Architectural Design Guide
for Achieving Speech Privacy
1.
Office Spaces...................................................................................... 2
1.1.
1.1.1.
1.1.2.
1.1.3.
Open Plan Areas..................................................................................... 2
Knowledge worker cubicles ...................................................................... 2
Call Centers ........................................................................................... 3
Administrative workspaces ...................................................................... 3
1.2.
Closed Plan Areas ................................................................................... 3
1.2.1. Private offices ........................................................................................ 3
1.2.2. Conference rooms .................................................................................. 4
2.
Healthcare Spaces .............................................................................. 5
2.1.
Patient Treatment Rooms ........................................................................ 5
2.2.
Reception Areas ..................................................................................... 5
2.3.
Pharmacy Areas ..................................................................................... 6
3.
Hallways and Transition Zones ........................................................... 7
3.1.
Corridors in the Closed Plan ..................................................................... 7
3.1.1. Separating wall is constructed floor-to-slab above. ..................................... 7
3.1.2. Separating wall is constructed floor-to-ceiling only. .................................... 7
3.2.
Aisles in the Open Plan ........................................................................... 8
3.2.1. Entire ceiling of same height .................................................................... 8
3.2.2. Ceiling in aisle is not at same height ......................................................... 8
3.3.
Aisle ways between Closed and Open Plan ................................................. 8
3.4.
Transition zones ..................................................................................... 9
4.
Special Considerations ..................................................................... 10
4.1.
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7.
4.1.8.
Ceiling & Plenum Issues ........................................................................ 10
No Ceiling/No Plenum ........................................................................... 10
Ceiling Clouds/Interrupted Plenum ......................................................... 10
Plenum congestion ............................................................................... 11
Plenum air returns................................................................................ 11
Deep or Shallow plenums ...................................................................... 12
Pitched plenums (roofs) ........................................................................ 12
Low or High ceilings.............................................................................. 12
Lighting fixtures and other devices in the ceiling plane .............................. 13
4.2.
Under-Floor air distribution .................................................................... 13
4.3.
Wall & Furniture Issues ......................................................................... 14
4.3.1. Wall partitions, fixed and demountable ................................................... 14
4.3.2. Furniture Panels ................................................................................... 15
4.4.
Open Plan “Private Office” ..................................................................... 15
© 2004 Armstrong World Industries, Inc.
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INTRODUCTION
The achievement of speech privacy in the built environment is dependant on a
combination of intruding speech level and the background noise at the listener
location. The level of intruding speech depends on both the vocal effort used by the
talker, and the effectiveness of the architectural design in reducing the transmission
of sound between the talker and the listener. The level of the background noise can
either be controlled by the vagaries of the mechanical and office equipment and
appliances in an unrestrained way, or by the use of a specified electronic masking
sound.
Following are guidelines that should be considered in making architectural design
choices, and some indication of the consequences of the design choices made.
1. Office Spaces
In any type of office space, the speech privacy requirements will vary according
to the type of work performed in that space. Some areas such as legal and
human resource departments will generally require ‘Confidential’ privacy due to
the sensitive nature of the work performed. Other areas such as administrative
departments may function effectively with ‘Poor’ speech privacy, since speech
distractions are generally not a significant issue with this work. In any case ...
owner, facility manager, and occupant expectations will all affect privacy goals.
1.1. Open Plan Areas
Open plan office layouts are generally employed when design flexibility is
important, and when ‘Confidential’ speech privacy is not required. In all
open plan designs it is assumed that the talker is speaking with a normal
voice level. But even then, there are several possible speech privacy goals
depending on the type of work function as described below:
1.1.1. Knowledge worker cubicles [PI 80-95%]
This category includes engineers,
scientists, software developers,
professionals, etc. In this case it is
important that the occupants not be
distracted by adjacent conversations
since these distractions will adversely affect their concentration and
thus productivity. The target speech privacy level is usually
considered to be ‘Non-Intruding’ privacy. This means that speech
from adjacent areas may be partially heard but generally not
distracting.
The architectural design should be acoustically robust, which for a
typical 8’x8’ cubicle (9’6” ceiling) will suggest the following design
choices:



high performance ceiling: min. 180 AC rating with 200 AC
preferred [generally fiberglass ceiling panels]
standard furniture panels: min. 60” height with 72” preferred,
and min. 20 STC with 25 STC preferred
sound masking: specified content @ 46-50 dBA
© 2004 Armstrong World Industries, Inc.
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1.1.2. Call Centers [PI 70-80%]
This category includes technical
services, computer answer desk,
telephone sales, etc. In this case
the occupants should not be overly
distracted or annoyed while on the
phone, but at the same time, they may want to share information
between themselves. The target speech privacy level is usually a
marginal level between ‘Non-Intrusive’ and ‘Poor’ privacy. This
means that speech from adjacent areas will be mostly heard but
generally not distracting.
The architectural design should be acoustically moderate, which for a
typical 6’x6’ cubicle (9’6” ceiling) will suggest the following design
choices:



moderate performance ceiling: min. 180 AC rating
typical furniture panels: min. 54” height, and min. 15 STC
sound masking: specified content @ 44-46 dBA
1.1.3. Administrative workspaces [PI less than 70%]
This category includes data transcription,
filing, scheduling, etc. In this case speech
distractions are not a significant issue
relative to job performance. The target
speech privacy level is usually ‘Poor’ to
‘None’. This means that speech from adjacent areas will be entirely
heard and probably distracting at times.
The architectural design can be acoustically simple, which for a
typical 6’x6’ cubicle (9’6” ceiling) will suggest the following design
choices:



standard performance ceiling: min. 0.55 NRC rating
typical furniture panels: 48” height
sound masking: none
1.2. Closed Plan Areas
Closed plan office layouts are generally employed when ‘Confidential’
speech privacy is required. In all closed plan speech privacy designs it is
assumed that the talker is speaking with a raised voice level.
1.2.1. Private offices [PI 95-100%]
This category includes legal, human
resources, management, financial
departments, etc. In this case it is important
that the occupants not be overhead in
adjacent spaces, whether they be other offices or corridors, etc. The
target speech privacy level is always ‘Confidential’, even with a talker
speaking with a raised voice. This means that speech from adjacent
areas may rarely be heard, but certainly will not be intelligible.
© 2004 Armstrong World Industries, Inc.
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The architectural design should be acoustically robust, which for a
typical 10’x10’ office (9’6” ceiling) will suggest the following design
choices:



high performance ceiling: min. 35 CAC with 40 CAC preferred,
and min. 0.60 NRC with 0.70 preferred
wall partition: min. demountable 35 STC with fixed slab-to-slab
45 STC preferred
sound masking: specified content @ 41-45 dBA
1.2.2. Conference rooms [PI 95-100%]
This category includes conference rooms,
boardrooms, A/V teleconference rooms,
training rooms, etc. In this case it is
important that the occupants not be
overhead in adjacent spaces, whether they
be other conference rooms, offices or corridors, etc. The target
speech privacy level is always ‘Confidential’, even with a talker
speaking with a raised voice. This means that speech from adjacent
areas may rarely be heard, but certainly will not be intelligible.
Additionally, it is very important that there be good speech
intelligibility within the conference room itself, which requires both
low reverberation time (high NRC ceiling) and low background noise
(lower masking level).
The architectural design should be acoustically robust, which for a
typical 20’x20’ room (9’6” ceiling) will suggest the following design
choices:



high performance ceiling: min. 35 CAC with 40 CAC preferred,
and min. 0.70 NRC
wall partition: min. demountable 35 STC with fixed slab-to-slab
45 STC preferred
sound masking: specified content @ 40-42 dBA
© 2004 Armstrong World Industries, Inc.
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2. Healthcare Spaces
In all of the healthcare spaces covered below, one of the driving needs for speech
privacy is the Privacy Rule within the federal HIPAA regulations, which mandates
that “reasonable safeguards” be taken to protect the oral privacy of “personal
health information”. As of yet, the meaning of speech privacy has not been
objectively defined by third parties for healthcare settings, such as it has for
office spaces. The office applications are defined by ASTM standard test methods
and metrics, so it can be anticipated that similar definitions will eventually be
adopted for these healthcare applications.
Meanwhile, we can safely assume that oral privacy generally translates to
‘Confidential’ privacy in patient treatment rooms and doctors offices, since that
would be a normal expectation from the patients for closed rooms. It might be
argued that the expectation for reception areas and pharmacies may be slightly
lower since these are open spaces. But it’s very unlikely that we can treat an
open space in healthcare as we would in an office environment, since the issue in
healthcare is about not being overheard, not one of productivity.
2.1. Patient Treatment Rooms [PI 95-100%]
This category includes medical offices, examination
rooms, treatment rooms, etc. In this case it is
important that the occupants not be overhead in
adjacent spaces, whether other rooms or corridors,
etc. The target speech privacy level is always
‘Confidential’, even with a talker speaking with a
raised voice. This means that speech from adjacent areas may rarely be
heard, but certainly will not be intelligible.
The architectural design should be acoustically robust, which for a typical
10’x10’ room (9’6” ceiling) will suggest the following design choices:



high performance ceiling: min. 35 CAC with 40 CAC preferred, and min.
0.60 NRC, 0.70 preferred
wall partition: min. demountable 35 STC with fixed slab-to-slab 40 STC
preferred
sound masking: specified content @ 41-45 dBA
2.2. Reception Areas [PI undefined, likely in range of 90-100%]
This category includes medical reception and waiting
areas, etc., but not corridors. In this case it is
important that the counter conversation not be
overhead by an unintended listener such as a waiting
patient within the reception space. It is assumed
that the receptionist speaks with a normal voice
level. The target speech privacy level is probably some compromise
between ‘Confidential’ and ‘Normal’ privacy. This means that the counter
conversation may be partially heard, but mostly not intelligible.
Administrative measures should be used to ensure that the reception desk
is physically separated from the waiting areas as much as reasonably
possible.
© 2004 Armstrong World Industries, Inc.
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The architectural design should be acoustically robust, which for a typical
20’x30’ room (9’6” ceiling) will suggest the following design choices:


high performance ceiling: min. 180 AC rating with 200 AC preferred
sound masking: min. specified content @ 50–54 dBA, with possible
addition of targeted music mix, and applied primarily to the waiting area
beyond the counter
2.3. Pharmacy Areas [PI undefined, likely in range of 90-100%]
This category includes all pharmacies whether in a
healthcare facility or in a retail space. In this case
it is important that the counter conversation not be
overhead by an unintended listener such as a
waiting customer within the pharmacy space. It is
assumed that the pharmacist at the counter speaks
with a normal voice level. The target speech privacy level is probably some
compromise between ‘Confidential’ and ‘Normal’ privacy. This means that
the counter conversation may be partially heard, but mostly not intelligible.
Administrative measures should be used to ensure that the pharmacy
counter is physically separated from the waiting areas as much as
reasonably possible.
The architectural design should be acoustically robust, which for a typical
20’x20’ area (9’6” ceiling) will suggest the following design choices:


high performance ceiling: min. 180 AC rating with 200 AC preferred
sound masking: min. specified content @ 50–54 dBA, with possible
addition of targeted music mix, and applied primarily to the waiting area
beyond the counter
© 2004 Armstrong World Industries, Inc.
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3. Hallways and Transition Zones
Both the hallways themselves, and the adjacent spaces need to be very carefully
considered when designing for speech privacy goals. The primary function of a
hallway is to provide access between spaces for the occupants, which of course
means that people in transit could become ‘unintended listeners’ to confidential
information, or they could become distracters to others.
Three important issues need to be considered:



Conversations in private offices or conference rooms adjacent to the hallways
must be secure and not overheard by people passing by or waiting in the
hallway.
Conversations and other noises in the hallway must not be distracting to
people in the adjacent offices (open or closed), conference rooms, etc.
Occupants walking between spaces should not be subjected to significant
variations in the loudness of the background noise from space to space.
3.1. Corridors in the Closed Plan [PI 95-100%]
The confidentiality of the conversations within
the closed spaces must be preserved into the
corridors, which can be accomplished in either
of 2 ways:
3.1.1. Separating wall is constructed floor-to-slab above.



A wall with the specified STC rating (see Section 1.2) is
constructed continuously from the floor through the ceiling plane
and into the ceiling plenum all the way to the bottom of the floor
slab above.
All wall penetrations by air ducts, pipes, wires, etc. must be
properly sealed with resilient acoustical caulking.
Since the wall will effectively control the sound intrusion between
spaces, the ceiling tile chosen for the corridors may be the same
as used in the closed spaces (see Section 1.2) or could be any
other ceiling tile with min 0.55 NRC. In this case it’s more
important to control the reverberant sound in the corridor, thus
the min. NRC requirement.
3.1.2. Separating wall is constructed floor-to-ceiling only.




