Fine Tunes #4 Page 3
Finally, focus the image. The basic technique is to rotate only one speaker baffle to change the dispersion pattern. Toe-in, as it's called, is best done with an audio bud on hand. Sit in the listening chair and start with the speakers aimed slightly behind your head, with the same distance from ear to tweeter on both sides. Play a recording with voice or violin and listen for focus while your assistant rotates one speaker around the inside front spike for a reference.
Allen: "The listener will then signal to indicate the best speaker location." I bet . . . by falling off the chair and plotzing, no doubt. "When this is done, neither speaker has to be readjusted to 'look' like the other. The reason the speakers are not usually symmetrical is that rooms are not symmetrical, and these differences affect dispersion."
Fig.5 Types of Motion for Speaker Adjustments
A few final suggestions from Bernd Theiss and the other engineering boys at Audio Physic: One change affects another, so go back and keep refining the steps until you're really happy with the sound. While this plan works without room treatments, their judicious use can be a great help. For example, since the listening position is close to a rear wall, try a towel, a pillow, or some other light damping material behind your head—it might well improve the sound. (We listen in a modified version of the Perkins Plan; I find I have to damp or disperse the reflections behind the listening position.)
Also, by moving your head back and forth—yes, like an Egyptian!—you'll find the distance from the wall where there's the most energy. This is a result, audio engineers will have you know, of slow wave velocities close to room boundaries. And last, as I recommended in the previous column, the amount of toe-in can affect the sound quite drastically. Listen to the difference between tweeters pointed directly at your ears and then aimed behind the listening position. To some extent, you can adjust for a bright or dull room this way.