Lexicon CP-1 PLUS V2.0 Owner's Manual page 63

Theory
and
Design
Page 58
Speaker Set-Ups for Pro Logic
The requirements for film sound are quite different from those for the
playback of music. The most important track in any film is the dialog. When
the two stereo channels are played back through two speakers with no
decoder, dialog will appear to come more or less from the center, but only
for those listeners on the center line of the main stereo pair.
The most important job for a Pro Logic decoder is canceling the dialog from
left and right loudspeakers. To be able to hear this you have to set up a center
speaker. We strongly recommend that a center channel speaker be used
with any surround decoder; the difference it can make to the subjective
quality of a film is enormous.
Assuming some form of center speaker has been provided, the next most
important point is providing enough spatial impression. Once again, the
best way to do this is with loudspeakers at the sides of the listeners. When
we tried this with the CP-1 we made an interesting discovery. When the Left
and Right loudspeakers are spread wide enough to fall within 20 degrees of
the listeners' sides, there is a tremendous change in the impact of the film.
The sound stage becomes much wider than the screen - so wide in fact that
the listener is literally drawn into the action. This effect should not be
surprising - lateral sound is known to grab our attention in a way that front
sound does not. Occasional extra wide sound effects can seem peculiar at
first for being so much wider than the screen but when the mix is good the
emotional impact of the wide sound can be very great. The disparity
between the size of the video screen and the size of the sound is usually easy
to accept, and the added impact is hard to give up once you have heard it.
A few theaters are beginning to wake up to the power of this effect. It is being
used presently and has been used in the past. Some theaters, such as Imax
and Omnimax, use it routinely with multi-track masters, and older tech-
niques such as Todd-AO had wonderful multichannel soundsystems.
One reason standard theaters do not use this is the poor accuracy of
previous surround decoders when used with commercially available stereo
prints. Azimuth errors on both optical and magnetic masters are common
and in theaters there can often be considerable dialog leakage into the left
and right channels. To increase the seating area with acceptable dialog,
theaters place the left and right speakers within the confines of the screen.
The needed spatial impression is supplied by the acoustics of the theater
itself, augmented by surround speakers placed all around the audience. The
surround speakers are driven in parallel from the surround channel output
of the decoder.
The CP-1 can be used to create a similar set-up in the home by connecting
the side speakers to the rear amplifiers. However, our experiments indicate
that most people find this far from optimal. The use of auto azimuth, auto
Lexicon