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8/8/2019 Acoustical Design Guide for Open Offices
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Acoustical Design Guide for Open Offices
Warnock, A.C.C.
IRC-RR-163
March 2004
http://irc.nrc-cnrc.gc.ca/ircpubs
http://irc.nrc-cnrc.gc.ca/ircpubshttp://irc.nrc-cnrc.gc.ca/ircpubs8/8/2019 Acoustical Design Guide for Open Offices
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Acoustical Design Guide for Open Offices
INTRODUCTION
This design guide was prepared as part of a research project funded by
PWGSC to investigate speech privacy in open-plan offices. Two major
types of work area in open offices are currently in vogue:
cubicles where individual workstations are delineated by barriers and
the more open team-style where groups of workers have
unrestricted visual access among themselves but are shielded from
adjacent work areas by barriers.
Within the team-style work area, where sound paths are usually quite
unobstructed, speech can be very intrusive. Since team-style work areas
are usually separated from each other by fairly high barriers, offices
incorporating this type of work area have the same problems with
intrusive speech between work areas as found in offices having mainlycubicles.
Thus, this guide gives, without detailed explanation, sets of
recommendations to reduce the intrusiveness of speech in both types of
office. (More information is available in the appendix and related reports.)
Criteria are first given for reducing speech intrusion between cubicles
because the same factors are important when considering sound
transmission between team-style work areas. The problems specific to
sound transmission within team-style areas are then dealt with.
While it is possible to estimate the degree of speech intrusion between
neighboring workstations, it is not considered a reasonable approach to
office design because of the immense number of variables to be dealt
with, many beyond the control of the designer. Thus this document gives
a list of minimally acceptable properties for office materials and
furnishings that, if adhered to, will be good enough in practice.
A critical consideration when placing workers in an open office is the kind
of work being done and the degree of privacy needed for the work. It is
often suggested that workers required to concentrate for extended
periods should not be in open offices to keep them free from distraction.
Some part of the distraction in an open office is due to the activities in
that office; if there are no telephone calls or conversations, distraction
will be minimal. With a combination of acoustical treatment, careful
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arrangement of furniture and the inducement of considerate behavior,
distraction may be minimized.
It must be accepted, however, that the acoustical isolation
between adjacent work stations in an open office can never be
as good as that between two offices enclosed by walls.
The appendix gives an overview and some explanation of those physical
factors that influence speech intelligibility in open offices. Speech
intelligibility or privacy is determined by the characteristics of the talker,
the sound propagation paths and the level of background noise in the
office. The appendix reviews the basic properties of human speech and
the basic factors influencing sound transmission in open offices.
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CUBICLE TYPE WORKSTATIONS
In cubicle-style workstations, a single employee occupies an area
defined by barriers and the furniture (Figure 1).
Figure 1: Cubicle-style work stations
Factors determining the sound attenuation between workstations are:
The sound-absorbing properties of the ceiling
The height of the barrier between adjacent workstations
Reflections from vertical surfaces
Diffraction around the vertical edges of barriers and furniture
The position and orientation of the workers in the cubicle
The ceiling is a critical element in any open office. There are no
obstacles to prevent sound from reaching the ceiling and being reflected
down into adjacent cubicles.
The more sound-absorbing, the ceiling, the less sound reflects
from it into adjacent workstations.
The higher the barrier between workstations, the less sound
bends over the top of the barrier to reach adjacent workstations.
The choice of ceiling panels and barrier height is a delicate compromise
between the acoustics of the office and visual and other factors. In the
more detailed summary later in this document, the consequences of
choices are discussed. Here, it is assumed that the goal of the design is
primarily to minimize speech transmission between workstations so the
following criteria are given:
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The ceiling sound absorption average, SAA, tested according to
ASTM C4231
on an E4002
mounting should be at least 0.9. This is a
minimum recommendation. Ceilings with higher SAA values will
reflect less sound and give better sound isolation between work
stations. Barriers should be at least 1.65 m high.
The sound absorption average (SAA) for the barrier tested as a free-
standing screen according to ASTM C423 should be greater than
0.75. If the barrier can not be so tested then the SAA for the sound
absorbing material covering the surface should be at least 0.7 when
tested on an A mount2.
The edges of barriers should be sound-absorbing, not covered with
wood or metal trim.
Sound transmission through the body of the barrier should be
negligible. This will be so if the STC for the barrier measured
according to ASTM E903
is greater than 204.
