Effect of speech on performance – an evidence-based model promoting noise control in offices

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Valtteri Hongisto

Senior research scientist, FIOH @ Turku

Adjunct professor, Aalto University @ Helsinki +358405851888 valtteri.hongisto@ttl.fi

SAFE Workshop, Dortmund Germany 4-5 November 2015 Bundesanstalt für Arbeitsschutz und Arbeitsmedizin (BAuA)

Effect of speech on performance – an evidence-based model promoting

noise control in offices

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Background

• According to several independent field surveys, noise is the most adverse factor of IE in open-plan offices.

• Frontzcac et al 2012 Indoor Air

• Speech is the most distracting type of office noise

• Haapakangas et al. ICBEN 2008

• Laboratory experiments have shown that speech impairs the performance of cognitively demanding tasks

• Colle and Welsh 1976 J Verbal Learn Verbal Behav

• Vast number of successors; see review by Hongisto 2005 Indoor Air

• Speech intelligibility

determines the distracting power of speech primarily, not the sound pressure level of speech.

• Colle 1980 J Verbal Learn Verbal Behav

• A well-documented objective descriptor of subjective speech

intelligibility is STI

• IEC 60268-16

• Houtgast&Steeneken 1985 J Acoust Soc Am

• Could we explain the performance effects of speech in such the

terms of engineering so that these findings could benefit noise control in open-plan offices?

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Frontzcac et al, Indoor Air 2012

52.920 occupants in 351 buildings U.S. Offices

2000-2010

dissatisfiedvery very

satisfied

Background

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STI

• STI can be reduced by

• reducing speech-to-noise ratio

• Increasing background level

• Reducing speech level

• increasing reverberation time (EDT)

0.0 0.5 1.0 1.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

g f e d c b a

a)L

SN = 15 dB b)L_SN = 10 dB c)L

SN = 5 dB d)L

SN = 0 dB e)L

SN = -5 dB f) L

SN = -10 dB g)L

SN = -15 dB

SpeechTransmissionIndexSTI

Early decay timeT [s]

STI Speech intelligibility Speech privacy Examples in offices

0.00 … 0.05 very bad confidential Between two single-person office rooms, high sound insulation 0.05 … 0.20 bad good Between two single-person office rooms, normal sound insulation 0.20 … 0.40 poor reasonable Between workstations in a high-level open-plan office

Between two single-person office rooms, doors open 0.40 … 0.60 fair poor Between desks in a well designed open-plan office

0.60 … 0.75 good very poor Between desks in an open-plan office, reasonable acoustical design 0.75 … 0.99 excellent no Face-to-face discussion, good meeting rooms

Between desks in an open-plan office, no acoustical design

Hongisto 2005 Indoor Air

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Review of experimental work prior to 2004

Change in performance DP [%]

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

0.00 0.20 0.40 0.60 0.80 1.00

Speech Transmission Index STI

1 2 3 4

5 6 7 8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

1 2 3 4

5 6 7 8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Data points from 32 experiments reviewed

Silence

Speech WHAT HAPPENS

HERE THEN?

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Alternatives of functional shapes

Change in performance [%]

-8 -7 -6 -5 -4 -3 -2 -1 0

0.00 0.20 0.40 0.60 0.80 1.00

Speech Transmission Index STI

Linear Ramp

Exponential Logarithmic Sigmoidal

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Dependence of subj. intelligibility on STI

Subjective speech intelligibility [% correctly heard]

0 10 20 30 40 50 60 70 80 90 100

0.0 0.2 0.4 0.6 0.8 1.0

Phonetically balanced (PB) words

Consonant-vocal- consonant (CVC) syllables

Sentences

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Original model

• Hypothetic model

• Speech intelligibility vs. STI curve is applied for performance loss

• Various task types are combined

• Lack of data

• Perfect performance when STI below 0.20

• Max. performance loss is achieved when 0.50

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Recent update

Jahncke, Hongisto, Virjonen 2012 Appl Acoust

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Recent experimental work

• More or less support has been given to the model

• Keus van de Poll 2014 Appl Acoust

• Ebissou et al 2015 Appl Acoust

• Jahncke et al. 2012 Appl Acoust

• Schlittmeier and Liebl 2015 Facilities

• Hongisto et al. 2015 (Published in Finnish)

• A more general model also exists

• Schlittmeier et al. 2012 Atten Percept Psychophys

• Working memory performance as a function of fluctuation strength

• True shape may not be sigmoidal but steeper

• The exact form of the model may never be found

• Type of task, type of speech, other factors

• Nevertheless, the detriments of irrelevant speech can be controlled by reducing STI

-14 -12 -10 -8 -6 -4 -2 0 2

0.0 0.2 0.4 0.6 0.8 1.0

STI Performance decrement [%]

Hongisto 2005 Indoor Air Suggested new shape

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Application

• STI was could be proven to be such an important objective quantity that it should be measured in open-plan offices

• STI was chosen to ISO 3382-3:2012

• Acoustics – Measurement of room acoustic parameters. Part 3. Open-plan offices

• STI of normal effort speech is

measured as a function of distance, as well as the SPL of speech

• Distraction distance r_D is the distance where STI falls below 0.50.

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Global promotion of noise control

• 2007: ICA preliminary method

• 2008: First national guidelines for rD and D_2S in Finland

• 2012: ISO 3382-3 in 2012

• 2010: Numbers of cross-sectional studies have emphasized the noise problem in open-plan offices

• Research in the area is still growing – Health aspects have received larger interest

• Business possibilities of acoustic consultancy has increased

• Room acoustic models and measurement apparatus have improved w.r.t. new compact features needed in open-plans

• Material manufacturers disseminate the r&d evidence to improve their business