Page 177 - Master Handbook of Acoustics

means that the sound field of the room is not completely homogeneous during this transient decay
period. Inhomogeneities of the sound field are one reason why reverberation times vary from point to
point in the room, but there are other factors as well. Uncertainties in fitting a straight line to the
decay also contribute to the spread of the data, but this effect should be relatively constant from one

position to another. It is reasonable to conclude that spatial variations in reverberation time are
related, at least partially, to the degree of diffusion in the space.

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FIGURE 9-4 Reverberation time characteristics of a 22,000-ft video studio with acoustics
adjustable by hinged panels, absorbent on one side and reflective on the other. At each frequency, the
variation of the average reverberation time at each of the three positions indicates nondiffuse
conditions. This is particularly evident at low frequencies.

Standard deviations of the reverberation times give us an insight of the spread of the data as
measured at different positions in a room. When we calculate an average value, we lose all evidence
of the spread of the data going into the average. The standard deviation can be used to quantify the
data spread. Plus or minus one standard deviation from the mean value embraces 68% of the data