ASTM E2638-10(2017)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2638 − 10 (Reapproved 2017)
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 1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method describes a test procedure for measur-
standard.
ing the degree of speech privacy provided by a closed room,
1.7 This standard does not purport to address all of the
forconversationsoccurringwithintheroom,andwithpotential
safety concerns, if any, associated with its use. It is the
eavesdroppers located outside the room.
responsibility of the user of this standard to establish appro-
1.2 The degree of speech privacy measured by this method
priate safety, health, and environmental practices and deter-
is that due to the sound insulation of the room structure—the
mine the applicability of regulatory limitations prior to use.
walls, floor, ceiling and any other elements of the room
1.8 This international standard was developed in accor-
boundaries—and to the background noise at listening positions
dance with internationally recognized principles on standard-
outside the closed the room.
ization established in the Decision on Principles for the
1.3 Potential eavesdroppers are assumed to be unaided by Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
electronic or electroacoustic equipment, and not touching the
room boundaries. Determined efforts to eavesdrop are not Barriers to Trade (TBT) Committee.
addressed.
2. Referenced Documents
1.4 The method may be applied to any enclosed room,
2.1 ASTM Standards:
whether specifically intended to be protected against eaves-
C634 Terminology Relating to Building and Environmental
dropping or not.
Acoustics
1.5 The method does not set criteria for adequate speech
E1130 Test Method for Objective Measurement of Speech
privacy.Anon-mandatory appendix provides guidance on how
Privacy in Open Plan Spaces Using Articulation Index
the results of this test method may be used to estimate the
2.2 ANSI Standards:
probability of an eavesdropper being able to understand speech
S1.11 Specification for Octave-Band and Fractional-Octave-
outside a closed room, and how to set criteria for such rooms.
Band Analog and Digital Filters
1 2
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Environmental Acoustics and is the direct responsibility of Subcommittee contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
E33.02 on Speech Privacy. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2017. Published December 2017. Originally the ASTM website.
approved in 2008. Last previous edition approved in 2010 as E2638 – 10. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/E2638-10R17. 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 − 10 (2017)
S1.43 Specifications for Integrating-Averaging Sound Level 5.2 People speak at different levels and vary their voice
Meters level in reaction to room noise and other acoustical factors.
Consequentlyitisnotpossibletosaydefinitelywhetheraroom
3. Terminology is protected against eavesdropping. One can only assign a
probability of being overheard. The owners or managers of the
3.1 The following terms used in this test method have
closed room under consideration must set criteria for this
specific meanings that are defined in Terminology C634:
probability according to their specific goals and circumstances.
airborne sound sound attenuation
The non-mandatory appendix gives an approach to setting
average sound pressure level sound isolation
background noise sound level criteria.
decibel sound pressure level
level source room
6. Sound Sources
octave band white noise
pink noise
6.1 Sound sources shall be loudspeaker systems driven by
3.2 Definitions of Terms Specific to This Standard:
power amplifiers.
3.2.1 receiving point—a location outside the closed room
6.2 The input signal to the amplifiers shall be random noise
under consideration where someone might accidentally over-
containing an approximately uniform and continuous distribu-
hear or deliberately listen to speech occurring within the room.
tion of energy and frequencies over each test band. White or
3.2.2 speech privacy class (SPC)—an objective rating of the
pink electronic noise sources satisfy this condition.
speech privacy provided by a closed room, calculated as a sum
of factors related to sound isolation provided by the room, and
7. Frequency Range
background noise at the receiving point.
7.1 Bandwidth and Filtering—The overall frequency re-
sponse of the electrical system, including the filter or filters in
4. Summary of Test Method
the source and microphone sections, shall for each test band
4.1 Sound is generated at a high level in the closed room
conform to the specifications in ANSI S1.11 for a one-third
under consideration. To improve spatial uniformity, a source
octave band filter set, class 1 or better.
loudspeaker is to be placed successively at two or more
7.2 The frequency range for measurement shall be the
locations within the room.
sixteen one-third octave bands from 160 to 5000 Hz.
4.2 Receiving points outside the closed room under consid-
eration that are near potential weak spots in the sound 8. Measurement of Sound Pressure Levels
insulation or that are possible locations for an eavesdropper are
8.1 Overview:
selected for measurement.