A wall with the specified STC rating (see Section 1.2) is
constructed continuously from the floor only to the ceiling plane,
with an open plenum above.
The wall-ceiling interface must be properly sealed with foam
stripping or resilient acoustical caulking, etc. and special care
must be taken with any tegular ceiling tile, as the face surface is
lower than the metal grid level.
Since the combination of wall and ceiling will effectively control
the sound intrusion between spaces, the ceiling tile chosen for
the corridors must have the same CAC rating (see Section 1.2) as
that used within the closed spaces, and a min 0.55 NRC.
If backloading of the ceiling tile (e.g. R11 fiberglass blanket) is
used above the ceiling within the closed spaces to meet the CAC
requirement, then it must also be used in the corridor.
© 2004 Armstrong World Industries, Inc.
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If these design steps are taken, then noise intrusions from the
corridors into the closed spaces will generally not be a problem
either.
3.2. Aisles in the Open Plan [PI 80-95%]
There are no expectations of confidential
speech privacy in open plan designs, but
there is an expectation of low distraction
so that work performance will not be
adversely affected. Accordingly, the primary issue is sound coming from
those in the aisles ways intruding into the cubicles. Since anyone in
transit is obviously standing whereas the listeners in cubicles are seated,
the furniture panels should be taller at the aisles than those between the
cubicles, and the minimum effective height is 66”– 72”. The choice of
ceiling tile for the aisle ways should follow these guidelines:
3.2.1. Entire ceiling of same height

If the entire ceiling throughout open office is of the same
height, then the ceiling tile in the aisles need to meet the same
AC rating as for the ceiling above the cubicles (see Section
1.1).
3.2.2. Ceiling in aisle is not at same height


If the ceiling in the aisles is higher than the rest of the open
office area, then the ceiling tile chosen for the aisles may be of
the same or lower AC rating (see Section 1.1). Generally, the
chosen tile for the aisles should not be more than 30 AC points
lower even for an aisle ceiling that is 50% higher.
If the ceiling in the aisles is lower than the rest of the open
office area, then the ceiling tile chosen for the aisles must be at
least of equal or preferably higher AC rating (see Section 1.1).
Generally, the chosen tile for the aisles should be about 20 AC
points higher for an aisle ceiling that is 20% lower, unless of
course, if the open plan ceiling is already an AC 200 or higher.
3.3. Aisle ways between Closed and Open Plan
When the aisle way is between the closed and
open plan areas, then the ceiling choice for
the aisle way should follow the same
approach as was described in Section 3.1,
with the following modifications for a floor-toceiling wall:



The high CAC ceiling requirement of the closed plan should be carried for
the full width of the aisle or a maximum of 4-6 ft away from the closed
space (to provide confidential privacy, closed-to-aisle way), since
beyond that distance the AC rating of the open plan should have a
higher priority (to provide low distractions, aisle way-to-open).
The effective CAC of a ceiling comprised of 2 different CAC rated tiles on
opposite sides of the dividing wall is approximately the average of the 2
values, thus a combination of 35 & 25 will result in an effective rating of
only 30.
If the ceiling height is less than 9’, then the high CAC tile should
be carried out to 6’, otherwise 4’ is generally satisfactory.
© 2004 Armstrong World Industries, Inc.
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3.4. Transition zones
Transition zones refer more to the background noise environment in a
space, than to the architectural design, which actually defines that space
and thus necessitates the use of transition zones. For instance, the general
design objectives for good speech privacy and low sound distractions are as
follows:
Open plan offices
Closed offices
Conference rooms
48 dBA
43 dBA
41 dBA
If a well designed traditional HVAC (heating, ventilation, AC) system is in
use, the background noise from that system will generally be within the
range of 35–45 dBA, with some time variations based on solar loads, etc.
On the other hand, if a UFAD (under floor air delivery) system is in use, the
background noise from that system will generally be much lower, being
within the range of 30-35 dBA.
If a building is designed solely on the above basis, there very likely will be
noticeable background noise variations over the floor space, especially as
one goes from one type of space to another. A difference of 10 dB will be
perceived to be twice as loud, and that can happen if going from a corridor
supplied with UFAD (35 dBA) and no masking, to an open plan office with
electronic masking (48 dBA). This would become quite annoying to most
occupants as they walk around.
The purpose of transition zones is to “smooth” the transition between areas
with significantly different background noise. This is accomplished with
electronic masking sound by tapping the speaker transformers in 3 dB
increments for a sequence of 1 to 3 speakers based on the space layout and
the amount of noise difference being made-up. Since most
“unsophisticated” listeners will not distinguish anything less than a 3 dB
variation, a noise difference of 12 dB for instance can be easily made-up
with a 3-speaker transition zone.
© 2004 Armstrong World Industries, Inc.
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4. Special Considerations
Listed below are issues that come up time-and-again when discussing why
achieving good speech privacy is not easy to do. You might even say that these
are answers to FAQ’s dealing with things that could go wrong with architectural
design, sound masking systems, and speech privacy.
4.1. Ceiling & Plenum Issues
4.1.1 No Ceiling/No Plenum
An architectural design style
being seen more often in
commercial buildings can be
termed the ‘warehouse’ look,
which means exposed deck ... no ceiling. This design approach often
results in issues relating to both the room acoustics, and how to use
electronic sound masking systems.
This design causes problems with sound reflecting off the hard slab
above. The problems are twofold:
1. specular reflections between adjacent open plan cubicles for
ceiling heights less than about 15’, which cause distractions for
nearby occupants and affect work performance
2. reverberation in the high ceiling areas as a result of all distant
sources, including people and equipment, which causes
annoyance to all occupants
Since there is no ceiling plenum, “No ceiling/no plenum” means that
uniform sound masking can only be introduced using a direct
radiator speaker that has a wide sound dispersion pattern over a
broad frequency range. The usual in-plenum sound masking
systems do not work adequately in this application.
Many noise issues related to this design can be addressed by using
“ceiling clouds”, see Section 4.1.2
4.1.2 Ceiling Clouds/Interrupted Plenum
Ceiling clouds (discontinuous ceiling plane)
can be used to reduce occupant distractions
in the open plan by controlling specular
reflections between adjacent cubicles. This
is accomplished by the use of high
performance ceilings (200 AC) located in
partial sections above sensitive work areas.
or
Ceiling clouds can also be used to reduce
distant reverberation within the space. This is accomplished by the
use of medium to high performance ceilings (0.65 to 0.95 NRC)
located in partial sections somewhere within the work areas.
© 2004 Armstrong World Industries, Inc.
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When discontinuous ceilings are used, uniform sound masking can
only be introduced using a direct radiator speaker that has a wide
sound dispersion pattern over a broad frequency range. Since the
plenum is exposed between the clouds, using an in-plenum masking
system will result in ‘hot spots’ between the clouds.
4.1.3 Plenum congestion
A ceiling plenum
congested with structural
beams, air ducts, HVAC
equipment, plumbing,
cabling, etc. will cause
significant problems with the design and installation of traditional
“in-plenum” sound masking systems. If the plenum is filled with
many devices, it will be difficult to properly install the sound masking
speakers in a consistent geometric pattern. If the plenum speakers
are not uniformly installed or if there are large plenum obstructions,
then the masking sound will not be uniformly distributed within the
plenum. If the masking sound is not uniformly distributed within the
plenum, then it will not be uniformly distributed at the occupant level
