User Guide

Sound System Design Reference Manual
Combining Delayed Sine Waves
If two coherent wide-range signals are
combined with a specified time difference between
them rather than a fixed phase relationship, some
frequencies will add and others will cancel. Once the
delayed signal arrives and combines with the original
signal, the result is a form of “comb filter,” which
alters the frequency response of the signal, as
shown in Figure 1-4. Delay can be achieved
electrically through the use of all-pass delay
networks or digital processing. In dealing with
acoustical signals in air, there is simply no way to
avoid delay effects, since the speed of sound is
relatively slow.
1-3
Figure 1-4A. Combining delayed signals
Figure 1-4B. Combining of coherent signals with constant time delay