Acoustics of Concert Halls and Rooms

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Pressure squared:

ρc ≈ 400

I = p2 /ρc ρ = density

c = speed of sound

We define sound pressure level:

Lp = 20 log p/p0 p0 = 2 x 10-5 Pa (or N/m2)

(or SPL)

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TYPICAL SOUND LEVELS

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MULTIPLE SOURCES

Example:Two uncorrelated sources of 80 dB each will produce a sound level of 83dB

(Not 160 dB)

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Multiple sources

What we really want to add are mean-square

average pressures (average values of p2)

This is equivalent to adding intensities

Example: 3 sources of 50 dB each

Lp = 10 log [(P12+P22+P32)/P02] = 10 log (I1 + I2 + I3)/ I0)

= 10 log I1/I0 + 10 log 3 = 50 + 4.8 = 54.8 dB

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Sound pressure and intensity

Sound pressure level is measured with a sound level meter (SLM)

Sound intensity level is more difficult to measure, and it requires

more than one microphone

In a free field, however, LI LP

≈

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