Observation

Office Noise

Observation

Office NoiseCauses and Improvements

Stephen Whitlow and Alan WymanChapter 11Hearing, Sound, Noise, and Vibration

SoundHuman ear transduces sound waves into nerve impulsesBrain interprets impulses leading to perception/recognition of sounds

DecibelsSound measured in decibels (dB)relative scale based on infant hearing threshold, express in log scale10 dB increase represents doubling of loudness

Human hearing sensitivity varies across frequency:maximum between 1000 to 4000 Hz (human speech)

NoiseNoise-induced damage to EarExposure to loud noise causes threshold shift at 4000 HzPain is experienced at 130 dB, damage at 140 dB (jet engine at 30m)

Tinnitus (ringing in ears) occurs in nearly of noise exposed workers (construction, shipbuilding)

NoiseExposure to continuous and transient sounds regulated:OSHA has defined 90 dB(A) as maximum exposure to continuous noise over 8 hour shiftOSHA 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 65Sound at 4000 Hz need to be > 4x louder to be detected by 65 year compared to 45 year old

NoiseWhile sound can be objectively measured, Noise is a subjective perceptionNoise defined as sound at an amplitude that causes annoyance or disruption to communicationNoise survey can be useful in assessing noise distribution and impact in working areasNoiseManagement of industrial noiseShort term:earplugs/muffsMedium term: Moving and/or soundproofing noisy machinesWarning signsWorker rotation between noisy and quiet jobsLong term: Comprehensive programReplacing noisy machineAcoustic refuges Audiometric testing

NoiseHearing protectionUp to 40 dB reduction in SPL at eardrumSimple ear protection inadequate at noise levels > 140 dB Correct training is required to maximize reduction

Design of Acoustic Environment: managing ambient and transient noiseAmbient55 dB upper limit for mental work and complex supervisory tasks45 dB upper limit for creative workTransient75 dB maximum for office spaces

ReverberationNoise level determined by noise source intensity and reverb of the roomMore reflection = more reverb timeExcessive reverb can blur speech signalsRoom shape has little effect on reverb timeReverb field intensity depends on:Source SLVolume of spaceAmount of sound-absorbing material in roomReverberationReverb can be minimized by increasing sound-absorbing material in room

Speech Intelligibility and Speech Transmission Index (STI)STI--intelligibility of speech in environmentDesigners should try to minimize STI in office environmentsMinimizing direct and reflected speech at each workstationResearch indicated STI < .2 needed in open plan officeSpeech 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)

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

EffectsEffect of Noise on Task PerformanceDisruption of verbal communications due to noise known as maskingContinuous noise can impact inner speech many people use to support short term memoryMeta analysis concluded that high levels of irrelevant noise increase error rate in continuous attention task but not work outputExposure to other peoples speechIncreased error rate in cognitively demanding tasks, but not RT on more perceptual tasksNoise reductionIndustrial Noise ReductionFans: higher noises at higher speed-- use larger fan running at lower speedMuffing: pneumatic tool produce noise due to compressed air release-- pipe away from operator or use muffler on air outputPositive effect of noise reduction23% reduction in absenteeism in punch card workers after noise reduction90% reduction in breakage and machine shutdowns after acoustical treatment

Noise on StressResearchers identified physiological response to increased noise:heart rate and stress hormone levelsCorrelated with subjective reports of stress and annoyanceSelected research

IntroductionBackground noise most frequent complaint about open-office environmentConflicting requirements must co-existGood speech communicationGood speech privacyLit Review200 workers67% disturbed by telephones ringing55% by people talking~ 50% by air conditioning and office machineryBoyce 19742000 workers54% bothered by noise especially talking and telephones ringingSundstrom et al. 1994Lit ReviewCognitive psychology literature shows the bad effects of background speechSupported by observational studiesBanbury et al. 2001Memory for math and reading impaired by office noiseBanbury and Berry 1997, 1998Validation StudyQuestionnaires and sound level measurements2 locations in U.K.Open plan officesOne with 5-foot panelsOther office furnitureBoth about 140 employeesOffice 1Banking organizationManagement had windows clerical in middle of buildingMeasured sound level at 55 dB(A)Office 2IT organizationManagement intermixed with clericalMeasured sound level at 60 dB(A)Demographics88 employees participated (75% response rate)65% male, 35% femaleMean of 9 months working thereAges 20 59 with a mean of 33 years22% managerial, 22% supervisory, 56% clericalDisturbance by noiseAsked how their concentration was affectedNot leading questions using bothered or disturbedDisturbance by noiseSource 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 improvement5 Major deterioration to concentrationCorrelationsOnly one significantLong they have worked, the more keyboard annoyanceNo habituation found (correlation = zero)Noted resultsTelephones left ringing highly disruptivePossibly due to perception that co-workers should have been at their deskSimply due to longer disruption?Noise abatementAcoustic panels and ceilingsRespondents felt it would helpBabbleNeed multiple voicesNaturally occurring in larger officesWhite noisePeople have been concerned about the hiss and think it is HVAC and report being coldWhat?Huh?