ASTM E2638-08

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E2638–08
Standard Test Method for
Objective Measurement of the Speech Privacy Provided by
a Closed Room
This standard is issued under the fixed designation E2638; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method is one of a set of standards for evaluating speech privacy in buildings. It is
designed to measure the degree of speech privacy provided by a closed room, indicating the degree
to which conversations occurring within are kept private from listeners outside the room. A related
method (Test Method E1130) deals with assessing speech privacy in open plan spaces.
1. Scope 2. Referenced Documents
1.1 This test method describes a test procedure for measur- 2.1 ASTM Standards:
ing the degree of speech privacy provided by a closed room, C634 Terminology Relating to Building and Environmental
forconversationsoccurringwithintheroom,andwithpotential Acoustics
eavesdroppers located outside the room. E1130 Test Method for Objective Measurement of Speech
1.2 The degree of speech privacy measured by this method Privacy in Open Plan Spaces Using Articulation Index
is that due to the sound insulation of the room structure—the 2.2 ANSI Standards:
walls, floor, ceiling and any other elements of the room S1.11 Specification for Octave-Band and Fractional-
boundaries—and to the background noise at listening positions Octave-Band Analog and Digital Filters
outside the closed the room. S1.43 Specifications for Integrating-Averaging Sound Level
1.3 Potential eavesdroppers are assumed to be unaided by Meters
electronic or electroacoustic equipment, and not touching the
3. Terminology
room boundaries. Determined efforts to eavesdrop are not
3.1 The following terms used in this test method have
addressed.
1.4 The method may be applied to any enclosed room, specific meanings that are defined in Terminology C634:
whether specifically intended to be protected against eaves- airborne sound sound attenuation
average sound pressure level sound isolation
dropping or not.
background noise sound level
1.5 The method does not set criteria for adequate speech
decibel sound pressure level
privacy.Anon-mandatory appendix provides guidance on how level source room
octave band white noise
the results of this test method may be used to estimate the
pink noise
probability of an eavesdropper being able to understand speech
3.2 Definitions of Terms Specific to This Standard:
outside a closed room, and how to set criteria for such rooms.
3.2.1 receiving point—a location outside the closed room
1.6 The values stated in SI units are to be regarded as
under consideration where someone might accidentally over-
standard. No other units of measurement are included in this
hear or deliberately listen to speech occurring within the room.
standard.
3.2.2 speech privacy class (SPC)—anobjectiveratingofthe
1.7 This standard does not purport to address all of the
speech privacy provided by a closed room, calculated as a sum
safety concerns, if any, associated with its use. It is the
of factors related to sound isolation provided by the room, and
responsibility of the user of this standard to establish appro-
background noise at the receiving point.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and Environmental Acoustics and is the direct responsibility of Subcommittee Standards volume information, refer to the standard’s Document Summary page on
E33.03 on Sound Transmission. the ASTM website.
Current edition approved Nov. 15, 2008. Published December 2008. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/E2638-08. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2638–08
4. Summary of Test Method 7.2 The frequency range for measurement shall be the
sixteen one-third octave bands from 160 to 5000 Hz.
4.1 Sound is generated at a high level in the closed room
under consideration. To improve spatial uniformity, a source
8. Measurement of Sound Pressure Levels
loudspeaker is to be placed successively at two or more
locations within the room.
8.1 Overview:
4.2 Receiving points outside the closed room under consid- 8.1.1 For multiple positions of the source, sound pressure
eration that are near potential weak spots in the sound
levels shall be measured inside the closed room under consid-
insulation or that are possible locations for an eavesdropper are eration with multiple fixed microphone positions, or with a
selected for measurement.
moving microphone.
4.3 With the source operating in each successive location, 8.1.2 Foreachpositionofthesourceinsidetheclosedroom,
measurements of sound pressure level are made within the
sound pressure levels shall be measured at each receiving point
closed room to obtain source room levels, and at receiving outside the room.
points outside the closed room to obtain received levels.
