ASTM E1374-93(1998)e1
(Guide)Standard Guide for Open Office Acoustics and Applicable ASTM Standards
Standard Guide for Open Office Acoustics and Applicable ASTM Standards
SCOPE
1.1 This guide discusses the acoustical principles and interactions that affect the acoustical environment and acoustical privacy in the open office. In this context, it describes the application and use of the series of ASTM standards that apply to the open office.
1.2 The values stated in inch-pound units are to be regarded as standard. The SI units in parentheses are provided for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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e1
Designation: E 1374 – 93 (Reapproved 1998) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Guide for
Open Office Acoustics and Applicable ASTM Standards
This standard is issued under the fixed designation E 1374; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Keywords were added editorially in March 1998.
INTRODUCTION
There are no full height partitions in an open-plan office to block sound transmission between
adjacent work stations. Instead, partial height barriers, a sound absorbing ceiling and absorption on
vertical surfaces are used to provide sound attenuation between individuals. These, in combination
with work station layout and appropriate levels of broad band masking sound are used to obtain
acceptable degrees of acoustical privacy.
1. Scope tion of Sound Reflected by Wall Finishes and Furniture
Panels
1.1 This guide discusses the acoustical principles and inter-
E 1414 Test Method for Airborne Sound Attenuation Be-
actions that affect the acoustical environment and acoustical
tween Rooms Sharing a Common Ceiling and Plenum
privacy in the open office. In this context, it describes the
application and use of the series of ASTM standards that apply
3. Summary of Guide
to the open office.
3.1 Acoustical Privacy—The attenuation of sound between
1.2 The values stated in inch-pound units are to be regarded
neighboring work stations in an open-plan office is typically
as standard. The SI units in parentheses are provided for
much less than that potentially available between closed-plan
information only.
offices. Nevertheless, a degree of acoustical privacy can be
1.3 This standard does not purport to address all of the
achieved if component selection and interaction are under-
safety concerns, if any, associated with its use. It is the
stood. A successful open plan office is the result of careful
responsibility of the user of this standard to establish appro-
coordination of the several components, ceiling, wall treat-
priate safety and health practices and determine the applica-
ments, furniture and furnishings, heating, ventilating and
bility of regulatory limitations prior to use.
air-conditioning system, and masking sound system. (See
2. Referenced Documents Section 7.)
3.1.1 This guide delineates the role and interaction of the
2.1 ASTM Standards:
several components and the application of the relevant ASTM
E 1041 Guide for Measurement of Masking Sound in Open
2 Standards.
Offices
E 1110 Classification for Determination of Articulation
4. Significance and Use
Class
4.1 This guide is intended for the use of architects, engi-
E 1111 Test Method for Measuring Interzone Attenuation of
neers, office managers, and others interested in designing,
Ceiling Systems
specifying, or operating open offices.
E 1130 Test Method for Objective Measurement of Speech
4.2 It is not intended to be applied to other than office
Privacy in Open Offices Using Articulation Index
environments, for example, open plan schools.
E 1179 Specification for Sound Sources Used for Testing
4.3 While this guide attempts to clarify the many interacting
Open Office Components and Systems
variables that influence office privacy, it is not intended to
E 1375 Test Method for Measuring the Interzone Attenua-
supplant the experience and judgment of experts in the field of
tion of Furniture Panels Used as Acoustical Barriers
acoustics. Competent technical advice should be sought for
E 1376 Test Method for Measuring the Interzone Attenua-
success in the design of open offices, including comparisons of
test results carried out according to ASTM standards.
This guide is under the jurisdiction of ASTM Committee E-33 on Environ-
mental Acoustics and is the direct responsibility of Subcommittee E33.02on Open
5. General Open Office Acoustical Considerations
Plan Spaces.
Current edition approved July 15, 1993. Published September 1993. Originally
5.1 Introduction—Attenuation with Distance—In almost
published as E 1374 – 90. Last previous edition E 1374 – 92.
any enclosed space, there is some reduction of sound level with
Annual Book of ASTM Standards, Vol 04.06.
