1、Designation: C 634 02e1Standard Terminology Relating toBuilding and Environmental Acoustics1This standard is issued under the fixed designation C 634; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num
2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEThe title was editorially updated in June 2007.INTRODUCTIONIn some of the entries, those that are measures of physical quantities, the term is
3、followed by threeitems: symbol, dimensions, and unit. The symbol, in italics, stands for the magnitude of the quantityin mathematical expressions. The dimensions of a quantity express its measure in terms of threefundamental quantities: M for mass, L for length, and T for time. Speed, for instance,
4、is the quotientobtained when the distance an object moves is divided by the time involved. The dimensions areLT1, the negative exponent indicating division. The unit is consistently in SI, Le SystmeInternational dUnits. Those still using the cgs (centimetre-gram-second) or the inchpound system ofuni
5、ts are referred for most of the conversion factors to Practice E 380. A few conversion factors arelisted in Section 4 of this terminology.The dimensions of a quantity are the same regardless of the units in which the quantity is measured.Speed has the dimensions LT1 whether it is measured in miles p
6、er hour, feet per second, or metresper second. Quantities with different dimensions are not the same. Flow resistance and specific flowresistance, for instance, are quantities of different kinds even though the names are similar. On theother hand, quantities with the same dimensions are not necessar
7、ily of the same kind. Sound energydensity, for instance, has the same dimensions as sound pressure, ML1T2, but it is not a kind ofsound pressure. Nor is absorption with the dimensions L2 a kind of area.1. Scope1.1 This terminology covers terms and definitions related toenvironmental acoustics. Only
8、definitions common to two ormore standards under the jurisdiction of Committee E33 arelisted here. The purpose of this terminology is to promoteuniformity of key definitions. Definitions pertinent to only onestandard and exceptions to the definitions listed below arecontained in the individual stand
9、ards and should be used whenfollowing those standards.2. Referenced Documents2.1 ASTM Standards:2C 423 Test Method for Sound Absorption and Sound Ab-sorption Coefficients by the Reverberation Room MethodE90 Test Method for Laboratory Measurement of AirborneSound Transmission Loss of Building Partiti
10、ons and Ele-mentsE 336 Test Method for Measurement of Airborne SoundAttenuation between Rooms in BuildingsE 413 Classification for Rating Sound InsulationE 492 Test Method for Laboratory Measurement of ImpactSound Transmission Through Floor-Ceiling AssembliesUsing the Tapping MachineIEEE/ ASTM SI 10
11、 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System2.2 ANSI Standard:ANSI S1.4 Specification for Sound Level Meters3ANSI S1.6 Preferred Frequencies, Frequency Levels, andBand Numbers for Acoustical MeasurementsANSI S1.11 Octave-Band and Fractional Octave-BandAna-log
12、and Digital Filters, Specifications for3. Terminology3.1 If the term sought by the user cannot be found in 3.2,itmay be found in 4.1.3.2 Terms and Definitions:1This terminology is under the jurisdiction of ASTM Committee E33 onBuilding and Environmental Acoustics and is the direct responsibility of
13、Subcom-mittee E33.07 on Definitions and Editorial.Current edition approved April 10, 2002. Published June 2002. Originallyapproved in 1969. Last previous edition approved i n 2001 as C 634 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
14、viceastm.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.1Copyright ASTM International, 100 Barr Ha
15、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.acoustic impedance, Z R + jX; ML4T1; mks acousticohm (Pas/m3)of a surface, for a given frequency, thecomplex quotient obtained when the sound pressure aver-aged over the surface is divided by the volume velocitythrough the surf
16、ace. The real and imaginary components arecalled, respectively, acoustic resistance and acoustic reac-tance.acoustical barriercontiguous objects such as solid walls,buildings, or earthen berms that substantially block the directpath of sound between a source and receiver, and which, ifthey have an o
17、pen edge or edges allowing diffraction aroundthem, are sufficiently wide and high to cause significantreduction of the sound traveling from the source to thereceiver.acoustical materialany material considered in terms of itsacoustical properties. Commonly and especially, a materialdesigned to absorb
18、 sound.admittance ratio, yrc grcjbrc; dimensionlessthereciprocal of the impedance ratio. The real and imaginarycomponents are called, respectively, conductance ratio andsusceptance ratio.airborne soundsound that arrives at the point of interest,such as one side of a partition, by propagation through
