Speech privacy unmasked

1. Speech privacy unmasked 4th Joint ASA/ASJ Meeting, Honolulu, HI 30 November 2006 Paper 3PNSc6 David Lubman, FASA, Acoustical Consultant dlubman@ix.netcom.com 14301 Middletown Lane Westminster, CA 92683 Voice/fax 714/373-3050 Louis C. Sutherland, FASA, Consultant in Acoustics lou-sutherland@juno.com 27803 Longhill Dr, Rancho Palos Verdes, CA 90275 Voice 310/541-7654, Fax 310/541-7795

2. Office employees want speech privacy between office work stationsBuilding owners want low-cost work stations • Closed offices • Cubicle farm

3. Less masking noise Lower speech privacy Better speech communication More masking noise Better speech privacy Poorer speech communication Building owners achieve office speech privacy through a combination of sound insulation and masking noise • Sound insulation costs more, per dB, than masking noise • Owners minimize costs by maximizing reliance on masking noise & minimizing reliance of sound insulation • This tradeoff assigns zero value to good speech communication, worker comfort, and “inclusiveness”

4. Result: Inexpensive, but intentionally noisy workplaces in which privacy is achieved at the expense of intelligible speech communication, worker comfort, and accommodation for communication disabilities Also known as …

5. Open plan offices

6. Speech communication in typical open plan offices with masking noise is marginal or poor This is shown by estimating the speech-to-noise (SNR) (SNR is a widely accepted measure of speech intelligibility)

7. How good is speech communication in open plan offices? • SNR = speech level - noise level (measured at listeners position) • What is the speech level • What is the noise level?

8. Average speech levels in open offices • Source: Warnock & Chu (2002) LEQ =50.2 dBA, s = 3 dBA • Source: Pearson et al (1977) Casual voice levels Male: LEQ = 52 dBA, s = 4 dBA Female: LEQ = 50 dBA s = 4 dBA

9. What is the noise level? • Background masking noise levels (BMNL) in open plan offices typically range from 45 to 48 dBA

10. SNR for “average” speech effort in open offices (50.2 dBA @ 1 m) Normal listeners work performance degrade when SNR < 10 dB(Listeners makemore errors and experience increased stress) Performance degradation & stress is greater for “challenged” listeners Poor SNR prompts talkers to raise their vocal effort

11. A maximum office BMNL of 40 dBA can accommodate hearing & speech disabilities, & reduce worker stress

12. SNR for “average” speech effort in open offices (50.2 dBA @ 1 m) Normal listener’s work performance degrades when SNR < 10 dB(Listeners makemore errors and experience increased stress) Performance degradation and stress is greater for challenged listeners

13. Observations on background masking noise levels • BMNLs above 45 dBA are self-defeating since talkers raise their voice levels to compensate (Lombard effect) • 45 dBA BMNLs provide a mere 5.2 dB SNR @ 1 m. This seems marginal - even for ideal talkers and listeners. • Workplaces must become inclusive. 45 dBA leaves no margin for persons with hearing or language disabilities. These are now common in the workplace and will become more common in the future • A recognized rule-of-thumb to accommodate listeners with hearing or language disabilities is to increase the SNR by 5 dB • Therefore, BMNLs in offices should not exceed 40 dBA

14. Summary I • Office speech privacy is a good thing, and a certain amount of background noise is desirable • But reliance on high background masking noise (BMN) levels to achieve speech privacy is inconsistent with inclusive design • Typical BMN levels of 45-48 dBA presents difficulties even for normal listeners • BMN levels over 45 dBA are self-defeating, since talkers raise their voice levels to compensate (Lombard effect)

15. Summary II • High BMN levels are unfriendly to all workers, but especially to non-native listeners and those with hearing and speech limitations • Fact: Hispanics account for half the US population growth from 2004 to 2005, including 500K Hispanic immigrants. Many will join the white-collar work force in coming decades. Non-native listeners need better listening conditions for speech understanding • Fact: The problem of hearing-impaired workers increases as the workforce ages. More older workers have hearing loss. These workers are less tolerant of BMN

16. Summary III • Speech privacy can be achieved with lower BNL with better acoustical design • The higher initial costs of low-noise speech privacy systems are returned by cost-benefits of a friendlier environment • Sources of cost-benefits (to be quantified) • Larger worker pool • Lower employee turnover • Retention of valuable workers • Better office communication - fewer errors and misunderstandings • ?

