1、Designation: E2235 04 (Reapproved 2012)Standard Test Method forDetermination of Decay Rates for Use in Sound InsulationTest Methods1This standard is issued under the fixed designation E2235; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, 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.INTRODUCTIONThis test method is part of a set of methods used to evaluate the sound-insulating properties ofbu
3、ilding elements. It is intended for use in conjunction with methods for measuring the transmissionof sound through a partition or partition element in a laboratory or in a building. These methodsinclude the laboratory measurement of airborne sound transmission loss of building partitions andelements
4、 (Test Method E90), the measurement of sound isolation in buildings (Test Method E336), thelaboratory measurement of impact sound transmission through floors (Test Method E492), themeasurement of impact sound transmission in buildings (Test Method E1007), the measurement ofsound transmission through
5、 building facades and facade elements (Guide E966), and the measurementof sound transmission through a common plenum between two rooms (Test Method E1414).1. Scope1.1 This test method covers the measurement of sounddecay rate in rooms and the calculation of the sound absorptionof the room and its co
6、ntents. The sound absorption so calcu-lated may be used in calculations in sound insulation testmethods.1.2 The method shall be used only in conjunction with othertest methods where the logarithm of the sound absorption isused in formulas. It is not sufficiently precise for use insituations where ro
7、om sound absorption is to be used withouttaking logarithms.1.3 For laboratory measurements of the sound absorption ofmaterials and objects, Test Method C423 should be used.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibilit
8、y 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:2C423 Test Method for Sound Absorption and Sound Ab-sorption Coefficients by the Reverberation Room M
9、ethodC634 Terminology Relating to Building and EnvironmentalAcousticsE90 Test Method for Laboratory Measurement of AirborneSound Transmission Loss of Building Partitions and Ele-mentsE336 Test Method for Measurement of Airborne SoundAttenuation between Rooms in BuildingsE492 Test Method for Laborato
10、ry Measurement of ImpactSound Transmission Through Floor-Ceiling AssembliesUsing the Tapping MachineE966 Guide for Field Measurements of Airborne SoundAttenuation of Building Facades and Facade ElementsE1007 Test Method for Field Measurement of TappingMachine Impact Sound Transmission Through Floor-
11、Ceiling Assemblies and Associated Support StructuresE1414 Test Method for Airborne Sound Attenuation Be-tween Rooms Sharing a Common Ceiling Plenum2.2 ANSI Standards:3S1.4 Specification for Sound-Level MetersS1.6 Standard Preferred Frequencies, Frequency Levels,and Band Numbers for Acoustical Measur
12、ementsS1.11 Specification for Octave-band and Fractional-Octave-Band Analog and Digital Filters1This 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 A
13、pril 1, 2012. Published August 2012. Originallyapproved in 2003. Last previous edition approved in 2004 as E2235 041. DOI:10.1520/E2235-04R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vol
14、ume 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
15、28-2959, United States.3. Terminology3.1 Definitions of the acoustical terms used in this testmethod are given in Terminology C634.3.2 Definitions of Terms Specific to This Standard:3.2.1 output interval, Dt; T; sof a real-time analyzer, thetime between successive outputs of sound pressure levelsdur
16、ing a single decay measurement.4. Summary of Test Method4.1 Sound decay rate in rooms is a function of frequency someasurements are made in a series of frequency bands. Bandsof random electrical noise are used as signals to drive loud-speakers in the room until the sound pressure level reaches astea
17、dy state. When the sound is then turned off, the soundpressure level decays at a rate determined by the soundabsorption in the room. The decay rate is measured in eachfrequency band by measuring the slope of a straight line fittedto the average decay curve. The absorption of the room and itscontents
18、 is calculated from the Sabine formula:A 5 0.921Vdc(1)where:A = sound absorption, m2,V = volume of reverberation room, m3,c = speed of sound, m/s, andd = decay rate, dB/s.4.1.1 The speed of sound changes with temperature and itshall be calculated for the conditions existing at the time of testfrom t
19、he equation:c 5 20.047=273.15 1 t m/s (2)where:t = room temperature, C.5. Significance and Use5.1 Several ASTM test methods to evaluate the sound-insulating properties of building elements require the measure-ment of room sound absorption as part of the procedure. Theroom sound absorption in these s
