Lexicon CP-1 User Manual download pdf (Page 40)

Lexicon

Page 36

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Side sound must be within this angle.

Theory

and

Design

Understanding the importance of lateral reflections enabled more accurate

evaluation of architectural acoustics. The best halls were usually found to

have high lateral energy for obvious architectural reasons, such as a long

narrow shape with high ceilings. Fan-shaped halls, although they have

better sight lines, are more adaptible to multiple uses and hold a greater

number of seats for their total volume than a shoe-box hall, tend to have

fewer attractive, sideways reflections and more of the unpleasant, monau-

ral overhead and rear-wall kind. These differences can be overcome by

design. A notable example is the Boston Symphony’s fan-shaped Tangle-

wood music shed. Tanglewood sounds good because the reflectors above

and in front of the orchestra (known as clouds) have angled sides that reflect

energy sideways onto the audience instead of just downward.

Lateral Sound in your Listening Environment

In an ordinary listening room, conventional stereo set-ups (with loudspeak-

ers separated by 60 degrees or less) do not excite enough SI to sound

pleasant without some help from the room. (A similar speaker arrangement

in the artificial environment of an anechoic chamber is exceedingly detailed

and precise, but unpleasant.) Some lateral reflections are needed to make

the sound musical.

Ordinary two-speaker stereo works as well as it does because sideways-

moving reflections can be excited at low frequencies by two loudspeakers

if they are placed asymmetrically in the room or if they are driven with out-

of-phase low-frequency information.

3,4

(Out-of-phase bass is intentionally

provided in the best stereo recordings.) Another reason is that most

listening rooms have reflective surfaces to the sides of the listener. A

popular listening room treatment puts absorptive material at the front of the

room, leaving the walls by the listener reflective. This improves the clarity

by removing the front reflections, while retaining those from the side. This

also explains the appeal of loudspeakers that produce lots of sideways-

reflected energy.

Unfortunately, in most two-speaker set-ups the mid- and high-frequency

lateral sound is reduced unless the speakers are unusually widely placed.

The listener can hear a little of the original hall, stretched between the stereo

loudspeakers, but never really becomes a part of it. What is worse, the

lateral sound that exists in most playback rooms has so little delay that the

ear can not separate it from the direct sound. The reflections generate some

SI but they also cause coloration and muddiness. Small rooms usually

sound better if these reflections are broken up (with wall hangings, furni-

ture or bookcases) or absorbed (with curtains or sound-absorbent panels).

When this is done the room becomes quieter and clearer but not in any way

like the original hall.

The Lexicon CP-1 resolves this deficiency by supplying appropriate signals

to loudspeakers at the sides of the listener or by modifying signals to the

main loudspeakers to fool the ear into thinking there are loudspeakers at the

Sound from the side is vital to lis-

tener comfort and involvement....It

must really be from the side!

In an ordinary room, the room sup-

plies these directions, and the sound

is cramped, but tolerable. The overall

impression, however, may be muddy

due to unwanted frontal reflections.

No Sound

In an anechoic chamber, this side-

ways sound is missing...and music

sounds unpleasant.

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Lexicon CP-1 User Manual Page 40

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