1. Speech Levels in Open Offices
National Research Council Canada
Conseil national
de recherches Canada
Speech Levels in Open Offices
Alf Warnock & W.T. Chu
Indoor Environment Program, Acoustics
Institute for Research in Construction
National Research Council
Ottawa, Ontario
Some results from a project supported by Public Works and Government Services Canada.
Canada

2. Project: Team style open offices
Can some degree of speech privacy be attained?
Need typical levels to make calculations
In team-style open offices there are often unrestricted paths between workers. There is some hope of reducing intrusive speech because orientation is controlled to some degree by the location of computers and telephones.
ASA December 2001

3. Team-style areas - real
A real life view. There are clear sight lines and thus unobstructed sound propagation between work stations.
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4. Previous Work Pearsons, Bennet & Fidell McKendree
Different voice efforts measured but none in open office
McKendree
Anechoic room
No information on speech levels measured in open offices
Earlier studies of speech levels were not made in open offices. We decided to measure conversational levels in open offices.
Pearsons, K.S., Bennett, R.L., and Fidel, S., ‘Speech Levels in Various Noise Environments,’ EPA , U. S. Environmental Protection Agency, May 1977, p. 39. Available from National Technical Information Services as No. PB
F.S. McKendree, “Directivity Indices of Human Talkers in English Speech”, Proceedings Inter-Noise 86, pp , July, 1986
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5. Recording Voice Levels
To measure voice levels, subjects were asked to wear a mic and speak to the researcher sitting next to them in a voice that would be normal for that situation. Several minutes were spent explaining the task so a normal pattern for side-by-side conversation was established. Speech was recorded on a DAT recorder. The head mounted mic and the DAT were calibrated before each measurement session.
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6. Sites and subjects Nine offices - mix of team- and cubicle-style
118 subjects, 53 male, 65 female
Also measured attenuations between work stations
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7. Analysis 30 second segments with no prolonged silences.
1/16 second integration time spectra
Levels corrected to distance of 0.9 m by measurements in an anechoic chamber
The measurement procedure was repeated with several subjects in our anechoic chamber. As well as the head mic, a calibrated condenser mic was placed 0.9 m from the subjects. This enabled calibration of the whole system.
ASA December 2001

8. Attenuation
This is not part of the speech level measurements. We used a head and torso simulator as a source. There is a loudspeaker in the head. An array of 5 mics was used to measure the received sound. The attenuations are used later to show the effects of voice level in these offices.
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9. Result for one subject L1 L10 L50 Leq L90
The data collection allowed us to calculate Leq and other levels as shown in the chart for one subject.
L90
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10. Average for each office - Males
The average spectrum in each office for males has roughly the same shape although the average levels change. Similar results are found for females.
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11. Grand Average - Males 51.0 ± 3 dBA
Average spectrum and SD for all males in the study.
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12. Grand Average - Females
49.7 ± 3.8 dBA
Average spectrum and SD for all females in the study.
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13. Voice Spectra
Spectra from standards and other sources. NRC results are significantly lower.
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14. Casual vs. Open Office
NRC results agree very well with casual voice levels measured by Pearsons et al.
People don’t always speak at this level in an open office. Some call out across work stations in a louder voice. Some passers-by might have conversations with occupants inside a work area.
These levels should be typical for side-by side discussions and probably telephone conversations.
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15. Average Voice Levels
The average voice level found was about 51 dBA but there is clearly a wide range.
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16. SII and voice level Measured attenuations Same noise spectrum
Different voice levels
Correlation between Speech Intelligibility Index (SII), and Articulation index was found to be high but SII values were about 0.05 higher than AI values. AI=0.15 is commonly taken as the upper limit for normal privacy, so this becomes SII=0.2.
Assume a background spectrum with a level of 45 dBA. Using the attenuations and the voice levels measured, we can see that about 50% of the occupants experience SII<=0.2.
If higher voice levels are assumed, the percentage drops to about 10%.
If occupants can be induced to behave in a subdued way, then privacy can be greatly increased. Calling across work stations and loud speech should be discouraged in some subtle way.
In the offices visited, there were observable differences in behaviour; some occupants were fairly subdued, others not.
ASA December 2001