Phantom center?

bobinnv -- Thu, 01/01/2009 - 20:07

I am continually frustrated by the center channel performance of my 5.1 system. My front speakers are Quad 22Ls, with a Quad L-Center, so things should be matched up pretty well, at least in theory. But in real life, not so much. For most HD broadcasts, and for DVDs, I find I have to boost the center about +4db, else the dialog gets overwhelmed by music and other sounds coming from the other speakers. Or, if I don't boost the center channel, I end up turning up the volume, and getting overwhelmed when some explosion or other loud event happens.
I should also note that much of this is source dependent: some DVDs and HD broadcasts sound fine, others have seem to have very low volume on the center channel.
Is there a good solution for this? One idea is to revert to two speakers, with a "phantom center"; this should match the volumes correctly. Or make more use of the Dynamic Range Control on my receiver, so turning up the volume to hear the dialog won't result in losing my hearing when some on-screen explosion takes place.
Any ideas or comments appreciated.

Robert Harley -- Thu, 01/01/2009 - 23:26

It's not unusual to have to boost the center-channel level by a few dB to compensate for its lower sensitivity compared with the left and right speakers. This isn't a deficiency of the center speaker or of your system.
Nonetheless, horizontal center speakers in general have different frequency response and dispersion than the vertical left and right speakers, leading to a lack of seamlessness across the front soundstage. This is true even of expensive models. One solution is DSP speaker and room correction, which does an amazing job of making the center speaker sound more like the left and right speakers. Dialogue intelligibilty improves.
You can tell your controller or AVR that there's no center speaker, which will cause the controller or AVR to route the center-channel information to the left and right speakers, creating a "phantom" center-channel. This works only if you sit exactly between the left and right speakers. Listeners off to the side will hear the front soundstage collapse into the speaker that they are sitting closest to.
I'm of the opinion that you should use a center speaker for film-soundtrack reproduction.

bobinnv -- Sat, 01/03/2009 - 13:08

Thanks for the reply.

Do you see an advantage to a center speaker other than anchoring the dialog for off center listeners? My current setup, which I use for music, too, has a couch centered between the left and right speakers - so the "usual" viewers - my wife and I - are pretty much centered 95% of the time.

And of course, many TV broadcasts are in stereo, not 5.1, so much of what we view doesn't use the center channel anyway.

I would like to try a DSP system. Unfortunately my Cambridge Audio AVR doesn't have DSP built in. I was not as educated as I should have been when I bought the my AVR a coupe of years ago..

Bob in NV

Robert Harley -- Sat, 01/03/2009 - 20:31

It occurred to me that I could have given you a much shorter and direct reply that might solve your problem: boost the center-channel level by about 2-3dB above the level established during calibration with an SPL meter. A sound-pressure level meter is essential to setting the levels of a multichannel speaker system. You can get one at Radio Shack for $29.95. Get the one with the analog readout (CAT #33-2050). After you set the channel levels so that the meter says each speaker is producing equal sound-pressure level, boost the center channel level by 2dB. This makes dialogue easier to hear.
I would try this before getting rid of the center speaker. It really does anchor the soundstage, and also increases the system's overall dynamic range by adding additional drivers reproducing the signal.

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