17. Backup Slides

18. Why speech privacy must be augmented in open plan offices* Occupants can be easily seen, heard, and disrupted when there are no walls or doors Open-plan office occupants often feel that they do not have enough acoustic or visual privacy. Employees can feel overwhelmed by distractions, exposed to colleagues and supervisors, & restricted in their behavior without adequate privacy Employees need to concentrate, avoid unwanted disruptions, & keep their work private when necessary *From COPE study - NRC (Canada)

19. Is there excessive reliance on background masking noise (BMN) for office speech privacy? • Open office speech privacy is achieved by a combination of BMN and noise isolation • Typical BMN levels of 45-48 dBA create avoidable problems for noise-sensitive persons and critical communication • Noise levels are lower in typical homes: 25-35 dBA • Many who hear well in homes cannot cope with BMN in open plan offices • Adversely impacted: Older workers, those with hearing, language or voice disabilities, and visually impaired

20. Reverse Lombard effect • Lombard effect causes talkers to increase their voice effort to compensate for higher background noise levels • Lombard effect “kicks in” when BNLs exceed ~ 40-45 dBA* • Increasing BNLs above the Lombard threshold is self-defeating since talkers raise their voices in compensation • Lombard effect also works in reverse. (Reducing BNLs cause talkers to reduce their voice levels) • Limitingcing BNLs to 40 dBA benefits speech privacy because of reverse Lombard effect • *The Lombard research data we reviewed so far seems incomplete. Additional reverse Lombard benefits may accrue for BNMLs below 40 - 45 dBA

21. The percent of Americans reporting hearing problems grows with age Age Group Source: The National Health Interview Survey (Pleis and Coles, 2002)

22. Aging of the work force* • In 2006, 12% of the US population is aged 65 or older • By 2030, about 24% of the US will be 65 or older • Today, about 7% of the world’s population is 65 or older • By 2050, about 15% of the world will be 65 or older • Over half of survey respondents agreed this would lead to a workforce shortage and a “brain drain” • The # 1 concern of nearly 40% of respondents was the availability of talent over the next 5 years • 90% of corporate America is committed to putting formal retention programs in place in the coming years • Source: The Aging of the US Work Force: Employer Challenges • and ResponsesErnst and Young (Jan 2006)

23. Office environments must become friendlier to older workers • In coming decades, workers with disabilities will comprise an increasing portion of the American workforce. This change is driven by many factors, among them: the aging of American workers and the impact of anti-discrimination laws, such as the Americans with Disabilities Act (ADA)[i] of 1990, and the impact of policy changes in health care and welfare reform • [i] Schwochau S, Blanck PD. The economics of the Americans with Disabilities Act, Part III: does the ADA disable the disabled? Berkeley Journal of Employment and Labor Law. 2000;21(1): 271-313. • [ii] Blanck PD, Schartz HA. Employment policy and the ADA: research questions and challenges, in emerging workforce issues: W.I.A., Ticket to Work, and Transition. R. McConnell (ed.), Switzer Seminar Monograph Series. 2001;1-10.

