PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

ISO 3382-3: NECESSARY BUT NOT SUFFICIENTA NEW APPROACH TO ACOUSTIC DESIGN FOR ACTIVITY-BASEDWORKING OFFICESJack HARVIE-CLARK1; Felix LARRIEU1; Cecilie OPSANGER2
1

Apex Acoustics Ltd, Gateshead, UK
2

Multiconsult, Oslo, Norway

ABSTRACT
Since the room acoustic parameters in ISO 3382-3 were published, there have been various
international attempts to classify offices achieving different values. However, recent summaries of
acoustic satisfaction demonstrate little correlation with the room acoustic parameters that may drive
the design. While the parameters of ISO 3382-3 are essential to understand how the room responds tosound, they are of limited use in helping designers to understand how people respond to their officeenvironment.
A new approach – proposed for inclusion within ISO/WD 22955 - assesses acoustic conditions
within activity-based working (ABW) offices, or between different use types generally. The Livelinessterm can be used to characterise suitable acoustic environments for different types of activities;
background sound levels can also be attributed, by measurement or design. A matrix of signal -to-noise
ratios can be derived for a particular office, to account for source level vibrancy and receiversensitivity. This enables a design framework for the in-situ attenuation of speech between workstations,
D n, A, s . From the in-situ attenuation requirement, the ABW layout design can be developed accordingly.
This method can identify potential for conflicts between different types of use or activity where there
is insufficient attenuation between them, to inform the workspace designer where enhanced in -situ
attenuation can improve the acoustic conditions for occupants.
Keywords: Acoustics, Open plan office, ABW, activity-based working office, flex office

1. INTRODUCTION
The acoustic requirements for people within a workspace are strongly dependent on the workspaceculture, and cannot be realistically determined without understanding how people operate within theworkspace. A model originally proposed by Hongisto (1) has been followed with many studies
identifying the extent of distraction by intelligible speech – the irrelevant speech effect (ISE).
Laboratory experiments by many researchers including Chevret (2), Kostallari (3), Ellermeier (4), andSchlittmeier (5) demonstrate the decrease in performance that can be objectively measured whenpeople perform tasks when subject to noise containing intelligible speech. The concept of a distanceat which the intelligibility of speech at normal levels crosses a threshold for in telligibility (typically
STI = 0.5) has informed acoustic parameters for office design. ISO 3382-3 describes the room acoustic
parameters that can be measured in an open plan office; these metrics are increasingly being used todescribe Classes of performance for the office.
Haapakangas (6) et al conclude that distraction distance predicts perceived disturbance by noise inopen-plan ofﬁces. The data shown in Figure 1 from reference (6) with a solid circle are conventional
offices, while triangle symbols denote activity-based working offices. The data presented by would
suggest that there are many other factors that may be more significant in determining noise annoyanceor acoustic satisfaction than distraction distance alone. The conclusion on distraction distance was1

jhc@apexacoustics.co.uk

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made by looking at 21 workspaces with a mix of different study types as changing from private office
to open plan office, relocation from open plan office to another open plan office, evaluation due tocomplaints and more. Interview studies from three major Norwegian companies (7), employees
randomly selected from different business areas and different job descriptions (n=200), showed that
76 % preferred the office type (cell office, open plan office or flex office) they already had.
Haapakangas denotes activity-based offices differently, and the data indicates that noise annoyancein these offices is generally much lower than the average. Haapakangas also demonstrates that there
is also little or no correlation with noise annoyance with other parameters such as speech level at 4 m,
Lp,A,S,4m, spatial decay of speech, D 2,S, and background sound level, L p,B.
Achieving lower (better) values for distraction distance has significant design implicatio ns for theheight of screens between desks, the sound absorption, and the background sound level, as illustratedby Larrieu (8) et al. The design implications noted by Larrieu often do not match either the design
aspirations of clients or workplace designers. Does this mean that “good acoustic design” according
to the emerging national guidelines for the parameters in ISO 3382 -3 is simply inevitably in conflictwith the current workplace design aesthetics?
The parameters from ISO 3382-3 can be useful to demonstrate how acoustic conditions may be
improved by increasing sound attenuation between desks in traditional open plan offices; however,these parameters are determined in an unoccupied office. These parameters cannot tell us anything
about the occupants’ activities, the type of work, individual control over place of work, office culture,occupation density, or other factors that may be significant when considering acoustic satisfaction.
Acoustic design can begin with the occupants’ acoustic needs, rather than the room response to sound.
This represents a paradigm shift. We start by exploring the typical practice of workplace designers,
and then look at the development of a new ISO Standard for acoustics in open plan offices. The
opportunities to align these activities offers benefits for designers and the future occupants of theworkspaces that may be developed.

