1、Designation: E 2638 08Standard Test Method forObjective Measurement of the Speech Privacy Provided bya Closed Room1This standard is issued under the fixed designation E 2638; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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 one of a set of standards for evaluating speech privacy in buildings. It isdesigned to measure
3、 the degree of speech privacy provided by a closed room, indicating the degreeto which conversations occurring within are kept private from listeners outside the room. A relatedmethod (Test Method E 1130) deals with assessing speech privacy in open plan spaces.1. Scope1.1 This test method describes
4、a test procedure for measur-ing the degree of speech privacy provided by a closed room,for conversations occurring within the room, and with potentialeavesdroppers located outside the room.1.2 The degree of speech privacy measured by this methodis that due to the sound insulation of the room structu
5、rethewalls, floor, ceiling and any other elements of the roomboundariesand to the background noise at listening positionsoutside the closed the room.1.3 Potential eavesdroppers are assumed to be unaided byelectronic or electroacoustic equipment, and not touching theroom boundaries. Determined effort
6、s to eavesdrop are notaddressed.1.4 The method may be applied to any enclosed room,whether specifically intended to be protected against eaves-dropping or not.1.5 The method does not set criteria for adequate speechprivacy. A non-mandatory appendix provides guidance on howthe results of this test me
7、thod may be used to estimate theprobability of an eavesdropper being able to understand speechoutside a closed room, and how to set criteria for such rooms.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This standard do
8、es 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 Sta
9、ndards:2C 634 Terminology Relating to Building and Environmen-tal AcousticsE 1130 Test Method for Objective Measurement of SpeechPrivacy in Open Plan Spaces Using Articulation Index2.2 ANSI Standards:S1.11 Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters3S1.43 Spec
10、ifications for Integrating-Averaging Sound LevelMeters33. Terminology3.1 The following terms used in this test method havespecific meanings that are defined in Terminology C 634:airborne sound sound attenuationaverage sound pressure level sound isolationbackground noise sound leveldecibel sound pres
11、sure levellevel source roomoctave band white noisepink noise3.2 Definitions of Terms Specific to This Standard:3.2.1 receiving pointa location outside the closed roomunder consideration where someone might accidentally over-hear or deliberately listen to speech occurring within the room.3.2.2 speech
12、 privacy class (SPC)an objective rating of thespeech privacy provided by a closed room, calculated as a sumof factors related to sound isolation provided by the room, andbackground noise at the receiving point.1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmen
13、tal Acoustics and is the direct responsibility of SubcommitteeE33.03 on Sound Transmission.Current edition approved Nov. 15, 2008. Published December 2008.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM
14、Standards 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 Harbor Drive, PO Box C700, West Conshoh
15、ocken, PA 19428-2959, United States.4. Summary of Test Method4.1 Sound is generated at a high level in the closed roomunder consideration. To improve spatial uniformity, a sourceloudspeaker is to be placed successively at two or morelocations within the room.4.2 Receiving points outside the closed r
16、oom under consid-eration that are near potential weak spots in the soundinsulation or that are possible locations for an eavesdropper areselected for measurement.4.3 With the source operating in each successive location,measurements of sound pressure level are made within theclosed room to obtain so
17、urce room levels, and at receivingpoints outside the closed room to obtain received levels.4.4 With the source turned off, measurements of soundpressure level are made at the receiving points to obtainbackground noise levels.4.5 The differences in average source room levels inside theclosed room and
