ASTM E596-96(2002)e1
(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
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.
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.
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.
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.
Specifications for sound-isolating enclosures may include reference to noise reduction and noise isolation class measured in accordance with this test method.
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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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.
e NOTE—Equation 6 was editorially updated in September 2003.
1. Scope 3.2.2 useful volume of a sound isolating enclosure—the part
of the space inside the enclosure in which the noise reduction
1.1 This test method covers the reverberation room mea-
is of interest. For example, in an audiometric booth, the useful
surement of the noise reduction of sound-isolating enclosures.
volume is the part of the space inside the booth where a test
1.2 The noise isolation class may be determined from the
subject’s head is likely to be during audiometric tests.
noise reduction measured in accordance with this test method.
1.3 This standard does not purport to address all of the
4. Summary of Test Method
safety concerns, if any, associated with its use. It is the
4.1 The enclosure to be tested is placed in a reverberation
responsibility of the user of this standard to establish appro-
room and prepared for testing. The background noise levels
priate safety and health practices and determine the applica-
inside the enclosure and in the reverberation room are mea-
bility of regulatory limitations prior to use.
sured in one-third octave bands. After bands of random noise
2. Referenced Documents are produced in the reverberation room, one-third octave band
sound pressure levels are measured at several points in the
2.1 ASTM Standards:
reverberation room and at appropriate points inside the enclo-
C 423 Test Method for Sound Absorption and Sound Ab-
sure. The noise reduction in each one-third octave band is the
sorption Coefficients by the Reverberation Room Method
difference between the space-averaged sound pressure level in
C 634 Terminology Relating to Environmental Acoustics
the reverberation room and the space-averaged sound pressure
E 413 Classification for Rating Sound Insulation
level inside the enclosure. The noise isolation class (NIC) may
2.2 ANSI Standards:
be determined from the noise reduction data.
S1.4 Specification for Sound Level Meters
S1.11 Specification for Octave-Band and Fractional-
5. Significance and Use
Octave-Band Analog and Digital Filters
5.1 The noise reduction of an enclosure is a property of the
3. Terminology enclosure, the location of the sound source used to measure
noise reduction, and the space in which the enclosure is placed.
3.1 Definitions and Symbols—Except as noted in 3.2, the
It is not a property of the enclosure alone, and its measurement
terms and symbols used in this test method are defined in
under different conditions can be expected to give different
Terminology C 634.
results. When the noise reduction is measured in accordance
3.2 Definitions of Terms Specific to This Standard:
with this test method, the sound source is outside the enclosure
3.2.1 sound-isolating enclosure—any enclosure that com-
and the sound field outside the enclosure approximates a
pletely encloses a space, is intended to provide sound isolation
diffuse sound field. Measurements made in accordance with
for the enclosed space, and can be tested in a reverberation
this test method can be expected to be reproducible from one
room.
laboratory to another.
5.2 The noise reduction measured in accordance with this
This test method is under the jurisdiction of ASTM Committee E33 on
test method may be used for the following purposes:
EnvironmentalAcousticsandisthedirectresponsibilityofSubcommitteeE33.03on
5.2.1 To rank the order of sound-isolating enclosures ac-
Sound Transmission.
Current edition approved Jan. 10, 1996. Published April 1996. Originally cording to noise isolation class, NIC.
published as E 596 – 77. Last previous edition E 596 – 94a.
5.2.2 To estimate the highest one-third octave band sound
Annual Book of ASTM Standards, Vol 04.06.
pressure levels that can occur outside the enclosure without
Available from American National Standards Institute, 25 W. 43rd St., 4th
exceeding specified sound pressure levels inside the enclosure.
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E 596 – 96 (2002)
5.2.3 To estimate the one-third octave band sound pressure signal and the background noise level is less than 10 dB and
levels that will occur inside the enclosure with specified sound greater than 5 dB, the adjusted value of the signal level is
pressure levels outside. calculated by:
5.3 The noise reduction measured in accordance with this
.1L .1L
c b
L 5 10 log ~10 2 10 ! (2)
a
test method may not estimate accurately the isolation that the
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
L = level of combined signal and background noise, dB,
when using noise reductions measured by this test method to
c
evaluate enclosures used to enclose noise sources. and
L = level of background noise, dB.
5.4 Sound-isolating enclosures are frequently made from
b
prefabricated modular panels. The noise reduction measured 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
by this test method applies to the complete enclosure and not
to individual panels from which it is made and cannot be used from the level of the combined signal and background noise
and use this adjusted level. When the difference between the
to infer the sound transmission loss of the individual panels.
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.
C 423. 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
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
Forfrequenciesbelow f = 2000/V (wherethenumber2000
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
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
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E 596 – 96 (2002)
preferred one-third octave bands from 125 to 4000 Hz and may 9.3.1 Determine the useful volume of the enclosure.
be extended, if desired. 9.3.2 Distribute microphone positions evenly throughout
7.1.3 A level meter, graphic level recorder, or other device
the useful volume.
from which the sound pressure level can be read. The averag-
9.3.2.1 Microphone positions or traverses should not be
ing time of the instrumentation shall be sufficient to permit
located or pass within 0.30 m of the enclosure interior walls
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 Thesignalsourceshallbeplacedsothattheenclosureto 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
at each microphone position or traverse. Corrections shall be
wall.
9.1.2 The enclosure is at least one-half wavelength away made unless the background level is more than 10 dB below
the combination of signal and background. (The signal is the
from the reverberation room walls and ceiling and any diffus-
ing surfaces at the center frequency of the lowest one-third sound pressure level due to transmission through the test
enclosure.) If the background level is between 5 and 10 dB
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 below the combined level, correct the signal level using:
as when it is in normal use. Do not mount the enclosure on L /10 L /10
sb b
L 5 10 log@10 2 10 # (6)
s
beams, rails, or vi
...
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