Lexicon CP-1 User Manual download pdf (Page 46)

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Page 42

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.

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Lexicon CP-1 User Manual Page 46

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