I Know Dual Centers are Wrong, But...

Discussion in 'Speakers & Subwoofers' started by John Robert, Sep 7, 2003.

  1. John Robert

    John Robert Stunt Coordinator

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    First, I have been lurking on this site for a while and enjoyed it so finally joined! I have partially finished system with Infinity 4.1t fronts and Il 50 rears. Since I haven't decided on center, I decided to use a "y' connected pair of Polk Lsi 15s from my bedroom system on either side of Panny 50" LCD. I'm using 45tx as pre/pro and after Rabos / MCACC, I was blown away by increase in clarity and presence as compared to other setups I've heard...Anyone else tried this? Thanks in advance for your feedback.
     
  2. Bob Brick

    Bob Brick Extra

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    Wrong? If so, why do some receivers have speaker outputs for dual centers?

    As long as there isn't an impedance problem and it sounds good, there is no wrong...although if you feel extra guilty you can send me that evil 50" LCD as a gesture of true penance, and all will be forgiven, my son.
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    Somewhere over at Secrets is a really good article on why two center channels is not a good idea. www.hometheaterhifi.com . Mostly due to interaction of the low frequencies (comb filtering) from each.
     
  4. Bob Brick

    Bob Brick Extra

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    Comb filtering!!!!

    Sure, I guess anything is possible when it comes to audio interactions, but then why wasn't this considered a problem for the two identical rear channels back in the Dolby Pro Logic days when they were not discrete channels? Hmmmm?


    I say don't fear, just use your ears. I seriously doubt anyone here will say that they tried two centers and that it was awful because of comb filtering.

    Kevin, I hope you don't take offense, it's always cool to warn us fellow enthusiasts about possible problems.

    And John, I'll pay for shipping if you're sending that LCD to me. It's the least I could do.
     
  5. John Robert

    John Robert Stunt Coordinator

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    I appreciate the feedback. I always try and let my ears be the final judge. I was just struck by the clarity of SACDs and movie dialogue using this "different" setup.

    By the way Bob, I'm returning LCD to BB...just have not been able to get a great picture from it. I'll probably bite the bullet and spend a few $ more for Samsung DLP. If you want Panny, you'll have to pick it up there...
     
  6. Mark All

    Mark All Second Unit

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    What receivers have speaker outputs for dual center channel speakers? I know Rotel has a habit of putting pre-outs for two subwoofers and two center channels on their receivers, but don't know of any others. Denon and Onkyo don't. I can understand the two subwoofer thing because that's pretty standard in more high end home theaters. I have heard of people using two or even three center channel speakers and two sets of speakers for mains.

    Although I don't see the need to have more than three properly set up speakers in front, I agree that if it sounds good to someone and there are no problems driving the speakers, keep doing it.
     
  7. John Robert

    John Robert Stunt Coordinator

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    So far no problem driving speakers. I'm using Adcom 5006 bridged to 175 wpc to drive centers while I await arrival of Cinenova Grande 3. 45tx drives mains and surrounds. Even though I calibrated levels, maybe power difference accounts for some of what I'm hearing. Plan was to use Cinenova to drive single center and mains and Adcom for surrounds (and maybe 6.1). Now I don't know...
     
  8. Kevin C Brown

    Kevin C Brown Producer

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    Bob- Typically, you don't put 2 rear speakers as close together as on either side of a TV set. [​IMG]

    (I am still trying to track down the actual article.)

    BTW, by definition, comb filtering isn't as apparent if you are seated perfectly down the center line of the speakers. The problem occurs as you move off-axis. So if you have a few people seated across the room, the people on the ends are going to be screwed.
     
  9. Bob Brick

    Bob Brick Extra

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    Kev, it's OK, John is enjoying the sound of his setup. Let it go. Once you have good sound, it's time to start enjoying some good DVDs.


    Not to get on your case too much, but damn...

    ...you actually list the exact model of tripod you use to mount your sound meter on, jeez.
     
  10. Brad Russell

    Brad Russell Stunt Coordinator

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    Mark,
    My Yamaha A-1 has binding posts for dual centers. I use a pair of Polk RT7s, One on the floor angled up and the other on top of my 32" TV. They are about 4' apart. I figure with as much material that comes through the center channel two centers is not overkill. I think it is the guys at Legacy Audio that say, "just like engines, there is no replacement for displacement." But what do I know.

