Chapter_03_Hearing_and Noise

# Chapter_03_Hearing_and Noise - Section 3.4 Hearing and...

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Section 3.4 Hearing and Noise Figure 3.27 Artist’s sketch illustrating the anatomy of a human ear (from US NIOSH, 1973). 173

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Define a sound pressure level : P1 0 0 P L2 0 l o g P ⎛⎞ = ⎝⎠ (3-17) where the term P 0 is a reference value, 5 0 2 N P2 1 0 m (3-18) Define a sound intensity level (L I ), I1 0 0 I L1 0 l o g I = ⎜⎟ (3-19) where the reference value I 0 corresponds roughly to the reference pressure level (P 0 ). At STP, 2 12 0 0 2 P watt 1 0 a m =≈ × ρ (3-20) We also define a sound power level or acoustic power level (L W ), W1 0 0 W 0 l o g W = (3-21) where 12 0 1 0 w a t t (3-22) The unit used to express the sound pressure level, sound intensity level, and sound-power level is called the decibel (dB). Multiplying each side by 10 and recognizing the definitions of Eqs. Error! Reference source not found. and Error! Reference source not found. , one obtains IP L (r) = (3-23) It is useful at this point to define a reference distance (r 0 ) equal to 1 meter, 0 r1 m = (3-24) Then, I W 10 10 0 r L (r) L 10log Q 11.0 20log r =+ −− (3-26) or, P W 10 10 0 r L (r) L 10log Q 11.0 20log r
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## This note was uploaded on 07/23/2008 for the course ME 521 taught by Professor Cimbala during the Fall '07 term at Penn State.

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Chapter_03_Hearing_and Noise - Section 3.4 Hearing and...

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