Wherever possible, vertical surfaces should be covered with sound-
absorbing material having an SAA of 0.7 or more when tested
according to ASTM C423 on an A mounting2.
The floor should be carpeted but normal commercial grade carpeting
will be acceptable.
A masking sound system should be provided and adjusted by a
consultant to give a level of approximately 45 dBA. The spectrum
should decrease in level by about 5 dB per octave increase in
frequency. (Masking sound systems are discussed briefly in the
appendix.)
Office Layout
During design of a cubicle-style office, sound paths in the horizontal and
vertical plane should be examined to identify possible direct or reflected
paths between workstations. Examples of the problems that may arise
are given in Figure 2. If vertical surfaces are made sound absorbing,
reflections from them are less important. If there is a direct line of sight
Ceiling systems may also be evaluated for use in open offices using atest method ASTM E11111. This method gives a rating called thearticulation class
1(AC). The requirement that SAA should be 0.9 or more
is equivalent to requiring AC to be greater than 180.
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between two nearby occupants, the layout should be changed to
eliminate the direct path.
Figure 2: Examples of direct, diffracted, and reflected paths betweencubicle type workstations.
Flat lighting panels mounted in the ceiling can significantly increase
speech intrusion and should not be used. The number of lighting panels
in the ceiling should be minimized and a type of luminaire selected that
will scatter sound instead of acting like a mirror. Lighting fixtures down at
the workstation level give fewer troublesome reflections. There are no
standards or ratings that address sound reflections from light fixtures.
Considerate behavior by the office occupants can greatly reduce
annoyance, distraction and intrusive speech. Closed rooms should be
provided for extended meetings. Occupants should be discouraged fromcalling to someone several metres away just because that person is
visible.
With computer workstations being almost universal, it has become much
easier to control the orientation and the location of work station
occupants. This allows the designer to significantly reduce speech
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intrusion. The closer an occupant is to a barrier, the greater the
attenuation for sound diffracting around it. Distraction from telephone
conversations will be minimized if talkers sit close to and facing a highly
sound-absorbing surface.
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TEAM-STYLE WORK AREAS
Figure 3 gives an example of a team-style work area. There are
essentially no barriers between occupants of the work area but there are
barriers or screens separating them from adjacent work areas. The
important point about this kind of work area is that since the occupantsare in full view of each other, and are separated by only a few metres,
clear speech communication among occupants exists if they desire it.
Simply by turning and addressing a co-worker, the voice will carry easily
across the intervening distance. This situation cannot be changed
because of the core design concept of the team-style work area.
The factors determining the level of speech within the work area are:
The sound reflecting properties of the barriers, furnishings and
equipment in the work area.
The use of small, low barriers that break the line-of-sight but do not
detract from the open feeling of the workspace.
The orientation of the people in the work area
The sound-absorbing properties of the ceiling.
The distance between the occupants.
A B
C D
Figure 3: Example layout for a team-style work area. The gray rectanglesrepresent barriers. The arrows show direct, reflected and one diffracted
path between occupants.
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All the requirements given for cubicle-style office fittings must be met if
speech in the team-style area is to be minimally intrusive. In addition, the
following factors should be optimized during the design of a team-style
work area.
Work stations should be arranged so occupants face away from
each other as much as possible especially when telephone calls are
being made. The surfaces around the phone area should be
absorptive to reduce sound reflection which is why barriers must
meet the minimum SAA criterion given earlier.
Short barriers between occupants, like that between C and D, should
be used to increase the attenuation between adjacent workstations .
They should be high and wide enough to break the line of sight
between adjacent workers without being so high as to destroy the
openness of the work area. An extension of 200 to 300 mm beyond
the line of sight is typical. Note that these barriers do not affect
transmission between diagonally opposite workstations.
Recent measurements14
have shown that furnishing barriers with an
absorptive edge significantly increases the attenuation of sound
propagating around the barrier. The same holds true for bookshelves
and filing cabinets; these should have an absorptive layer on their
upper surface although in practice such layers are likely to be
covered by books or papers. A 25-mm thick layer of glass fiber or the
equivalent on the edge of the barriers should be sufficient.
The behavior of the occupants in the work area will also determine
the degree of disturbance within the work area and in adjacent work
areas. If in Figure 3 B speaks to C by turning around and calling
across the work area, this is more disruptive than if B crosses the
space to talk quietly to C. If passers-by call across the work area,
this will clearly be disruptive.
Part of the commissioning of an open office should be a program to
encourage considerate behavior.