    Brad
     
  11. John Garcia

    John Garcia Executive Producer

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    You get a gain in SPL by using two speakers, and since you are running them both off of one channel, you have halved the impedance, so you are drawing twice as much current for the two. Did you recalibrate levels after hooking this up?
     
  12. Brad Russell

    Brad Russell Stunt Coordinator

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    John,
    I have been running this set up for about 5 years and I recalibrate about every six months. Anybody have recomendations about how often to recalibrate?

    Thanks!

    Brad
     
  13. John Garcia

    John Garcia Executive Producer

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    I only recal if I change something (new gear) or I'm REALLY bored. That means about once a year, unless I upgrade.

    I was referring to the original post, as he is running two speakers from one amp channel, while you, Brad, have separate outputs (assuming they are separate channels).
     
  14. John Robert

    John Robert Stunt Coordinator

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    John, I am splitting center pre out and running into two amp channels. I did complete recal, MCACC and rechecked RABOS (The latter probably a waste of time) after I hooked it up.

    I'm sorry that I wasn't specific in my original post...
     
  15. Kevin C Brown

    Kevin C Brown Producer

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    Hey Bobby- What's your problem?

    By the thread's title, he knows he's doing something wrong. I'm just trying to get across what it is. Comb filtering, i.e. lobing, is a real effect, and all center channels that have the ubiquitous woofer-tweeter-woofer design have that problem. Read the detail in any S&V or SGHT review of a center channel like that. What John is doing, is essentially replicating that poor design by using 2 speakers. You say, just enjoy it. I say, if he thinks his 2 center channel setup sounds good, try a well-designed single speaker, because it will probably sound even better.

    Not to get on *your* case too much...
     
  16. John Robert

    John Robert Stunt Coordinator

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    Kevin -

    I'll find out soon. Ordered today an Infinity IL36c to complete my system. I'll post my thoughts vs. current setup when it arrives.

    I meant by the thread title "wrong" in the unconventional sense...thanks for your thoughts
     
  17. Kevin C Brown

    Kevin C Brown Producer

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    John- Here's a test that might prove the point: with your current setup and when you get the new one. Play a DVD with a sound selection that you are familiar with. Or, a CD using some type of multichannel DSP program. Right in front of where you sit, walk across the room, from about in front of the left speaker through the center of the soundstage to in front of the right speaker. Listen for tonal differences from the center channel. Might even help to turn off the L & R mains to make it easier. Walk slowly, and focus on changes in the mid range to low frequencies. Men's voices to bass guitar notes to depth charge blasts, for example. [​IMG] Then repeat the test when you get the new center. You *should* hear less differences with the one box solution than with the 2 speakers. Make sure when you do the test, that you are getting the same SPL. (A "louder" speaker will appear to sound better, but it actually might be worse.) Report back and let us know what you find. [​IMG]

    One thing that I agree with Bob on, is that it isn't "wrong" if you like how it sounds. But there are fundemental acoustic reasons why one well designed speaker for a center channel is better than 2.
     
  18. Brad Russell

    Brad Russell Stunt Coordinator

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    John,
    Actaully, there is only one channel of amplification, two sets of binding posts and an impeadance switch for if you are running one or two centers.

    Kevin,
    Maybe I am remembering wrong, but I seem to remember Dolby suggesting two centers. I have been wondering about changing my set up. Maybe you can offer a suggestion? Currently I am using a pair of Polk RT55s as my mains, a set of Polk RT7s as my centers, Polk RTi15s as front effects, and a pair of Infinity 3-ways (RS5b?)that have a 10" woof, about a 4" polydome midrange, and a ribbon tweeter, as my rears. I have a Yamaha A-1 so it is there 7.1, which is 5.1 plus front effects for DSP. What I have been wondering is if I would be better of with the RT7s as rears, get a center that matched the RT55s and put the Infinity's somewhere else. In some ways it would be nice to have timbre matched speakers all the way around, but I have been told that the rears aren't as critical and I have about a 2700 cu/ft. room and I would be losing a fair amount of dislacement. Any suggestions?

    Thanks!

    Brad
     
  19. Kevin C Brown

    Kevin C Brown Producer

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  20. Harry Lincoln

    Harry Lincoln Stunt Coordinator

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    I had a Yammie DSP-A3090 that had dual centre terminals. I remember reading something in the manual that said it was for use with large projection screens that couldn't have the speaker placed behind them, instead one was placed above the screen and one below, to give an image from the centre of the screen.
     

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