2. THE WORKPLACE DESIGN PROCESSThe strategy for the workplace may consider the approach to working , and may be developed by aprofessional who specialises in that type of work (e.g. an architect or architectural technologist), or
may be inferred or explicitly developed by a workplace designer, facilities manager or client. Theremay be a wide range of formality for the workplace strategy - it may be simply inferred from the brief
for the workspace, or it may be systematically derived from an engagement process between theworkplace strategist and client.
Workplace designers will often consider those activities that may generate higher sound levels andlocate them in such a way as to minimise the impact on other areas: designers implicitly consider
acoustic requirements. A taxonomy of open plan offices is described by Neil Usher (9), revealing thesignificant variation of possibilities for workspace concept and design. Perha ps, from an acoustic
perspective, the most significant difference is the extent to which people are able to exercise choiceover where they work at any particular time. Control over one’s environment is a strong modifier ofannoyance. While the irrelevant speech effect (ISE) can objectively impair cognitive performance, it
may be that annoyance is a more significant impact. Annoyance may not be simply proportional to theISE, because of the modifying effect of the sense of personal control.

3. OPPORTUNITY IN THE NEW ISO/WD 22955
The new ISO/WD 22955 will have criteria for different types of space, where these predominate
across the floor plate. The new standard is inspired by the French Standard NF -S31-199 (10), andtakes the same approach, starting with the acoustic requirements of the workers who are the users.
There are three stages of description of the acoustic environment that workers need to undertake
different types of work. The open plan office is conceived in a traditional manner, comprising
workstations at desks. The acoustic targets and requirements are described for:x The acoustic conditions at the workstation - described with a target in-situ level for ambient
sound from all sources, including activities within the office. The range here is a tar get
rather than a requirement of the Standard.
x The acoustic relationship to the adjacent workstations - described as an in-situ attenuationof speech, D n,A,S from one workstation to another.

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x

The acoustic characteristics of the floorplate, described in terms of the spatial decay ofspeech, D 2,S , and the speech level at 4 metres, Lp,A,S,4m, as defined in ISO 3382-3.
The different types of activity currently proposed, for acoustic classification purposes, are:x Breakout
x Phonex Collaborativex Non-collaborative
An additional section considers acoustic requirements between different activity types. This has
led to the development of a new method proposed below.

4. A NEW APPROACH
A new approach is proposed to assess acoustic conditions between different types of functional
areas within an open plan office. This may be particularly suitable for assessing activity -based
working (ABW) offices, or for the partial remodeling of existing floor plates to introduce more varied
workplace settings within an otherwise traditional layout. For example, the introduction ofcollaborative areas, or seating for focused activity - either individual work or phone calls, adjacent totraditional desking, can all benefit from acoustic consideration. Previously there have been nopractical tools available to the acoustician to assess these adjacencies.
The new approach is summarised as:
1. Use Liveliness to characterise the acoustic environment that would be suitable for thedifferent activities - this may be measured if the environment already exists, or assessed.
2. Consider the source voice level – i.e. “normal”, higher or lower depending on the context
for the source.
3. Determine appropriate background noise levels - this can be measured if the environment
exists, otherwise it may be designed with a masking sound system, or assessed based on
the size of the open plan office and the activities taking place.
4. Adopt a suitable unwanted-speech signal-to-noise ratio (SNR) for the sensitive receptor
from the source in question. The difference in Liveliness ratings for the two spaces gives
the SNR requirement considered appropriate, but an alternative may be adopted.
5. Determine the requirement for the in-situ attenuation of speech between workplace settingsin terms of D n, A, s ., which informs the layout design.
This new approach can be used to identify potential for acoustic conflicts between different types
of use or activity - where the calculated D n, A, s falls short of the value determined for good acoustic
conditions. This method can assist the workplace designer to identify where enhanced in -situ
attenuation can improve the acoustic conditions for workers, or where less acoustic protection may beadequate. However, the context should always be considered and the values adopted modified to suitthe circumstances, rather than applying the method consistently in different offices. For example, theduration for which the particular source of noise may be pre sent can be considered: an impact which
may not be desirable if the source is continuous (e.g. a worker continually on the telephone) may be
acceptable if it is only occasional (e.g. occasional phone calls).
4.1 Use types to consider adjacencies
Although ISO/WD 22955 contains general use types that may prevail over an area or floor plate, a
few additional use types are necessary to consider adjacencies between specific functional uses. The
proposed use types are shown in Table 1. These are intended to cover the main acoustic categories ofuse type, as examples to compare with project-specific requirements. Note that the category “breakout”
can have a plethora of meanings as well as a wide variety of uses at different times.
4.2 Liveliness
The term “Liveliness” is used to characterise the in-use open plan office acoustic environment, as
described by Vellenga (11). The semantic description is correlated with an objective measure, basedon 5 minute sample periods. The objective measure is a combination o f the A-weighted sound level,
LAeq,5min, and the fluctuation strength. The fluctuation strength is measured as the difference between
the statistical level of A-weighted sound exceeded for 5 % of the time, L A5, 5 min, and the LAeq,5min.
Liveliness is measured by recording the sound in five minute samples at a workstation (i.e. a normal
working position) that is unoccupied during the measurements. Liveliness is likely to vary both
spatially across an office, and also temporally at any one position, as bot h local and more distant2409

