Causes and Improvements Stephen Whitlow and Alan Wyman

Hearing, Sound, Noise, and Vibration

Human ear transduces sound waves into nerve impulses Brain interprets impulses leading to perception/recogniti on of sounds

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)

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)

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

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

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

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

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

Reverb can be minimized by increasing sound- absorbing material in room

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

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)

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

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 peoples speech Increased error rate in cognitively demanding tasks, but not RT on more perceptual tasks

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

Researchers identified physiological response to increased noise: heart rate and stress hormone levels Correlated with subjective reports of stress and annoyance

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

200 workers 67% disturbed by telephones ringing 55% by people talking ~ 50% by air conditioning and office machinery Boyce workers 54% bothered by noise – especially talking and telephones ringing Sundstrom et al. 1994

Cognitive psychology literature shows the bad effects of background speech Supported by observational studies Banbury et al Memory for math and reading impaired by office noise Banbury and Berry 1997, 1998

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

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

IT organization Management intermixed with clerical Measured sound level at 60 dB(A)

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

Asked how their concentration was affected Not leading questions using bothered or disturbed

Source of NoiseMean ratings (std dev) Combined noise score3.60 (0.32) Telephones ringing3.73 (0.71) Telephones left ringing4.33 (0.74) Printer noise3.45 (0.68) Typewriter / keyboard noise3.10 (0.48) Computer noise3.24 (0.43) Outside noise3.06 (0.49) Other peoples conversations3.99 (0.67) Other peoples phone conversations3.82 (0.74) 1 Major improvement 5 Major deterioration to concentration

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

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

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

Huh?