Now we have sufficient volume under the balcony, but the sound from the two speakers
arrives at the listener’s ears some 76 to 84 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 SDA-102 delay to 76 or 84
milliseconds? Obviously, the geometry will not allow us to exactly synchronize every location
under the balcony; we have to compromise.
First, you must consider the program type. For spoken word programs, you will produce the
best intelligibility 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 84-86 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.4.) Use the
SDA-102 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.
Application II: Center Cluster with Front Fills
Fig. 6 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
SDA-102, you can improve the intelligibility and add a new quality without ringing up any
significant costs. Use the SDA-102 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.
Find a central place in the audience where the center cluster is 6 to 8dB louder than the direct
sound from the performer. Delay them so that their sound arrives 5 to 8 milliseconds after
the direct sound from the performer. Experiment by bypassing the SDA-102 in and out to
hear how the source of the sound seems to move from the loudspeakers to the performer and
back. Now your ears have the same directional information as your eyes, so the perfor-
mance will sound more natural and exciting. The best seats in the house just got better.
What about the front fills? Their purpose is to add intelligibility and listening comfort to the
first few rows nearest the stage by filling in the areas missed by the center clusters. Simply
7
Fig. 6:
Synchronizing
center clusters
and front fills.
