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

Liveliness as a design parameter for open plan offices
Tom BOUWHUIS1; Theodoor HÖNGENS2
1,2

M+P Consulting engineers, the Netherlands

ABSTRACT
Human activity is crucial regarding the sound level in open plan offices. However, design and evaluation
standards such as ISO 3382-3, as well as most measurements in office environments, do not take into accounthow much noise is being produced or acceptable to receive in actual work situations. The Liveliness index classifying sound environments as 'Quiet', 'Tranquil', 'Lively' or 'Turbulent' - aims to fill this gap.
Different types of work come with different requirements for, or sensitivity to sound production. Using ahigh density sensor grid, the Liveliness method allows for accurate sound activity measurements specific toeach type of work present in a certain organisation. Combined with room acoustical parameters, these can beused as a design tool, indicating the desired privacy or nuisance distances specific to the types of work thatcharacterise an organisation. Such dedicated design helps avoiding discomfort and productivity loss. Since
the method uses descriptions rather than decibels to qualify the sound environment, communication withpeople unfamiliar with acoustics is also simplified. This paper suggests how to use Liveliness as a design
input, and summarises our recent experience applying it in different office environments.
Keywords: human activity, design tool, zoning

1. INTRODUCTION
Noise is considered one of the most significant causes of discomfort and productivity loss in open
plan offices. The perceived level of discomfort increases when the noise level in an office rises (1),but the sound pressure level (SPL) itself barely affects performance (2,3). When it comes to
productivity, the presence and loudness of intelligible irrelevant speech is more important. It causes
distraction, which results in loss of performance in a number of common office tasks, particularly
those involving word processing (4–6). The second most important source of distraction is the soundof ringing phones, followed by machine noise and the sounds of people walking by (7–9).
This means that human activity in the office is by far the most important reason for office
employees to experience discomfort and productivity loss. Designers and consultants involved in thedevelopment of such office environments therefore have a great responsibility to carefully consider
their required room acoustical quality and the spatial layout. ISO 3382-3:2012 proves to be a useful
guideline in this context, but not one without limitations. Excluding human activity from themeasurements benefits their accuracy, but as a consequence the results are not entirely representative
to qualify the room acoustical quality of an open plan office in use, which is the very reason todetermine the quantities described in ISO 3382-3 in the first place.
Activity Based Working, which has become a standard way to design open offices, incorporates avariety of possible activities. As demonstrated by Vellenga-Persoon et. al., sound levels also differ
significantly between office types (10). Every organisation and type of work has its own requirementswith regard to silence, liveliness and privacy. To adequately design an open office with acousticalproperties that fit the organisation that uses it, additional information is required that can qualify theway in which that organisation would use its office.

1
2

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tombouwhuis@mp.nl
theodoorhongens@mp.nl

2. Assessing room acoustical quality in open offices
2.1 ISO 3382-3
To quantify the room acoustical quality of an office room or area, ISO 3382-3:2012 describes anumber of measurements with which a set of single number quantities can be determined. These
quantities, intended for describing the degree of sound propagation and predicted level of distraction,
are most importantly:
 spatial decay rate of speech SPL (D2,S ); SPL of speech at 4 meters, (Lp,A,S,4m);
 background noise level, (Lp,A,B);
 speech transmission index, (STI);
 distraction distance (rD ); privacy distance (r P).
A large D 2,S means that the sound level will drop quickly when moving away from the source.
L p,A,S,4m is derived from D2,S assuming a normalised speech SPL. Both quantities can be used todetermine the expected loudness of a sound source (normally a speaking person) at a certain distance.
Looking at speech transmission in a more detailed way, the Speech Transmission Index (STI) in
comparison does not predict how loud a voice will be at a certain distance, but how much of it is beingtransmitted in an intelligible way. This can be used to determine how many words, sentences or soundsof a speaking person can be understood at the receiving end. The distance from a speaker at which
STI = 0.50 is described as rD . At this distance, roughly 90 % of sentences can be understood (4). Only
when STI decreased to 0.2, almost no sentences can be understood anymore. This is considered r P.
Since the intelligibility of irrelevant speech is one of the main sources of distraction andproductivity loss, STI is an important quantity to predict the room acoustical quality. ISO 3382-3
considers any STI above 0.50 to impose a risk of distraction. This value corresponds with values
reported by Hongisto (4), who predicts a performance loss up to 7 % in situations with an equal or
greater STI. For difficult tasks, the performance loss may even increase up to 11.5 % (6). Using the
STI, also the privacy distance and distraction distance can be calculated.
The abovementioned quantities, as well as reverberation time, are commonly used to predict theroom acoustical quality of a space, although they are not necessarily representative for an office inuse. In fact, the standard specifically prescribes that the measurements have to be carried out whenpeople are absent. Acoustic conditions with people talking are explicitly not part of its scope. All of
the abovementioned quantities do however, to a certain extent, depend on the way in which the room
is being used. Most office employee working in an open office will only use their work environment
while other people are present. This is especially true for offices that have been designed toaccommodate Activity Based Working (ABW). ABW involves a variety of activities located on one
office floor, sometimes within the same space, each creating and demanding its own acousticalenvironment. A critical part of information about the use of the office is therefore missing in theassessment, when relying solely on ISO 3382-3.
The background noise level for example, is defined as the SPL when no people are present, caused
by e.g. road traffic noise, sound masking and building services. As mentioned earlier, the noise level
influences the perceived comfort. It is uncertain whether constant noise remains a source of discomfort
over time, as several researchers report signs of habituation (7,11), while others claim that theseeffects cannot be found except in laboratory studies (5,9). Fluctuating sounds are considered to cause
distraction and therefore discomfort, as they require a short period of reorientation (3). The soundlevel in an office space and especially its variation is normally caused by people, meaning that themost important aspects of background noise can only be measured when the office is being used.
Measurement of the STI requires input about the real use as well, as it is based on, among otherquantities, a predefined speech SPL and the background noise level. Whether or not the predefined
speech SPL is applicable to an office, cannot be determined without carrying out measurements while
the office is being used. Also the background noise of traffic and ventilation systems may be irrelevant
compared to the background noise produced by (distant) speech. Consequently, STI will also not be
as reciprocal as measurements in an empty office may suggest. It is not hard to imagine that speechfrom someone engaged in a lively phone call will be better intelligible to someone doing quiet,
focussed work than the other way around. Accurate predictions of the STI while the office is being
used, can therefore not be made without collecting additional data that is specific to the office in2391

