ASTM E596-22

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2022
• ICS: 17.140.20 - Noise emitted by machines and equipment
• ICS: 71.040.20 - Laboratory ware and related apparatus
• Technical Committee: E33 - Building and Environmental Acoustics
• Drafting Committee: E33.03 - Sound Transmission

Relations

• Refers: ASTM C634-13 - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Sep-2013
• Refers: ASTM C634-11 - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Dec-2011
• Refers: ASTM C634-10a - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Sep-2010
• Refers: ASTM E413-10 - Classification for Rating Sound Insulation
• Effective Date: 01-Sep-2010
• Refers: ASTM C634-10 - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Jun-2010
• Refers: ASTM C423-09a - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 15-Oct-2009
• Refers: ASTM C423-09 - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Oct-2009
• Refers: ASTM C634-09 - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Apr-2009
• Refers: ASTM C423-08a - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Oct-2008
• Refers: ASTM C634-08a - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 01-Sep-2008
• Refers: ASTM C634-08 - Standard Terminology Relating to Building and Environmental Acoustics
• Effective Date: 15-Mar-2008
• Refers: ASTM C423-08 - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Mar-2008
• Refers: ASTM C423-07a - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Jun-2007
• Refers: ASTM C423-07 - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Jan-2007
• Refers: ASTM C423-06 - Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
• Effective Date: 01-Dec-2006

Overview

ASTM E596-22: Standard Test Method for Laboratory Measurement of Noise Reduction of Sound-Isolating Enclosures establishes a reliable method for measuring the noise reduction performance of sound-isolating enclosures within a laboratory environment. This standard, maintained by ASTM International, outlines procedures using reverberation rooms, specific instrumentation, and test signals to assess the ability of full enclosures to reduce noise transmission from external sources. The results help ensure consistency and comparability between laboratories and support accurate assessment of enclosure performance for noise isolation.

Key Topics

• Noise Reduction Measurement: The standard specifies laboratory procedures to determine the noise reduction of a complete sound-isolating enclosure. Measurement focuses on the difference in sound pressure levels between the reverberation room (outside the enclosure) and inside the enclosure, using one-third octave band analysis.

• Noise Isolation Class (NIC): The standard allows calculation of the Noise Isolation Class-a single-number rating that ranks enclosures according to their noise isolation capabilities, making it easier to compare performance across products.

• Sound Field Conditions: Measurements assume a diffuse sound field in the reverberation room, which is critical for reproducibility.

• Instrumentation and Calibration: Use of calibrated microphones, one-third octave band filters, and precise procedures are required to ensure measurement accuracy and confidence in results.

• Limitations of Measurement: The test method is designed for sound sources located outside the enclosure. The measured values may not accurately represent performance when the enclosure is used to contain noise from sources inside it.

• Complete Enclosure Assessment: The method applies to full enclosures rather than individual panels, providing an overall measure of noise reduction but not the transmission loss of single components.

Applications

ASTM E596-22 is widely used to assess and compare the acoustic isolation of sound-isolating enclosures in sectors where noise control is critical. Typical applications include:

• Testing of Audiometric Booths: Ensures that hearing test environments reliably reduce external noise to meet regulatory requirements.
• Industrial Noise Control: Evaluation of operator cabins, machine enclosures, and modular sound rooms to ensure safer and quieter workplaces.
• Product Development: Manufacturers can rank enclosures according to noise isolation class (NIC), enabling informed choices and supporting marketing claims.
• Specification Compliance: Project specifications may reference this standard for third-party verification of enclosure performance.
• Laboratory Accreditation: Laboratories seeking accreditation for acoustic testing follow this method to demonstrate competence and procedural compliance.

Related Standards

For effective and recognized noise isolation testing, several associated standards are referenced:

• ASTM C423 - Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.
• ASTM C634 - Terminology Relating to Building and Environmental Acoustics.
• ASTM E413 - Classification for Rating Sound Insulation.
• ANSI S1.4 - Specification for Sound Level Meters.
• ANSI S1.11 - Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters.

These documents provide foundational terminology, measurement techniques, ratings systems, and instrumentation requirements essential to thorough and credible noise reduction testing.

