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Chapter 3
Auditory (Alarms (Criteria for alarms (Must be heard above…
Chapter 3
Auditory
Alarms
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Auditory alarms create greater compliance vs visual alarms (cannot close our ears vs can close our eyes)
Criteria for alarms
- Must be heard above background ambient noise
- at least 15 dB above threshold of hearing above the noise level.
- requires about 30 dB difference to guarantee detection.
- can include alarm at several different frequencies and well distributed across the spectrum in case malfunctions create its own noise similar to the alarm.
- Should not be above danger level of hearing
(around 85 to 90 dB)
- Should not be overly startling and abrupt
- Should not disrupt the perceptual understanding of other signals (other alarms or background speech)
- Alarm should be informative
- signal the nature of emergency
- indication of appropriate action to take
- e.g. in hospital, each patient has 10 alarms with 60 signals to identify
- must not be confusable with other alarms
- should not be more than human's restrictive limit of absolute judgement = maximum allowable is 4 different alarms.
Designing alarms
- Undertake environmental and task analysis
- understand quality and intensity of other sounds to guarantee detectability and minimize disruption
- Guarantee informativeness and minimize confusability
- stay within limits of absolute judgement
- can contain 4 dimensions:
-pitch
-envelope (rising, woop woop, beep beep)
-rhythm (synchronous da da da da vs asynchronous dada dada)
-timbre
- Design specifics of the individual sound:
- unique set of pauses between each pulse create a unique rhythm to avoid confusions
- increase then decrease in intensity gives perception of approaching then receding sound
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Masking
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Design Principles
Minimum intensity difference for a sound to be heard is 15 dB above the masking sound.
May be larger when the pitch of the target sound is unknown
Sounds tend to be masked most by others in the critical frequency band surrounding the masked sound.
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