How many woofers does a center channel really need? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 48 Old 02-01-2010, 04:12 PM - Thread Starter
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Why do center channel speakers typically have two mids and a tweeter? I'm new to all of this, but I'm planning on building speakers to go under my projection screen and I'm wondering if a single woofer and a tweeter would work ok.
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post #2 of 48 Old 02-01-2010, 04:27 PM
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Because they look like they would have a wide dispersion and because a single larger woofer would not fit into a slim horizontal cabinet. Single woofer/tweeter would work best if oriented vertically.

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post #3 of 48 Old 02-01-2010, 04:52 PM
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Two or more woofers oriented horizontally is not good at all as this article will demonstrate :

http://www.audioholics.com/education...peaker-designs

To improve the black level performance of your projector: Shine bright light into your eyes every 5 minutes.
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post #4 of 48 Old 02-01-2010, 05:04 PM
 
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Quote:
Originally Posted by DL86 View Post

Two or more woofers oriented horizontally is not good at all as this article will demonstrate :

http://www.audioholics.com/education...peaker-designs

Close, no cigar. Drivers can be successfully arrayed horizontally so long as they're crossed over to the next element low enough so that they mutually couple throughout their bandwidth without combing. The disadvantage is that a wider source has narrower dispersion. OTOH two smaller woofers can give the same output as one larger driver in a lower profile cab, and that can be an advantage. So it boils down to the usual question of where your priorities lie and where you're willing to compromise to achieve them.
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post #5 of 48 Old 02-01-2010, 05:58 PM
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I encourage readers to check out the article I authored that counters our original article Horizontal vs Vertical center channels referenced here.

http://www.audioholics.com/education...hannel-speaker

Best Regards;

Gene DellaSala (GDS)
President, Audioholics.com
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post #6 of 48 Old 02-01-2010, 06:34 PM
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Quote:
Originally Posted by TSD444 View Post

Why do center channel speakers typically have two mids and a tweeter? I'm new to all of this, but I'm planning on building speakers to go under my projection screen and I'm wondering if a single woofer and a tweeter would work ok.

I have a vertical 10" 3-way for a center. I have also used 2-ways with various size woofers.
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post #7 of 48 Old 02-03-2010, 07:07 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Close, no cigar. Drivers can be successfully arrayed horizontally so long as they're crossed over to the next element low enough so that they mutually couple throughout their bandwidth without combing. The disadvantage is that a wider source has narrower dispersion. OTOH two smaller woofers can give the same output as one larger driver in a lower profile cab, and that can be an advantage. So it boils down to the usual question of where your priorities lie and where you're willing to compromise to achieve them.

Kinda like this?




dbl

Let's all go to the lobby
....Let's all go to the lobby
........Let's all go to the lobby
............To get ourselves a treat!
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post #8 of 48 Old 02-03-2010, 07:20 PM
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I am making that but with 12 tweeters.
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post #9 of 48 Old 02-03-2010, 07:31 PM
 
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Originally Posted by dbldare View Post

Kinda like this?




dbl

Actually, no. With a horizontal line array the situation is quite different than a MTM or WMTMW.
They're not crossed over to the tweeters low enough so that there's no response lobing. Instead the concave baffle reduces the size of the holes between the lobes to render them inaudible. It's not perfect, but if you want line array sensitivity in a horizontal box it's a far better alternative to a flat baffle.
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post #10 of 48 Old 02-03-2010, 08:02 PM
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Quote:
Originally Posted by TSD444 View Post

Why do center channel speakers typically have two mids and a tweeter? I'm new to all of this, but I'm planning on building speakers to go under my projection screen and I'm wondering if a single woofer and a tweeter would work ok.

Modern media is really I mean really demanding of the center channel, if you ever have the chance disconnect or turn down the fronts and the surrounds to see how much goes through the center channel. Try it on the fronts and turn the center down. All music and some effects go through the fronts with very little dialogue. The center carries all of the dialogue and a suprising amount of effects from what I played around with.
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post #11 of 48 Old 02-04-2010, 01:44 AM
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Quote:
Originally Posted by Gene DellaSala View Post

I encourage readers to check out the article I authored that counters our original article Horizontal vs Vertical center channels referenced here.

http://www.audioholics.com/education...hannel-speaker

Unfortunately perceived timbre comes from both direct sound (where people aren't far enough into a lobe to have problems) and early reflections where human perception takes into account that attenuation goes with delays (IOW, a low level signal with a longer delay is given more weight).