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Keywords: ASTM E596-22, noise reduction, sound-isolating enclosure, noise isolation class, NIC, sound pressure level, reverberation room, acoustic testing, laboratory measurement, noise control, enclosure performance, ASTM standards, industrial noise, building acoustics.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E596 − 22
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. Terminology
1.1 This test method covers the reverberation room mea- 3.1 Terms used in this standard are defined either in Termi-
surement of the noise reduction of sound-isolating enclosures. nology C634 or within this standard. The definitions of terms
explicitly given within this standard take precedence over
1.2 The noise isolation class may be determined from the
definitions given in Terminology C634. The definitions within
noise reduction measured in accordance with this test method.
Terminology C634 and this standard take precedence over any
1.3 This standard does not purport to address all of the
other definitions of defined terms found in any other
safety concerns, if any, associated with its use. It is the
documents, including other documents referenced in this stan-
responsibility of the user of this standard to establish appro-
dard.
priate safety, health, and environmental practices and deter-
3.2 Definitions of Terms Specific to This Standard:
mine the applicability of regulatory limitations prior to use.
3.2.1 sound-isolating enclosure, n—any enclosure that com-
1.4 This international standard was developed in accor-
pletely encloses a space, is intended to provide sound isolation
dance with internationally recognized principles on standard-
for the enclosed space, and can be tested in a reverberation
ization established in the Decision on Principles for the
room.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical 3.2.2 useful volume of a sound isolating enclosure,
3 3
Barriers to Trade (TBT) Committee. UV[L ](m ), n—the part of the space inside the enclosure in
which the noise reduction is of interest. For example, in an
2. Referenced Documents audiometric booth, the useful volume is the part of the space
2 inside the booth where a test subject’s head is likely to be
2.1 ASTM Standards:
during audiometric tests.
C423 Test Method for SoundAbsorption and SoundAbsorp-
tion Coefficients by the Reverberation Room Method
4. Summary of Test Method
C634 Terminology Relating to Building and Environmental
4.1 The enclosure to be tested is placed in a reverberation
Acoustics
E413 Classification for Rating Sound Insulation room and prepared for testing. The background noise levels
inside the enclosure and in the reverberation room are mea-
2.2 ANSI Standards:
3 sured in one-third octave bands. After bands of random noise
S1.4 Specification for Sound Level Meters
are produced in the reverberation room, one-third octave band
S1.11 Specification for Octave-Band and Fractional-Octave-
3 sound pressure levels are measured at several points in the
Band Analog and Digital Filters
reverberation room and at appropriate points inside the enclo-
sure. The noise reduction in each one-third octave band is the
difference between the space-averaged sound pressure level in
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
the reverberation room and the space-averaged sound pressure
and Environmental Acoustics and is the direct responsibility of Subcommittee
level inside the enclosure. The noise isolation class (NIC) may
E33.03 on Sound Transmission.
be determined from the noise reduction data.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
approved in 1977. Last previous edition approved in 2016 as E596 – 96 (2016).
DOI: 10.1520/E0596-22.
5. Significance and Use
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.1 The noise reduction of an enclosure is a property of the
Standards volume information, refer to the standard’s Document Summary page on
enclosure, the location of the sound source used to measure
the ASTM website.
noise reduction, and the space in which the enclosure is placed.
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. It is not a property of the enclosure alone, and its measurement
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E596 − 22
under different conditions can be expected to give different
A = room sound absorption in metric sabins.
results. When the noise reduction is measured in accordance
1/3
For frequencies below f = 2000⁄V (where the number
with this test method, the sound source is outside the enclosure
2000isanempiricalconstantwiththeunitssecondspermetre),
and the sound field outside the enclosure approximates a
somewhat higher absorption may be desirable to accommodate
diffuse sound field. Measurements made in accordance with
other test requirements (for example, ANSI S1.32, ISO 3741);
this test method can be expected to be reproducible from one
in any case, the absorption should be no greater than three
laboratory to another.
times the value given by Eq 1. For frequencies above 2000 Hz,
5.2 The noise reduction measured in accordance with this
atmospheric absorption may make it impossible to avoid a
test method may be used for the following purposes:
slightly higher value of sound absorption.
5.2.1 To rank the order of sound-isolating enclosures ac-
6.1.3 Diffusing devices such as rotating and stationary
cording to noise isolation class, NIC.
diffusing surfaces are useful for creating an adequate approxi-
5.2.2 To estimate the highest one-third octave band sound
mation to a diffuse sound field.
pressure levels that can occur outside the enclosure without
6.2 Background Noise:
exceeding specified sound pressure levels inside the enclosure.
6.2.1 The sound pressure level of the background noise
5.2.3 To estimate the one-third octave band sound pressure
inside the enclosure should be at least 10 dB below the level of
levels that will occur inside the enclosure with specified sound
the test signal. If the difference between the level of the test
pressure levels outside.
signal and the background noise level is less than 10 dB and
5.3 The noise reduction measured in accordance with this
greater than 5 dB, the adjusted value of the signal level is
test method may not estimate accurately the isolation that the
calculated by:
enclosure will provide when it is used to isolate a noise source
.1L .1L
c b
L 5 10log 10 2 10 (2)
~ !
