1、Designation: E 596 96 (Reapproved 2002)e1Standard Test Method forLaboratory Measurement of Noise Reduction of Sound-Isolating Enclosures1This standard is issued under the fixed designation E 596; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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.e1NOTEEquation 6 was ed
3、itorially updated in September 2003.1. Scope1.1 This test method covers the reverberation room mea-surement of the noise reduction of sound-isolating enclosures.1.2 The noise isolation class may be determined from thenoise reduction measured in accordance with this test method.1.3 This standard does
4、 not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Stand
5、ards:C 423 Test Method for Sound Absorption and Sound Ab-sorption Coefficients by the Reverberation Room Method2C 634 Terminology Relating to Environmental Acoustics2E 413 Classification for Rating Sound Insulation22.2 ANSI Standards:S1.4 Specification for Sound Level Meters3S1.11 Specification for
6、Octave-Band and Fractional-Octave-Band Analog and Digital Filters33. Terminology3.1 Definitions and SymbolsExcept as noted in 3.2, theterms and symbols used in this test method are defined inTerminology C 634.3.2 Definitions of Terms Specific to This Standard:3.2.1 sound-isolating enclosureany enclo
7、sure that com-pletely encloses a space, is intended to provide sound isolationfor the enclosed space, and can be tested in a reverberationroom.3.2.2 useful volume of a sound isolating enclosurethe partof the space inside the enclosure in which the noise reductionis of interest. For example, in an au
8、diometric booth, the usefulvolume is the part of the space inside the booth where a testsubjects head is likely to be during audiometric tests.4. Summary of Test Method4.1 The enclosure to be tested is placed in a reverberationroom and prepared for testing. The background noise levelsinside the encl
9、osure and in the reverberation room are mea-sured in one-third octave bands. After bands of random noiseare produced in the reverberation room, one-third octave bandsound pressure levels are measured at several points in thereverberation room and at appropriate points inside the enclo-sure. The nois
10、e reduction in each one-third octave band is thedifference between the space-averaged sound pressure level inthe reverberation room and the space-averaged sound pressurelevel inside the enclosure. The noise isolation class (NIC) maybe determined from the noise reduction data.5. Significance and Use5
11、.1 The noise reduction of an enclosure is a property of theenclosure, the location of the sound source used to measurenoise reduction, and the space in which the enclosure is placed.It is not a property of the enclosure alone, and its measurementunder different conditions can be expected to give dif
12、ferentresults. When the noise reduction is measured in accordancewith this test method, the sound source is outside the enclosureand the sound field outside the enclosure approximates adiffuse sound field. Measurements made in accordance withthis test method can be expected to be reproducible from o
13、nelaboratory to another.5.2 The noise reduction measured in accordance with thistest method may be used for the following purposes:5.2.1 To rank the order of sound-isolating enclosures ac-cording to noise isolation class, NIC.5.2.2 To estimate the highest one-third octave band soundpressure levels t
14、hat can occur outside the enclosure withoutexceeding specified sound pressure levels inside the enclosure.1This test method is under the jurisdiction of ASTM Committee E33 onEnvironmental Acoustics and is the direct responsibility of Subcommittee E33.03 onSound Transmission.Current edition approved
15、Jan. 10, 1996. Published April 1996. Originallypublished as E 596 77. Last previous edition E 596 94a.2Annual Book of ASTM Standards, Vol 04.06.3Available from American National Standards Institute, 25 W. 43rd St., 4thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO
16、 Box C700, West Conshohocken, PA 19428-2959, United States.5.2.3 To estimate the one-third octave band sound pressurelevels that will occur inside the enclosure with specified soundpressure levels outside.5.3 The noise reduction measured in accordance with thistest method may not estimate accurately
17、 the isolation that theenclosure will provide when it is used to isolate a noise sourceinside it from the space outside. The user should be cautiouswhen using noise reductions measured by this test method toevaluate enclosures used to enclose noise sources.5.4 Sound-isolating enclosures are frequent
18、ly made fromprefabricated modular panels. The noise reduction measuredby this test method applies to the complete enclosure and notto individual panels from which it is made and cannot be usedto infer the sound transmission loss of the individual panels.5.5 Specifications for sound-isolating enclosu