8.1.1 For multiple positions of the source, sound pressure
4.3 With the source operating in each successive location,
levels shall be measured inside the closed room under consid-
measurements of sound pressure level are made within the eration with multiple fixed microphone positions, or with a
closed room to obtain source room levels, and at receiving
moving microphone.
points outside the closed room to obtain received levels. 8.1.2 Foreachpositionofthesourceinsidetheclosedroom,
sound pressure levels shall be measured at each receiving point
4.4 With the source turned off, measurements of sound
outside the room.
pressure level are made at the receiving points to obtain
8.1.3 Measurements of sound pressure level shall be made
background noise levels.
at each receiving point with the source not operating, to
4.5 The differences in average source room levels inside the
measure the background noise levels.
closed room and received levels at each receiving point are
8.1.4 The number of source positions used will affect the
determined, and are used to calculate a single number for each
uncertainty in the final result, which can be calculated accord-
receiving point that indicates the degree of sound isolation
ing to Appendix X1. More source positions will result in a
provided by the room boundaries.
smalleruncertainty.Usersofthistestmethodcanchoosetouse
4.6 Thesinglenumberratingofsoundisolationiscombined the minimum number of source positions specified and obtain
with the measured background noise levels to obtain the a result with unknown, but limited, uncertainty. Users can
Speech Privacy Class—a single number rating for each receiv- alternatively decide upon a maximum acceptable uncertainty
ing point that is related to the degree of speech privacy at each and repeat measurements with additional source positions until
receiving point. satisfactory results are obtained.
8.2 Measuring Equipment:
5. Significance and Use
8.2.1 Measurement quality microphones that are 13 mm or
5.1 This test method provides a means of measuring the smaller in diameter and that are close to omnidirectional below
sound isolation between the interior of a closed room and 5000 Hz shall be used.
locations outside the room, and also the background noise 8.2.2 Microphones, amplifiers, and electronic circuitry to
levelsatthelocationsoutsidetheroom.Theresultscanbeused process microphone signals and perform measurements shall
to rate the degree of speech privacy, or to estimate the satisfy the requirements ofANSI S1.43 for Type 1 sound level
probability of speech being intelligible or audible at each meters, except that B and C weighting networks are not
receiving point. required.
E2638 − 10 (2017)
8.3 Source Room: diameter in front of their body to evenly sample as much as
8.3.1 The sound pressure level in the closed room under practical of the measurement space. The sound level meter or
consideration will depend on the position of the source. To microphone shall be held well away from the operator’s
accountforthis,atleasttwosourcepositionsshallbeused.The body—at least 0.5 m (a boom serves to increase the distance).
sound pressure level measured in the closed room will also The microphone speed shall remain as constant as practical.
vary with microphone position, so several microphone posi- The operator shall take care to assure that the path does not
tions or a moving microphone shall be used for each source significantly sample any part of the allowable room volume for
position. more time than other parts. The microphone shall always be
8.3.2 Select source positions in the closed room according more than 1.5 m from the sound source and more than 1 m
to one of the following two ways, depending on the direction- fromthewallsoftheclosedroom.Theintegrationtimeshallbe
ality of the loudspeakers used: at least 30 seconds. This measurement shall be repeated for
8.3.2.1 Method 1—For approximately omnidirectional each source position i to give L ~f!, the average source room
si
loudspeakers, such as those in the shape of a regular polyhe- level in each band, for source position i.
dron with a driver mounted in each face (1), source positions NOTE 3—Measurement of the levels in the closed room with a moving
microphone and an integrating sound level meter will enable only
shall be at least 1.2 m apart and shall be representative of
approximate estimation of the uncertainty in the final result.
typical locations of talkers in the room. The source positions
NOTE 4—Different microphone locations or moving microphone paths
shall be 1.5 m above the floor.
may be required for each source position. Once a source has been moved
to a subsequent location, microphone positions are allowed in its previous
NOTE 1—Source positions for omnidirectional loudspeakers should
vicinity. This approach can be useful in particular for measurements in
normally be located in the central part of the room, at least 1.0 m from the
small rooms.
walls. In smaller rooms, it may be necessary to locate the source near a
wall or corner.
8.4 Receiving Points:
8.3.2.2 Method 2—For conventional directional
8.4.1 Select receiving points outside the closed room under
loudspeakers, source positions shall be selected in the corners
consideration.Measurementsshouldbemadeatalllocationsin
of the room opposite the wall that is being used for receiving
the receiving area where the speech privacy is of interest. The
points. The loudspeakers shall be moved to different corners to
regions near doors, windows and other types of weak elements
measure receiving points near different walls. Using a conven-
in the boundaries of the room are obvious locations that should
tional directional loudspeaker will increase the total number of
be included.
measurements required.