While listeners are not far enough off-axis to cause problems with the direct sound, even a centrally seated listener will have a significant notch from the side-wall reflections due to the path length differences to the two mid-bass drivers in their pass-band (although the cross-over frequency itself will be wonderful with odd order filters as in a D'Appolito array). The effect is somewhat analogous to a phantom center image from two speakers sounding darker in the center seat than off-axis or a physical center speaker.

I don't hear accurate sound from vertical MTM arrays with conventional cross-over frequencies and would correlate that with research showing the ceiling/floor first reflections to be important for timbre as well.

I'd encourage readers to check out Floyd Toole's book

_Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms_

http://www.amazon.com/Sound-Reproduc.../dp/0240520092
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post #12 of 48 Old 02-04-2010, 01:56 AM
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random opinion fwiw...forget the center channel, use good mains with controlled directivity and phantom center. alternatively, get acoustically transparent screen and put a very capable center behind it.

Listen. It's All Good.
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post #13 of 48 Old 02-04-2010, 04:38 AM
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Quote:
Originally Posted by Drew Eckhardt View Post

I'd encourage readers to check out Floyd Toole's book

_Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms_

http://www.amazon.com/Sound-Reproduc.../dp/0240520092

Well, that book is certainly well-reviewed! The top three (all 5-start) reviews on amazon.com are listed as being from Siegfried Linkwitz, Paul Scarpelli, and Kevin Haskins
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post #14 of 48 Old 02-04-2010, 07:52 AM
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Quote:
Originally Posted by TSD444 View Post

Why do center channel speakers typically have two mids and a tweeter? I'm new to all of this, but I'm planning on building speakers to go under my projection screen and I'm wondering if a single woofer and a tweeter would work ok.

To answer your question, how many woofers does a center channel really need? They need just as many as your L/R's because they should match.

YID DIY
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post #15 of 48 Old 02-04-2010, 08:31 AM
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No shortage of woofers here.
LL
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post #16 of 48 Old 02-04-2010, 10:46 AM
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"forget the center channel, use good mains with controlled directivity and phantom center. alternatively, get acoustically transparent screen and put a very capable center behind it."

Exactly what I was going to do, but it turns out Audyssey strongly recommends against it when using DSX height speakers because some center information will end up there.

Noah
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post #17 of 48 Old 02-04-2010, 10:56 AM
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Originally Posted by Genelec Man View Post

No shortage of woofers here.

It wouldn't surprise me but is that some ones home theater? The white door looks like a home install.
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post #18 of 48 Old 02-04-2010, 10:58 AM
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Quote:
Originally Posted by LTD02 View Post

random opinion fwiw...forget the center channel, use good mains with controlled directivity and phantom center. alternatively, get acoustically transparent screen and put a very capable center behind it.

Only problem with this approach is that the dolby digital spec has you handcuffed. Meaning that some level of dynamic compression will be enabled when choosing no for the center. There is no indication of this and from what I have seen no way to get around it.
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post #19 of 48 Old 02-04-2010, 12:26 PM
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It is a "private screening room". From the looks of it I would guess it's in a home! Unbelievable. Those speakers are the newest QSC cinema speakers. The subs are a 21" design. The projector isn't normal for home either.
LL
LL
LL
LL
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post #20 of 48 Old 02-04-2010, 12:38 PM
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better pics. The mains use a 10" midrange. 21" subs are the latest B&C drive units. BTW the best approach for a center is to utilize the same as your L&R no matter what type it is.
LL
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post #21 of 48 Old 02-04-2010, 02:11 PM
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Quote:
Originally Posted by zamboniman View Post

Only problem with this approach is that the dolby digital spec has you handcuffed. Meaning that some level of dynamic compression will be enabled when choosing no for the center. There is no indication of this and from what I have seen no way to get around it.

Split the signal in the analog domain.

I'd use two dual channel op-amps. Each channel would get an inverting summing stage with -3dB gain input for "center" and 0dB input for left or right followed by an inverting unity gain buffer.
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post #22 of 48 Old 02-04-2010, 03:11 PM
 
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Quote:
Originally Posted by zamboniman View Post

Only problem with this approach is that the dolby digital spec has you handcuffed. Meaning that some level of dynamic compression will be enabled when choosing no for the center. There is no indication of this and from what I have seen no way to get around it.