20、tandards appears in anequation in the form 10 log (x/A), where x is a quantity with thesame units as A,m2. Room sound absorption is calculated fromthe decay rate using Eq 1.5.2 The requirements of this standard have been chosen sothe uncertainty associated with the measurement of roomsound absorptio
21、n will be acceptably small so long as thelogarithm of the absorption is being used in calculations.5.3 Other test methods should specify explicitly that theymake use of this test method.5.4 Where measurement requirements in the parent standarddiffer from those given here, the requirements in the par
22、entstandard shall be satisfied.5.5 This test method shall not be used when room soundabsorption or decay rate is to be used directly to satisfy somecriterion, for example in a room that must not be overlyreverberant so speech will be intelligible.NOTE 1The uncertainty of the room sound absorption ob
23、tained willusually be too high and additional measurements are necessary.5.6 Any companion standard may specify the use of theprocedures in this method for determining whether the decayrates in a room are slow enough to satisfy the requirements ofthe companion standard. The measured decay rates shal
24、l stillbe used only to calculate the logarithm of the room absorption.6. Sound Source Requirements6.1 Sound sources shall be loudspeaker systems driven bypower amplifiers.NOTE 2Loudspeaker systems should be omnidirectional. In practice,using multiple driver elements to cover different frequency rang
25、es andplacing sources in trihedral corners of the room will be adequate.7. Sound Source Positions7.1 At least one source position shall be used in the room.NOTE 3Where more than one source position is used, decay rate datamay be collected for each source position in sequence and then the decayrates
26、averaged. Alternatively, multiple loudspeakers may be activatedsimultaneously. If this is done, the sound power emitted by the loud-speaker sources should be approximately equal. Separate electronic noisegenerators and amplifiers for each system are not necessary.8. Electrical Signal8.1 The electric
27、al signal fed to each power amplifier shall bea band of random noise with a continuous spectrum coveringthe frequency range over which measurements are made.9. Frequency Range9.1 The frequency range of the measurements shall be thatspecified in the companion standard for which the measure-ments are
28、being made.9.2 BandwidthFor each test band, the overall frequencyresponse of the electrical system, including the filter or filtersin the source or microphone systems, shall satisfy the specifi-cations given in ANSI Specification S1.11 for a one-thirdoctave band filter set, Order 3 or higher, Type 1
29、.NOTE 4The shape of the filter response curve can influence theminimum decay rate that can be measured. This problem is dealt with bythe requirement in 13.5.10. Microphone Requirements10.1 A microphone used to measure decay rate shall beomnidirectional with a 61 dB random-incidence amplituderesponse
30、 within any one-third octave band for all frequenciesand sound pressure levels used for decay rate measurements.11. Microphone Positions11.1 Stationary Microphones:11.1.1 In the absence of an over-riding requirement in thecompanion standard, the number of stationary microphonepositions shall be at l
31、east three.11.1.2 In the absence of an over-riding requirement in thecompanion standard, stationary microphone positions shall beat least 1.5 m apart, and at least 0.75 m from any surface of theroom.11.2 Moving Microphones:11.2.1 Only one location of a moving microphone assemblyis required in the ro
32、om.E2235 04 (2012)211.2.2 The length of the path for a moving microphone shallbe that specified in the companion standard for which mea-surements are being made.NOTE 5Longer paths are preferred since they improve the precisionof the measurements at low frequencies.11.2.3 All points on the path shall
33、 be at least 0.75 m fromany surface of the room.11.2.4 The moving microphone shall be at a different pointon its path at the start of each decay measurement.12. Number of Sound Decays to be Collected12.1 Stationary MicrophonesThe product of the numberof microphone positions, the number of decays col
34、lected ateach microphone position and the number of sound sourcepositions shall be at least 15.12.2 Moving MicrophonesCollect a total of at least 10decays with a moving microphone.13. Instrument of Analysis13.1 The instruments used for analysis shall be digital.Analog devices such as level recorders