8.4.2 To evaluate speech transmission through walls and
NOTE 2—For the same number of source positions, the uncertainty in
othercomponents(forexample,doors),microphonesshouldbe
the measurement of average source room levels will be higher for
0.25 m from the nearest outer surface of the closed room and
conventional loudspeakers than for approximately omnidirectional loud-
between 1.2 and 2 m above the floor.
speakers such as one with drivers mounted in the faces of a regular
polyhedron (2). Additionally, for conventional loudspeakers, the number
NOTE 5—If the microphone is closer than 0.25 m, the measured level is
ofsourcepositionspossibleforagivenreceivingpointisgenerallylimited
sensitive to distance from the wall.
to the two opposite corners in the room, whereas for approximately
omnidirectional loudspeakers, additional source positions can be selected
8.4.3 Survey for additional locations where sound leaks
in the central area of the room, to reduce uncertainty.
may occur by performing initial listening tests. Position the
8.3.3 With the source operating at each source position in
sound source near the middle of the closed room under
the closed room, the average sound pressure level in the room
consideration and generate a signal so that the A-weighted
shall be measured in one of the two following ways: averagesoundpressurelevelintheroomisatleast80dB.With
8.3.3.1 Method 1—Measure the sound pressure level using
all doors closed, listen carefully near the boundaries of the
at least five fixed microphone positions. The microphone room and identify the locations of probable sound leaks where
positions shall be at least 1.2 m apart, at least 1.5 m from the
measurements should be made to assess the speech privacy. In
sound source and at least 1 m from the surfaces of the room. somecases,spotmeasurementlocationsmaynotbeadjacentto
The microphone positions should provide as complete and
theroomboundary.Wherethereissoundtransmissionfromthe
uniform coverage of the allowable part room volume as room via flanking sound paths such as through ducts, spot
possible. The sound pressure level L f in each frequency
~ ! measurements should be made at locations where a potential
sij
band, f, shall be measured for at least 15 seconds for each eavesdropper might be located.
source position i and each microphone position j.
8.4.4 Inadditiontothelocationsidentifiedasprobableweak
spots, select other positions around the closed room so as to
8.3.3.2 Method 2—Measure the average sound pressure
providecompleteanduniformcoverageoftheperiphery.Some
level in each ⁄3-octave band in the closed room with a moving
receiving points will be close to the surfaces of the closed
microphone and using a sound level meter or an equivalent
room. Others may be selected close to suspected weak spots
analyzer set to measure the time-averaged sound levels also
such as ventilation duct openings.
known as L . For larger rooms, the operator shall walk slowly,
eq
moving the microphone in a circular path of at least 0.5 m 8.4.5 The sound pressure level shall be measured at each
stationary receiving point for each source position i in the
closed room for at least 15 seconds. Measure the received
levels with the source operating, L ~f!, and the background
The boldface numbers in parentheses refer to the list of references at the end of rbi
this standard. noise levels with the source switched off, L f .
~ !
bi
E2638 − 10 (2017)
9. Calculations
L avg 5 L f /16 (6)
~ ! ~ !
r ( r
f5160
9.1 All calculations shall be made using unrounded, mea-
sured values. 9.4 Background Noise Levels at Each Receiving Point:
9.4.1 Calculate L f , the average background noise level in
~ !
b
9.2 Source Room Levels:
each band for each receiving point using:
9.2.1 If source room measurements were made using fixed
n
microphone positions, determine L ~f!, the average sound
si
L f /10
~ !
bi
L f 5 10log 10 (7)
~ ! F G
b
(
pressure level in each band, for source position i, as follows:
n
i51
m
1 where:
L ~f!/10
sij
L ~f! 5 10log 10 (1)
F G
si (
m
j51
n = the number of source positions.
where:
9.4.2 For each receiving point, calculate L (avg), the
b
arithmetic average of background noise level over the 16
m = the number of microphone positions.
⁄3-octave frequency bands from 160 to 5000 Hz from:
9.2.2 Calculate L f , the mean source room sound pressure
~ !
s
level in each frequency band, using:
L avg 5 L f /16 (8)
~ ! ~ !
b ( b
f5160
n
L f /10
~ !
si
L f 5 10log 10 (2)
~ ! F G
s 9.5 Level Differences:
(
n
i51
9.5.1 For each receiving point, calculate the difference in
where:
average source room level and average received level in each
n = the number of source positions.
band:
9.2.3 Calculate L ~avg!, the arithmetic average of source LD f 5 L f 2 L f (9)
~ ! ~ ! ~ !
s s r
room level over the 16 ⁄3-octave frequency bands from 160 to
9.5.2 For each receiving point, calculate LD(avg), the aver-
5000 Hz from:
age level difference over the 16 ⁄3-octave frequency bands
from 160 to 5000 Hz from:
L ~avg! 5 L ~f!/16 (3)
s ( s
f5160
LD~avg! 5 LD~f!/16 (10)
(
9.3 Received Levels at Each Receiving Point:
f5160
9.3.1 For each source position i, the received level in each
9.6 Speech Privacy Class:
frequency band f at each receiving point shall be corrected for
9.6.1 For each receiving point, calculate SPC from the
background noise as follows:
arithmetic sum of LD~avg! and L ~avg!:
b
9.3.1.1 If the difference L ~f!2L ~f! is more than 10 dB
rbi bi
SPC 5 LD avg 1L avg (11)
~ ! ~ !
then no correct
...