No matter what the digital spec is using L/R only will never duplicate the imaging of L/C/R. I can't imagine going back to a 4.1.
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post #23 of 48 Old 02-04-2010, 04:43 PM
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Quote:
Originally Posted by LTD02 View Post

random opinion fwiw...forget the center channel, use good mains with controlled directivity and phantom center. alternatively, get acoustically transparent screen and put a very capable center behind it.

I am about to toss the entire 5.1 out and go back to stereo full-range tri-amped for everything. I guess I care for music quality over special effects.

I will admit, if you sit far off-center, then the center fill will help the sound placement on the screen. I don't have that problem sitting between the mains. My MTM center actually stands on end under the TV. As I did not build this speaker, I can not say if it was constructed to DeApollito design, or is just thrown in the box. I suspect the latter as it does not control the dispersion that much either way. Speakers built to his technique can clearly be heard by moving around them in both positions.
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post #24 of 48 Old 02-04-2010, 05:00 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

No matter what the digital spec is using L/R only will never duplicate the imaging of L/C/R. I can't imagine going back to a 4.1.

Can you describe this in more detail?

Which is worse, a center that is below the screen or L/R? I might agree with you in an ideal setup, but most people's home situation is far from ideal.
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post #25 of 48 Old 02-04-2010, 05:16 PM
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Originally Posted by stgdz View Post

It wouldn't surprise me but is that some ones home theater? The white door looks like a home install.

That's Bill Gate's new Home Theater room.
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post #26 of 48 Old 02-04-2010, 05:27 PM
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Quote:
Originally Posted by Genelec Man View Post

It is a "private screening room". From the looks of it I would guess it's in a home! Unbelievable. Those speakers are the newest QSC cinema speakers. The subs are a 21" design. The projector isn't normal for home either.

Yeah if I ever had a "private screening room" I would want the screen as big as possible so I can view as many naughty movies as possible
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post #27 of 48 Old 02-04-2010, 07:53 PM
 
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Quote:
Originally Posted by vantagesc View Post

Can you describe this in more detail?

Which is worse, a center that is below the screen or L/R? I might agree with you in an ideal setup, but most people's home situation is far from ideal.

A center below the screen is fine, assuming you're listening from more than four feet out. Your brain will still place the source at the center of the screen because it's hard wired for visual location cues to over-ride audio triangulation. To some extent that will happen with L/R too, but the L/R sources never 'disappear'.
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I am about to toss the entire 5.1 out and go back to stereo full-range tri-amped for everything. I guess I care for music quality over special effects.

Just turn off the decoding when listening to music. I never watch TV in stereo and I never listen to music in 5.1, because video sound tracks are mastered in x.1, music is mastered in stereo.
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post #28 of 48 Old 02-04-2010, 08:16 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

music is mastered in stereo.

Most is but not all. I listen to multichannel music, recorded and mastered in multichannel, about 40% of the time.

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post #29 of 48 Old 02-04-2010, 08:35 PM
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"Exactly what I was going to do, but it turns out Audyssey strongly recommends against it when using DSX height speakers because some center information will end up there."

noah, you are pushing for diminishing returns--not that that is a bad thing, just way beyond the question in the op. i'm curious to see what you choose.

"I am about to toss the entire 5.1 out and go back to stereo full-range tri-amped for everything. I guess I care for music quality over special effects."

tvr, a good compromise might be to go with awesome stereo speakers and then add a pair of side mounted thx-style bipole speakers to add ambience by providing diffuse reflected sound off of the front and rear walls for movies.

(for example: http://www.jblsynthesis.com/products...=US&Region=USA)

Listen. It's All Good.
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post #30 of 48 Old 02-04-2010, 10:00 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

A center below the screen is fine, assuming you're listening from more than four feet out. Your brain will still place the source at the center of the screen because it's hard wired for visual location cues to over-ride audio triangulation. To some extent that will happen with L/R too, but the L/R sources never 'disappear'.

I have not found this to be the case in my experience. For a one person theater, I prefer a center behind an AT screen or no center. Can't even tell my L/R speakers are playing when there is only dialog "on screen". Again, this is only for a one person theater. Maybe I need to let my brain go and just concentrate on the movie. Edit: I will add that I can envision certain setups where the center channel is close enough to the center of the screen where you would be okay, especially if the screen is small. The added intelligibility that a center could offer may be worth the tradeoff that I perceive.

YMMV.
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