Correcting the Room
Acoustic correction circuits are home theater's missing piece
By Mark Fleischmann
The advent of high-definition television, the digitizing of surround sound and the steady rise of custom installation have all contributed to the ongoing improvement of the home theater experience. But the best may be yet to come. Using digital processing to correct a room's acoustic flaws may be the most important innovation of the next 10 years.
As any good system designer or installer knows, the room — after good hearing and eyesight — is the most crucial of home theater system components. Rooms with poor acoustic properties suck energy from speakers and electronics alike, making even the best gear operate distinctly beneath its potential. Imaging becomes vague. Subwoofers become one-note wonders. Music loses its snap, and movies rumble instead of roar. Customers wonder why they spent as much as they did, and reputations hang in the balance.
If a consumer is building his dream home, he'll have the luxury of dictating acoustically ideal dimensions for the home theater, preferably with the help of a consultant who's knowledgeable about acoustics. But most installations are born into existing rooms. Then the challenge is to minimize the acoustic problems of that space.
Acoustic room correction isn't a new idea — just look at any recording studio, or any listening room damped with diffusors and absorbers. But the idea of doing it digitally has been building steam for almost a decade, and the solutions, in various shapes, are finally coming to market. Room correction may well be the ultimate audio tweak for the end user, and the installer who hopes to make the customer happy.
Every room — except for the anechoic chambers in which manufacturers test speakers — has resonant or room modes. These modes cause peaks in certain areas of the audio spectrum, so that even a speaker designed to provide a relatively flat frequency response will sound louder at certain frequencies. Peaks that result from parallel walls are called axial modes. Where four surfaces are involved, tangential modes result. Oblique modes involve the ceiling and floor as well as the walls.