Why large center channel builds.

[servicetech]

I've seen a few very cool center channel projects using large woofers. If the bass in a HT comes mostly from a sub why the large center channels speakers? Is it just to look cool or is there sonic reasoning?

[Bear]

I've seen a few very cool center channel projects using large woofers. If the bass in a HT comes mostly from a sub why the large center channels speakers? Is it just to look cool or is there sonic reasoning?

Greater SPL. Possibly lower distortion for a given output level. Smoother interaction with a subwoofer. Etc. All else being equal, a large radiating surface will require less power to generate a given SPL than a smaller radiating surface. There are inertia and beaming issues at higher frequencies to consider, but at lower frequencies, an 8" woofer will need less excursion to generate a given SPL than a 7" or 5.25" woofer will. As a result, that would mean that the larger woofer is working less hard and producing less distortion.

Caveat: in the real world, all else is NEVER equal. You can find 5.25" woofers that are cleaner at 40 Hz than many 8" woofers, and you can find an 8" woofer that is cleaner at 800 Hz than many 5.25" drivers. Budget plays a factor here as well as overall design and execution (crossovers, box alignment, cabinet quality, etc.).

Finally, Hoffman's Iron Law plays a big factor in this, as well. If you need to fill a big room with a lot of sound, even if you are rolling off the speaker at 80Hz, then you need bigger woofers in a bigger box or you need big amplifiers. Since there is only so much power you can dump into a given speaker before the voice coil turns to slag, the bigger woofers would really be the only practical way to go.

[servicetech]

Why is it so difficult to find commercially made CC with more than dual 5.25" woofers? Even the WMTW designs only use 5.25" drivers... Perhaps they are made to fit entertainment centers that only accommodate small center speakers.

[cjd]

You really don't want your subwoofer playing above 80Hz, and if you can push it lower, all the better.

A 5.25" needs to be ported to properly cover even to 80Hz normally (sealed they probably average F3 100Hz or higher) though I'm generalizing quite a bit when I say this - lower F3 will mean lower sensitivity though, and from what I've seen they're not down close to 82dB on these designs...

7" often gets you notably lower F3 in a sealed system - I cross mine at 70Hz (RS-180). The Anarchy could probably go 50Hz sealed (but sensitivity is down...)

It's all about trade-offs. Most commercial speakers aren't designed for accurate sound, but to sell. So fitting into a tiny space takes priority over adequate sound, evidenced by the crazy high output levels many people feel they need to understand speech in movies... I watched a movie the other night at about 70dB (~3.5M from screen) and sometimes nominal is below that.

[BobEllis]

The obvious answers?

1.Bigger is always better and

2. Because we can.

Bear and Chris covered the serious answers well. I think that as long as you can get far enough away for the drivers to integrate you can't really get too big.

[Paul Spencer]

How big is big? At a GTG in 2010 we heard some JTR speakers, each with a 12" pro coax and two 12" woofers. That's more like what I'd call big! In a large room they went to rock concert levels, quite a bit louder than the cinema and they were powered with an Onkyo receiver, maybe 100w.

For most setups, I'd say a pair of 6.5" woofers in a sealed box would suit. That gets an F3 around 80 Hz. It would be quite large by most standards.

[Paul W]

The center is the most important speaker in a multichannel system...it's gotta be a good one.

[ClosetSciFiGeek]

I just finally got my ZDT3.5C finished before Christmas. I built it as the vented enclosure because it just looks cooler. Realistically though it made a big difference when I replaced an old Infinity Studio Monitor series with two 6 1/2" woofers in a ported enclosure. It isn't louder, but it does go lower cleanly so I have it rolled off at 60hz(where the distortion in the RS180 starts to rise) just like my ZDT3.5 mini-Towers. The most important change this accomplished for me was WAY WAY cleaner; more intelligible speech and the handoff from left to center to right speaker disappeared and I just watch the movie rather than noting the differences among the speakers.

[SpeakerGuy]

Why is it so difficult to find commercially made CC with more than dual 5.25" woofers? Even the WMTW designs only use 5.25" drivers... Perhaps they are made to fit entertainment centers that only accommodate small center speakers.

A pair of (good) 5.25" woofers is MORE than sufficient for reproducing LOUD and clear dialog. Personally, dialog is all I'd really be concerned with for a CC.

I'd be more concerned with (moderate) off-axis performance/lobing and the over-all quality of voice reproduction (when thinking about commercial CC compared to what could be done in a good DIY design).

One option I've never seen done for a CC is: close spaced sealed MTM with small woofers on one shelf, then a vented box with a couple ~ 6.5?" woofers on the next shelf down (or nearby) to handle the low end.

