Rethinking Room Correction

Room correction systems that optimize your audio system for the acoustics of your room have been around for more than a decade — but frankly, they’ve never won me over, and I’m finally starting to understand why.

It seems like such a good idea: Put a microphone in the primary listening position (and sometimes others, too), run some test tones, and electronically adjust the sound to minimize or eliminate the negative effects of the room and the imperfections of your speakers. But some recent discussions with audio experts have made me question the wisdom of this approach. Consider the following quotes.

Laurie Fincham, THX Chief Scientist, during a discussion on his patio: “We’re sitting here talking outdoors, your voice sounds fine to me, and I’m having no problems understanding you. But if we go into the car, into a completely different acoustical environment, I don’t suddenly think, ‘I’ve got to EQ Brent’s voice to make it sound right in this different space.’ Your hearing adapts instantly to it.”

Paul Hales, president of Pro Audio Technology, while he was showing me the digital signal processing technology built into his company’s amplifiers: “A grand piano sounds right no matter where you place it, whether it’s in a concert hall or your living room. You don’t go in and start EQ’ing it for different acoustical environments.”

What they’re getting at is the remarkable ability of the human senses to adapt to different surroundings, a topic discussed in depth in Chapter 11, “Adaptation,” in Dr. Floyd Toole’s book Sound Reproduction: Loudspeakers and Rooms. After discussing humans’ ability to “separate acoustical aspects of a reproduced musical or theatrical performance from those of the room within which the reproduction takes place,” Toole concludes ". . . all aspects of room acoustics are not targets for ‘treatment.’ It would seem to be a case of identifying those aspects that we can, even should, leave alone and focusing our attention on those aspects that most directly interact with important aspects of sound reproduction.”

You may conclude from this that by adjusting all aspects of the sound to compensate for the acoustics of a room, we can actually make the sound less natural, because we’re adding a lot of EQ and phase correction to sound that our hearing system has already corrected for us.

This, I think, is why I’ve gotten mixed results from the automatic room correction technologies incorporated into many A/V receivers. With some movie scenes and pieces of music, the post-correction response sounds better to me. With some, it sounds worse.

And what are those aspects of room acoustics Toole refers to that we should focus our efforts on? Mainly, bass.

As I’ve explained previously, every room has major resonances in the bass, but relatively even response in the midrange and treble. Typically, the frequency at which a residential listening room’s response transitions from huge resonances to smooth response is around 200 Hz.

You can hear the effects of these resonances in two ways. First, some bass notes will be boosted and others attenuated, so melodic bass lines will sound uneven. Second, bass notes that occur at the room’s resonant frequencies will “ring,” hanging on past the time when they were supposed to stop, and obscuring details in the midrange and treble.

A few who get it right

To my knowledge, Lexicon was the first to make a room correction system that fixed bass problems and left everything else alone. I encountered this technology in a Lexicon processor I reviewed eight or nine years ago, and loved it. Pro Audio Technology is doing much the same thing in its latest amplifiers, giving the installer the option to perform corrective equalization only below a certain frequency.

Granted, those are both expensive and exotic products, but bass-only room correction may be trickling down. At the recent CEDIA Expo, I saw a prototype of the new Krell Foundation preamp/processor, which includes room correction that you can set to function only below a certain frequency. It’s not necessarily because Krell’s getting the room-EQ religion, though. It’s for a reason I hadn’t even considered.

“Our customers are buying Thiel or Wilson speakers because they want to hear the characteristics of those speakers,” Krell president Bill McKiegan told me. “This lets them fix the important room problems without changing the essential character of the speaker.”

The Foundation is still very much in prototype mode — according to McKiegan, the final product will look much different from the plain black box you see here — and it won’t be available for a few more months. And of course, it’s a Krell so it ain’t cheap: Even though it’s the company’s “starter” pre/pro, it’ll cost about $6,000. But still, of all the pieces of audio electronics I’ve seen this year, this is the one I really can’t wait to get into my listening room.

I don’t often review receivers or surround processors, so maybe I’ve overlooked another company offering bass-only room correction. If so, let us know about it in the Comments section below.

3dit0r's picture

I believe Meridian were the first to advocate 'bass only' correction, and do so in the time, rather than frequency, domain. They have a white paper 'The Gentle Art of Room Correction' which is an interesting read.