8.1.3 Measurements of sound pressure level shall be made
4.4 With the source turned off, measurements of sound at each receiving point with the source not operating, to
pressure level are made at the receiving points to obtain
measure the background noise levels.
background noise levels.
8.1.4 The number of source positions used will affect the
4.5 The differences in average source room levels inside the
uncertainty in the final result, which can be calculated accord-
closed room and received levels at each receiving point are
ing to Appendix X1. More source positions will result in a
determined, and are used to calculate a single number for each
smalleruncertainty.Usersofthistestmethodcanchoosetouse
receiving point that indicates the degree of sound isolation
the minimum number of source positions specified and obtain
provided by the room boundaries.
a result with unknown, but limited, uncertainty. Users can
4.6 Thesinglenumberratingofsoundisolationiscombined
alternatively decide upon a maximum acceptable uncertainty
with the measured background noise levels to obtain the
and repeat measurements with additional source positions until
Speech Privacy Class—a single number rating for each receiv-
satisfactory results are obtained.
ing point that is related to the degree of speech privacy at each
8.2 Measuring Equipment:
receiving point.
8.2.1 Measurement quality microphones that are 13 mm or
smaller in diameter and that are close to omnidirectional below
5. Significance and Use
5000 Hz shall be used.
5.1 This test method provides a means of measuring the
8.2.2 Microphones, amplifiers, and electronic circuitry to
sound isolation between the interior of a closed room and
process microphone signals and perform measurements shall
locations outside the room, and also the background noise
satisfy the requirements ofANSI S1.43 for Type 1 sound level
levelsatthelocationsoutsidetheroom.Theresultscanbeused
meters, except that B and C weighting networks are not
to rate the degree of speech privacy, or to estimate the
required.
probability of speech being intelligible or audible at each
8.3 Source Room:
receiving point.
8.3.1 The sound pressure level in the closed room under
5.2 People speak at different levels and vary their voice
consideration will depend on the position of the source. To
level in reaction to room noise and other acoustical factors.
accountforthis,atleasttwosourcepositionsshallbeused.The
Consequentlyitisnotpossibletosaydefinitelywhetheraroom
sound pressure level measured in the closed room will also
is protected against eavesdropping. One can only assign a
vary with microphone position, so several microphone posi-
probability of being overheard. The owners or managers of the
tions or a moving microphone shall be used for each source
closed room under consideration must set criteria for this
position.
probability according to their specific goals and circumstances.
8.3.2 Select source positions in the closed room according
The non-mandatory appendix gives an approach to setting
to one of the following two ways, depending on the direction-
criteria.
ality of the loudspeakers used:
8.3.2.1 Method 1—For approximately omnidirectional
6. Sound Sources
loudspeakers, such as those in the shape of a regular polyhe-
6.1 Sound sources shall be loudspeaker systems driven by
dron with a driver mounted in each face (1), source positions
power amplifiers.
shall be at least 1.2 m apart and shall be representative of
6.2 The input signal to the amplifiers shall be random noise
typical locations of talkers in the room. The source positions
containing an approximately uniform and continuous distribu-
shall be 1.5 m above the floor.
tion of energy and frequencies over each test band. White or
NOTE 1—Source positions for omnidirectional loudspeakers should
pink electronic noise sources satisfy this condition.
normally be located in the central part of the room, at least 1.0 m from the
7. Frequency Range walls. In smaller rooms, it may be necessary to locate the source near a
wall or corner.
7.1 Bandwidth and Filtering—The overall frequency re-
sponse of the electrical system, including the filter or filters in
the source and microphone sections, shall for each test band
conform to the specifications in ANSI S1.11 for a one-third
The boldface numbers in parentheses refer to the list of references at the end of
octave band filter set, class 1 or better. this standard.
E2638–08
8.3.2.2 Method 2—For conventional directional loudspeak- regions near doors, windows and other types of weak elements
ers, source positions shall be selected in the corners of the in the boundaries of the room are obvious locations that should
room opposite the wall that is being used for receiving points. be included.