either, causing problems with annoyance and distractions. Some
occupants will become annoyed by masking that’s too loud, whereas
others will be distracted by adjacent conversations due to masking
that’s too low.
A direct radiating masking speaker system may be a better choice in
this situation since it is not affected by in-plenum issues.
4.1.4 Plenum air returns
Most overhead air systems
(HVAC) use either of two
methods to return the supply
air, 1) ducted air returns, and
Air Supply
2) plenum air returns. In the
Air Return
later case, the returned air
from a room is passed upward into the ceiling plenum through a
simple 2’x2’ air return grill (2’x2’ metal panel with holes or slats over
the surface).
When using an in-plenum masking system in combination with the
ceiling plenum as the air return, the masking sound will often have
‘hot spots’, which is not a problem if using a ducted air return. Inplenum masking can only work well if the entire ceiling plane has the
same uniform sound transmission loss performance (ceiling CAC).
However, ceiling tile typically have a transmission loss of between 15
dB and 20 dB, whereas an open air return grill will have a 0 dB loss.
This means that masking sound will pass through the ‘open’ air
returns without loss, thus resulting in a ‘hot spot’ that may sound as
much as 4 times as loud as the adjacent areas.
This can be resolved by the use of an acoustic ‘boot’ (short lined
turn) over the air return grill, or by using a direct radiating masking
speaker system since it is not affected by in-plenum issues.
© 2004 Armstrong World Industries, Inc.
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Note: any system or device penetrating the ceiling plane may also
affect the transmission of the masking sound and could cause “ hot
spots”. See Section 4.1.8 for details.
4.1.5 Deep or Shallow plenums
The ceiling plenum depth can have a significant effect upon the
uniformity of the masking sound radiated into the occupied space
below when using an in-plenum sound masking system.
Deep ceiling plenums can be a problem due to both the reflection
paths caused by obstructions in the plenum, and the sound
absorption within the large volume. Often this will require that the
masking speakers be oriented horizontally as opposed to vertically in
hopes of reducing the power loss within the plenum and preserving
the spatial uniformity of the in-plenum sound field.
Shallow plenums may also present problems since it may not be
possible to physically install the in-plenum masking speakers pointed
upwards, or there may be large obstructions that “shadow” large
volumes. In any case, shallow plenums always require closer
speaker spacing to preserve the spatial uniformity of the in-plenum
sound field, and to keep from developing ‘hot spots’ in the occupied
area below.
If the masking sound is not uniformly distributed within the plenum,
then it will not be uniformly distributed at the occupant level either,
causing problems with annoyance and distractions.
Neither of these are issues when using a direct radiating masking
speaker system since it is not affected by in-plenum issues.
4.1.6 Pitched plenums (roofs)
This is a special problem for top floors
in low buildings with pitched roofs
when using in-plenum masking
speakers. At the ridge, the plenum
may be 10 ft high or more, whereas at
the eaves it may be 2 ft high or less.
Getting the masking sound to be
uniform within this type of plenum will require either special nonuniform speaker spacing (higher speaker density closer to peak) or
progressive ‘tapping’ of the speaker transformers.
If the masking sound is not uniformly distributed within the plenum,
then it will not be uniformly distributed at the occupant level either,
causing problems with annoyance and distractions.
A direct radiating masking speaker system has an obvious advantage
in this situation since it is not affected by in-plenum issues.
4.1.7. Low or High ceilings
Ceiling height is one of the key factors affecting both the
architectural and masking system performance. It is much easier to
achieve good speech privacy and low annoyance with higher
ceilings, and the range of ceiling tile choices is also expanded.
© 2004 Armstrong World Industries, Inc.
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High ceilings allow the best performance due to the long paths sound
must travel, whether it is the voice intruding between adjacent
offices, or the masking sound radiating down from the ceiling plane.
A wider range of ceiling tile choices, even less than 200 AC may be
used in the open plan. And masking speakers can have greater oncenter spacing with superior uniformity, but of course may require a
higher power setting.
Low ceilings on the other hand may provide unique design
challenges. The ceiling tile selection is more critical due to the
shorter path sound must travel, and this generally suggests a 200
AC choice for the open plan. In-plenum masking systems will need
closer speaker spacing to preserve the spatial uniformity, and to
keep from developing ‘hot spots’ in the occupied area below. Direct
radiating speakers are not recommended for sound masking when
the ceiling height is less than 8’6”. This is because the ear height of
a person standing may be only 2’–3’ from the speaker for many tall
people when walking around, and they may well detect the presence
of the masking speaker.
Many times the low ceiling height is a result of building height
restrictions. This also causes congested plenums, see Section 4.1.3,
and deep or shallow plenums, see Section 4.1.5.
4.1.8. Lighting fixtures and other devices in the ceiling plane
To most architects and interior designers the ceiling is a visual
element of the architectural design, but to the mechanical engineer it
is an element to hide the mechanical equipment in the plenum, and
