1376 Chapter 35
35.3.4.2 SPL Calculations
After the loudspeakers have been correctly aimed, one
may begin to calculate the sound-level conditions
attainable by these. The first results are given for the
direct sound pressure level (SPL). As long as we predict
a good direct sound coverage over the listener area we
have also to expect perfect intelligibility numbers, of
course under the condition that the reverberation level is
not too high.
A complex summation—phase conditions including
travel-time differences should be included—has to be
used as the standard method of calculating the direct
SPL. This method is exact for a planar wave, but only
an approximation for the superposition of waves with
different propagation directions. But the complex sound
pressure components of different coherent sources must
first be added and afterward squared to obtain SPL
numbers. In so-called DLL or GLL approaches one
always calculates the complex sum of all sources in the
array.
Today simulation programs are usually still only
analyzing programs, capable of calculating which levels
can be obtained by which loudspeakers and under which
acoustical conditions. But questions are more and more
asked the other way around. The program of the future
also should query the user for a desired average SPL of
the system, and automatically adjust the power provided
to each loudspeaker—with a warning when the power
required exceeds the capabilities for the loudspeaker,
based on the desired SPL of the design, the sensitivity
and directivity of the loudspeaker, the distance of throw,
and the number of loudspeakers. This presupposes, of
course, new algorithms that in most of the simulation
programs are just being developed.Figure 35-43. Reflectogram and ray visualization in
EASE 4.2.
A. Reflectogram.B. Ray visualization in an EASE model.C. Control folder for visualization.Figure 35-44. Reflectogram and Impact hedgehogs in
ODEON 9.0.Figure 35-45. Reflectogram with tail and Schroeder plot.