19、 air.airflow resistance, R; ML4T1; mks acoustic ohm (Pas/m3)the quotient of the air pressure difference across aspecimen divided by the volume velocity of airflow throughthe specimen. The pressure difference and the volumevelocity may be either steady or alternating.airflow resistivity, ro; ML3T1; m
20、ks rayl/m (Pas/m2)of ahomogeneous material, the quotient of its specific airflowresistance divided by its thickness.ambient noisethe composite of airborne sound from manysources near and far associated with a given environment.No particular sound is singled out for interest.arithmetic mean sound pre
21、ssure levelof several relatedsound pressure levels measured at different positions ordifferent times, or both, in a specified frequency band, thesum of the sound pressure levels divided by the number oflevels.DISCUSSIONThe arithmetic mean sound pressure level is sometimesused to approximate the aver
22、age sound pressure level. The accuracyof this approximation depends upon the range of sound pressure levels.average sound pressure levelof several related soundpressure levels measured at different positions or differenttimes, or both, in a specified frequency band, ten times thecommon logarithm of
23、the arithmetic mean of the squaredpressure ratios from which the individual levels were de-rived.DISCUSSION1An average sound pressure level obtained by aver-aging the A-weighted sound level continuously over a specified periodis called the time-average sound level.DISCUSSION2Since, by definition, a
24、squared pressure ratio, pi2/p02, is equal to 10Li/10, average sound pressure level is calculated fromthe expression:Li5 10 logS1n(i 5 1n10Li/10Dwhere:Lp= average sound pressure level, dB,n = number of individual sound pressure levels,pi= rms pressure at an individual position or time, or both,Pa,p0=
25、 20 Pa, reference sound pressure, andLi= an individual sound pressure level, dB.If conditions warrant, an integral expression may be used:Lp5 10 logS1T*t1t2p2t!/p02! dtDwhere:Lp= average sound pressure level during a specified timeinterval, dB,T =t2t1= a specified time interval, s, min, h, or day,p(
26、t) = instantaneous sound pressure, Pa, andp0= 20 Pa, reference sound pressure.background noisenoise from all sources unrelated to aparticular sound that is the object of interest. Backgroundnoise may include airborne, structureborne, and instrumentnoise.characteristic impedance of the medium, rc; ML
27、2T1;mks rayl (Pas/m)the specific normal acoustic impedanceat a point in a plane wave in a free field. It is a pure specificresistance since the sound pressure and the particle velocityare in phase and it is equal in magnitude to the product of thedensity of the medium, r, and the speed of sound in t
28、hemedium, c. Its value when the medium is air at 20C and101.325 kPa is 413 mks rayl (Pas/m).cutoff frequencyof an anechoic wedge or set of wedges, thelowest frequency above which the normal incidence soundabsorption coefficient is at least 0.990.dampto cause a loss or dissipation of the oscillatory
29、orvibrational energy of an electrical or mechanical system.decay rate, d; T1; dB/sfor airborne sound, the rate ofdecrease of sound pressure level after the source of soundhas stopped; for vibration, the rate of decrease of vibratoryacceleration, velocity, or displacement level after the exci-tation
30、has stopped.decibel, dBthe term used to identify ten times the commonlogarithm of the ratio of two like quantities proportional topower or energy. (See level, sound transmission loss.)Thus, one decibel corresponds to a power ratio of 100.1andn decibels corresponds to a power ratio of (100.1)n.DISCUS
31、SIONSince the decibel expresses the ratio of two likequantities, it has no dimensions. It is, however, common practice totreat “decibel” as a unit as, for example, in the sentence, “The averagesound pressure level in the room is 45 decibels.”diffractiona change in the direction of propagation of sou
32、ndenergy in the neighborhood of a boundary discontinuity,such as the edge of a reflective or absorptive surface.diffuse sound fieldthe sound in a region where the intensityis the same in all directions and at every point.direct sound fieldthe sound that arrives directly from asource without reflecti
33、on.dummy microphonea microphone substitute which haselectrical characteristics identical to a functional micro-phone, but which has essentially no sensitivity to incidentsound pressure.C63402e12field sound transmission class, FSTCsound transmissionclass calculated in accordance with Classification E
34、 413using values of field transmission loss.field transmission loss, FTLsound transmission loss mea-sured in accordance with Annex A1 of Test Method E 336.flanking transmissiontransmission of sound from thesource to a receiving location by a path other than that underconsideration.impact insulation
