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/ircpubs


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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

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-


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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-


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-


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Documents

Acoustical Design Guide for Open Offices