19、res may in-clude reference to noise reduction and noise isolation classmeasured in accordance with this test method.6. Reverberation Room6.1 Sound DiffusionThe sound field in the reverberationroom shall closely approximate a diffuse field when theenclosure to be tested is in place for testing. In ge
20、neral, therequirements for the reverberation room are those listed in thesection dealing with Reverberation Room of Test MethodC 423. These requirements include:6.1.1 The effective room volume (actual room volumeminus the volume occupied by the enclosure) should not beless than 200 m3.NOTE 1Experien
21、ce and experimental data have shown that as long asthe requirements of 9.1.2 and 9.5 are satisfied, the room volume is notcritical.6.1.2 The sound absorption in the reverberation room shallbe made as low as possible in order to achieve the best possiblesimulation to an ideal diffuse field and in ord
22、er to keep theregion dominated by the direct field of the source as small aspossible. Within the frequency range described below thesound absorption of the reverberation room should be nogreater than the following:A 5 V2/3/3 (1)where:V = room volume, m3, andA = room sound absorption in metric sabins
23、.For frequencies below f = 2000/V1/3(where the number 2000is an empirical constant with the units seconds per metre),somewhat higher absorption may be desirable to accommodateother test requirements (for example, ANSI S1.32, ISO 3741);in any case, the absorption should be no greater than threetimes
24、the value given by Eq 1. For frequencies above 2000 Hz,atmospheric absorption may make it impossible to avoid aslightly higher value of sound absorption.6.1.3 Diffusing devices such as rotating and stationarydiffusing surfaces are useful for creating an adequate approxi-mation to a diffuse sound fie
25、ld.6.2 Background Noise:6.2.1 The sound pressure level of the background noiseinside the enclosure should be at least 10 dB below the level ofthe test signal. If the difference between the level of the testsignal and the background noise level is less than 10 dB andgreater than 5 dB, the adjusted va
26、lue of the signal level iscalculated by:La5 10 log 10.1Lc2 10.1Lb! (2)where:La= adjusted signal level, dB,Lc= level of combined signal and background noise, dB,andLb= level of background noise, dB.If the difference between the level of the test signal and thebackground noise level is not at least 5
27、dB, then subtract 2 dBfrom the level of the combined signal and background noiseand use this adjusted level. When the difference between thesignal level and the background noise level is less than 5 dB,the measurements provide only an estimate of the lower limitof the noise reduction of the enclosur
28、e. Identify such limitedmeasurements in the test report.6.2.2 Structureborne noise within the reverberation roomstructure can excite the enclosure to be tested and cause thesound pressure level within the enclosure to be higher thanwould be measured due to the test signal alone. Therefore, thereverb
29、eration room floor should be adequately isolated againststructureborne vibrations which are propagated into the rever-beration room from the outside.NOTE 2When the background noise inside the enclosure is the sameas the background noise in the reverberation room, it is likely that eitherthe vibratio
30、n isolation (if any) between the enclosure and the reverberationroom floor is ineffective or the measured background noise is the internalnoise of the measuring instruments.6.3 ConstructionIn accordance with 6.1.2, the reverbera-tion room should be constructed of materials that have lowsound absorpt
31、ion coefficients. Normally, when a reverberationroom is to be used to measure sound absorption, sound powerlevel, or sound transmission loss, it must be constructed usingmaterials and design details that will provide needed soundinsulation against outside noise sources. If a reverberationroom is to
32、be constructed solely for testing sound-isolatingenclosures in accordance with this test method, the soundisolation requirements are not so critical, and lighter materialsmay be used as long as the requirements of 6.1 and 6.2 are met.7. Measuring Instrumentation7.1 The minimum instrumentation requir
33、ed for this testmethod is:7.1.1 A microphone and amplifier that satisfy the require-ments of ANSI S1.4 for Type 1 or better sound level meterswith the exception that A and B-weighting networks are notrequired.NOTE 3A flat characteristic is desirable and, when available, shouldbe used in place of the
34、 C-weighting network.7.1.2 A one-third octave filter set satisfying the require-ments of ANSI S1.11 for a one-third octave band filter set,Order 3 or higher, Type 1 or better. The nominal centerfrequencies of the filters shall be those frequencies that arewithin the frequency range where the noise r