E 1374
distance. In many typical spaces, this decrease of sound level 5.8 Undivided Workspaces—Acoustical comfort may be
with distance is affected by sound reflections from the ceiling, improved in undivided workspaces such as “bull-pen” offices,
the walls, and floor. In the open plan office the goal is to drafting rooms, and typing pools by the addition of acoustical
maximize this loss with distance in order to improve acoustical absorption to horizontal and vertical surfaces, but no such
privacy. This requires a highly absorbent ceiling, some absorp- treatment alone will provide speech privacy.
tion on the floor, and careful treatment of nearby vertical 5.9 ASTM test methods exist for testing components and
surfaces. The ideal is to approach the conditions of the systems for open plan offices. These include measuring the
outdoors, where there are no reflecting surfaces. attenuation between work stations by the ceiling path (see Test
Method E 1111), the effect of barriers such as furniture panels
5.2 Attaining acoustical privacy between work stations,
(see Test Method E 1375), the effect of flanking or reflections
open or closed plan, is determined by the degree to which the
from vertical surfaces (see Test Method E 1376), measurement
intruding sounds from adjacent work stations exceed the
of masking sound in the open office (see Guide E 1041), and
ambient sound levels at the listener’s ear.
the determination of the articulation class (see Classification
5.3 The sound pressure levels arriving at the listener’s ear
E 1110), that is a single number rating of system component
from sources in adjacent work stations depend on the follow-
performance. Articulation class does not account for the effect
ing:
of masking sound.
5.3.1 The sound source amplitude, directivity, and orienta-
5.10 Objective Determination of Speech Privacy—Test
tion.
Method E 1130 describes a method of objectively measuring
5.3.2 The total attenuation of the sound due to a combina-
the speech privacy in open plan offices. It is based on a
tion of distance and shielding by intervening barriers.
determination of the articulation index.
5.3.3 The reinforcement of the direct sound due to reflec-
5.10.1 Articulation Index—The articulation index (AI) is a
tions from office surfaces such as the ceiling, furniture panels,
computational method for predicting the intelligibility of
light fixtures, walls, and windows.
speech for groups of talkers and listeners. The AI is a weighted
5.3.4 The level of ambient sound at the listener’s ear. This
fraction representing, for a given speech frequency band and
will often be generated and controlled by a sound masking
noise condition, the effective proportion of the standard speech
sound system, but in certain positions and frequency ranges,
signal that is available at the listener’s ear for conveying
heating, ventilating, and air conditioning equipment (HVAC)
speech intelligibility.
may contribute significantly to the ambient sound level.
5.10.1.1 The articulation index ranges from 0.00 to 1.00,
5.4 The attributes in 5.3.1 through 5.3.4 apply regardless of
with 0.00 representing zero intelligibility and 1.00 complete
the source of the intruding sound. In the open plan, both office
intelligibility.
equipment and speech are the dominant intruding sources. In
5.10.1.2 Speech privacy may be described as confidential
many cases, the provision for acceptable speech privacy is the
when speech may be detected but not understood.
major concern.
5.10.1.3 Speech privacy may be described as normal or
5.5 Office layout should be designed to avoid obvious noise
non-intrusive when effort is required to understand the intrud-
intrusion possibilities. Individual work stations should be
ing speech. Normal speech privacy may also be described as
positioned relative to columns, walls, and each other to avoid
the absence of distraction.
uninterrupted sound paths between contiguous work stations.
5.10.1.4 Confidential speech privacy occurs at an AI of 0.05
Occupant orientation is also important, because there is a
or less. Speech becomes more readily understood with AI
significant difference between the sound level when a talker
values greater than 0.20; at values greater than 0.40 there is
faces a listener versus the talker facing away from the listener,
essentially no privacy.
of the order of 9 dB.
NOTE 1—Additional research is needed to verify the relation between
5.6 Loud Noises— Distractions caused by raised voices or
the AI and the subjective judgement of normal privacy in the open plan.
loud office equipment usually cannot be controlled by normal
(See the appendix of Test Method E 1130.)
open office constructions. It is recommended that some closed
6. Components of the Open Plan Acoustical Environment
plan spaces be provided to contain such loud equipment or
enclose noise sensitive spaces such as conference rooms.