activities vary. The temporal variation at different places can exhibit different patterns. In an ABW
office the acoustic environment should vary for the different areas to be suitable for different activities.
Liveliness is simple to measure, and understanding its meaning is straight forward, as the objective
rating is correlated with semantic descriptions.
4.3 Determining Liveliness ratings and background sound level
When remodeling an existing office, it is prudent to measure the ambient sound around thelocations that will remain with their current use. The temporal distribution of Liveliness andbackground sound levels can be evaluated from the survey data. When designing a new officeenvironment, assumptions must be made to determine suitable values for Liveliness and backgroundsound level.
The principal source of background sound in larger open plan offices is usually the distant activityof people; in smaller open plan offices, background sound levels can be low. Paradoxical ly, lowbackground sound levels can lead to complaints from occupants that “it is too noisy”; this may beinterpreted as “speech is too distracting” in the acoustician’s lexicon. Thus as well as the type ofactivities being undertaken, the size of the office is a significant factor when assessing potential
background sound levels. Background sound levels can vary spatially across an open plan office,particularly if there is significant screening between different areas or zones. Depending on the typeof office and type of work being undertaken, the example values shown in Table 1 may be suitable toadopt.
Table 1 – Use types, example values of Liveliness and assumed background sound that may be suitable
Use type

Breakout

Meetings

Phone(call centre)
Collaborative
Noncollaborative
Focusedphone

LivelinessBackgroundratingLb, dB(A)-“Breakout” can refer to a wide range of different typesof activity. In this example, Breakout is assumed to be
an amenity space where people seek refreshment,
restoration, and talk about non-work-related topics.

7

48

Meetings are collaborative in nature, hence a relatively
Lively rating is assumed. Meeting spaces for two people
are likely to have a different impact from larger meeting
spaces within an open plan area

6

48

The background sound level here is taken from the lower
end of the target range for ambient sound fromNF S31-199.

6

45

The background sound level is taken from the lower endof the target range for ambient sound in NF S31-199.

542

Preferably calmer than collaborative spaces. The
background sound level is taken from the middle of thetarget range for ambient sound in NF S31-199.

6/4

42

A protected area for making phone calls, rated with ahigher Liveliness as a source compared to rating as a
receptor.

3

40

A specially-protected area, enabling lower backgroundsound levels. May be in a shared cellular room or area
for acoustic protection, or an individual booth.

8

Focusedindividual
work

Notes

4.4 Signal to noise ratio to describe intrusion and impact of unwanted speech
ISO 3382-3 relies on STI to assess speech intelligibility. The new method uses signal to noise ratio(SNR) in the first instance, so that the acoustic designer can gain more insight into the different

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acoustic components that combine to give the STI - ie source level, attenuation in transmission,
reverberation, and masking sound level. SNR has been correlated with other measures of intelligibility
by Lazarus (12), an extract of which is reproduced in Table 2.
Table 2 – Speech Intelligibility Evaluation, from Lazarus, 1987
Parameter