The greater the distance between occupants, the greater the sound
attenuation. The changes in attenuation due to increasing distance
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APPENDIX: REVIEW OF OPEN OFFICE ACOUSTICS
Speech Intelligibility Index and Speech Privacy
In offices, the degree of speech privacy attained is determined by the
loudness or level of the intruding voice and the level of the background
sound at the receiving position. Obviously the louder the background
noise or the quieter the intruding speech, the more difficult it is to
understand what is being said.
Standard methods have been developed for evaluating speech
intelligibility in the presence of background noise. ANSI S3.55
gives a
detailed procedure wherein each frequency band contributes differently
to the aggregate intelligibility. The index that is calculated is called the
Speech Intelligibility Index (SII). ASTM E11306
is a test method that
uses an index, Articulation Index (AI), based on an earlier version of
ANSI S3.5. Both indices range from 0 to 1.
Pivotal to both standards is the level and spectrum of the voice used in
calculations. Figure 4 shows the idealized spectrum for normal speech
defined in ANSI S3.5. As noted in the figure caption, the overall level is
59.2 dBA. In different circumstances, people raise or lower their voice as
they perceive it necessary. The ANSI standard leaves it to the user to
decide on the appropriate level. ASTM E1130 specifies a different
spectrum at a specific level to be used in open office work; that spectrum
is also shown in Figure 4.
It has been suggested, and measurements7
support the suggestion, that
the ANSI normal voice shown in Figure 4 is not appropriate for
estimations of speech privacy in open offices; it is too loud. The ASTM
spectrum is slightly lower but measurements conducted during this
project7 by NRC in open offices give even lower voice levels. The mean
spectrum is also shown in Figure 4. The differences in level are highly
significant; a change in voice level of 3 dB corresponds to a change in
SII or AI of approximately 0.1. It should be remembered however, that
these are mean values; 50% of the measured voice levels were higher
than this value.
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25
30
35
40
45
50
55
60
125 250 500 1k 2k 4k 8k
Frequency, Hz
SPL,
dB
ANSI S3.5 1997
ASTM E1130
NRC
Figure 4: Spectrum for normal speech defined in ANSI S3.5. The overalllevel is 59.2 dBA. Also shown is the voice spectrum to be used inmeasurements and calculations according to ASTM E1130. The overalllevel is 57.5 dBA. The NRC data is the average of measurements ofmale and female speakers in open offices. The overall level is 50.3 dBA.
With the same voice and background noise levels, the two standards
give slightly different ratings. The relationship found in research
conducted by NRC as part of this project8
is
SII = 1.03 *AI + 0.06.
The values of AI given in the past as delimiting confidential and normal
privacy are 0.05 and 0.15 respectively. Corresponding values of SII are
therefore 0.1 and 0.2.
Acceptable speech intrusion
Recent work at NRC9
has clarified the relationship between SII and the
percentage of speech understood. From that work, Figure 5 shows the
mean test score as a function of SII for 29 subjects presented with 100
sentences in different acoustical simulations of offices. The relationship
is clearly not linear and intelligibility only begins to decrease significantly
when SII drops below about 0.3. At SII = 0.2, the mean score is almost
80%. Different individuals have different listening skills and the scatter in
the experiment is not shown in Figure 5.
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0%
20%
40%
60%
80%
100%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Speech Intelligibility Index
Score
Figure 5: Mean test score for 29 subjects versus speech intelligibilityindex.
Figure 6 shows the distribution of subjects scoring in a specific range of
values when SII was in the range 0.15 to 0.2. This shows that although
many of the subjects had difficulty understanding; about 44% of them
scored more than 90% on the tests.
0
10
20
30
40
0 10 20 30 40 50 60 70 80 90 100
Score
Frequency,
%
0.15SII0.2
Figure 6: Distribution of scores in the interval 0.15SII 0.2.
In the subjective work in reference 9, subjects were asked to rate the
acceptability of masked speech and to say whether it was distracting.
Five point scales were used and the mean results are shown in Figure 7
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0.0 0.1 0.2 0.3 0.4
SII
Privacy
Confidential
moderately
good
acceptable
a little
none
Distracting
extremely
very
moderately
a little
not at all
Figure 7: Subjective ratings of privacy and distraction for several SIIvalues.