35、 shall not be used.13.2 Instruments used for measurements according to thisstandard shall meet the provisions of either 13.3 or 13.4.13.3 A sound level meter or other instrument that calculatesreverberation time or decay rate values using internal algo-rithms and presents the calculated values but n
36、ot individualdecay curves.13.3.1 The algorithm used by the instrument shall satisfythe procedures of Method 2 (see 15.2) for calculation of decayrate.13.4 An instrument that provides decay curves for eachone-third-octave band with or without calculated reverberationtime or decay rates.13.5 Instrumen
37、t decay rates in each frequency band shall beat least 3 times the room decay rates.NOTE 6The instrument decay rate can be measured by attaching anelectronic noise source directly to the input, switching off the generatorand then measuring the decay.14. Measurement Procedures14.1 Measurement of Decay
38、s:14.1.1 Turn on the test signal until the sound pressure levelin each measurement band is steady.14.1.2 Turn off the test signal and measure sound pressurelevels in each measurement band during the decay. Start andstop times are determined as necessary to suit measurementconditions.14.1.3 Where a r
39、eal-time analyzer is used to collect decaycurves, the output interval, Dt, shall be small enough that atleast five samples are used in the calculations described in 15.2.In furnished rooms, this may require a Dt of 20 ms or less.14.2 Measurement of Background Sound Pressure Level:14.2.1 Measure the
40、background sound pressure levels in theroom using the same microphone and analyzer gain settingsused to measure decays.NOTE 7This accounts properly for residual noise in the instrumenta-tion.15. Calculation of Decay Rates15.1 Method 1:15.1.1 Where the sound level meter or analyzer calculatesreverber
41、ation times or decay rates, no additional calculationsare necessary.15.1.2 When different decay ranges for calculating rever-beration time are available, the range closest to 25 dB shall beselected.15.2 Method 2:15.2.1 The procedures in 15.2.2 and 15.2.3 shall be usedwhen the instrument used to meas
42、ure decay rates provides theuser with individual or averaged decay curves.15.2.2 Where the instrument provides curves for singledecays, transfer each decay at each frequency from theinstrument to a computer and form an average decay curveusing Eq 3 or Eq 4.Li! 51N(j51NLij! (3)Li! 5 10logF1N(j51N10Li
43、j!/10G(4)where:i and j = integers,Li()= average of the sound pressure levels measured attime iDt in frequency band ,N = the number of decays, andLij() = the sound pressure level measured at the time iDtduring the jth decay in frequency band .NOTE 8It is assumed that the i-th time point is always at
44、the sametime after the cessation of the sound.NOTE 9Although Eq 4 is technically more correct, for the purposes ofthis standard either Eq 3 or Eq 4 is satisfactory.15.2.3 Where the instrument provides average decay curves,they shall be used in the determination of decay rate providedthe average deca
45、y curves are obtained using Eq 3 or Eq 4.16. Determination of Decay RateNOTE 10Fig. 1 gives an example of an averaged decay curve and mayclarify the following paragraphs.16.1 All points used in the determination of decay rate mustbe 10 dB or more above the background noise level.16.2 The first point
46、 to be included in the analysis shall be assoon as practical after the sound has been switched off. Thesound pressure level for the first point shall be no more than 5dB below the level when the sound was on. (See Fig. 1)16.3 For laboratory measurements, the last point to beincluded in the determina
47、tion of decay rate shall be the firstpoint that is at least 25 dB below the sound pressure level of thefirst analysis point provided that the level of the last pointsatisfies 16.1. (See Fig. 1)16.3.1 For field measurements, the last point to be includedin the determination of decay rate shall be mor
48、e than 15 dB butless than 25 dB below the sound pressure level of the firstanalysis point provided that the level of the last point satisfies16.1.NOTE 11Background noise levels in field situations are often muchhigher than those encountered in laboratories. The required decay range isE2235 04 (2012)
49、3therefore relaxed so measurements can be made in such situations.NOTE 12It may be necessary, especially in field measurements, toincrease the level of sound from the loudspeaker to increase the signal tobackground noise ratio so an adequate decay range is obtained.16.3.2 When the signal level can not be increased suffi-ciently to comply with 16.3.1, a smaller amount of the decaymay be used for the calculation. The last point shall be incompliance with 16.1 and shall be at least 15 dB below the firstpoint.16.4 For each frequency band, calculate th
