Center Cluster With Front Fills - SABINE Power-Q Operating Information Manual

Fig. 12 shows a typical situation where the performer is amplified by a center cluster hanging
above the stage. Almost everybody in the audience will enjoy good sound, except those seated in
the shadow of the balcony. So we add an under-balcony speaker to fill in the shadow.
Now we have sufficient volume under the balcony, but the sound from the two speakers arrives at
the listener's ears some 55 to 69 milliseconds apart. The two signals, along with their echoes,
result in an unintelligible cacophony. We must delay the sound from the under-balcony speaker to
synchronize the signals. Do we set the POWER-Q delay to 55 or 69 milliseconds? Obviously, the
geometry will not allow us to exactly synchronize every location under the balcony; we have to
compromise.
First, consider the program type. For spoken word programs, you will produce the best intelligibil-
ity if the signals from the under-balcony speakers arrive within 10 msec. of the signals from the
center cluster. Therefore we should set the delay to 65-69 msec. You can allow a little more
reverberation for programs that are mostly music.
Next, we must eliminate comb filter distortion. Find the axis where the levels of the center cluster
and under-balcony speaker are equal. (See "Comb Filter Distortion," p.15.) You can use the
POWER-Q to precisely synchronize the speakers along this axis to eliminate the most severe
comb filters. Comb filters off the equal-level axis are much less of a problem since a louder signal
is not affected very much by a weaker signal.
Finally, you can experiment with adding 5 to 10 milliseconds delay to both sets of speakers to
enhance the Precedence Effect for the audience seated near the performer.
In the final analysis, every setting is a compromise, and your ear has to be the final judge. Check
the sound in several different locations throughout the auditorium and correct the most severe
irregularities.
Fig. 13 below describes a typical application that has a stage with a microphone, a center cluster
above the stage, and front fills in front of the stage. There must be thousands of installations
throughout the world like this that "get by" without digital delays. But with the POWER-Q, you can
improve the intelligibility and add a new quality without ringing up any significant costs. Use the
POWER-Q in this situation to align the visual image with the acoustic image. The program is
much more enjoyable when the amplified sound seems to be originating with the performer, not
the loudspeakers.