18、 received levels at each receiving point aredetermined, and are used to calculate a single number for eachreceiving point that indicates the degree of sound isolationprovided by the room boundaries.4.6 The single number rating of sound isolation is combinedwith the measured background noise levels t
19、o obtain theSpeech Privacy Classa single number rating for each receiv-ing point that is related to the degree of speech privacy at eachreceiving point.5. Significance and Use5.1 This test method provides a means of measuring thesound isolation between the interior of a closed room andlocations outs
20、ide the room, and also the background noiselevels at the locations outside the room. The results can be usedto rate the degree of speech privacy, or to estimate theprobability of speech being intelligible or audible at eachreceiving point.5.2 People speak at different levels and vary their voiceleve
21、l in reaction to room noise and other acoustical factors.Consequently it is not possible to say definitely whether a roomis protected against eavesdropping. One can only assign aprobability of being overheard. The owners or managers of theclosed room under consideration must set criteria for thispro
22、bability according to their specific goals and circumstances.The non-mandatory appendix gives an approach to settingcriteria.6. Sound Sources6.1 Sound sources shall be loudspeaker systems driven bypower amplifiers.6.2 The input signal to the amplifiers shall be random noisecontaining an approximatel
23、y uniform and continuous distribu-tion of energy and frequencies over each test band. White orpink electronic noise sources satisfy this condition.7. Frequency Range7.1 Bandwidth and FilteringThe overall frequency re-sponse of the electrical system, including the filter or filters inthe source and m
24、icrophone sections, shall for each test bandconform to the specifications in ANSI S1.11 for a one-thirdoctave band filter set, class 1 or better.7.2 The frequency range for measurement shall be thesixteen one-third octave bands from 160 to 5000 Hz.8. Measurement of Sound Pressure Levels8.1 Overview:
25、8.1.1 For multiple positions of the source, sound pressurelevels shall be measured inside the closed room under consid-eration with multiple fixed microphone positions, or with amoving microphone.8.1.2 For each position of the source inside the closed room,sound pressure levels shall be measured at
26、each receiving pointoutside the room.8.1.3 Measurements of sound pressure level shall be madeat each receiving point with the source not operating, tomeasure the background noise levels.8.1.4 The number of source positions used will affect theuncertainty in the final result, which can be calculated
27、accord-ing to Appendix X1. More source positions will result in asmaller uncertainty. Users of this test method can choose to usethe minimum number of source positions specified and obtaina result with unknown, but limited, uncertainty. Users canalternatively decide upon a maximum acceptable uncerta
28、intyand repeat measurements with additional source positions untilsatisfactory results are obtained.8.2 Measuring Equipment:8.2.1 Measurement quality microphones that are 13 mm orsmaller in diameter and that are close to omnidirectional below5000 Hz shall be used.8.2.2 Microphones, amplifiers, and e
29、lectronic circuitry toprocess microphone signals and perform measurements shallsatisfy the requirements of ANSI S1.43 for Type 1 sound levelmeters, except that B and C weighting networks are notrequired.8.3 Source Room:8.3.1 The sound pressure level in the closed room underconsideration will depend
30、on the position of the source. Toaccount for this, at least two source positions shall be used. Thesound pressure level measured in the closed room will alsovary with microphone position, so several microphone posi-tions or a moving microphone shall be used for each sourceposition.8.3.2 Select sourc
31、e positions in the closed room accordingto one of the following two ways, depending on the direction-ality of the loudspeakers used:8.3.2.1 Method 1For approximately omnidirectionalloudspeakers, such as those in the shape of a regular polyhe-dron with a driver mounted in each face (1),4source positi
32、onsshall be at least 1.2 m apart and shall be representative oftypical locations of talkers in the room. The source positionsshall be 1.5 m above the floor.NOTE 1Source positions for omnidirectional loudspeakers shouldnormally be located in the central part of the room, at least 1.0 m from thewalls.