Value for comparison

STI

0.1

0.2

0.3

0.4

0.5

0.6

SNR, dB

-12

-9

-6

-3

0

3

The new approach is based on the impact of one workstation on another in terms of signal to noise
ratio (SNR), where the “signal” is the unwanted speech. The “noise” level is based on the backgroundsound level that includes sound from the more distant activity within the office. The acoustic
parameter used to describe this noise level is the statistical parameter for the A -weighted sound levelexceeded for more than 90% of the time, L A90, T. This parameter reflects more a measure of the “quiet”
rather than the “noise”, as it is only for 10% of the time that the ambient sound is below this level.
Hence it may be a reliable level when considering the effect of masking unwanted speech.
This is a deliberately simplistic approach to quantifying the impact of the ISE. There are many
advantages of a simplistic approach, not least the ease of understanding and accessibility to a wide
range of people. The simplification means that many of the subtleties around factors governing theimpact of the ISE are lost. For example, the reduced intelligibility of speech due to the reverberant
characteristics of the room is not included in a simple SNR assessment. This may be included in themanner proposed by Wenmaekers et al (13), by reducing the effective SNR by 3 dB to account for thereverberant effect of the room on speech intelligibility. The general simplification of using SNR rather
than STI is considered an acceptable compromise for most situations; of course, the assessment canrevert to using STI if transmission has strong frequency characteristics, for example.
4.5 Annoyance depends on control, expectations and sensitivity
The expectation for and tolerance to intrusive or distracting sounds is highly dependent on the typeof activity undertaken, and the level of control that the user has over the source of noise and which
workplace location they occupy. For example, people engaged in individual focused work are likely
to be more sensitive to intrusive sounds compared to people collaborating on a task. However, if they
can choose where they go within the office to perform their work, and the source noise is in characterwith the environment they have chosen, they may be less annoyed than people at assigned desks
subject to the same intrusive sound level.
A requirement for an increase in acoustic protection from one location to another can becharacterised in terms of a preference for a decreased SNR. The increase in acoustic protection thatis appropriate between dissimilar uses or tasks can be related to the difference in the expected
Liveliness rating between those uses, but this approach should not be applied without considerationof the context.
The activity described as “focused phone” is used to describe a place for making phone calls that
requires more than the normal level of attention. Such a place would preferably have lower ambient
noise levels than a call centre, and a lower SNR for speech from other workers compared with a callcentre. This is an example of a type of activity that does not supp ort many workers engaging in thesame activity to be grouped together within an open plan office without acoustic protection between
workstations. The Liveliness rating of this activity as a source of noise differs from its rating fortolerance to noise.
4.6 Identifying suitable SNRs
A matrix of SNRs to describe the enhanced protection from one particular activity to another would
be of great use in the design process. However, there are so many contextual factors that any such
example matrix must be approached with a large degree of caution. The initial concept to grade theacoustic separation between dissimilar spaces is to use the difference in Liveliness rating between
source of noise and receptor as a multiplier for the SNR requirement in decibels. A mult iplier of 3
is used in the example values to determine a predicted SNR requirement, as shown in Equation 1.
This predicted value is then modified by considering each adjacency pair in turn to identify a SNR

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that may be suitable; the modified values are shown in Table 3. In practice the particular context
should be considered rather than simply adopting the values in Table 3.
ܲ‫ ݐ݊݁݉݁ݎ݅ݑݍ݁ݎܴܰܵ݀݁ݐܿ݅݀݁ݎ‬ൌ ሺܵ‫ ݃݊݅ݐܽݎݏݏ݈݁݊݅݁ݒ݅ܮ݁ܿݎݑ݋‬െ ‫݃݊݅ݐܽݎݏݏ݈݁݊݅݁ݒ݅ܮݎ݋ݐ݌݁ܿ݁ݎ‬ሻ ‫ܤ݀͵ כ‬ሺͳሻ

4.7 From SNR to in-situ attenuation
Background sound levels may be assumed for each type of space, as illustrated in Table 1. A
suitable source noise level can also be assigned to the particular source area. This may be a standard
speech source level of 57 dB(A) @ 1m as described in ISO 3382 -3; it may also be a raised voice (63dB(A) @ 1m), a low voice (51 dB(A) @ 1m), or another level. The in -situ level difference, D n,A,s
can be determined between different types of spaces, based on the SNR requirement, speech source
level, background noise level. The calculation for D n,A,s is shown in Equation 2, with potential values
illustrated in Table 4 based on a standard speech source level.
‫ܦ‬௡ǡ஺ǡ௦ ൌ ‫ܮ‬௦ǡ஺ െ ܴܵܰ െ ‫ܮ‬௕ ሺʹሻWhere, from Table 3:
SNR is the potential signal to noise ratio required
Lb is the background sound level, described for example in Table 1.
Ls,A is the speech source level at 1 m in the freefield, based on the speech sound power.
Table 3 – Potential SNR ratings between different activities, and associated background sound levels
Meetings

Phone

Collab

Non –

Focus

Focused

(open

(call

orativecollaboed

individual

plan)

centre)rative

phone

work

Liveliness rating

7

6

6

5

4

3

Assumed Lb

48

48

45

42

42

40

Source / receiver space

Livelinesstype

ratingBreakout

8

-6

-6

-6

-9

-12

-15

Meeting (open plan)

