304%20October%2027%20%28Noise%20%26%20Radiation%29%20students

304%20October%2027%20%28Noise%20%26%20Radiation%29%20students

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HSCI 304: Perspectives on Environmental Health October 27, 2011 Physical Hazards: Noise & Radiation
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Noise
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What is Noise? Often thought of as “unwanted” sound But even “wanted” or “desirable” sound (e.g. music) can cause hearing loss Potential for noise to damage hearing is related to the noise properties… Loudness (amplitude) Frequency …and exposure properties Duration Continuous/Transient Moller in Wallace (Ed), 2008
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What is Sound? Pressure “waves” in a medium (air, water, etc.) i.e., variations in pressure above and below the ambient pressure of a medium Sound is a “longitudinal wave” Displacement is parallel to direction of wave propogation (see next slide) Characteristics of sound Amplitude (how loud is it?) Frequency (i.e. pitch; what does it sound like?)
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What is Sound? “High” Air Pressure Direction of Sound “Low” Air Pressure “Low” Air Pressure Sound is a longitudinal wave, or a “pressure wave”: Animations
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What is Sound? Two key characteristics of sound Amplitude (how loud is it?) Frequency (what does it sound like?) Amplitude (or loudness) Amount the air pressure max/min varies from ambient pressure E.g., in air, the loudness is determined by how high the high pressure is, and how low the low pressure is, relative to atmospheric pressure Frequency (or pitch) The rate of oscillation
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Frequency Measured as the number of waves passing a given point per second Units: Hertz (Hz) Low frequency = low “pitch”; high frequency = high “pitch” Humans can hear sound between approximately 20 and 20,000 Hz Human speech varies from ~500 to 2,000 Hz
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Loudness Measured as the sound pressure level Units: decibels (dB) Because sound pressures vary by orders of magnitude, we convert them to decibels - a logarithmic scale Units are relative to the minimum loudness detectable by human ears i.e. 0 dB is the very minimum sound pressure level that human hearing can detect Humans do not detect all frequencies equally well Peak hearing ~1,000 to 3,000 Hz Often “weight” different frequencies to human hearing (A or C weighting): dBA or dBC
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Loudness Nadakavukaren, 2006
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Worksafe BC Hearing Video
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Human Perception of Sound Slide courtesy of Chuck Treser, UW THINK OF THE RED LINE AS HOW LOUD THE SOUND ACTUALLY IS; THE BLUE LINE IS HOW LOUD THE SOUND IS PERCEIVED BY HUMAN BEINGS. EXAMPLE : TWO SOUNDS OF EQUAL LOUDNESS, ONE AT 100 Hz AND THE OTHER AT 1000 Hz. THE 100 Hz SOUND WOULD SOUND 20 dB QUIETER.
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Weighting Loudness by Frequency Berger et al., The Noise Manual , 2000 (You can ignore B and C in this figure)
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How do we hear? Slide courtesy of Chuck Treser, UW
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This note was uploaded on 11/05/2011 for the course HSCI 304 taught by Professor Allen during the Fall '11 term at Simon Fraser.

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304%20October%2027%20%28Noise%20%26%20Radiation%29%20students

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