question. By extension, this applies to the distraction distance and privacy distance as well.
Also when using the speech to noise ratio (SNR) to predict distraction, both the actual speech SPL
and the actual noise level need to be known, in order to make an informed prediction about the present
quality. This issue is recognised by Harvie-Clark and Larrieu (12), who propose the use of a matrix
that describes a SNR specific to the type of sending and receiving function. Depending on a higher orlower expectation of noise production and sensitivity to noise, a higher or lower SNR is proposed.
2.2 LivelinessTo qualify the sound environment and summarise the average activity level and its fluctuation,
Vellenga et al. (13) coined the term Liveliness. It is based on a linear numerical scale called the MACH
Index (MI), ranging from 1 (very quiet) to 10 (very turbulent). Intended as an instrument to make asound environment understandable also to laymen who might find decibels vague and hard tounderstand, Liveliness categorises a sound environment as one of four possible options: Quiet (MI =1.0-2.0), Tranquil (MI = 2,5-5.0), Lively (MI = 5.5-8.0) and Turbulent (MI = 8.5-10.0).
Liveliness and MI are based on the equivalent sound level during five minutes LA,eq,5min as well as
the degree of sound fluctuation. The latter has been defined as the difference between the
aforementioned equivalent SPL, and its fifth percentile during the same period L A5,5min. Using theassessment matrix described in (13), both quantities are added up, leading to a MACH Index, whichcorresponds to a certain degree of Liveliness as described above. Through several questionnaires, thisscore has been verified to correspond with the average subjective perception of a sound environment.
Liveliness varies over time and between working stations. For a useful qualification of a soundenvironment, which is not affected by temporary exceptions (e.g. holidays, or more employees doinghome office on a certain day), Liveliness will have to be monitored during longer period of time,
which has to be at least several weeks. Growing opportunities that originate from rapid advances withregard to the Internet of Things make it possible to monitor sound levels on a large scale at relatively
low cost, using a network of sensors that are installed at a representative amount of work stations.
The Liveliness score can then be used as a means of communication with other people involved in
the design process, indicating to which extent the Liveliness of the area or room corresponds with theintended use. An architect that sees that a certain area qualifies as ‘Lively’ over 70 % of the time,
while it is supposed to accommodate silent and focused work, will immediately understand thatmeasures need to be taken to make the office space fit its purpose. Reporting a histogram of measured
sound levels is far less likely to have the same result. These sound levels will still remain available tothe acoustical consultant of course, to be used as detailed input in the consulting process, e.g. in
combination with D 2,S or STI.
2.3 Non-physical measures
Not every measure has an effect that can be quantified using measurements as described in
ISO 3382-3. When for example a call centre is being equipped with better headsets, this has no effecton the spatial decay rate, or reverberation time. The reduction of the sound level in that space, as wellas the need for this reduction, can only be quantified by measuring the actual human activity in thatroom.
Furthermore, psychological processes or behavioural guidelines may influence a soundenvironment in ways that are not reflected by the degree physical changes. Where the Lombard effectexplains how the SPL rises exponentially when people start to speak louder in a loud room, the reverseis also true. Adding sound absorption to a room results in a decreased SPL, due to which people lower
their voice and an even greater reduction is achieved. Measurements of reverberation time alone
cannot explain this, but measurements of the degree of Liveliness will clearly show the change. Finally,changes in behaviour (such as walking to a designated area when receiving a phone call) will show adifference in Liveliness, without displaying any change of room acoustical qualities measured
according to ISO 3382-3.
Examples like these illustrate why Liveliness as a result of human activity cannot be ignored when
designing and improving open office environments.

