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Excerpts
from ASTM E 1374-02: Standard Guide for Open Office Acoustics.
3. Summary of Guide
3.1 Acoustical Privacy- The attenuation of sound between
neighboring work stations in an open-plan office is typically much
less than that potentially available between closed-plan offices.
Nevertheless, a degree of acoustical privacy can be achieved if
component selection and interaction are understood. A successful
open plan office is the result of careful coordination of the several
components, ceiling, wall treatments, furniture and furnishings,
heating, ventilation and air-conditioning system, and masking sound
system.
4. Significance and Use
4.3 While this guide attempts to clarify the many interacting variables
that influence office privacy, it is not intended to supplant the
experience and judgment of experts in the field of acoustics. Competent
technical advice should be sought for the success in the design
of open offices, including comparisons of test results carried out
according to ASTM standards.
5. General Open Office Acoustical Considerations
5.2 Attaining acoustical privacy between work stations, open or
closed plan, is determined by the degree to which the intruding
sounds from adjacent work stations exceed the ambient sound levels
at the listener's ear.
5.5 Office layout should be designed to avoid obvious noise intrusion
possibilities. Individual work stations should be positioned relative
to columns, walls, and each other to avoid uninterrupted sound paths
between contiguous work stations. Occupant orientation is also important,
because there is a significant difference between the sound level
when a talker faces a listener versus the talker facing away from
the listener, of the order of 9 dB.
5.6 Loud Noises- Distractions caused by raised voices or
loud office equipment usually cannot be controlled by normal open
office constructions. It is recommended that some closed plan spaces
be provided to contain such loud equipment or enclose noise sensitive
spaces such as conference rooms.
5.7 Problem Noise Sources- Computers, business machines,
copiers, typewriters, and other noise generating devices should
be located in isolated (enclosed) rooms or areas to minimize their
noise intrusion into the work station. Where this is impractical,
care should be exercised in eliminating or minimizing the noise
generation aspects. Telephones and "speaker phones" are a frequent
problem. The former should be equipped with flashing lights, rather
than ringers (audible annunciators). Large typing pools or word
processing centers can generate A-weighted sound levels up to 80
dB. These activities should be contained in special work areas affording
adequate noise isolation from the surrounding open plan spaces.
5.8 Undivided Workspaces- Acoustical comfort may be improved
in undivided work spaces such as bull-pen offices, drafting rooms,
and typing pools by the addition of acoustical absorption to horizontal
and vertical surfaces, but no such treatment alone will provide
speech privacy.
6. Components of the open plan Acoustical Environment
6.1 Ceilings:
6.1.1 The sound absorbing characteristics required of the ceiling
plane for open plan systems are different than those for private
offices or conference rooms. In open plan spaces, sound from the
source not controlled by part-height space dividers travels toward
the ceiling plane, where part can be reflected back into the adjacent
work space. To minimize the reflected sound, the ceiling must absorb
most of it. In private offices or conference rooms, some lesser
absorption or greater reflection may be desirable.
6.1.2 The sound barrier characteristics of the ceiling plane helps
provide spatially uniform masking sound from loudspeakers located
in the ceiling plenum. If the sound barrier performance is low or
variable, it may lead to the perceptions of "hot spots" in the masking
sound. Some masking system designs may compensate for these deficiencies
or variations.
6.1.3 Lighting fixtures mounted in the ceiling must be chosen with
care. Flat, lensed fixtures tend to reflect sound specularly and
should be avoided. Parabolic cell fixtures, are preferred because
they tend to scatter incident sound. The sound barrier characteristics
of the fixtures should also be similar to that of the ceiling, to
avoid masking sound "hot spots" underneath them.
6.1.4 Other ceiling elements, such as return air grilles or fixtures,
must also be selected with care, to avoid leakage of sound from
the masking system or surface reflections of incident sounds.
6.2 Sound Barriers and Vertical Surfaces:
6.2.1 Sound generated within the work station and potentially intruding
into adjacent work spaces is of major concern. This potentially
intrusive sound is reduced in the following two ways: (1) using
barriers that are properly absorptive and appropriately impervious
to sound penetration, and (2) reducing the tendency of sound to
"flank" or diffract around the perimeters of such barriers.
6.2.2 Sound Reflectors- All vertical surfaces are possible
sound reflectors if not specifically treated. Hard, flat, smooth
surfaces represent the worst condition. To reduce or eliminate these
reflections, such surfaces should be highly absorptive to sound
in the frequency range of concern. A particularly difficult area
to treat in this regard is the glass in the typical exterior wall
of the office area. Note that materials used to achieve sound absorption
usually are not effective sound barriers.
6.2.3 Sound Barriers- Reduction of sound transmission through
barriers separating adjacent work spaces is normally achieved by
adding an impermeable septum to the center of the barrier. Care
must be exercised in eliminating any possible "through holes" offering
unencumbered passageways for sound to "leak" through to adjacent
work spaces.
6.2.3.1 Flanking Transmission- Flanking can be controlled
by proper consideration of the height and length of the barrier,
the horizontal distance between adjacent barriers, and the sound
absorptive characteristics of the adjacent barriers. The most practical
method of reducing flanking is to employ vertical barriers that
are as high and as long as possible. This may be in conflict with
the desire for "openness" or clear view through the office space.
The clearance between the bottom of the barriers and the floor should
be minimal, although this path is not as critical as clearance above
the barrier.
6.2.3.2.1 Barrier Height- Barrier heights of less than 60
in. (1.5m) are not effective in performing as acoustical barriers
in open plan offices. As a general rule, barrier heights greater
than 80 in. (2 m) provide diminishing returns. "Tradeoff" decisions
in the determination of the required height against the original
motive for considering the aesthetic factors associated with such
systems are required.
6.2.3.3 Electrical Raceways- Current trends are to include
the electrical raceway on the bottom of panels; there is also a
shift towards including "wire management" features at the top and
middle of panels. Unless treated to the contrary, such features
can diminish both the barrier and absorptive properties of the barrier.
6.2.3.4 Hang-On Components- Most contemporary open plan office
systems incorporate furniture concepts into the overall system.
These components include storage compartments, file bins, work surfaces,
tack boards, task and ambient lighting modules, communication and
power management items, etc. Most of these items will degrade the
absorption properties of the system and may also affect privacy
characteristics.
6.4 Masking Sound:
6.4.1 Since acoustical privacy is a signal (intruding sound) to
noise (prevailing ambient) consideration, precise control of the
ambient sound is an essential element for achieving sound privacy
in the open plan office. A properly designed, installed, and adjusted
electronic sound masking system is the most effective means of controlling
the ambient sound...
For the complete masking system standard, click
here.
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