Room Correction

Many new systems come with room correction features. There are even some components dedicated to room correction. What's it all about and does it work?

Nearly all of the home theater processors/receivers currently on the market today boast a feature called room correction. The idea is that by plugging in a special microphone, the processor can "listen" to the sound in your room and correct for resonances and delays in the sound fo each speaker. You place the microphone in your favorite listening position, press a button and a burst of noise is played through each speaker in turn. With a bit of luck, after the process is complete, your system sounds significantly better.

The first thing the processor will do is calculate the arrival time or delay of each speaker. Chances are, your favorite listening position is not equi-distant from each speaker. This variation is distance means that sounds from each speaker arrive at your ears at slightly different times, blurring the soundscape slightly. Delay correction will tighten up the soundtrack on movies and generally improve the spacial imaging of sounds and instruments.

Next, the processor will analyze the frequency response to identify peaks and dips common to all speakers that are due to the room. It will then apply a customized filter to iron out the response , boosting the dips and cutting the peaks. With a flat frequency response, the sound is natural and balanced and the sound system seems to disappear, leaving you enveloped in sound that just seems to exist.

Where things can go wrong is that, typically, these systems only look at a single listening position. While it is possible to make the sound perfect at a single point in space, moving away from that point usually results in a degraded sound quality. Obviously, as you move around the room, the distance from each speaker changes; so the delay adjustments can only be valid at that one position. But worse, at low frequencies the room resonances result in spots where a particular frequency is magnified but just a quarter wavelength (1-5 feet) away that frequency is cancelled. If you were to place the microphone in one of these cancellation zones, the system would boost that frequency making it doubly boosted in a magnification zone.

Successful room correction is best done in conjunction with a measurement system so that you can see what you're doing. The room responses at all seating positions should be evaluated and averaged so that the correction filter improves the sound for everyone. When the correction process is complete, a final measurement can then confirm the improvements.

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