Center vs. Mains-as-Center

Discussion in 'Speakers & Subwoofers' started by ericX, Feb 3, 2006.

  1. ericX

    ericX Auditioning

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    I've been shopping around a lot for a full set of speakers lately and I've noticed that, like a lot of things, once you buy into a set, the remaining pieces that match are quite expensive. In this case, it seems that the cost of a center speaker vs. the cost of same make & model of front L/R speakers is quite high, and the sound quality seems quite a bit lower, especially in the bass response. In every set I've looked at, the centers sounded very hollow compared to the main front speakers. Perhaps centers are intentionally middy?

    I had this idea last night that I could get two mains and put them on their sides, head to head so that they are aligned just like a center with the tweeters in the middle. This should keep the sound very centered, and it might sound a lot better than a "real" center. Buying four mains seems to only add about 15% - 20% to the total cost of what I would pay for two mains + center. Seems like a worthwhile investment if it sounds significantly better...

    Is this a crazy idea?


    A secondary problem, if I were to do this, is impedence. If I hook the two mains in parallel, I've cut the impedence in half, which, depending on the speakers, might go below the minimum spec on my amp. Would there be any significant sound quality degradation with hooking them in series rather than in parallel, effectively doubling the impedence? I might have to boost the center channel to compensate, but would it kill the sound?

    Thx!
     
  2. Sami Kallio

    Sami Kallio Screenwriter

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    Why not just use one? That's what I do with my setup which consists of 5 Polk LSi7's.
     
  3. ericX

    ericX Auditioning

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    I considered that but I guess the thinking was that the reason centers have a tweeter in the middle and a cone on each side, equally spaced, is the ensure the sound really seems to come from the center, without any perceivable offset. I guess you don't perceive any offset, or you wouldn't be recommending this approach?
     
  4. Sami Kallio

    Sami Kallio Screenwriter

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    Well, mine have always been in a FP setup so I haven't put any of them on their side, always standing up. I have used both a tower (RTi70) and a bookshelf on a stand (LSi7).

    What kind of TV do you have? What kind of mains? Get a matching bookshelf, not a tower, that should take care of the tweeter problem.
     
  5. John Garcia

    John Garcia Executive Producer

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    I use 5 of these: http://www.gr-research.com/kits/av2.htm It works great [​IMG]

    Most centers have dual mids to yeild more sensitivity and greater midrange capability because the focus is usually on dialogue clarity in movies. Using an identical bookshelf would not give you an offset. I've used 3 LSi7s across the front before also, and I had to lay the center one on it's side because the drivers are offset and do image slightly differently.

    If you want to use two for the center, you can wire them in series instead of parallel. This will give you twice the impedance, so the level of each will drop slightly, but you will also have twice as much sound coming from those two speakers, and once calibrated, it should blend OK. You may have to play around with positioning for the best sound though.
     
  6. Sami Kallio

    Sami Kallio Screenwriter

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    Did you actually notice this while watching a movie? I haven't so I am using it standing up normally.
     
  7. Philip Hamm

    Philip Hamm Lead Actor

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    I just use one center which is identical to my main L/R fronts, three B&W 602s across the front. The center 602 is on it's side, the tweeter isn't perfectly centered on the screen. It sounds fantastic - WAY WAAY WAAAAAAAY better than a "dedicated center" would. Using two may cause phase cancellations.
     
  8. John Garcia

    John Garcia Executive Producer

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    No, I actually didn't have the room to stand it up anyway [​IMG] But according to Polk, this is the case, and that is why they identify them specifically as Right and Left versions.
     
  9. ericX

    ericX Auditioning

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    Forgot to include, I'm only looking at bookshelfs for space reasons, so it would be three or four identical speakers across the front, all bookshelfs. So you're saying that with a bookshelf speaker, the tweeter and mid/bass cone are so close together I wouldn't notice the offset?

    Interesting idea to only use one in the center. Anybody else have issues with the center offset, or good experience where the center was physically offset, but they couldn't hear it?