Figure 7 suggests that although, according to Figure 5, many people will
be able to understand speech quite well when the SII is in the range 0.1
to 0.2, they perceive this as acceptable privacy and find it between a
little and moderately distracting. Thus a design goal of SII = 0.15
seems acceptable for open offices. With correct use of masking sound,
screens, highly absorbing furnishings and reserved behavior from the
occupants, this value of SII can be achieved.
These considerations deal only with acoustics. An SII of 0.15 does notnecessarily indicate occupant satisfaction with all aspects of an open
office. Other psychological factors play a role in determining overall
satisfaction.
Directivity of Human Speakers
Human talkers do not radiate speech uniformly in all directions. More
sound energy is radiated forward than to the rear. Thus it is easier to
understand speech when the speaker faces the listener than when thespeaker is turned away. To illustrate, Figure 8 shows one measurement
of directivity10
for male talkers for the 250 and 1000 Hz octave bands.
Levels directly behind the speaker are about 10 dB below those
measured directly in front. Levels to the side are about 5 dB below the
frontal levels. These changes in level correspond roughly to changes in
SII of 0.3 and 0.15 respectively.
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This factor can be utilized when planning office layouts. If the normal
working positions have occupants facing away from each other, then
speech intrusion will be decreased but only so long as the talker does
not turn from the working position. During telephone conversations, it is
likely that the talker will remain turned away from adjacent employees.
However, if a face-to-face conversation is taking place at one
workstation, the talkers might well turn toward other nearby workers.
30
40
50
60
0
30
60
90
120
150
180
210
240
270
300
330 250 Hz
1 kHz
Figure 8: Directivity measured for male talkers for the 250 and 1000 Hzoctave bands.
Transmission paths with no barriers
In the absence of any barriers to sound propagation, sound travels
directly from speakers to listeners. The attenuation that occurs is that
due to the spreading of the energy over an expanding spherical surface
as it propagates away from the source. This leads to an attenuation of
6 dB for each doubling of the distance from the source. In addition to this
direct path, sound may reflect from the ceiling and floor several times
(See Figure 9). With materials normally found in offices, each reflection
results in a loss of energy. In offices there are also vertical surfaces with
varying degrees of reflectivity that decrease the sound attenuation
between speaker and listener. These additional paths involving
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reflections mean that sound usually attenuates at about 4 to 5 dB for
each doubling of the distance from the source.
A computer monitor is shown at the receiving position in Figure 9.
Although no sound paths are shown involving this monitor, experiments11
show that large monitors can reflect significant amounts of sound. The
problem is alleviated to some extent if the sound is blocked by the body
of the person in front of the monitor, or if the monitor is tilted so it reflects
sound up to the ceiling. There is no practical solution for this situation.
Figure 9: Sound propagation in the absence of barriers
Transmission paths with barrier
When there is a barrier between occupants, sound propagation becomes
more complicated. When sound encounters the edge of a barrier it bends
around the barrier (diffraction) to reach listener locations on the other
side of the barrier (Figure 10). The attenuation during this diffraction
process depends on the angle through which the sound has to bend: the
greater the angle, the greater the attenuation. Thus higher and wider
barriers give more attenuation. As seen in Figure 10, the barrier and the
desk interfere with reflections from the floor and such reflections can
probably be ignored. More complicated paths involving several
reflections may be possible. While this figure shows a vertical section, it
should not be forgotten that diffraction occurs at vertical edges of barriers
too. When examining open office designs, both plans and vertical
sections should be considered. Figure 11 illustrates diffraction and
reflections in the horizontal plane. In a cubicle, the barriers forming the
workstation will block some of the diffracted paths around the vertical
edges of the barrier.
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Figure 10: Sound propagation in the presence of barriers
Figure 11: Sound diffraction around barriers and reflection from walls andfurniture in the horizontal plane.
Barrier Diffraction
Diffraction around a barrier has been studied by many authors. Perhaps
the best-known experimental study is that by Maekawa12
. Yamamoto and
Takagi13
present some simple empirical expressions that fit Maekawas
data well. The important factor that determines the degree of speechprivacy between two office occupants separated by a barrier is the height
of the barrier. Sound energy can diffract around the vertical edges of the
barrier but this is usually much less than that diffracting over the top or
blocked so it is completely negligible. The higher the barrier, the greater
the attenuation it provides. Figure 12 shows the decrease in SII due to
increasing barrier height above 1.2 m. Substantial improvements are
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possible but only if the ceiling is perfectly absorbing. Work within this
project14
showed that absorbing material on the upper edge of the barrier
increases the attenuation.
