3Com CP-1 owner manual Theory Design

Theory

and

Design

CP-1 Digital Audio Environment Processor

quency.

Lexicon’s implementation, called the Panorama program, was designed using measured data on sound diffraction around the head to shape the frequency spectrum of the canceling signal. This signal is then itself canceled by a second signal, and so on, so that both the crosstalk and the

Speaker	Input	Higher order	Speaker
Level	Signal	Correction	Level	First order
L			R
				Higher order
		L		R
		L	R

signal that is canceling it are eliminated.

This works extremely well when the room is well damped and the listener’s head is correctly positioned. The first order devices described earlier required the listener to sit on the center line between the loudspeakers, and to arrange the angle between the speakers to correspond to the pro- grammed delay. Although the CP-1 provides adjustments to compensate for off-center listening and for varying speaker angles, maintaining a consistent listening position is still important and becomes more so with increasing frequency. With wide speaker angles, a movement of as little as 1 inch can make a perceptible difference. Fortunately, the effect is usually fairly good everywhere within a zone about one foot wide.

To achieve the fullest Panorama effect, your main loudspeakers should have good imaging. The smaller speakers that tend to be used with video systems may have an inherent advantage here but the most important requirement is that the two speakers have identical frequency response and symmetrical dispersion. It is not necessary, or desirable, to turn your listening room into an anechoic chamber but moving the speakers away from the walls can be helpful, as can adding absorption (as provided by carpets, curtains and/or sound-absorbent panels) to reduce the reflectivity of the floor, walls and ceiling.

First order correction travels to left ear, where it will be heard unless canceled by an additional correction. When these higher order corrections are supplied, accurate cancellation is possible.

Page 39