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Observation

Observation. Office Noise. Causes and Improvements Stephen Whitlow and Alan Wyman. Chapter 11. Hearing, Sound, Noise, and Vibration. Sound. Human ear transduces sound waves into nerve impulses Brain interprets impulses leading to perception/recognition of sounds . D ecibels.

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Observation

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  1. Observation

  2. Office Noise Causes and Improvements Stephen Whitlow and Alan Wyman

  3. Chapter 11 Hearing, Sound, Noise, and Vibration

  4. Sound • Human ear transduces sound waves into nerve impulses • Brain interprets impulses leading to perception/recognition of sounds

  5. Decibels • Sound measured in decibels (dB) • relative scale based on infant hearing threshold, express in log scale • 10 dB increase represents doubling of loudness • Human hearing sensitivity varies across frequency: • maximum between 1000 to 4000 Hz (human speech)

  6. Noise • Noise-induced damage to Ear • Exposure to loud noise causes threshold shift at 4000 Hz • Pain is experienced at 130 dB, damage at 140 dB (jet engine at 30m) • Tinnitus (ringing in ears) occurs in nearly ¼ of noise exposed workers (construction, shipbuilding)

  7. Noise • Exposure to continuous and transient sounds regulated: • OSHA has defined 90 dB(A) as maximum exposure to continuous noise over 8 hour shift • OSHA does not permit exposure to continuous noise > 115 dB(A) • EU advises hearing protection at 80 dB(A) • Age-related shift at 4000 Hz: • 12 dB at age 45, 35 dB at age 65 • Sound at 4000 Hz need to be > 4x louder to be detected by 65 year compared to 45 year old

  8. Noise • While sound can be objectively measured, Noise is a subjective perception • Noise defined as sound at an amplitude that causes annoyance or disruption to communication • Noise survey can be useful in assessing noise distribution and impact in working areas

  9. Noise • Management of industrial noise • Short term: • earplugs/muffs • Medium term: • Moving and/or soundproofing noisy machines • Warning signs • Worker rotation between noisy and quiet jobs • Long term: • Comprehensive program • Replacing noisy machine • Acoustic refuges • Audiometric testing

  10. Noise • Hearing protection • Up to 40 dB reduction in SPL at eardrum • Simple ear protection inadequate at noise levels > 140 dB • Correct training is required to maximize reduction • Design of Acoustic Environment: managing ambient and transient noise • Ambient • 55 dB upper limit for mental work and complex supervisory tasks • 45 dB upper limit for creative work • Transient • 75 dB maximum for office spaces

  11. Reverberation • Noise level determined by noise source intensity and reverb of the room • More reflection = more reverb time • Excessive reverb can blur speech signals • Room shape has little effect on reverb time • Reverb field intensity depends on: • Source SL • Volume of space • Amount of sound-absorbing material in room

  12. Reverberation • Reverb can be minimized by increasing sound-absorbing material in room

  13. Speech Intelligibility and Speech Transmission Index (STI) • STI--intelligibility of speech in environment • Designers should try to minimize STI in office environments • Minimizing direct and reflected speech at each workstation • Research indicated STI < .2 needed in open plan office

  14. Speech Intelligibility and Speech Transmission Index (STI) • Sound-absorbent ceiling tiles reduce speech from 55 dB(A) to 40 dB(A) • But hard to reduce speech > 10 dB(A) within 2.5M of source (most open offices have desks closer than this)

  15. Noise Reduction Coefficient (NRC) • 0 = no ambient sound absorbed, 1= all sound absorbed • Researchers recommend .85 for upholstered screens in office • Thick carpets with padding NRC as high as .7

  16. Effects • Effect of Noise on Task Performance • Disruption of verbal communications due to noise known as masking • Continuous noise can impact inner speech many people use to support short term memory • Meta analysis concluded that high levels of irrelevant noise increase error rate in continuous attention task but not work output • Exposure to other people’s speech • Increased error rate in cognitively demanding tasks, but not RT on more perceptual tasks

  17. Noise reduction • Industrial Noise Reduction • Fans: higher noises at higher speed-- use larger fan running at lower speed • Muffing: pneumatic tool produce noise due to compressed air release-- pipe away from operator or use muffler on air output • Positive effect of noise reduction • 23% reduction in absenteeism in punch card workers after noise reduction • 90% reduction in breakage and machine shutdowns after acoustical treatment

  18. Noise on Stress • Researchers identified physiological response to increased noise: • heart rate and stress hormone levels • Correlated with subjective reports of stress and annoyance

  19. Selected research

  20. Introduction • Background noise most frequent complaint about open-office environment • Conflicting requirements must co-exist • Good speech communication • Good speech privacy

  21. Lit Review • 200 workers • 67% disturbed by telephones ringing • 55% by people talking • ~ 50% by air conditioning and office machinery • Boyce 1974 • 2000 workers • 54% bothered by noise – especially talking and telephones ringing • Sundstromet al. 1994

  22. Lit Review • Cognitive psychology literature shows the bad effects of background speech • Supported by observational studies • Banburyet al. 2001 • Memory for math and reading impaired by office noise • Banbury and Berry 1997, 1998

  23. Validation Study • Questionnaires and sound level measurements • 2 locations in U.K. • Open plan offices • One with 5-foot panels • Other office furniture • Both about 140 employees

  24. Office 1 Banking organization Management had windows – clerical in middle of building Measured sound level at 55 dB(A)

  25. Office 2 IT organization Management intermixed with clerical Measured sound level at 60 dB(A)

  26. Demographics 88 employees participated (75% response rate) 65% male, 35% female Mean of 9 months working there Ages 20 – 59 with a mean of 33 years 22% managerial, 22% supervisory, 56% clerical

  27. Disturbance by noise Asked how their concentration was affected Not leading questions using “bothered” or “disturbed”

  28. Disturbance by noise 1 Major improvement 5 Major deterioration to concentration

  29. Correlations • Only one significant • Long they have worked, the more keyboard annoyance • No habituation found (correlation = zero)

  30. Noted results • Telephones left ringing highly disruptive • Possibly due to perception that co-workers should have been at their desk • Simply due to longer disruption?

  31. Noise abatement • Acoustic panels and ceilings • Respondents felt it would help • Babble • Need multiple voices • Naturally occurring in larger offices • White noise • People have been concerned about the ‘hiss’ and think it is HVAC and report being cold

  32. What? Huh?

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