Axiom Home Page Forums General Discussion Home Theater Dual M22's as a center channel

Hi John,

I would certainly agree with you that the degree of sonic improvement of using two centers is very dependent on the room setup, seating locations and the vagaries of the room itself.

But my proposal of using two centers wasn't to deliver sonic improvement; rather, it was to remove the extremely off-putting sensation that may occur with some large-screen front projection systems where the dialog gets localized at the single center channel speaker because it's too far away from the visual screen center. That is what using two centers (above and below) is meant to correct, and it does that quite well in the installations I've heard with no audible downsides.

You also said:

"The main problem with dual identical centre speakers is the havoc they play with dialogue because of the cancellations and reinforcement at various frequencies right across the room not just on axis."

I have not noted any of these effects in several installations nor in my own experiments with single and dual centers, and I would point out that "cancellations and reinforcements" are always occuring in any multiple speaker installation in any given room. Despite these effects, multi-channel music reproduction and home theater can be enormously satisfying and highly realistic.

You also noted:

"Audibility of comb filtering depends on several factors including frequency, delay, phase, reflection etc. While in some rooms the two speakers may act to anchor sound in the middle of the screen, in others there could be directivity to one or the other speaker because of the comb filtering. Duals will not always centre the channel in the middle of the screen because of these artifacts."

So far, I have not heard any installations where the use of dual centers resulted in any degradation of center channel sound or intelligibility.

Regards,

Hi Nick,

I know Audyssey Multi-EQ makes these claims but I've not been able to participate in a really good comparison so I can't comment. I'm suspicious of multi-EQ and over-processing, but we live in an era of amazing chips that have enormous processing capacity so I don't rule out the possibility that it just might work well with no "artificial" artifacts.

Regards,

Hi Murph,

Heh, heh, heh, indeed. It's an interesting topic. From the evidence so far, there is no perfectly acoustically transparent screen material, and certainly conventional perforated screens can cause all kinds of nasty colorations. There seems to be some reasonable evidence that woven screens are superior to perforated in reducing various problems but I'll wait until I can see some indenpendent measurements and conduct some listening tests.

It's a subject worthy of investigation and one that I'm sure we'll consider in the future at Axiom. However, until really good evidence--not sponsored by a screen maker--is in, my advice is to avoid putting loudspeakers behind perforated screens if at all possible.

Regards,

Sorry, I meant how would a single M60 work as a center under my configuration. I have no intentions of replacing my TV.

Ahh, Sorry Drew, I misunderstood.

and thanks Alan
for helping me not feel so bad about my suspicions over just how well it could really work.

Edited: I was apologizing for not mentioning the link was sponsored by a screen film vendor, but upon going back, it appears to be written by the staff of "Home Theater"'s webzine but you just never know for sure. Anyways, it's still the best written, laymans' explanation I have read so far, as long as you take it with the obligatory grain of salt required.

Hijack victims released and unharmed....

Great comments as usual Alan, however this comment has me concerned.

Quote:

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But my proposal of using two centers wasn't to deliver sonic improvement; rather, it was to remove the extremely off-putting sensation that may occur with some large-screen front projection systems where the dialog gets localized at the single center channel speaker because it's too far away from the visual screen center. That is what using two centers (above and below) is meant to correct, and it does that quite well in the installations I've heard with no audible downsides.

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No one can argue with trying to centre the channel in the middle of the display. I'm not so sure two identical speakers above and below the screen achieves that objective and it has the unfortunate effect of creating less linear frequency response throughout the room. Two identical signals in phase running through two identical speakers symetrically positioned would produce a lobe running down the vertical axis. And given the height of most screens the lobe would be fairly wide over several seats. Not my idea of good sound reproduction across the room.

On the other hand, if you have no other choice, and you sit pretty much on center, it may acceptable despite the acoustical problems dual centres create from comb-filtering, lobing, cancellations, and different arrival times.

Quote:

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I have not noted any of these effects in several installations nor in my own experiments with single and dual centers, and I would point out that "cancellations and reinforcements" are always occuring in any multiple speaker installation in any given room. Despite these effects, multi-channel music reproduction and home theater can be enormously satisfying and highly realistic.

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I can see why you would make these observations if you sit in one sweet spot and don't move. However, as you stated earlier, the whole point of a center is to anchor dialogue to the screen. By using dual centers the voices will move to the left or right depending on where you're sitting. In light of the acoustical damage done by duals I would lean toward not wasting money on dual centers, and instead either running without a center and use the left and right to derive the (phantom) center, or go with a carefully placed horizontal centre. I guess I've been in enough HTs using duals where the audibilty of voices is too heavily compromised by the resulting artifacts to blame on room acoustics.

My room isn’t very big, so the ‘sweat spot’ is really three but-spaces on the couch across the width of the room. With my two vertical centers I can’t detect this comb filtering or any other undesirable effects when I sit in the middle, right or left side of the couch. I suppose if someone had a pretty large room (20 feet wide or so), there may be some sonic anomalies…..but there are none in my 12’ wide room. I did have to experiment quite a bit with placing the M22’s. If I had them 12” apart or closer, the center channel was localized to the center of the screen. If I moved them too far apart, the center channel just sounded “off”. I’ve got them about 30” apart now and they sound great. I also tried towing them in and out and that didn’t do much. I leave them pointing straight into the room now.

One of these days I may try two VP’s under/over the screen, but I’ve got better things to spend money on for the time being.

I don't like sleeping in my own sweat spot, but sleeping in someone else's sweat spot is worse.