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B
A
Theory
and
Design
The best way to generate spatial im-
pression (SI) is with appropriate sig-
nals from loudspeakers at the side.
Reverb, Ambience and the Surround
programs can all be used to generate
these signals.
be the sound that comes from the sides.
Early research with quadraphonics involved extensive experimentation
with speaker placement, and confirmed that additional speakers beside the
listener sounded better than the conventional approach of putting pairs of
speakers in front and behind. Our research into speaker placement with
Ambience confirmed the previous results of others: The side speakers
should be directly to the side of the main listening position, plus or minus
about 20 degrees. Beyond this critical angle the spatial impression is greatly
reduced.
The sides are the most important additional speakers, much more so than
the rears. Keep in mind that, although you can use the left and right main
speakers to simulate a phantom center speaker, you cannot produce SI with
one speaker in the front and one at the rear . (You can perform this
experiment for yourself with the CP-1 using the Ambience program: Try the
side speakers both in their usual positions and in the front corners. If your
listening room has enough absorption to damp its side-wall reflections, the
side location will provide much more spatial impression, and will sound
substantially better.) Speakers in the front are useful - if you want the best
possible sound from Ambience you may want to try an additional pair in the
front corners, wired in parallel with the rear. This additional pair, as well as
the rear speakers, may sound best if placed above the listener.
The effectiveness of the CP-1’s Ambience simulation is heavily dependent
on the source material and the playback room. If the playback room is large
and reverberant, its reflections may dominate those generated by the
program. Carpet, drapes and furniture can all be used to break up or absorb
undesirable reflections, making it easier to hear the processor’s output. The
balance between the side, rear and front speakers is also very important. If
the channels are set up properly, no single speaker will be audible by itself.
There are two basic hall shapes in Ambience: Rectangular and Fan. In a
listening room with sufficient acoustical absorption, using source material
without too much reverberation of its own, the two shapes are clearly
distinguishable. For most classical recordings the rectangular hall sounds
somewhat better because of its stronger side reflections. In our fan-shaped
hall (unlike actual physical designs) you can increase the proportion of side
to rear sounds, by increasing the Effect Level and shifting the F/B Balance
controls toward the front. When this is done, another different but also
pleasant sound results.
Although the Ambience program can provide some recirculation (adjust-
able with the Liveness parameter), for long decay times it is better to use
Reverb. The Large Hall ambiences are not intended to be used on material
which is more appropriate to a smaller ambience, such as a small hall or a
club. Highly percussive material is almost always better in the Small
program which is quite successful in livening and expanding popular
Placement of side loudspeakers is
critical! Placement B sounds much
better than A, especially when the
room is well damped.