The loudspeakers shall be moved to different corners to 8.4.2 To evaluate speech transmission through walls and
measure receiving points near different walls. Using a conven- othercomponents(forexample,doors),microphonesshouldbe
tional directional loudspeaker will increase the total number of 0.25 m from the nearest outer surface of the closed room and
measurements required. between 1.2 and 2 m above the floor.
NOTE 2—For the same number of source positions, the uncertainty in NOTE 5—If the microphone is closer than 0.25 m, the measured level is
the measurement of average source room levels will be higher for sensitive to distance from the wall.
conventional loudspeakers than for approximately omnidirectional loud-
8.4.3 Survey for additional locations where sound leaks
speakers such as one with drivers mounted in the faces of a regular
may occur by performing initial listening tests. Position the
polyhedron (2). Additionally, for conventional loudspeakers, the number
sound source near the middle of the closed room under
ofsourcepositionspossibleforagivenreceivingpointisgenerallylimited
consideration and generate a signal so that the A-weighted
to the two opposite corners in the room, whereas for approximately
omnidirectional loudspeakers, additional source positions can be selected
averagesoundpressurelevelintheroomisatleast80dB.With
in the central area of the room, to reduce uncertainty.
all doors closed, listen carefully near the boundaries of the
room and identify the locations of probable sound leaks where
8.3.3 With the source operating at each source position in
measurements should be made to assess the speech privacy. In
the closed room, the average sound pressure level in the room
somecases,spotmeasurementlocationsmaynotbeadjacentto
shall be measured in one of the two following ways:
theroomboundary.Wherethereissoundtransmissionfromthe
8.3.3.1 Method 1—Measure the sound pressure level using
room via flanking sound paths such as through ducts, spot
at least five fixed microphone positions. The microphone
measurements should be made at locations where a potential
positions shall be at least 1.2 m apart, at least 1.5 m from the
eavesdropper might be located.
sound source and at least 1 m from the surfaces of the room.
8.4.4 Inadditiontothelocationsidentifiedasprobableweak
The microphone positions should provide as complete and
spots, select other positions around the closed room so as to
uniform coverage of the allowable part room volume as
providecompleteanduniformcoverageoftheperiphery.Some
possible. The sound pressure level L ~f! in each frequency
sij
receiving points will be close to the surfaces of the closed
band, f, shall be measured for at least 15 seconds for each
room. Others may be selected close to suspected weak spots
source position i and each microphone position j.
such as ventilation duct openings.
8.3.3.2 Method 2—Measure the average sound pressure
8.4.5 The sound pressure level shall be measured at each
level in each ⁄3-octave band in the closed room with a moving
stationary receiving point for each source position i in the
microphone and using a sound level meter or an equivalent
closed room for at least 15 seconds. Measure the received
analyzer set to measure the time-averaged sound levels also
levels with the source operating, L ~f!, and the background
known as L . For larger rooms, the operator shall walk slowly, rbi
eq
noise levels with the source switched off, L ~f!.
moving the microphone in a circular path of at least 0.5 m bi
diameter in front of their body to evenly sample as much as
9. Calculations
practical of the measurement space. The sound level meter or
9.1 All calculations shall be made using unrounded, mea-
microphone shall be held well away from the operator’s
sured values.
body—at least 0.5 m (a boom serves to increase the distance).
9.2 Source Room Levels:
The microphone speed shall remain as constant as practical.
9.2.1 If source room measurements were made using fixed
The operator shall take care to assure that the path does not
microphone positions, determine L ~f!, the average sound
si
significantly sample any part of the allowable room volume for
pressure level in each band, for source position i, as follows:
more time than other parts. The microphone shall always be
m
more than 1.5 m from the sound source and more than 1 m 1
L ~f!/10
sij
L ~f! 5 10log 10 (1)
F ( G
si
fromthewallsoftheclosedroom.Theintegrationtimeshallbe m
j51
at least 30 seconds. This
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