0
0.1
0.2
0.3
0.4
0.5
1.2 1.3 1.4 1.5 1.6 1.7 1.8
Barrier Height, m
DecreaseinSII
Talker-Listener separation = 2.4 m
Figure 12: Improvement (decrease) in SII for increasing barrier height.Improvements are shown relative to the 1.2 m height barrier. The ceilingis assumed to be perfectly absorbing.
Reflections f om horizontal and vertical surfacesr
To estimate how much sound is reflected from a surface, one needs to
know the reflection coefficient at each frequency. The reflection
coefficient is the ratio of the sound power reflected from a surface to that
incident on the surface. There are no standard tests for measuring
reflection coefficients of materials, instead, absorption coefficients are
measured. The absorption coefficient is defined as the ratio of the sound
power absorbed by a surface to that incident on the surface. The
relationship between the two coefficients is simply
=1
where and are the reflection and absorption coefficients respectively.
The reflected sound is reduced in amplitude by 10 log .
This relationship has important consequences for open offices. Figure 13
shows the attenuation in decibels of reflected sounds for a range of
absorption coefficients. When the absorption coefficient changes from
0.8 to 0.9, the attenuation changes by only 3 dB, whereas the change
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from 0.9 to 0.99 results in a change in attenuation of 10 dB. The curve
turns upward markedly as the absorption coefficient increases. High
absorption coefficients are needed to obtain high attenuation of reflected
sound.
0
5
10
15
20
25
0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
Absorption Coefficient
Attenuationofreflection,
dB
Figure 13: Attenuation of reflected sound for a range of absorptioncoefficient.
Sound absorption coefficients are measured in reverberation rooms
according to ASTM C4231. The coefficients are increased because of
diffraction effects and are frequently greater than unity for highly
absorbing materials. This is an accepted artifact of the test method but
makes direct use of such coefficients inappropriate in open office
calculations.
Ceiling panels are placed in an E400 mount (described in ASTM E7952)
for testing according to C423. An empirical relationship between C423
absorption coefficients and reflection coefficients that can be used on
open office calculations has been found15
. ASTM E111116
is a test
method that specifically evaluates ceiling panels for use in open offices.
This method gives a rating called the articulation class
17
(AC). Althoughthere is a lack of test data for many ceiling products, research within this
project18
has led to the development of two empirical relationships
between articulation class and sound absorption average of ceiling
panels tested.
For a 1.5 m high test barrier, AC and SAA are related by
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AC = 102 * SAA + 91.4.
For a 1.8 m high test barrier, the relationship is
AC = 118 * SAA + 93.
Thus, if only AC data area available, the corresponding SAA value can
be reliably estimated.
Combined effects of ceiling reflection and barrier a tenuationt
The ceiling and the floor in an office present the largest surfaces that
might reflect sound. Typical absorption coefficients for carpet in an office
are low, so sounds will reflect with little loss of energy. In mitigation,
however, there are usually many obstacles (screens, desks, filing
cabinets, chairs) that block and interfere with reflections from the floor.
Thus in some cases, floor reflections could be very important but not in
others. Reflections from the ceiling, however, are seldom interfered with
by office furnishings.
The combined effect of sound reflected from a ceiling and sound
diffracted over a barrier has been calculated for a single frequency in
Figure 14 for several barrier heights and a range of average ceiling
absorption coefficients*. The divergence of the lines in the figure shows
that when the ceiling is a good sound absorber, increasing the barrier
height is much more effective than when the ceiling is a poor sound
absorber. If the barrier height is low, then the benefits due to a highly
absorbing ceiling are small.
If the design goal is to obtain minimal speech intrusion, then both
barrier and ceiling absorption must be high.
If the design mandates low screens, then a highly absorptive
ceiling is less important and attenuation of speech sounds will be
low.
*The absorption coefficients used in this calculation are theoretical
values that do not directly relate to values obtained from reverberationroom measurements.
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10
15
20
25
30
0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05
Ceiling absorption coefficient
Attenuation,
dB
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
Screen Height, m
Figure 14: Attenuation between workstations for combined ceilingreflection and diffracted sound. Listener-talker separation and ceilingheight are both 3 m. Values of absorption coefficient around 0.7 aretypical for mineral fibre ceiling boards. Values greater than 0.85 aretypical for glass fibre ceiling boards.