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3. In situ monitoring of Liveliness and SPL
3.1 Method
Since the development of MI and the corresponding Liveliness, M+P have implemented as aconsulting tool in several office buildings. The data gathered during these measurements and thesubsequent insights, are summarised in this chapter. Figure 1 shows a selection of the physicalenvironment at several of the measurement locations.

Figure 1 – impression of a number of office environments mentioned in this paper, clockwise from left top:bank, government, telecom, wholesale
This paper describes data from a total of 18 sensors, distributed over six different office buildings,
where they gathered data for a period that varied between several weeks and more than a year. All
measurements were carried out in the Netherlands, on office floors that were designed with ABW in
mind. Usually a mixture of activities took place within the same space. Some of the measurement
locations were in call centres, however most were situated on an open office floor. This paperemphasizes on the data obtained on regular open office floors (14 sensors, four buildings). For equal
comparison, only the data measured on weekdays between 09.00 – 17.00 hours has been considered.
3.2 Measurement data
The measurement data and the corresponding conclusions serve as illustration to the examples of
how to use Liveliness as a design tool, which is described in the following chapter.
3.2.1 Average Liveliness and MACH Index
The average MACH Index on all open office floors that were part of this research, has beensummarised in figure 2. The first bar of the box plot shows significantly lower Liveliness values thanthe other examples, which is due to unexpected lower occupancy of this office space. Althoughbecause of that, this cannot be qualified as a typical office space, it has been included to illustrate that
also the absence of human activity can be input for design.

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Figure 2 – Distribution of MACH Index for all measured open office environments (excluding call centres),displayed per sensor (x = mean value, • = outlier)
Other bars display a difference between the 1st and 3 rd quartile of the MACH Index of 2-3 points.
All sensors display a maximum between MI = 9 and MI = 10 (‘Turbulent’), and a minimum between
MI = 1 and MI = 2 (‘Quiet’). The 1st and 3 rd quartile values are all within the range of MI = 4(‘Tranquil’) and MI = 7 (‘Lively’). The median shows fairly wide range, varying from 4.5 to 7. Whenignoring ‘telecom-1’, the average MACH Index on these floors was MI = 6 with a standard deviationof 0.6. Table 1 shows the average MI and the corresponding standard deviation. In general, the datashows that an open office environment in the Netherlands requires at least brief monitoring of thesound environment to fit the desired purpose, due to the fairly large difference in MACH Indicesbetween office floors. Should for a certain reason in situ measurement not be possible, a MACH Indexof 6 (which only just corresponds to ‘Lively’) can be used as a starting point, since based on thesemeasurement data MI = 6.0 seems to fit the average office environment.
Table 1 – Average MACH Index and standard deviation per sensor located in an open office environment
sensoraverage MISDsensoraverage MI

SDtelecom-1

2,7

2,39

government-6

6,6

1,74

telecom-3

6,6

1,66

wholesale-1

4,6

1,78

government-1

6,4

2,37

wholesale-2

5,7

1,75

government-2

6,0

1,44

bank-1

6,8

2,07

government-3

6,0

1,31

bank-2

5,2

1,57

government-4

5,8

1,44

bank-3

5,9

1,75

government-5

6,7

1,68

bank-55,6

1,58

The Dutch guideline NPR 3438:2007 EN describes a target and maximum equivalent SPL thresholdfor several types of work, among which ‘using a computer in an office environment’. An equivalent
SPL that does not exceed 45 dB(A) is considered ideal for an office floor, while a SPL higher than
55 dB(A) should disqualify it to be used as such. Figure 3 shows how often the sound environment at
each sensor location qualifies as a certain Liveliness category, and how often the abovementioned
thresholds are being exceeded. The added value of including these thresholds can be seen whencomparing e.g. B3 and B5, which have an almost equal distribution of Liveliness categories, as well
as a very similar average SPL, but at B3 the target value is exceeded 39 % of the time, compared to
89 % for B5. Based on this, B3 should be suitable for focused work substantially more often than B5.
The maximum threshold is rarely exceeded at any of the measurement locations.

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Figure 3 – Percentage of time [%] during which the sound environment at each measurement location
qualifies as a certain Liveliness category, as well as the percentage of time during which the SPL washigher than 45 dB(A) and 55 dB(A), respectively.

