Copyright Catherine M. Burns SOUND and NOISE Chapter 5 Copyright Catherine M. Burns

Copyright Catherine M. Burns Anatomy of the Ear White: ear drum (tympanic membrane) Beige: hammer and anvil Yellow: cochlea Blue/Yellow/white: semi-circular canals Teal: auditory nerve Source: internet “earspin” Copyright Catherine M. Burns

Copyright Catherine M. Burns Tech Details! Ear: pressure/force to electrical wave transducer interpretation in the brain Sound basically air pressure waves frequency determines tone, vibrations per second (Hz), "pitch" amplitude of pressure variation is intensity tone loudness Copyright Catherine M. Burns

Copyright Catherine M. Burns Intensity/Volume really measured in pressure units (Pa) human range is from 20mPa to about 20, 000 Pa (one million times more) max idea is jet engine large range so use a log scale, decibel scale Copyright Catherine M. Burns

Copyright Catherine M. Burns The Decibel Scale 20mPa is reference. every increase of x10, is addition of 20dB Sound pressure level (dB) = 20 log (P/Pref) for absolute measures where Pref = 20mPa So absolute sound intensity (dB) of P = 20 log (P/20mPa) See Table 5.1 for example sounds and their volume Copyright Catherine M. Burns

Copyright Catherine M. Burns Pitch or Tone Young people typically 16Hz to 20, 000 Hz about 9 octaves below 16Hz you feel as vibrations above 20 000 Hz is "ultrasonic", we can't hear Copyright Catherine M. Burns

Loudness (versus intensity) Loudness is the psychological experience of sound volume Differs from intensity Figure 5.3 Key idea: Very loud sounds seem even louder Loudness Intensity (of 1000HZ tone) Copyright Catherine M. Burns

Copyright Catherine M. Burns Loudness and Pitch generally high pitched sounds sound louder most sensitive range is about 4000Hz dB(A) weights sounds by pitch to reflect psychological loudness Human speech: vowels below 1000Hz, consonants higher frequency Copyright Catherine M. Burns

Copyright Catherine M. Burns Equal Loudness Curves Fletcher.H. and Munson.W., ``Loudness, its definition, measurement and calculation,'' J. Acoust. Soc. Am., vol. 5, pp. 82-108, 1933. Copyright Catherine M. Burns

Copyright Catherine M. Burns Masking Sounds can be masked by other sounds Minimum intensity difference to ensure a sound is heard is 15dB above the masking sound Sounds in the same frequency band are masked Low pitch sounds mask high pitched more than the reverse. Copyright Catherine M. Burns

Copyright Catherine M. Burns Alarm Design Auditory signals are used for alarms because they don’t require orientation to be heard People can’t “close their ears” Auditory alarms should be reserved for highly critical events, affecting multiple personnel (fire alarms) Copyright Catherine M. Burns

Criteria for Alarm Design must be heard over the background (15dB more minimum, usually 30dB is suggested) cover different frequencies to avoid masking (chord alarms) shouldn’t exceed 85-90dB (dangerous levels) avoid startling people not interfere with communications, other alarms be informative Copyright Catherine M. Burns

Copyright Catherine M. Burns Other Alarms Voice Alarms can be confused with speech can be clearer in meaning False Alarms people will ignore and distrust the alarm maybe even turn it off Copyright Catherine M. Burns

Copyright Catherine M. Burns Sound localization Demo Copyright Catherine M. Burns

Copyright Catherine M. Burns Noise unwanted sound generally “too loud” Copyright Catherine M. Burns

Noise Induced Hearing Loss slow progressive degeneration of cells in the inner ear increases with intensity and repetition high frequency and intermittent is worse usually starts at 4000 Hz and moves to lower frequencies How measured - "pure tone audiometry" - progressively trying tones and adjust volume level Copyright Catherine M. Burns

Basic Pure Tone Audiometry 500Hz 1000Hz 2000Hz 3000Hz Calibrate to a test tone (about 1000) at lowest level person can here Can you hear the tone Copyright Catherine M. Burns

Temporary Hearing Loss hearing returns to normal, temporary threshold shift begins at 80-90dB, causes 8-10dB shift also affected by duration 100dB sound for 10min shifts 16dB, 100 minutes, 60 dB Copyright Catherine M. Burns

Permanent Hearing Loss Permanent Threshold Shift Extensive exposure to noise Often high frequencies (e.g. 4000 Hz) Copyright Catherine M. Burns

Age Related Hearing Loss worse men than women 50 years 10dB 60 years 25dB 70 years 35dB High frequency losses Copyright Catherine M. Burns

What life is like if you have hearing loss Normal Speech Loss at 2000 Hz (2000Hz_9) Typical of noise exposure Loss at 4000 Hz (4000Hz_9) General loss due to middle ear infection (mild_hl) Masking effects of noise Copyright Catherine M. Burns

Noise Level Guidelines ISO standards - considers anything above 90db(A) to be damaging 90dB must reduce noise, 85dB must provide ear protection Equivalence over duration Hours dB(A) 8 90 6 92 3 97 1.5 102 0.5 110 Copyright Catherine M. Burns

Physiological and Psychological Effects of Noise impaired alertness disturbed sleep annoyance loss of communication Copyright Catherine M. Burns

Physiological Effects increased blood pressure accelerated heart rate contracted blood vessels on the skin slowed digestion increased muscular tension waking people from sleep - connect with circadian rhythms research is unsure whether people adapt to noise or become increasingly sensitive about it Copyright Catherine M. Burns

Designing to reduce noise recommending ear protection designing quieter equipment designing buildings and surfaces that don't propagate noise sound absorption enclosing the noise source acoustic tiles Designing to avoid masking Copyright Catherine M. Burns

Ear Protection Solutions Ear plugs - can reduce about 30dB Ear muffs - about 40dB Problems though - workers can't hear other workers don't like wearing them sound reduction is somewhat isolating Copyright Catherine M. Burns

Copyright Catherine M. Burns Touch/Haptic Alternative form of information (force feedback mouse) Identification of shape, texture Alerting when sounds can’t be used (cell phones that vibrate) Braille Could be used more powerfully Copyright Catherine M. Burns

Copyright Catherine M. Burns Kinesthetic Senses Knowledge of where your limbs are Critical when doing tasks without looking (e.g. touch typing, driving) Copyright Catherine M. Burns

Copyright Catherine M. Burns Vestibular Senses Sense of acceleration (in the ear) Sense of turning and motion Key role in motion sickness, vertigo, simulator sickness Copyright Catherine M. Burns