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fundies-ch3 - Measurement of Sound Decibel Notation Types...

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Measurement of Sound Decibel Notation Types of Sounds Adding Sound Levels/Spectrum Level Spectral Analysis Shaping Spectra Temporal Factors Distortion
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Decibel Notation Intensity is measured in Watts/cm 2 Range of : Just Audible 10 -16 W/cm 2 to to Just Painful 10 -4 W/cm 2
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Can You Imagine? AUDIOLOGIST: “Mr. Smith, you hearing in the right ear is down to about 3 times ten to the negative twelfth Watts per square centimeter, while your left ear is a little bit better at ten to the negative fourteenth…” MR. SMITH: “ZZZZZZZZZZZZZ”
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SO, We need a simpler set of numbers Something less unwieldy The Solution is the BEL (after A.G. Bell)
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The Genesis of the Bel the logarithm of the ratio of a measurement to a reference value
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What is a log? Log (x) = power you would raise 10 to to get x e.g., log (10) = 1 because 10 1 = 10 or, log (0.01) = -2 because 0.01 = 10 -2 You can use a calculator to obtain logs
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Inside the Logarithm is A ratio of two numbers (or fraction) An absolute measurement over A reference value
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The Reference Value for Intensity Level is 1 x 10 -16 Watts/cm 2 Bels IL = log ( Im/ 1 x 10 -16 W/cm 2 ) Where Im = measured intensity
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The Range of Human Hearing Detection 10 -16 W/cm 2 OR 0 Bels Pain 10 -4 W/cm 2 OR 12 Bels
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The Bel Is Too Gross a Measure For Us So, We work in TENTHS OF BELS The DECIBEL (dB) dB IL = 10 log ( Im/ 1 x 10 -16 W/cm 2 )
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EXAMPLE: What is IL of sound with absolute intensity of 2 x 10 -16 W/cm 2 = 10 log (2 x 10 -16 W/cm 2 / 1 x 10 -16 W/cm 2 ) = 10 log (2) = 10 (0.3010) = 3 dBIL
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Example--Relative Change How will the intensity level change if you move to twice as far from a source?
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