ASTM C423-2007a Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method《用混响室法测定吸声和吸声系数的标准试验方法》.pdf
《ASTM C423-2007a Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method《用混响室法测定吸声和吸声系数的标准试验方法》.pdf》由会员分享,可在线阅读,更多相关《ASTM C423-2007a Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method《用混响室法测定吸声和吸声系数的标准试验方法》.pdf(11页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: C 423 07aStandard Test Method forSound Absorption and Sound Absorption Coefficients bythe Reverberation Room Method1This standard is issued under the fixed designation C 423; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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.1. Scope1.1 This test method co
3、vers the measurement of soundabsorption in a reverberation room by measuring decay rate.Procedures for measuring the absorption of a room, theabsorption of an object, such as an office screen, and the soundabsorption coefficients of a specimen of sound absorptivematerial, such as acoustical ceiling
4、tile, are described.1.2 Field MeasurementsAlthough this test method prima-rily covers laboratory measurements, the test method describedin 4.1 can be used for making field measurements of theabsorption of rooms (see also 5.5). A non-standard method tomeasure the absorption of rooms in the field is d
5、escribed inAppendix X2.1.3 This test method includes information on laboratoryaccreditation (see Annex A1), asymmetrical screens (see An-nex A2), and reverberation room qualification (see Annex A3).1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its u
6、se. 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 634 Terminology Relating to Environmental AcousticsE 548 Guide for Gener
7、al Criteria Used for EvaluatingLaboratory Competence3E 795 Practices for Mounting Test Specimens DuringSound Absorption Tests2.2 ANSI Standards:S1.6 Preferred Frequencies, Frequency Levels, and BandNumbers for Acoustical Measurements4S1.11 Specification for Octave-Band and Fractional-Octave-Band Ana
8、log and Digital Filters4S1.26 Method for the Calculation of the Absorption ofSound by the Atmosphere42.3 ASTM Adjuncts:Historical Applications Note on Sound Absorber53. Terminology3.1 Except as noted in 3.3, the terms and symbols used inthis test method are defined in Terminology C 634. Thefollowing
9、 definition is not currently included in TerminologyC 634:3.1.1 sound absorption average, SAAa single numberrating, the average, rounded off to the nearest 0.01, of thesound absorption coefficients of a material for the twelveone-third octave bands from 200 through 2500 Hz, inclusive,measured accord
10、ing to this test method.3.1.1.1 DiscussionThe sound absorption coefficients shallbe rounded off to the nearest 0.01 before averaging. If theunrounded average is an exact midpoint, round to the nexthigher multiple of 0.01. For example, report 0.625 as 0.63.3.2 In previous versions of this test method
11、 a single numberrating, called the noise reduction coefficient (NRC), wasdefined as follows:9Round the average of the sound absorption coefficientsfor 250, 500, 1000, and 2000 Hz to the nearest multipleof 0.05. If the unrounded average is an exact midpoint,round to the next higher multiple of 0.05.
12、For example,0.625 and 0.675 would be reported as 0.65 and 0.70, respectively.9The noise reduction coefficient shall be reported in order toprovide comparison with values reported in the past see12.1.3).3.3 Definition of Term Specific to This StandardThefollowing term has the meaning noted for this t
13、est method only:1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmental Acoustics and is the direct responsibility of SubcommitteeE33.01 on Sound Absorption.Current edition approved June 1, 2007. Published June 2007. Originallyapproved in 1958. Last previous edi
14、tion approved 2007 as C 423 07.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Available from Ame
15、rican National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.5A drawing of this specimen is available at a nominal charge from ASTMInternational Headquarters. Order Adjunct No. ADJC0423.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P
16、A 19428-2959, United States.3.3.1 output interval, Dt, T, sof a real-time analyzer, thetime between successive outputs; this time is not necessarilythe same as the integration time.4. Summary of Test Method4.1 Measurement of the Sound Absorption of a Room:4.1.1 A band of random noise is used as a te
17、st signal andturned on long enough (about the time for 20 dB decay in thetest band with the smallest decay rate) for the sound pressurelevel to reach a steady state. When the signal is turned off, thesound pressure level will decrease and the decay rate in eachfrequency band may be determined by mea
18、suring the slope ofa straight line fitted to the sound pressure level of the averagedecay curve. The absorption of the room and its contents iscalculated, based on the assumptions that the incident soundfield is diffuse before and during decay and that no additionalenergy enters the room during deca
19、y, from the Sabine formula:A 5 0.9210Vdc(1)where:A = sound absorption, m2or Sab,V = volume of reverberation room, m3or ft3,c = speed of sound (calculated according to 11.13), m/s orft/s, andd = decay rate, dB/s,These conditions must be fulfilled if the measurement is tohave meaning. The sound absorp
20、tion calculated according toEq 1 is sometimes called the Sabine absorption.4.1.2 In general, sound absorption is a function of frequencyand measurements are made in a series of frequency bands.4.2 Measurement of a Sound Absorption CoeffcientTheabsorption of the reverberation room is measured as outl
21、ined in4.1 both before and after placing a specimen of material to betested in the room. The increase in absorption divided by thearea of the test specimen is the dimensionless sound absorptioncoefficient. In inch-pound units it is reported with the dimen-sionless “unit” sabin per square foot, Sab/f
22、t2.4.3 Measurement of the Sound Absorption of an Object Suchas an Offce Screen, a Theater Chair, or a Space AbsorberThe absorption of the reverberation room is measured asoutlined in 4.1 both before and after placing one or severalidentical objects in the room. The increase in absorptiondivided by t
23、he number of objects is the absorption in squaremeters per object or sabins per object.5. Significance and Use5.1 Measurement of the sound absorption of a room is partof the procedure for other acoustical measurements, such asdetermining the sound power level of a noise source or thesound transmissi
24、on loss of a partition. It is also used in certaincalculations such as predicting the sound pressure level in aroom when the sound power level of a noise source in the roomis known.5.2 The sound absorption coefficient of a surface is aproperty of the material composing the surface. It is ideallydefi
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