound level meters
other test requirements (for example, ANSI S1.32, ISO 3741);
with the exception that A and B-weighting networks are not
in any case, the absorption should be no greater than three
required.
times the value given by Eq 1. For frequencies above 2000 Hz,
NOTE 3—A flat characteristic is desirable and, when available, should
atmospheric absorption may make it impossible to avoid a
be used in place of the C-weighting network.
slightly higher value of sound absorption.
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
E596 − 96 (2016)
frequencies of the filters shall be those frequencies that are 9.2.3 If the enclosure is equipped with a connector for
within the frequency range where the noise reduction is to be external air conditioning and ventilation, connect the enclosure
measured. This frequency range shall include all of the to an external duct system that satisfies the manufacturer’s
preferred one-third octave bands from 125 to 4000 Hz and may specifications or recommendations for the enclosure.
be extended, if desired.
9.3 Inside Measuring Positions—Select at least four micro-
7.1.3 A level meter, graphic level recorder, or other device
phone positions inside the enclosure as follows:
from which the sound pressure level can be read. The averag-
9.3.1 Determine the useful volume of the enclosure.
ing time of the instrumentation shall be sufficient to permit
9.3.2 Distribute microphone positions evenly throughout
reading the average sound pressure level with adequate preci-
the useful volume.
sion (see Section 11).
9.3.2.1 Microphone positions or traverses should not be
7.2 Additional microphone systems may be used. If addi-
located or pass within 0.30 m of the enclosure interior walls
tional microphones are used, differences in their responses unless the useful volume necessarily includes these regions.
should be accounted for either by careful calibration or by an
9.3.2.2 Microphone positions should not approach one an-
appropriate measurement procedure (see 9.6). other to within a distance of one-half-wavelength at the lowest
frequency of interest.
8. Test Signal
9.3.2.3 For low frequencies it is almost never possible to
selectfourmicrophonepositionsthatsatisfytherequirementof
8.1 The test signals shall be bands of random noise at least
9.3.2.2. Whenever this is the case, microphone positions inside
one-third octave wide and including every one-third octave
the enclosure should be selected to get the best estimate of the
band within the test range. The test range shall include all of
space-time average sound pressure level within the useful
the preferred one-third octave bands from 125 to 4000 Hz and
volume, disregarding spatial correlation among positions.
may be extended, if desired.
9.3.3 The potential number of statistically independent mi-
8.2 Thesignalsourceshallbeplacedsothattheenclosureto
crophone positions N within a space is calculated as
be tested is not in its direct field; the minimum distance from
λ
the source to any part of the enclosure shall be:
N 5 UV/ (4)
S D
1/2
r$ 0.63 A (3)
where UV is the useful volume.
where A is the sound absorption in the reverberation cham-
9.3.3.1 The effective number of independent measurement
ber with the enclosure present. Normally, the best practice is to
locations n shall be calculated as follows:
direct the source into a trihedral corner of the reverberation
n 5 N if N independent stationary microphone locations are used,(5)
room. If more than one loudspeaker is used, it is advisable that
each loudspeaker be driven by an independent noise source.
52πr/ λ/2 if rotating microphone traverse of radius r is used,
~ !
8.3 The signal level shall be at least 10 dB above the
5L/~λ/2! if linear microphone traverse of length L is used.
measured background noise inside the enclosure at each test
NOTE 4—A half-wavelength correlation distance is assumed, and the
frequency.
number of independent data samples is calculated on this basis. A
minimum of four independent data points is required for calculation of the
9. Procedure 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
9.1 Enclosure Placement—Place the enclosure in the rever-
identified in the report.
beration room so that:
9.4 Background Noise—With the sound sources not
9.1.1 No enclosure wall is parallel to a reverberation room
operating, measure the background noise levels in the receiv-
wall.
ing room at each microphone position or traverse. Corrections
9.1.2 The enclosure is at least one-half wavelength away
shall be made unless the background level is more than 10 dB
from the reverberation room walls and ceiling and any diffus-
below the combi
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E596 − 96 (Reapproved 2009) E596 − 96 (Reapproved 2016)
Standard Test Method for
Laboratory Measurement of Noise Reduction of Sound-
Isolating Enclosures
This standard is issued under the fixed designation E596; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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.
2. Referenced Documents
2.1 ASTM Standards:
C423 Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
C634 Terminology Relating to Building and Environmental Acoustics
E413 Classification for Rating Sound Insulation
2.2 ANSI Standards:
S1.4 Specification for Sound Level Meters
S1.11 Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters
3. Terminology
3.1 Definitions and Symbols—Except as noted in 3.2, the terms and symbols used in this test method are defined in Terminology
C634.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 sound-isolating enclosure—any enclosure that completely encloses a space, is intended to provide sound isolation for the
enclosed space, and can be tested in a reverberation room.