an opportunity to suspend lights and other technologies from a grid.
As building systems develop more technology the ceiling plane and
plenum will become more congested with all types of sensors and
actuators. Any element installed within the ceiling plane may
adversely affect both the sound absorbing (AC) and sound barrier
(CAC) performance of the ceiling tile, and this could become a
problem.
For instance, choosing the right type of lighting fixture for use in the
open office is critical to minimize the sound reflection off the fixture.
A flat lens lighting fixture is the worst offender, and a much better
choice would be to select a pendent lighting fixture.
In closed rooms, where ceiling transmission loss is most important, it
would not be wise to choose a lighting fixture with integral return air
vents, as this will compromise the ceiling sound barrier performance.
If such lighting fixtures are used, then an acoustic ‘boot’ (short lined
turn), or back box over the fixture will minimize sound leakage.
4.2. Under-Floor air distribution
More buildings are now being designed
with ‘raised floor’ systems for the purpose
Air Supply
of routing utilities and cabling, etc. Some
are also taking advantage of the raised
floor system to provide air delivery
upward from the floor, instead of downward from the ceiling. The
resultant HVAC background noise from an UFAD system is typically
© 2004 Armstrong World Industries, Inc.
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10 dB less than would otherwise be expected (except close to the entry
duct). This means that the application of a sound masking system is even
more important, since the degree of speech privacy achieved depends on
the ratio of intruding speech to the background noise, which in this case is
usually ½ as loud as expected.
4.3. Wall & Furniture Issues
4.3.1. Wall partitions, fixed and demountable
Wall partitions are dividing walls between closed spaces, and these
may be either of 2 types, fixed construction or demountable
(moveable) system.
Fixed Wall Construction
Walls are constructed from metal studs and drywall, fixed in place.
These walls may be ½” or 5/8” drywall on each side, with or without
building insulation in the gap. The sound transmission loss
performance of these walls should be at least 40 STC when R11
insulation is used in the gap.
The wall may be constructed a) from the floor up to the slab above,
b) up to slightly higher than the ceiling height (usually 4” – 12”
above ceiling), or c) up to the ceiling height only. Walls up to the
slab above obviously give the best sound blocking performance, but
of course are the most expensive and least flexible. There is
generally very little acoustical value to walls penetrating the ceiling
by only 4” – 12” as the plenum still allows most of the sound to pass
over this height anyways. Walls that go up only to the ceiling plane
are generally as good as walls that penetrate the ceiling plan by 4”12” because there is an opportunity to use good gasketing (resilient
foam or caulking) to seal the wall to the ceiling.
Care must be taken in sealing the gaps between the wall and ceiling
when a ‘tegular’ or ‘reveal’ edge ceiling tile is used (face of tile hangs
below level of the metal suspension grid).
In any case, fixed walls are just that ... fixed, and thus not easily
moved - and design flexibility is often an important issue.
Demountable Wall Systems
Demountable wall systems are constructed of metal frames and
some combination of metal and wood panels, and usually have some
type of sound absorption within the panel. The sound transmission
loss performance of these systems should be at least 35 STC and
preferably 40 STC. Most demountable wall systems will also come
with some type of floor and ceiling gasketing system.
These systems are usually floor-to-ceiling height and therefore easily
re-configurable for design flexibility.
More recently, these wall systems are also being used in the open
plan, especially when the ceiling height is much greater than 10 ft,
where the office walls do not have an integrated ceiling, these we
call “open plan private offices”, see Section 3.4.
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4.3.2. Furniture Panels
Furniture panels are used in open plan office layouts to define an
office space. Since most individuals when seated in a chair tend to
have both their ears and mouth at about 4 ft height, a furniture
panel of 48” height has no effect as a sound barrier between open
plan cubicles. These panels should therefore be at least 60” height,
and preferably 72” height to serve as good barriers. Additionally,
sound will want to go through the panel as well as over the panel, so
it’s construction is just as important as the height. Tall panels (72”)
should have a 25 STC rating, whereas short panels (less than 60”)
need not be more than 15 STC.
Of course tall panels need to be butted end to end (no gaps
between), and without gaps at the floor.
4.4.
Open Plan “Private Office”
A relatively new architectural design
concept, which really “blurs” the
meaning of a closed office, is the open
plan “private office”. Typically this
office is constructed of 9-10 ft height
wall partitions within an open plan
space with a higher ceiling, such that the “private office” partitions
do not extend all the way to the common ceiling. In this way it looks
like a closed office with closed door and all, but without an integral
ceiling of its own.
Occupants of closed offices with doors have an expectation of
confidential speech privacy, so it can be anticipated that the
occupants of these space will have the same expectations.
Unfortunately, since this architectural design is not as “robust” as a
real closed office, it is critical that the limitations are understood
prior to occupation.
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