speech privacy is needed for receptionists, clerical staff,
Closed Offices Versus Open Plan. Required levels of
and team-oriented workgroups where overheard
acoustic privacy should be included as a design criterion.
conversation can actually be beneficial.
For work that does not require acoustic and/or visual
privacy, an open plan environment with low or no
Appropriate levels of background sound. Continuous
partitions between workstations is appropriate. For work
background sound in offices is mostly generated by
that requires a balance between ongoing, active
heating, ventilation, and air conditioning (HVAC)
collaboration, easy workgroup reconfiguration, flexible
equipment. In conference spaces, courtrooms and
settings, and minimized unwanted acoustic distraction,
auditoria, it is important that this background sound
an open plan setting with a well-engineered acoustical
not interfere with the intelligibility of speech. In enclosed
design is recommended. Key components of such
offices, HVAC background sound is an important
engineered open plan designs are highly absorptive
component in achieving the required level of privacy
ceilings, suitable height partition panels that both absorb
because it helps to cover up or "mask" speech
and block sound, suitable levels of background sound
transmitted between adjacent spaces. In open plan areas,
(typically provided by electronic sound masking
the background sound provided by contemporary HVAC
systems), and ready access to acoustically private (closed
equipment is often not uniform and/or does not have the
office) meeting spaces. A protocol that encourages
tonal balance and loudness needed to mask speech
lowered voice levels is also recommended. Closed offices
transmitted between adjacent cubicles. For this reason,
are encouraged for workers who routinely require
additional electronic background noise or sound masking
extended periods of concentration, in-office meetings,
is often deployed in these areas.
and/or confidential conversation. Meeting spaces and
Control of intrusive noise, vibration, and reverberation.
closed offices that require speech security must be
Office equipment generating noise levels above the
designed in conjunction with a qualified acoustical
background should be located away from primary
work areas or should be surrounded by acoustically
isolating panels. Noise induced by mechanical equipment
Parameters Used in Acoustical Design. The following
should be controlled through vibration isolation devices,
parameters are used to specify acoustical standards for
appropriate placement of equipment and noise
attenuators in ducts. Reverberation and echoes must be
Background Noise-- the continuous noise within a space.
controlled in courtrooms, auditoria, conference, team, and
The loudness of noise is quantified by several assessment
training room spaces. Sound absorbing materials are used
schemes, including noise criteria (NC), balanced noise
to help control reflected sound energy and echoes.
criteria (NC-B) and room criteria (RC) contours. These
Particular attention must be paid to rooms with parallel
contours are published in the ASHRAE Handbook of
walls (causes "flutter" echoes) and rooms with curved or
Fundamentals. Lower values are quieter.
concave ceilings (leads to acoustical focusing effects).
Environmental Noise-- the continuous noise outside a
Isolation from exterior noise sources. Buildings located
building. The Day-Night Average Noise Level (DNL) is
near airports, highways, rail corridors or other sources of
a descriptor established by the U.S. Environmental
significant environmental noise levels must have exterior
Protection Agency to describe the average day-night
wall and window assemblies controlling noise intrusions.
sound level. Lower values are quieter.
76 F A C I L I T I E S S T A N D A R D S
3.4 Special Design Considerations
Revised March 2005 PBS-P100