3.2.2 useful volume of a sound isolating enclosure—the part of the space inside the enclosure in which the noise reduction is
of interest. For example, in an audiometric booth, the useful volume is the part of the space inside the booth where a test subject’s
head is likely to be during audiometric tests.
4. Summary of Test Method
4.1 The enclosure to be tested is placed in a reverberation room and prepared for testing. The background noise levels inside
the enclosure and in the reverberation room are measured in one-third octave bands. After bands of random noise are produced
in the reverberation room, one-third octave band sound pressure levels are measured at several points in the reverberation room
and at appropriate points inside the enclosure. The noise reduction in each one-third octave band is the difference between the
space-averaged sound pressure level in the reverberation room and the space-averaged sound pressure level inside the enclosure.
The noise isolation class (NIC) may be determined from the noise reduction data.
This test method is under the jurisdiction of ASTM Committee E33 on Building and Environmental Acoustics and is the direct responsibility of Subcommittee E33.03
on Sound Transmission.
Current edition approved April 1, 2009April 1, 2016. Published August 2009April 2016. Originally approved in 1977. Last previous edition approved in 20022009 as
E596 – 96 (2002).(2009). DOI: 10.1520/E0596-96R09.10.1520/E0596-96R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E596 − 96 (2016)
5. Significance and Use
5.1 The noise reduction of an enclosure is a property of the enclosure, the location of the sound source used to measure noise
reduction, and the space in which the enclosure is placed. It is not a property of the enclosure alone, and its measurement under
different conditions can be expected to give different results. When the noise reduction is measured in accordance with this test
method, the sound source is outside the enclosure and the sound field outside the enclosure approximates a diffuse sound field.
Measurements made in accordance with this test method can be expected to be reproducible from one laboratory to another.
5.2 The noise reduction measured in accordance with this test method may be used for the following purposes:
5.2.1 To rank the order of sound-isolating enclosures according to noise isolation class, NIC.
5.2.2 To estimate the highest one-third octave band sound pressure levels that can occur outside the enclosure without exceeding
specified sound pressure levels inside the enclosure.
5.2.3 To estimate the one-third octave band sound pressure levels that will occur inside the enclosure with specified sound
pressure levels outside.
5.3 The noise reduction measured in accordance with this test method may not estimate accurately the isolation that the
enclosure will provide when it is used to isolate a noise source inside it from the space outside. The user should be cautious when
using noise reductions measured by this test method to evaluate enclosures used to enclose noise sources.
5.4 Sound-isolating enclosures are frequently made from prefabricated modular panels. The noise reduction measured by this
test method applies to the complete enclosure and not to individual panels from which it is made and cannot be used to infer the
sound transmission loss of the individual panels.
5.5 Specifications for sound-isolating enclosures may include reference to noise reduction and noise isolation class measured
in accordance with this test method.
6. Reverberation Room
6.1 Sound Diffusion—The sound field in the reverberation room shall closely approximate a diffuse field when the enclosure to
be tested is in place for testing. In general, the requirements for the reverberation room are those listed in the section dealing with
Reverberation Room of Test Method C423. These requirements include:
6.1.1 The effective room volume (actual room volume minus the volume occupied by the enclosure) should not be less than 200
m .
NOTE 1—Experience and experimental data have shown that as long as the requirements of 9.1.2 and 9.5 are satisfied, the room volume is not critical.
6.1.2 The sound absorption in the reverberation room shall be made as low as possible in order to achieve the best possible
simulation to an ideal diffuse field and in order to keep the region dominated by the direct field of the source as small as possible.
Within the frequency range described below the sound absorption of the reverberation room should be no greater than the
following:
2/3
A 5 V /3 (1)
where:
V = room volume, m , and
A = room sound absorption in metric sabins.
1/3
For frequencies below f = 2000 ⁄V (where the number 2000 is an empirical constant with the units seconds per metre),
somewhat higher absorption may be desirable to accommodate other test requirements (for example, ANSI S1.32, ISO 3741); in
any case, the absorption should be no greater than three times the value given by Eq 1. For frequencies above 2000 Hz, atmospheric
absorption may make it impossible to avoid a slightly higher value of sound absorption.
6.1.3 Diffusing devices such as rotating and stationary diffusing surfaces are useful for creating an adequate approximation to
a diffuse sound field.
6.2 Background Noise:
6.2.1 The sound pressure level of the background noise inside the enclosure should be at least 10 dB below the level of the test
signal. If the difference between the level of the test signal and the background noise level is less than 10 dB and greater than 5
dB, the adjusted value of the signal level is calculated by:
.1L .1L
c b
L 5 10log~10 2 10 ! (2)
a
where:
L = adjusted signal level, dB,
a
L = level of combined signal and background noise, dB, and
c
L = level of background noise, dB.
b
If the difference between the level of the test signal and the background noise level is not at least 5 dB, then subtract 2 dB from
the level of the combined signal and background noise and use this adjusted level. When the difference between the signal level
E596 − 96 (2016)
and the background noise level is less than 5 dB, the measurements provide only an estimate of the lower limit of the noise
reduction of the enclosure. Identify such limited measurements in the test report.