35、class, IICa single-number rating derivedfrom measured values of normalized impact sound pressurelevels in accordance with Annex A1 of Test Method E 492.It provides an estimate of the impact sound insulatingperformance of a floor-ceiling assembly.impedance ratio, z/rc r/rc + jx/rc; dimensionlessthera
36、tio of the specific normal acoustic impedance at a surfaceto the characteristic impedance of the medium. The real andimaginary components are called, respectively, resistanceratio and reactance ratio.impulsive sound, na brief, intrusive sound, such as thatassociated with a tire blowout, operation of
37、 a punch press,the discharge of a firearm, a door slam, or a shout, usuallycharacterized by a rapid rise time in the initial pressure pulseof less than a few milliseconds, and by a decay time of lessthan a few seconds.DISCUSSIONNo mathematical description exists to unequivocallydefine the presence o
38、f impulsive sound.insertion loss, ILof a silencer or other sound-reducingelement, in a specified frequency band, the decrease in soundpower level, measured at the location of the receiver, whena sound insulator or a sound attenuator is inserted in thetransmission path between the source and the rece
39、iver.interference, nany activity or event that could produceanomalous measurements.level, Lten times the common logarithm of the ratio of aquantity proportional to power or energy to a referencequantity of the same kind. (See sound power level, soundpressure level.) The quantity so obtained is expre
40、ssed indecibels.level reduction, LRin a specified frequency band, thedecrease in sound pressure level, measured at the location ofthe receiver, when a barrier or other sound-reducing elementis placed between the source and the receiver.DISCUSSIONLevel reduction is a useful measure in circumstanceswh
41、en measures of transmission loss, insertion loss, or noise reductionare not possible.maximum sound level, LAFmaxnd, (dB) nTen times thecommon logarithm of the square of the ratio of the largestfrequency-weighted and exponential-time-weighted (orother wise time-averaged) sound pressure during the mea
42、-surement period to the square of the reference-sound-pressure of 20 micro pascals. The subscripts designate thefrequency weighting (A or C), and time the weighting oraveraging (F for fast, S for slow, I for impulse, or a numberwith proper units to indicate time interval).DISCUSSIONThe time weightin
43、g or averaging time must be speci-fied. The frequency weighting should be specified; otherwise,A-weighting will be understood.measurement plan, na document formally describing thespecific steps to be taken during a measurement, includingany unique requirements.measurement set, nthe set of acoustical
44、 measurements andrelated data obtained at a single measurement locationduring a specified time interval.DISCUSSIONThe specified time interval may include brief docu-mented periods during which data recording or analysis are paused forthe purpose of eliminating the effects of interference.metric sabi
45、n, L2the unit of measure of sound absorption inthe metre-kilogram-second system of units.noise isolation class, NICa single-number rating calculatedin accordance with Classification E 413 using measuredvalues of noise reduction. It provides an estimate of thesound isolation between two enclosed spac
46、es that are acous-tically connected by one or more paths.noise reduction, NRin a specified frequency band, thedifference between the average sound pressure levels mea-sured in two enclosed spaces or rooms due to one or moresound sources in one of them.DISCUSSIONIt is implied that in each room there
47、is a meaningfulaverage level; that is, that in each room the individual observations arerandomly distributed about the average value, with no systematicvariation with position within the permissible measurement region.Noise reduction becomes meaningless and should not be used insituations where this
48、 condition is not met.noise reduction coefficient, NRCa single-number ratingderived from measured values of sound absorption coeffi-cients in accordance with 11.7 of Test Method C 423.Itprovides an estimate of the sound absorptive property of anacoustical material.normal incidence sound absorption c
49、oefficient, an;dimensionless of a surface, at a specified frequency, thefraction of the perpendicularly incident sound power ab-sorbed or otherwise not reflected.normal modeof a room, one of the possible ways in whichthe air in a room, considered as an elastic body, will vibratenaturally when subjected to an acoustical disturbance. Witheach normal mode is associated a resonance frequency and,in general, a group of wave propagation directions compris-ing a closed path.n
