1、Designation: E 596 96 (Reapproved 2009)Standard 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 of
2、 revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test meth
3、od 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 not purport to address all of thesafety concerns, if any, ass
4、ociated 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 Standards:2C 423 Test Method for Sound Absorption and Sound Ab-sorp
5、tion Coefficients by the Reverberation Room MethodC 634 Terminology Relating to Building and Environmen-tal AcousticsE 413 Classification for Rating Sound Insulation2.2 ANSI Standards:S1.4 Specification for Sound Level Meters3S1.11 Specification for Octave-Band and Fractional-Octave-Band Analog and
6、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 enclosure that com-pletely encloses a space, is intende
7、d 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 audiometric booth, the usefulvolume is the part of t
8、he 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 enclosure and in the reverberation room are mea-sured
9、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 noise reduction in each one-third octave band is thedi
10、fference 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 Use5.1 The noise reduction of an enclosure is a proper
11、ty 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 differentresults. When the noise reduction is measure
12、d 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 onelaboratory to another.5.2 The noise reduction me
13、asured 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 that can occur outside the enclosure withoutexceedi
14、ng specified sound pressure levels inside the enclosure.5.2.3 To estimate the one-third octave band sound pressurelevels that will occur inside the enclosure with specified soundpressure levels outside.1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmental Acou
15、stics and is the direct responsibility of SubcommitteeE33.03 on Sound Transmission.Current edition approved April 1, 2009. Published August 2009. Originallyapproved in 1977. Last previous edition approved in 2002 as E 596 96 (2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org
16、, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1C
17、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3 The noise reduction measured in accordance with thistest method may not estimate accurately the isolation that theenclosure will provide when it is used to isolate a noise sourceinsid
18、e 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 frequently made fromprefabricated modular panels. The noise reduction measuredby this test method ap
19、plies 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 enclosures may in-clude reference to noise reduction and noise isolation classmeasured in accordanc
20、e 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 general, therequirements for the reverberation room are those listed in thesection dealing wit
21、h 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 1Experience and experimental data have shown that as long asthe requirements of 9.1.2 and 9.5 are sat
22、isfied, 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 order to keep theregion dominated by the direct field of the source as small aspossible. Within
23、 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.For frequencies below f = 2000/V1/3(where the number 2000is an empirical constant with the
24、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 the value given by Eq 1. For frequencies above 2000 Hz,atmospheric absorption may make it im
25、possible 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 field.6.2 Background Noise:6.2.1 The sound pressure level of the background noiseinside the enc
26、losure 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 value of the signal level iscalculated by:La5 10 log 10.1Lc2 10.1Lb! (2)where:La= adjusted sig
27、nal 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 dB, then subtract 2 dBfrom the level of the combined signal and background noiseand use this
28、 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 enclosure. Identify such limitedmeasurements in the test report.6.2.2 Structureborne noise within th
29、e 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, thereverberation room floor should be adequately isolated againststructureborne vibrations which are
30、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 vibration isolation (if any) between the enclosure and the reverberationroom floor is ineffective or
31、 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 absorption coefficients. Normally, when a reverberationroom is to be used to measure sound absorpti
32、on, 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 be constructed solely for testing sound-isolatingenclosures in accordance with this test met
33、hod, 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 required for this testmethod is:7.1.1 A microphone and amplifier that satisfy the require-ments of
34、 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 C-weighting network.7.1.2 A one-third octave filter set satisfying the require-ments of ANS
35、I 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 reduction is to bemeasured. This frequency range shall include all of thepreferred one-third
36、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 time of the instrumentation shall be sufficient to permitE 596 96 (2009)2reading the average sound pressure leve
37、l 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 calibration or by anappropriate measurement procedure (see 9.6).8. Test Signal8.1 The test signals s
38、hall 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 to 4000 Hz andmay be extended, if desired.8.2 The signal source shall be placed so that the enc
39、losure 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 the enclosure present. Normally, the best practice is todirect the source into a trihedral corner
40、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 background noise inside the enclosure at each testfrequency.9. Procedure9.1 Enclosure Placement
41、Place 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 walls and ceiling and any diffus-ing surfaces at the center frequency of the lowest one-thirdocta
42、ve 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 isolators unless they are normallyused with the enclosure.9.2 Enclosure Preparation:9.2.1 If the encl
43、osure 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 9.2.1 has been completed, openand close each enclosure door and access opening at least tentimes
44、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 manufacturersspecifications or recommendations for the enclosure.9.3 Inside Measuring PositionsSele
45、ct 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 Microphone positions or traverses should not belocated or pass within 0.30 m of the enclosure int
46、erior 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 interest.9.3.2.3 For low frequencies it is almost never possible toselect four microphone positio
47、ns 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 within the usefulvolume, disregarding spatial correlation among positions.9.3.3 The potential numbe
48、r 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 be calculated as follows:n 5 N if N independent stationary microphone locations are used,5 2pr/l
49、/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 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 back
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