6.1 Ceilings:
5.7 Problem Noise Sources—Computers, business ma- 6.1.1 The sound absorbing characteristics required of the
chines, copiers, typewriters, and other noise generating devices ceiling plane for open plan systems are different than those for
should be located in isolated (enclosed) rooms or areas to private offices or conference rooms. In open plan spaces, sound
minimize their noise intrusion into the work station. Where this from the source not controlled by part-height space dividers
is impractical, care should be exercised in eliminating or
travels toward the ceiling plane, where part can be reflected
minimizing the noise generation aspects. Telephones and back into the adjacent work space. To minimize the reflected
“speaker phones” are a frequent problem. The former should be sound, the ceiling must absorb most of it. In private offices or
equipped with flashing lights, rather than ringers (audible conference rooms, some lesser absorption or greater reflection
annunciators). Large typing pools or word processing centers may be desirable.
can generate A-weighted sound levels up to 80 dB. These 6.1.2 The sound barrier characteristics of the ceiling plane
activities should be contained in special work areas affording helps provide spatially uniform masking sound from loud-
adequate noise isolation from the surrounding open plan speakers located in the ceiling plenum. If the sound barrier
spaces. performance is low or variable, it may lead to the perceptions
E 1374
of “hot spots” in the masking sound. Some masking system Class (AC) determined in accordance with Classification
designs may compensate for these deficiencies or variations. E 1110.
6.2.3 Sound Barriers— Reduction of sound transmission
NOTE 2—There is currently no accepted objective method of specifying
through barriers separating adjacent work spaces is normally
single-pass sound barrier performance of ceiling materials.
achieved by adding an impermeable septum to the center of the
6.1.3 Lighting fixtures mounted in the ceiling must be
barrier. Care must be exercised in eliminating any possible
chosen with care. Flat, lensed fixtures tend to reflect sound
“through holes” offering unencumbered passageways for sound
specularly and should be avoided. Parabolic cell fixtures, are
to “leak” through to adjacent work spaces. The interzone
preferred because they tend to scatter incident sound. The
attenuation provided by a barrier can be determined in accor-
sound barrier characteristics of the fixtures should also be
dance with Test Method E 1375. The single number classifi-
similar to that of the ceiling, to avoid masking sound “hot
cation for barriers is the Articulation Class (AC) determined in
spots” underneath them.
accordance with Classification E 1110. Severe conditions, for
6.1.4 Other ceiling elements, such as return air grilles or
example, people being located in close proximity to each other
fixtures, must also be selected with care, to avoid leakage of
or high source levels, need to be assessed for unwanted sound
sound from the masking system or surface reflections of
transmission paths (“flanking”) or higher barrier performance.
incident sounds.
6.2.3.1 Flanking Transmission—Flanking can be controlled
6.1.5 In closed plan spaces frequently associated with open
by proper consideration of the height and length of the barrier,
plan areas, the absorption characteristics of the ceiling are of
the horizontal distance between adjacent barriers, and the
less importance than its sound barrier characteristics. An
sound absorptive characteristics of the adjacent barriers. The
accepted method of specifying this performance is by the
most practical method of reducing flanking is to employ
two-room method, in Test Method E 1414, that evaluates the
vertical barriers that are as high and as long as possible. This
sound passing through one ceiling into the plenum and then
may be in conflict with the desire for “openness” or clear view
back down through the ceiling into the adjacent space. Where
through the office space. The clearance between the bottom of
open and closed plan spaces are adjacent, masking sound is
the barriers and the floor should be minimal, although this path
frequently useful for providing speech privacy in both spaces.
is not as critical as clearance above the barrier.
The barrier and absorption characteristics of the ceiling system
6.2.3.2 Barrier Height— Barrier heights of less than 60 in.
should be optimized where open and closed spaces will be
(1.5 m) are not effective in performing as acoustical barriers in
mixed.
open plan offices. As a general rule, barrier heights greater than
6.1.6 Test Method E 1111 is the preferred method of deter-
80 in. (2 m) provide diminishing returns. “Tradeoff” decisions
mining the ceiling absorption characteristics. It is a component
in the determination of the required height against the original
test and is restricted to measurement with a fixed-height space
motive for considering the aesthetic factors associated with
divider, fixed sound source height, and microphone positions.
such systems are required.
A single number rating, convenient for ranking the perfor-
6.2.3.3 Electrical Raceways—Current trends are to include
mance of the ceiling, is obtained using Classification E 1110.
the electrical raceway on the bottom of p
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