7

-6

-3

-3

-6

-9

-12

Phone (contact centre)

6

0

0

-3

-6

-9

Collaborative

6

0

-3

-6

-9

Non-collaborative

5

0

-3

-6

Focused phone

4

-6

-9

Focused indiv’ work

30

Table 4 – Potential Dn,A,s requirements between different types of spaces, based on a standard speech level
Meetings

Phone

Collaborat

Non –Focused

Focused

(open

(call

ive

collaborati

phone

individual

plan)

centre)Breakout

15

15

18

24

27

32

Meeting (open plan)

15

12

15

21

24

29

12

18

21

29

18

21

26

Non-collaborative

18

23

Focused phone21

26

Source / receiverspace type

Phone (contact centre)
Collaborative

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ve

work

5. Design implications
The primary requirement for achieving acoustic satisfaction is to enable the set of project -specific
SNRs within an overall ambient noise environment that is also appropriate and conducive to the typeof work undertaken. As the SNR is achieved with the combination of attenuation between source
and receiver, and the background sound level, an appropriate balance is required between these twootherwise separate aspects of the acoustic design to facilitate effective functioning of the workspace.
5.1 Managing the background sound level
A raised background noise environment, if sufficiently loud, can mask any particular intrusive
sound. Sound masking systems may provide some assistance by avoiding the problem of offices
being so quiet that speech from greater distances becomes distracting. Workers often report this typeof office to be “too noisy”, when the acoustician may consider it to be “too quiet”. The use ofmasking sound systems is controversial; the level and type of soun ds that may be acceptable to mostpeople are often too quiet to provide much effective masking, according to Martin (14). Martin also
notes that annoyance at the level of masking sound may not preclude its benefits in reducing
distraction and improving task performance. Background sound levels that are found to be acceptablemay depend strongly on the size of the office, as well as the type of work being undertaken. In larger
offices there is likely to be more sound from greater distances, whereas in smalle r offices there is agreater risk of lower background sound levels. The German VDI 2569: 2016 makes a distinction
between “small” and “large” multi-person offices where the maximum distance between workstations
is 8 m. When considering background sound levels, a larger size may be required in order to rely on
the background sound from more distant activities.
5.2 Managing attenuation between workstations
The in-situ attenuation of speech, D n,A,s is a new parameter. It is important to gain some feeling forthe implications of the values described in Table 4 – to understand the design implications. As
currently described in the French Standard NF S31-199, the parameter D n,A,s is measured between thepositions of a seated talker and seated listener, unless otherwise noted, with source and microphone
positions 1.2 m above floor level. NF S31-199 does not describe A-weighted attenuation based on
the speech source spectrum – this additional detail is added in ISO/WD 22955. Figure 1 illustrates anextract from a CATT acoustic model, with the values of D n,A,S indicated between selected positions.
These calculated values are interpreted as a little higher than values that may be measured in practice.
Figure 1: Calculated values for Dn,A,S between particular positions from a CATT Acoustic model2413

6. CONCLUSIONSThe theory that reducing the intelligibility of unwanted speech can improve acoustic satisfaction
is well established and demonstrated in laboratory studies. However, acoustic satisfacti on in real
workplaces is only loosely correlated with the distraction distance, r D , measured over the floor plate.
If acoustic designers are only motivated and equipped to propose features in the pursuit of achieving
lower values of r D , the inferred design requirements may be in conflict with other aesthetic aspirations
for the accommodation and internal environmental conditions; more importantly, the overall goal of
acoustic satisfaction and workplace efficacy may be missed entirely.
Control over one’s environment is likely to be a stronger indicator for workers’ acoustic
satisfaction than any technical acoustic features. As the nature of the workplace changes to become
more fluid and less based on assigned workstations, people’s tolerance to intrusive sounds may wellalso adapt.
The proposed method for ISO/WD 22955 extends the concept of the impact of unwanted speech
and intrusive sounds; these preferences can be used to determine in -situ attenuation requirements
between specific workstations. This can be most effectively achieved within an environment that has
appropriate treatment for sound absorption. The proposed method for ISO/WD 22955 supports, rather
than conflicts, the work of the workplace designer.

ACKNOWLEDGEMENTS
As well as the authors, many other people contributed to the ideas in this paper, in particular Patrick
Chevret (INRS) and Remy Wenmaekers (Level Acoustics). Thanks also to the ISO /WD 22955
committee for sharing their views.

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