Background Noise Levels And Masking Sound
Speech intelligibility is determined by the ratio of the level of the intruding
speech to the level of the background noise. Because of the extensive
use of sound-absorbing materials, open offices can be rather quiet when
unoccupied and even when occupied. Voices can thus intrude in the
quiet background and be very distracting. Electronic masking sound is
often used to provide steady, raised background noise levels to decrease
annoyance and speech intelligibility. The masking sound itself can also
be a source of annoyance if it is too loud or has an objectionable
character. Masking sounds usually have a spectrum that decreases
about 5 dB per octave with an overall level around 45 dBA. The shape of
the spectrum is usually adjusted to give maximum masking of speech
without making the sound objectionable; the sound is perceived as
neutral in character, with no pronounced rumble, hiss, roar or tones. If
the level of the masking noise is greater than about 48 dBA, people talk
more loudly to be heard above the noise and some of the benefit of the
masking is lost. It is not possible to accurately predict the noise levels in
an office due to occupant activities and in any case this noise will vary
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greatly as activities change. So, occupant noise cannot be relied on to
provide masking. HVAC systems can provide noise but adjusting the
spectrum with reasonable precision is not feasible in practice and the
level will change as the system reacts to changes in the office
environment.
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REFERENCES
1ASTM C423. Standard Test method for sound absorption and sound
absorption coefficients by the reverberation room method.
2 ASTM E795. Standard Practices for mounting test specimens during
sound absorption tests.
3ASTM E90. Standard Test Method for Laboratory Measurement of
Airborne Sound Transmission Loss of Building Partitions.
4CBD-164.Acoustical Effects of Screens in Landscaped Offices, A.C.C.
Warnock. http://irc.nrc-cnrc.gc.ca/cbd/cbd164e.html
5ANSI S3.5.American National Standard Methods for the Calculation of
the Speech Intelligibility Index.
6ASTM E1130. Standard Test method for objective measurement of
speech privacy in open offices using articulation index.
7Voice and Background Noise Levels Measured in Open Offices, W.T.
Chu and A.C.C. Warnock. Internal Report IR-837. Institute for Research
in Construction. NRCC. August 2000. http://irc.nrc-cnrc.gc.ca/fulltext/irc-
ir-837/
8Measurements of Sound Propagation in Open Offices, A.C.C. Warnock
and W.T. Chu. Internal Report IR-836. Institute for Research in
Construction. NRCC. August 2000. http://irc.nrc-cnrc.gc.ca/fulltext/irc-ir-
836/
9Describing Levels of Speech Privacy in Open Offices. J.S. Bradley and
B.N. Gover. Research Report RR-138 Institute for Research in
Construction. NRCC. September 2003. http://irc.nrc-
cnrc.gc.ca/fulltext/rr138/
10Detailed Directivity of Sound Fields around Human Talkers, W.T. Chu
and A.C.C. Warnock. Research Report RR-104, Institute for Research in
Construction. NRCC. September 2001. http://irc.nrc-
cnrc.gc.ca/fulltext/rr104/
RR 163 - Page22 of 23 -
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Appendix: Review of Open Office Acoustics
11Sound Propagation in a Simulated Team-style Open Office, W.T. Chu
and A.C.C. Warnock. Research Report RR-156, Institute for Research in
Construction. NRCC. February 2004. http://irc.nrc-
cnrc.gc.ca/fulltext/rr156/
12Maekawa, Z. Noise Reduction by screens. Applied Acoustics, Vol 1.
p157, 1968.
13Expressions of Maekawas Chart for Computation. K. Yamamoto and
K. Takagi. Appl. Acoustics, 37, p75, 1992.
14Measurements of screen insertion loss in an anechoic chamber,
A.C.C. Warnock and W.T. Chu. Research Report RR-157. Institute for
Research in Construction. NRCC. February 2004. http://irc.nrc-cnrc.gc.ca/fulltext/rr157/
15Prediction of the speech intelligibility index behind a single screen in
an open-plan office.Applied Acoustics,63, (8), August 2002 and
Acoustic Behavior of a Single Screen Barrier in an Open-plan Office. C.
Wang and J.S. Bradley. Report B3205.1, January 2001.
16ASTM E1111 Standard Test method for measuring interzone
attenuation of ceiling systems
17ASTM E1110 Standard Classification for determination of articulation
class.
18Comparison of two test methods for evaluating sound absorption of
ceiling panels. A.C.C. Warnock. RR-158. Institute for Research in
Construction. NRCC. February 2004. http://irc.nrc-
cnrc.gc.ca/fulltext/rr158/
RR 163 P 23 f 23