35、eduction is to bemeasured. This frequency range shall include all of theE 596 96 (2002)e12preferred one-third octave bands from 125 to 4000 Hz and maybe extended, if desired.7.1.3 A level meter, graphic level recorder, or other devicefrom which the sound pressure level can be read. The averag-ing ti
36、me of the instrumentation shall be sufficient to permitreading the average sound pressure level with adequate preci-sion (see Section 11).7.2 Additional microphone systems may be used. If addi-tional microphones are used, differences in their responsesshould be accounted for either by careful calibr
37、ation or by anappropriate measurement procedure (see 9.6).8. Test Signal8.1 The test signals shall be bands of random noise at leastone-third octave wide and including every one-third octaveband within the test range. The test range shall include all ofthe preferred one-third octave bands from 125 t
38、o 4000 Hz andmay be extended, if desired.8.2 The signal source shall be placed so that the enclosure tobe tested is not in its direct field; the minimum distance fromthe source to any part of the enclosure shall be:r $ 0.63 A1/2(3)where A is the sound absorption in the reverberation cham-ber with th
39、e enclosure present. Normally, the best practice is todirect the source into a trihedral corner of the reverberationroom. If more than one loudspeaker is used, it is advisable thateach loudspeaker be driven by an independent noise source.8.3 The signal level shall be at least 10 dB above themeasured
40、 background noise inside the enclosure at each testfrequency.9. Procedure9.1 Enclosure PlacementPlace the enclosure in the rever-beration room so that:9.1.1 No enclosure wall is parallel to a reverberation roomwall.9.1.2 The enclosure is at least one-half wavelength awayfrom the reverberation room w
41、alls and ceiling and any diffus-ing surfaces at the center frequency of the lowest one-thirdoctave band in which the noise reduction is to be measured.9.1.3 The enclosure is mounted on the floor in the same wayas when it is in normal use. Do not mount the enclosure onbeams, rails, or vibration isola
42、tors unless they are normallyused with the enclosure.9.2 Enclosure Preparation:9.2.1 If the enclosure is equipped with a self-contained airconditioning or ventilating system, operate the system for atleast 10 min, turn the system off, and test without furtheradjustment.9.2.2 After the procedure of 9
43、.2.1 has been completed, openand close each enclosure door and access opening at least tentimes and test without further adjustment.9.2.3 If the enclosure is equipped with a connector forexternal air conditioning and ventilation, connect the enclosureto an external duct system that satisfies the man
44、ufacturersspecifications or recommendations for the enclosure.9.3 Inside Measuring PositionsSelect at least four micro-phone positions inside the enclosure as follows:9.3.1 Determine the useful volume of the enclosure.9.3.2 Distribute microphone positions evenly throughoutthe useful volume.9.3.2.1 M
45、icrophone positions or traverses should not belocated or pass within 0.30 m of the enclosure interior wallsunless the useful volume necessarily includes these regions.9.3.2.2 Microphone positions should not approach one an-other to within a distance of one-half-wavelength at the lowestfrequency of i
46、nterest.9.3.2.3 For low frequencies it is almost never possible toselect four microphone positions that satisfy the requirement of9.3.2.2. Whenever this is the case, microphone positions insidethe enclosure should be selected to get the best estimate of thespace-time average sound pressure level wit
47、hin the usefulvolume, disregarding spatial correlation among positions.9.3.3 The potential number of statistically independent mi-crophone positions N within a space is calculated asN 5 UV/Sl2D3(4)where UV is the useful volume.9.3.3.1 The effective number of independent measurementlocations n shall
48、be calculated as follows:n 5 N if N independent stationary microphone locations are used,5 2pr/l/2! if rotating microphone traverse of radius r is used,5 L/l/2! if linear microphone traverse of length L is used. (5)NOTE 4A half-wavelength correlation distance is assumed, and thenumber of independent
49、 data samples is calculated on this basis. Aminimum of four independent data points is required for calculation of the95 % confidence limits from the table. This is not often possible in smallenclosures at low frequencies. When this is the case, the data should be soidentified in the report.9.4 Background NoiseWith the sound sources not operat-ing, measure the background noise levels in the receiving roomat each microphone position or traverse. Corrections shall bemade unless the background level is more than 10 dB belowthe combination of signal and background. (The