24. Until now, building owners have had little incentive to reduce BMN levels • BMNLs are usually set as high as workers will tolerate • We suggest that BMN systems should be designed to minimize BMN! • Owners are driven by short-term cost saving • A dB of noise isolation (architecture) costs less than a dB of masking noise (electronics) • Impacted stakeholders (hearing-impaired, etc) generally have no say in these decisions, though they may be profoundly affected by them

25. Masking noise levels CAN be reducedwithout compromising speech privacy • Speech privacy CAN be achieved with lower noise levels & better noise isolation design • 1:1 tradeoff between sound isolation and noise • Result - a more inclusive, efficient, and humane office work environment • We have faith that the higher costs of better noise isolation will be repaid, at least partly, by the cost-benefits of a better work environment

26. Challenge for acousticians • AARP asked: What must employers do to recruit, retain, train, and address the needs of older workers? Their sheer numbers and experience make these workers an invaluable commodity in the workplace. Valuing these workers will enable employers to remain competitive • Reducing BMN levels by even as little as 3 - 5 dB can noticeably improve listening & talking conditions without compromising speech privacy • This is possible with careful attention to acoustical design tradeoffs • Acousticians should respond with proposals for low noise office acoustical designs

27. Thanks for listening! Constructive criticism is cordially invited

28. Backup slides

29. Levels of office speech privacy • Confidential Privacy: Confidential privacy exists if a listener can understand only a few words but no entire sentences or phrases. It is important for executive and sensitive spaces. Confidential Privacy has been given a Speech Intelligibility Index (SII) rating of 0.1 (Articulation Index [AI] 0.05) • Normal privacy: Normal privacy exists if the speech is intelligible to an active listener only; an uninterested listener would be able to tune-out the conversation. The normal privacy SII rating is 0.2 (AI 0.15) *NRC (Canada) COPE study

30. Psychosocial value of space* • Opportunity to engage in spontaneous social encounters • Opportunity for relaxation and psychological restoration • Opportunity for privacy and for movement between interaction and solitude, as desired • Opportunity for learning and information sharing • Opportunity for connection to the natural environment • Opportunity for regular exercise • Sound levels not much above or below that of nature • Meaningful change and sensory variability • An interesting visual environment with aesthetic integrity • Sense of social equity and respect • Ability to maintain and control personal comfort • Making sense of the environment *Judith Heerwagen, J.H. Heerwagen & Associates, Inc.

31. For any given level of speech privacy, greater sound insulation (STC) permits lower masking noise levels (LA) • STC + LA => K – 10 *log( AT *AL/S ) where, • STC = sound transmission loss required for desired privacy between the two offices (T & L) • LA [dB] = Background Noise level [BNL] in room to be protected • K [dB] = Constant depending on degree of privacy & voice level in source room • AT, AL [m2]= Total sound absorption in two rooms • S[m2] = Area of separating partition From Acoustical Measurements & Noise Control, Cyril Harris, 3rd Ed. (1998) Chapt. 33, Noise Control in Bldgs, A. C. C. Warnock & J. D. Quirt

32. K for various occupancies and privacy requirements* From Acoustical Msmts & Noise Control, Cyril Harris, 3rd Ed. (1998) Chapt. 33, Noise Control in Bldgs, A. C. C. Warnock & J. D. Quirt

33. Abstract Background masking noise is widely used to achieve speech privacy between work stations in open offices, and in nearby closed (executive) offices. Although speech privacy is often essential, high masking noise levels reduce the abilities of some workers to perform speaking and listening tasks effectively and without strain. Masking noise levels are usually set as high as office inhabitants will tolerate, typically about 45 – 48 dB (A-weighted). This is 10 to 20 dB higher than noise levels in typical home settings. Many who can communicate effectively in home settings are impaired in offices with background masking noise. People adversely impacted include those with mild or worse hearing of hearing, speech and language. Many are older workers, and non-native speakers. The current architectural trend to greater inclusiveness underscores the desirability of lower background masking noise levels. Designers can usually achieve speech privacy with lower masking noise levels by specifying partitions with higher noise isolation ratings. Higher noise isolation costs more than higher masking noise levels. But higher costs may be balanced by the benefits of a more inclusive and humane workspace.