Fine Tunes #2
While I suspect a majority of readers are in the same boat, a number of you have the resources to either custom-build or claim for your own a dedicated listening room. This is both a good and, strangely, a bad thing. The benefits are many, but let me suggest that, rather than hiding out in your lair, you drag in loved ones and good friends to join you from time to time. Make it easy for them to learn something more about your obsession and how good it can be. Infect someone today.
Now to the listening room. For the purposes of this discussion, let's assume your room is symmetrical and rectangular. (All bets are off with irregularly shaped rooms, or large, open spaces like my loft.) The commonly received wisdom on dynamic speaker placement is often referred to as the Rule of Thirds, which calls for the speakers to be placed a third of the way into the room from the wall behind the speakers (ie, the wall facing the listener) and a third of the way in from each side wall. That's a pretty decent place to start; fine-tuning is accomplished by nudging the speakers and the listening chair back and forth until the frequency response smooths out. What you want to avoid are frequency-related anomalies—nulls and peaks—caused by the interaction of standing waves. The modes, as they're called, are related to the distance between any two parallel walls, and the degree to which they are excited will depend on the speaker positions.
I found myself discussing this at length with George Cardas while he was here setting up Judy Spotheim's La Luce turntable. He pointed out that, even when applying the rule of thirds, you can wind up fighting the room's resonant modes. George's solution is to bite the bullet, do the math, and drop the speakers where they'll cause the fewest interactions. "And the way to do that," George continued, "is to make the modes as mathematically indivisible as possible."
I was never much good at math, but you knew that. So let's just hold our noses and jump right in—a little knowledge goes a long way. (The following information can also be found at the Cardas website.) According to George:
"The Audio Engineering Society's (AES) standard listening room [see following letter—Ed.] is a model of the math used in this system. This method will work with any panel or box speaker, in any reasonably sized rectangular room. The AES standard room is a Golden Cuboid 10' by 16' by 26'. Its dimensions progress in the Golden Ratio, or Fibonacci, sequence (5,8,13,21,34 . . . ). The three major modes created within the listening space are indivisible, and therefore will null rather than beat. The math used to create this perfect listening space can also be applied to speaker placement within any listening space. The key to this formula is the ratio Phi (peculiarly enough, this is both 0.6180339887 . . . to 1 or 1 to 1.6180339887 . . . ). The three major [lateral] room modes are created by the distances: ceiling to floor, side wall to side wall, and front wall to back wall.