inside it from the space outside. The user should be cautious a
when using noise reductions measured by this test method to
where:
evaluate enclosures used to enclose noise sources.
L = adjusted signal level, dB,
a
5.4 Sound-isolating enclosures are frequently made from L = level of combined signal and background noise, dB,
c
prefabricated modular panels. The noise reduction measured and
L = level of background noise, dB.
by this test method applies to the complete enclosure and not
b
to individual panels from which it is made and cannot be used
If the difference between the level of the test signal and the
to infer the sound transmission loss of the individual panels.
background noise level is not at least 5 dB, then subtract 2 dB
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.
6.1 Sound Diffusion—The sound field in the reverberation
6.2.2 Structure-borne noise within the reverberation room
room shall closely approximate a diffuse field when the
structure can excite the enclosure to be tested and cause the
enclosure to be tested is in place for testing. In general, the
sound pressure level within the enclosure to be higher than
requirements for the reverberation room are those listed in the
would be measured due to the test signal alone. Therefore, the
section dealing with Reverberation Room of Test Method
reverberation room floor should be adequately isolated against
C423. These requirements include:
structure-borne vibrations which are propagated into the rever-
6.1.1 The effective room volume (actual room volume
beration room from the outside.
minus the volume occupied by the enclosure) should not be
less than 200 m .
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
NOTE 1—Experience and experimental data have shown that as long as
thevibrationisolation(ifany)betweentheenclosureandthereverberation
the requirements of 9.1.2 and 9.5 are satisfied, the room volume is not
room floor is ineffective or the measured background noise is the internal
critical.
noise of the measuring instruments.
6.1.2 The sound absorption in the reverberation room shall
6.3 Construction—In accordance with 6.1.2, the reverbera-
bemadeaslowaspossibleinordertoachievethebestpossible
tion room should be constructed of materials that have low
simulation to an ideal diffuse field and in order to keep the
sound absorption coefficients. Normally, when a reverberation
region dominated by the direct field of the source as small as
room is to be used to measure sound absorption, sound power
possible. Within the frequency range described below the
level, or sound transmission loss, it must be constructed using
sound absorption of the reverberation room should be no
materials and design details that will provide needed sound
greater than the following:
insulation against outside noise sources. If a reverberation
2/3
A 5 V /3 (1)
room is to be constructed solely for testing sound-isolating
enclosures in accordance with this test method, the sound
where:
isolation requirements are not so critical, and lighter materials
V = room volume, m , and
may be used as long as the requirements of6.1 and 6.2 are met.
E596 − 22
7. Measuring Instrumentation 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
7.1 The minimum instrumentation required for this test
beams, rails, or vibration isolators unless they are normally
method is:
used with the enclosure.
7.1.1 A microphone and amplifier that satisfy the require-
ments of ANSI S1.4 for Type 1 or better sound level meters 9.2 Enclosure Preparation:
with the exception that A and B-weighting networks are not
9.2.1 If the enclosure is equipped with a self-contained air
required.
conditioning or ventilating system, operate the system for at
least 10 min, turn the system off, and test without further
NOTE 3—A flat characteristic is desirable and, when available, should
adjustment.
be used in place of the C-weighting network.
9.2.2 After the procedure of 9.2.1 has been completed, open
7.1.2 A one-third octave filter set satisfying the require-
and close each enclosure door and access opening at least ten
ments of ANSI S1.11 for a one-third octave band filter set,
times and test without further adjustment.
Order 3 or higher, Type 1 or better. The nominal center
9.2.3 If the enclosure is equipped with a connector for
frequencies of the filters shall be those frequencies that are
external air conditioning and ventilation, connect the enclosure
within the frequency range where the noise reduction is to be
to an external duct system that satisfies the manufacturer’s
measured. This frequency range shall include all of the
specifications or recommendations for the enclosure.
preferred one-third octave bands from 125 to 4000 Hz and may
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 p
...

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 2016) E596 − 22
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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.
3.1 Terms used in this standard are defined either in Terminology C634 or within this standard. The definitions of terms explicitly
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, 2016Oct. 1, 2022. Published April 2016October 2022. Originally approved in 1977. Last previous edition approved in 20092016 as
E596 – 96 (2009).(2016). DOI: 10.1520/E0596-96R16.10.1520/E0596-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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 − 22
given within this standard take precedence over definitions given in Terminology C634. The definitions within Terminology C634
and this standard take precedence over any other definitions of defined terms found in any other documents, including other
documents referenced in this standard.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 sound-isolating enclosure—enclosure, n—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 3
3.2.2 useful volume of a sound isolating enclosure—enclosure, UV[L ](m ), n—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.
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:
E596 − 22
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
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 StructureborneStructure-borne 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 structurebornestructure-borne 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.
E596 − 22
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
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