Ashly Electronic Amplifier none - Manual (Page 19)

too loud. Typically, high frequency speakers, particularly horn-loaded
compression drivers, are much more efficient than low frequency speakers.
Somehow, the system needs to be balanced for equal response across the audio
spectrum.
One of the inherent advantages of the "ideal" single-speaker system is that
the listener hears the entire frequency range radiating from a single "point-
source".
That is, all the audio information leaves the speaker from
essentially the same place and at the same time, ensuring that the listener
hears all frequencies in the correct time and spatial relation to each other.
As soon as the single speaker approach is abandoned, this important advantage
is lost. Now, the sound is coming from two or more speakers at two different
distances from the listener, and timing and phase errors are the result. See
figure 19.
Figure 19 A listener is unlikely to be equidistant froiri two
speakers in a multi-speaker setup, resulting in
time and phase inaccuracies at the listening
1ocation.
The resulting errors are most pronounced in that range of frequencies where
both speakers are contributing equal volume. In that case, you have the same
audio
information radiating from two discrete sources at the same time.
Ideally, the two resulting wavefronts should combine perfectly to reach the
listener at the same time, pushing and pulling the air in perfect
synchronization. What usually happens, however, is that the two wavefronts
reach the listener at different times and out of sync (out of phase). If the
two sound sources happen to be exactly 180® out of phase, then the listener
will experience a significant null (hole) in the sound over some range of
frequencies. If the listener then changes his position, all of the time and
phase relationships between himself and the speakers will change. These
relationships vary with frequency, too. In general, the mòre speakers that
are used in a system, the more errors that will result. This remains true in
most current professional sound systems.
Although there aren't many good solutions to this latter problem of physical
misalignment in a multi speaker system, there are, at least, solutions to the
problems of tweeter protection and sensitivity matching. By employing
frequency selective crossover networks, we can route low frequency material to
woofers and high frequency material to tweeters. This is accomplished by the
use of filters, either passive or active, which ensure that each speaker will
only "hear" that range of frequencies which it is capable of reproducing.
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