33、 In smaller rooms, it may be necessary to locate the source near awall or corner.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E26380828.3.2.2 Method 2For conventional directional loudspeak-ers, source positions shall be selected in the corners of th
34、eroom opposite the wall that is being used for receiving points.The loudspeakers shall be moved to different corners tomeasure receiving points near different walls. Using a conven-tional directional loudspeaker will increase the total number ofmeasurements required.NOTE 2For the same number of sour
35、ce positions, the uncertainty inthe measurement of average source room levels will be higher forconventional loudspeakers than for approximately omnidirectional loud-speakers such as one with drivers mounted in the faces of a regularpolyhedron (2). Additionally, for conventional loudspeakers, the nu
36、mberof source positions possible for a given receiving point is generally limitedto the two opposite corners in the room, whereas for approximatelyomnidirectional loudspeakers, additional source positions can be selectedin the central area of the room, to reduce uncertainty.8.3.3 With the source ope
37、rating at each source position inthe closed room, the average sound pressure level in the roomshall be measured in one of the two following ways:8.3.3.1 Method 1Measure the sound pressure level usingat least five fixed microphone positions. The microphonepositions shall be at least 1.2 m apart, at l
38、east 1.5 m from thesound source and at least 1 m from the surfaces of the room.The microphone positions should provide as complete anduniform coverage of the allowable part room volume aspossible. The sound pressure level Lsijf! in each frequencyband, f, shall be measured for at least 15 seconds for
39、 eachsource position i and each microphone position j.8.3.3.2 Method 2Measure the average sound pressurelevel in each13-octave band in the closed room with a movingmicrophone and using a sound level meter or an equivalentanalyzer set to measure the time-averaged sound levels alsoknown as Leq. For la
40、rger rooms, the operator shall walk slowly,moving the microphone in a circular path of at least 0.5 mdiameter in front of their body to evenly sample as much aspractical of the measurement space. The sound level meter ormicrophone shall be held well away from the operatorsbodyat least 0.5 m (a boom
41、serves to increase the distance).The microphone speed shall remain as constant as practical.The operator shall take care to assure that the path does notsignificantly sample any part of the allowable room volume formore time than other parts. The microphone shall always bemore than 1.5 m from the so
42、und source and more than 1 mfrom the walls of the closed room. The integration time shall beat least 30 seconds. This measurement shall be repeated foreach source position i to give Lsif!, the average source roomlevel in each band, for source position i.NOTE 3Measurement of the levels in the closed
43、room with a movingmicrophone and an integrating sound level meter will enable onlyapproximate estimation of the uncertainty in the final result.NOTE 4Different microphone locations or moving microphone pathsmay be required for each source position. Once a source has been movedto a subsequent locatio
44、n, microphone positions are allowed in its previousvicinity. This approach can be useful in particular for measurements insmall rooms.8.4 Receiving Points:8.4.1 Select receiving points outside the closed room underconsideration. Measurements should be made at all locations inthe receiving area where
45、 the speech privacy is of interest. Theregions near doors, windows and other types of weak elementsin the boundaries of the room are obvious locations that shouldbe included.8.4.2 To evaluate speech transmission through walls andother components (for example, doors), microphones should be0.25 m from
46、 the nearest outer surface of the closed room andbetween 1.2 and 2 m above the floor.NOTE 5If the microphone is closer than 0.25 m, the measured level issensitive to distance from the wall.8.4.3 Survey for additional locations where sound leaksmay occur by performing initial listening tests. Positio
47、n thesound source near the middle of the closed room underconsideration and generate a signal so that the A-weightedaverage sound pressure level in the room is at least 80 dB. Withall doors closed, listen carefully near the boundaries of theroom and identify the locations of probable sound leaks whe
48、remeasurements should be made to assess the speech privacy. Insome cases, spot measurement locations may not be adjacent tothe room boundary. Where there is sound transmission from theroom via flanking sound paths such as through ducts, spotmeasurements should be made at locations where a potentiale
49、avesdropper might be located.8.4.4 In addition to the locations identified as probable weakspots, select other positions around the closed room so as toprovide complete and uniform coverage of the periphery. Somereceiving points will be close to the surfaces of the closedroom. Others may be selected close to suspected weak spotssuch as ventilation duct openings.8.4.5 The sound pressure level shall be measured at eachstationary receiving point for each source position i in theclosed room for at least 15 seconds. Measure the receivedlevels with the source operating,
