# Loudness - Loudness October17,2007 What is it What The...

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Loudness Loudness                                           October 17, 2007

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The Process
At the Eardrum Pressure wave arrives at the eardrum It exerts a force The drum moves so that WORK IS DONE The Sound Wave delivers ENERGY to the EARDRUM at a measurable RATE. We call the RATE of Energy delivery a new quantity: POWER POWER

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Quickie Review Work = force x distance = energy Unit is either Joules or KWH (later) Energy is a good thing. Wasting energy is bad
POWER Watt second Joule second energy Power = = = Example: How much energy does a 60 watt light bulb consume in 1 minute? J 3600 seconds 60 second joules 60 second joules 60 watt 60 = × =

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By the way …. . You BUY KWH from the power company.
We PAY for Kilowatt Hours energy time time nergy KWH = × = e We PAY for ENERGY!! Not Power

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More Stuff on Power 10 Watt INTENSITY = power/unit area 10 Watts = 10 Joules per second.
Intensity 2 4 : r P I sphere A P I π = =

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Same energy (and power) goes through surface (1) as through surface (2) Sphere area increases with r 2 (A=4 π r 2 ) Power level DECREASES with distance from the source of the sound. Goes as (1/r 2 ) ENERGY So….
To the ear …. 50m 30 watt Area of Sphere =4 π r 2 =4x3.14 x 50 x  50 = 31400 m 2 Ear Area = 0.000025 m 2

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Continuing watts .000000237 power Ear At 000025 . 0
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Loudness - Loudness October17,2007 What is it What The...

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