1.7 ROOM ACCOUSTICS

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The basic idea is to determine how sound energy is distributed, absorbed and reflected in a closed space.

Sound is absorbed by walls, floors, etc.

the `a' absorption coefficients are determine experimentally, and can be found in the table below, [sources ??????]

The absorption coefficient `a' for a room can be calculated using the `a' for each surface,

`a' can also be corrected for temperature and humidity using factors in the table below,

previous assumptions were based on rooms with uniform power distribution, but this is not the case.

Sound pressure is more useful than energy density, and happens to be quite similar in formulation.

try problems S27, S28, S29, S30, S31, S32, S33

1.7.1 Sound Source Power Measurements Revisited Again

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Step 1: Measure sound on surrounding sphere,

- r > 2 times largest dimension

- over frequency ranges, e.g. octaves 31.5, 63, 125, 250, 500Hz

Step 2: Calculate R (via a) or experimentally with sound decay equation from before

Step 3: Calculate sound power level for each measurement position, and each frequency with,

Step 4: Calculate Lw for each frequency band.

Estimation of R from sound decay is based on equations,

1.7.2 How Sound Propagates

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When sound reflects off a flat surface it keeps the same spherical surface, but the center of propagation is mirrored across the reflecting surface. Like light the angle of incidence is equal to the angle of reflection.

When the sound is incident on a narrow slit or edge, it regenerates, as if the slit is a new source.

various other combinations of openings in wall, and half slits produce different sound propagation patterns.