If you're not restricted to a horizontal shelf, then by all means just skip the horizontal center paradigm and go with whatver size vertical speaker fits best.

There is always the option of just turning a TM sideways, just evaluate the vertical lobing if doing that.

[JonMarsh]

The center is the most important speaker in a multichannel system...it's gotta be a good one.

Totally agree - the demands on the center can be substantial if you want good dynamic peaks with low distortion- it also needs the broadest, best controlled dispersion, IMO, unless you have a limited seating area.

Commercial stuff tends to be built based on what they think will sell to the missus and fit in a small space. 5's have problems with efficiency, SPL, and LF extension- for an 80 Hz crossover, unless you plan on the box providing part of the high pass characteristics, the system itself should be well controlled and performing to 1 octave lower. My personal preference is center and mains L+R with basically the same characteristics, as close to identical as possible.

But to each his own- in some cases, WAF or space may dictate otherwise. But you ought to listen to a system sometime with a more optimum setup, just in case it's helpful to hear what you might be missing....

[owdi]

Is there a consensus on conforming to the THX spec when designing a center? I believe the spec is -3db @ 80hz 2nd order, which combined with a 2nd order butterworth hipass on the receiver gives you a 4th order slope, integrating with the 4th order lowpass on your subwoofer.

A pair of sealed 6.5" woofers could have an f3 of around 80hz, but I don't see any designs like that here, so I guess there is no consensus. Question answered

[bigbardmusiq]

Here's a good place for my question, Does anyone run left, right, center on full band? Audussey set mine to 40hz, should i leave it at 40hz?

[jheizer]

I just finally got my ZDT3.5C finished before Christmas. I built it as the vented enclosure because it just looks cooler. Realistically though it made a big difference when I replaced an old Infinity Studio Monitor series with two 6 1/2" woofers in a ported enclosure. It isn't louder, but it does go lower cleanly so I have it rolled off at 60hz(where the distortion in the RS180 starts to rise) just like my ZDT3.5 mini-Towers. The most important change this accomplished for me was WAY WAY cleaner; more intelligible speech and the handoff from left to center to right speaker disappeared and I just watch the movie rather than noting the differences among the speakers.

Echo... I also just went from a Infinity Studio monitor to ZD3C in December. I agree with everything you said 100% Amazing upgrade.

[mackintire]

Here's a good place for my question, Does anyone run left, right, center on full band? Audussey set mine to 40hz, should i leave it at 40hz?

Not usually. Full bandwidth is 20-20khz for most of us. 99% of the loudspeakers out there can not do that in one cabinet, " I'm not including CJD's massive Dayton RS's", let alone without significant distortion at a reasonable volume.

The bigger and usually lower your mains and center can play the lower you cross them over without damaging the quality of the sound or running out of driver excursion (which again damages the quality of the sound).

Most guys over here with larger mains/centers cross-over theirs between 80-60hz. Some guys have systems that can cross-over slightly lower and some cross-over as high as 150hz. But almost every one of those examples uses a subwoofer to play the lowest notes.

There are some things Audussey does fairly well, but you have to keep in mind that the guys here are a bit more perfectionistic than what Audusssey does.

If you give a listing of your equipment, room size, where the speakers are placed in the room, how far from the walls, etc there's a possibility we can give you a little better advice.

[cjd]

Is there a consensus on conforming to the THX spec when designing a center? I believe the spec is -3db @ 80hz 2nd order, which combined with a 2nd order butterworth hipass on the receiver gives you a 4th order slope, integrating with the 4th order lowpass on your subwoofer.

A pair of sealed 6.5" woofers could have an f3 of around 80hz, but I don't see any designs like that here, so I guess there is no consensus. Question answered

Khan-center is close. RS-180 is a 7" by frame size...

[bigbardmusiq]

Would a statement center be considered large?
Audussey sets left,right,center to -8 and both sub1 and 2 to -15. I never really found out what frequency should i have the subs set too, halfway? maxed?
My seating is about 13ft from L,R,C with a 19ft pointed ceiling, the room is about 18ft x18ft which opens up to the kitchen to the right. My equipment is Xp3 (3x300) and Onkyo 1007 (135 per channel). I hope someone can improve on audussey sound for me, I have all other bass and treble setting to 0

[ClosetSciFiGeek]

Try setting your subwoofer gain much lower.

This will allow your subwoofer amps to operate with less noise and your preamp section to put out what it ought to. Right now your sub amps sound like they are turned up really high and your preamp section is putting out a very attenuated signal to compensate. After turning the gain down on your sub amps run your setup again and see what you get for the sub gain. Your goal should be to get your sub about 0db vice the -15db you are at right now. Nothing you can do about your L/R/C being -8db as your gain on the XPA-3 is set and non-adjustable. Not a problem, though for your L/R/C. If you set your sub gains like I have mentioned both the Preamp section on you Onkyo and the Sub Amp will be operating in their optimal range.

