Lexicon DC-1 Supplementary Manual page 17

DC-1Theory
and Design
Ambience
The best way to generate spatial impres-
sion (SI) is with appropriate signals from
loudspeakers at the side. Reverb, Ambi-
ence and the Surround programs can all
be used to generate these signals.
14
While Panorama recreates the space that already exists in the recording, the
Ambience effects actually generate the side and rear reflection patterns of
ideal halls. The reflections were determined by computer ray-tracing using
architectural data, augmented by Lexicon's decades of experience with
digital concert hall simulation.
The ambience simulation is done in stereo. Instead of feeding a monaural
signal derived from the combined left and right channel inputs of the
processor, the DC-1 has two input points corresponding to instruments
placed on the left or right side of the stage. From these, the loudness and
delay of the reflections for the side and rear loudspeakers are calculated. By
using full stereo for the inputs to the simulation programs, the spread of the
soundstage is automatically preserved in the simulation process. This
obviates the need for adjustment on every different recording, a chore
required for decent results on some other systems.
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°. The spatial impression is greatly reduced outside of this critical
angle. The primary reason for this result is the critical importance of the
lateral energy at frequencies below 700Hz, which is usually insufficient in
playback rooms. Thus, speakers which can reproduce frequencies down to
100Hz or below are recommended for the sides. If tiny speakers with
subwoofers are used for the sides, it is best to use a separate subwoofer for
each side, and place the subwoofers on opposite sides of the room.
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 spa-
ciousness with one speaker in the front and one at the rear . (You can
perform this experiment for yourself with the DC-1 using the Ambience
effect: 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.) The DC-1 mixes some reverberant
sound into the front speakers, to create an overall impression.
Lexicon