Figure 4 – Average percentage of time [%] during which the sound environment at each measurement
location (including call centres, excluding telecom-1) qualifies as a certain Liveliness category
As shown in Figure 4, call centres generally impose a risk of turbulent sound environments, butthere is a big difference between the measured locations, implying that a different design or use canhave a considerable influence on the amount of turbulence.

4. Using Liveliness as a design tool
To inspire and illustrate the potential of including Liveliness measurements into the design process
for new or renovated open offices, we share real examples from our consulting praxis in which
Liveliness proved to be useful.
4.1 Sound environment within a work cluster
When redesigning a call centre with a retail function, that was located in a room of 7 by 7 meters,
the measurements in the original situation revealed an almost continuously turbulent work
environment (70-80 % of the time). Considering the intention to almost double the number of2395

employees from 6 to 11, it was evident that as many measures as possible had to be taken to evenslightly improve the situation. A better absorbing ceiling was introduced, as well as highly absorbing
wall panels and desk screens. Since the reverberation time decreased from 0.4 seconds to 0.3 seconds,
one would expect an increase of the average SPL of 1-2 dB(A), taking into account that the numberof employees doubled. The measurement in the new situation showed a decrease of 1-2 dB(A) instead,proving the effectiveness of a new behavioural code. After the renovation the percentage of time thatthe sound environment qualified as ‘Turbulent’, increased to approximately 90 %. This can be
explained by the higher fluctuation of the sound level after increasing the number of employees.
4.2 Communication of measures based on the current sound environment
Before the redesign of a large investment bank, measurements were carried out at multiple officespaces, one of which accommodated the service desk. In the original design, most office areas wereseparated from each other by enclosed meeting rooms. To improve connectivity between different
areas, these rooms were removed in the new design, and also the planned separating wall placedaround the future service desk was initially not approved by the client. The measurement results at
the present service desk, showing a turbulent sound environment over 57 % of the time, and virtuallyno ‘quiet’ or ‘tranquil’, helped the architect to convince the client however that this wall should not
be excluded. The easy-to-understand semantics of the Liveliness method helped parties that are notacoustical professionals to communicate about sound in a meaningful manner, leading to a crucialchange in the client’s attitude. The fact that the MACH Index is limited to a maximum of 10, whilesound levels can theoretically increase indefinitely, helps to put the measured data in perspective.
4.3 Qualifying the effect of a renovation
While measurements prior to a renovation or redesign can provide useful input to quantify the
specific needs of the organization in question, this also represents an ideal situation where theconsultant is invited to the design process while the process of refurbishing has not yet taken place.
Also after introducing measures, measurements can be a helpful support to the design process,verifying whether the intended quality has been reached. Monitoring in a large 24/7 Public Safety
Answering Point (PSAP) proved that employees had reason to not be satisfied with the soundenvironment. Monitoring on four locations proved that the two central work clusters were far louder
than the ones towards both ends of the room, causing disturbance to the employees working in thequieter areas. Liveliness was an easy instrument to show the main sources of noise in the PSAP.

Figure 5 – Heat map of the average Liveliness for four sensors per five minutes of the day, averaged over
all measured days during one month, showing the variation in Liveliness throughout the day.

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Furthermore, problems within the work clusters were addressed. Fast communication is crucial ina PSAP and this concept was highly valued in the design, but the consequential idea of each cluster
having to contain a mixture of police, fire brigade and ambulance employees proved to be
counterproductive, as certain professions required more frequent and more intense phone
conversations than others.
Finally, the liveliness measurements were able to address behaviour that caused a turbulent soundenvironment. Figure 5 displays the average distribution for all sensors, averaged over every measuredday, showing the Liveliness distribution per five minutes of the day. Three peaks in the turbulent
sound environment are evident, at 6:30, 14:30 and 22:30. These times were quickly matched to themoments at which shift changes take place, and helped encouraging more quiet shift changes to respect
those that are still or already working.

5. CONCLUSIONS
ISO 3382-3 offers a set of quantities which are a good starting point for the assessment of room
acoustical quality of open plan offices. It still lacks input about the actual use however, which isneeded to properly calculate most of the respective quantities and put them in the right perspective.
Since every user has its characteristic requirements for the sound environment, which also varies overtime and between locations, monitoring the SPL at a number of representative locations for multiple
weeks is necessary to determine how lively a certain office area is. Since the design process involves
many parties, several of which may not be familiar with the acoustical jargon, a means to avoid theuse of decibels will increase the communicative strength of the acoustical engineer’s message. The
Liveliness method is proposed as such a tool. The combined use of room acoustical quantities fromISO 3382-3, SPL monitoring data and the Liveliness index will lead to acoustical design that is easier
to explain and fits better with the intended purpose of the open plan office in question.

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