[bigbardmusiq]

Try setting your subwoofer gain much lower.

This will allow your subwoofer amps to operate with less noise and your preamp section to put out what it ought to. Right now your sub amps sound like they are turned up really high and your preamp section is putting out a very attenuated signal to compensate. After turning the gain down on your sub amps run your setup again and see what you get for the sub gain. Your goal should be to get your sub about 0db vice the -15db you are at right now. Nothing you can do about your L/R/C being -8db as your gain on the XPA-3 is set and non-adjustable. Not a problem, though for your L/R/C. If you set your sub gains like I have mentioned both the Preamp section on you Onkyo and the Sub Amp will be operating in their optimal range.

Sweet!!, thank you!!! :T

[ClosetSciFiGeek]

The frequency adjustment on your sub should be set to all the way up or the low pass crossover turned off if that is an option on your sub. Your Onkyo should use Audyssey to set the crossover frequency inside the preamp section and output the right frequencies to the XPA-3 inputs, sub input, and directly to your rear channels.

[bigbardmusiq]

The frequency adjustment on your sub should be set to all the way up or the low pass crossover turned off if that is an option on your sub. Your Onkyo should use Audyssey to set the crossover frequency inside the preamp section and output the right frequencies to the XPA-3 inputs, sub input, and directly to your rear channels.

at the risk of sounding like a noob, you said turn on LFE or use this Bash500 crossover? and what about the 180-0 phase switch?

[Jim Holtz]

Here's a good place for my question, Does anyone run left, right, center on full band? Audussey set mine to 40hz, should i leave it at 40hz?

Always! However, if the signal is actually 40hz, then most speakers and centers will be nearing the end of their frequency range.

I don't like any more crossover components in the signal path than necessary, particularly from receivers or ones that roll off the mains. My experience has been that the coloration of the sound extends into the midrange. I'd rather run the mains and center full range and let then roll themselves off.

My $.02 worth...

Jim

[Jim Holtz]

Would a statement center be considered large?
Audussey sets left,right,center to -8 and both sub1 and 2 to -15. I never really found out what frequency should i have the subs set too, halfway? maxed?
My seating is about 13ft from L,R,C with a 19ft pointed ceiling, the room is about 18ft x18ft which opens up to the kitchen to the right. My equipment is Xp3 (3x300) and Onkyo 1007 (135 per channel). I hope someone can improve on audussey sound for me, I have all other bass and treble setting to 0

I didn't realize you had Statements when I answered your other question. Hell ya, run them all full range. Use the sub crossover in the plate amp(s) set at around 50hz to start and adjust to taste.

Use a DB meter and test tones to balance your speakers rather than the Audussey. I suspect you'll be happier with the end result.

Jim

[---k---]

Everyone, every room, every system is different and requires different tweaks.

Jim has a very valid setup, and I can see benefits of it. But, to be a contrarian:
Audussey in my new Onkyo 3008 recommends 40 hz for my L&R and 50 hz for my center and surrounds. I put all the fronts all at 60hz and the rears at 70hz. I like the idea of taking the load off the woofers. My system has never sounded better. I had some serious doubts and reservations about Audussey, but I'm really impressed with what it's done. I've only had it for about about 2 weeks and still need to do more testing (though this receiver doesn't give that many knobs to turn!). In my system, I can really only hear a difference in the bass, and it has done wonders in that department.

In my view, the simple answer is try both and decide which you like better.

[Paul W]

I could but don't

Here's a good place for my question, Does anyone run left, right, center on full band? Audussey set mine to 40hz, should i leave it at 40hz?

Although my LCRs have high displacement capability, they are currently crossed to the subs at 60Hz. The reason is to reduce excursion related distortion to the lowest practical level. Subs and LCRs are located on the same baffle so there are no localization issues; crossovers are very carefully (manually) tuned for proper integration with the mains. The pre-pro has Audyssey but I've never used it so no opinion there.

So, if you can see or feel much cone excursion in your LCRs, I would experiment with higher crossover frequencies.

[ClosetSciFiGeek]

bigbard, Sorry I didn't answer you sooner. Got tied up. I meant that you should turn your LFE on and your Bash crossover setting all the way to its highest frequency so that the Onkyo could control the crossover setting. I DO NOT, however, own Statements so I would contend that Jim Holtz has more experience with them than anyone and you would do well to try his method as well. The method I described was how to set up using your Audyssey. Good luck whichever method you choose(I recommend trying both and seeing which one YOU like better in YOUR room).