6.2.2 Structureborne noise within the reverberation room structure can excite the enclosure to be tested and cause the sound
pressure level within the enclosure to be higher than would be measured due to the test signal alone. Therefore, the reverberation
room floor should be adequately isolated against structureborne vibrations which are propagated into the reverberation room from
the outside.
NOTE 2—When the background noise inside the enclosure is the same as the background noise in the reverberation room, it is likely that either the
vibration isolation (if any) between the enclosure and the reverberation room floor is ineffective or the measured background noise is the internal noise
of the measuring instruments.
6.3 Construction—In accordance with 6.1.2, the reverberation room should be constructed of materials that have low sound
absorption coefficients. Normally, when a reverberation room is to be used to measure sound absorption, sound power level, or
sound transmission loss, it must be constructed using materials and design details that will provide needed sound insulation against
outside noise sources. If a reverberation room is to be constructed solely for testing sound-isolating enclosures in accordance with
this test method, the sound 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.
7. Measuring Instrumentation
7.1 The minimum instrumentation required for this test method is:
7.1.1 A microphone and amplifier that satisfy the requirements of ANSI S1.4 for Type 1 or better sound level meters with the
exception that A and B-weighting networks are not required.
NOTE 3—A flat characteristic is desirable and, when available, should be used in place of the C-weighting network.
7.1.2 A one-third octave filter set satisfying the requirements of ANSI S1.11 for a one-third octave band filter set, Order 3 or
higher, Type 1 or better. The nominal center frequencies of the filters shall be those frequencies that are within the frequency range
where the noise reduction is to be measured. This frequency range shall include all of the preferred one-third octave bands from
125 to 4000 Hz and may be extended, if desired.
7.1.3 A level meter, graphic level recorder, or other device from which the sound pressure level can be read. The averaging time
of the instrumentation shall be sufficient to permit reading the average sound pressure level with adequate precision (see Section
11).
7.2 Additional microphone systems may be used. If additional microphones are used, differences in their responses should be
accounted for either by careful calibration or by an appropriate measurement procedure (see 9.6).
8. Test Signal
8.1 The test signals shall be bands of random noise at least one-third octave wide and including every one-third octave band
within the test range. The test range shall include all of the preferred one-third octave bands from 125 to 4000 Hz and may be
extended, if desired.
8.2 The signal source shall be placed so that the enclosure to be tested is not in its direct field; the minimum distance from the
source to any part of the enclosure shall be:
1/2
r $ 0.63 A (3)
where A is the sound absorption in the reverberation chamber with the enclosure present. Normally, the best practice is to direct
the source into a trihedral corner of the reverberation room. If more than one loudspeaker is used, it is advisable that each
loudspeaker be driven by an independent noise source.
8.3 The signal level shall be at least 10 dB above the measured background noise inside the enclosure at each test frequency.
9. Procedure
9.1 Enclosure Placement—Place the enclosure in the reverberation room so that:
9.1.1 No enclosure wall is parallel to a reverberation room wall.
9.1.2 The enclosure is at least one-half wavelength away from the reverberation room walls and ceiling and any diffusing
surfaces at the center frequency of the lowest one-third octave band in which the noise reduction is to be measured.
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 beams,
rails, or vibration isolators unless they are normally used with the enclosure.
9.2 Enclosure Preparation:
9.2.1 If the enclosure is equipped with a self-contained air conditioning or ventilating system, operate the system for at least
10 min, turn the system off, and test without further adjustment.
9.2.2 After the procedure of 9.2.1 has been completed, open and close each enclosure door and access opening at least ten times
and test without further adjustment.
E596 − 96 (2016)
9.2.3 If the enclosure is equipped with a connector for external air conditioning and ventilation, connect the enclosure to an
external duct system that satisfies the manufacturer’s specifications or recommendations for the enclosure.
9.3 Inside Measuring Positions—Select at least four microphone positions inside the enclosure as follows:
9.3.1 Determine the useful volume of the enclosure.
9.3.2 Distribute microphone positions evenly throughout the useful volume.
9.3.2.1 Microphone positions or traverses should not be located or pass within 0.30 m of the enclosure interior walls unless the
useful volume necessarily includes these regions.
9.3.2.2 Microphone positions should not approach one another to within a distance of one-half-wavelength at the lowest
frequency of interest.
9.3.2.3 For low frequencies it is almost never possible to select four microphone positions that satisfy the requirement of 9.3.2.2.
Whenever this is the case, microphone positions inside the enclosure should be selected to get the best estimate of the space-time
average sound pressure
...
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