    Anybody else have any thoughts about a full(er) range speaker in the center? Are 'real' centers intentionally crippled in the bass to improve dialog? Or is it just because the speaker makers think people won't notice the lack of bass in the center because the primary use is dialog, so they don't put as much into the engineering to make them reproduce those frequencies?
     
  10. John Garcia

    John Garcia Executive Producer

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    IMO, using identical front speakers is ideal because you can use one crossover point for them. The sound is very seamless.

    Not sure what you mean by "crippled" because there are plenty of centers out there that have respectable bass response, though "most" would probably not fall into that category. The average center has about the same bass response as the average small bookshelf. The fact is, bass response in an HT should be handled by the sub, so as long as you can set your crossover correctly for the center, deep bass production shouldn't be a big concern.
     
  11. Sami Kallio

    Sami Kallio Screenwriter

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    Ok, just wondering as I really haven't noticed any problem with the sound and where it is coming from. This setup is in a small (14x12) dedicated HT room. Here are pictures of my front setup.
     
  12. ericX

    ericX Auditioning

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    By 'crippled' I mean: are they intentionally 'middy' to ensure clear dialog, at the expense of overall performance, because they are a special purpose speaker? I certainly haven't listened to every speaker on the market, but 100% of the centers that I have listened to have been considerably less responsive in the low frequencies compared to their 'matched' front left and right counterparts. But I guess if you've seen centers by reputable makers that don't exibit this characteristic, then the only reason the ones that I've seen do is that the makers don't think the bulk of people will care, given the content delivered by the centers.

    I don't want to have to configure the amp to put the sub's crossover point up high to compensate for the center's weak bass, only to have that crossover take away from bass that could be going to the mains. I still want the sub on the mains to reproduce the very low frequencies (required for any smaller speaker), but I want them to handle as far down as they can go cleanly... so a center and mains that have near identical response is my objective (unless that can damage dialog, which we seem to have ruled out above).
     
  13. Sonnie Parker

    Sonnie Parker Second Unit

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    I agree with several of the others comments. I have three VMPS RM30's and the center is layed on its' side. Two 6.5 mid-woofer with two 6.5 passive radiators at the bottom (or at the extreme left end as it lays)... three mid panel ribbons in the center and one spiral tweeter at the top (or extreme right as it lays).

    I have no issues with the imaging or balance of sound as it relates to center of the screen. Sounds great... and centered.

    With bookshelf speakers I think you'll probably limit bass response to an extent... at loud volumes anyway. Depending on how high you need your center to be, you might be able to keep it standing upright just like the mains.
     
  14. ericX

    ericX Auditioning

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    It would seem that [postid=2924957] (URL removed because apparently I don't have sufficient seniority here... [​IMG]) cleary answers my question about using a full-range speaker for center channel. I think I might just go ahead and get five (or six) same speakers.

    The poster quoted from the Dolby Digital FAQ:

     
  15. LanceJ

    LanceJ Producer

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    1) a speaker's low bass capability doesn't have much to do with its midrange reproduction capability. If anything, a "large" woofer like a 6.5" or larger in a 2-way design can help many sounds sound better: pianos, male voices, certain guitars, and all kinds of movie soundtrack effects. And, if a speaker's woofer is too small or not of good quality, a speaker may be perceived to have better midrange simply because its overall sonic balance is tilted toward the upper frequencies. BTW: all this talk about a 80Hz crossver being the best for EVERY system I think has made it seem nothing below that frequency is that important to any speaker but the subwoofer. Nope! Without getting into it here, just realize that from what I can tell there was also a bit of marketing pressure behind picking that particular xover point.

    Just guessing here: I think to alleviate some of these problems I've noticed several companies use a sealed enclosure whereas all their other models are bass reflex types. Some Infinity centers are like this. Unless physics have changed recently, sealed designs compared to the same size bass reflex enclosure can go lower bass-wise though they will require more power to produce the same output level. Also, being small is very important to many people these days, so trying to sell a relatively large bass-reflex center speaker is a marketing no-no. But sometimes, it just doesn't matter: check out this Nautlius center I got to hear at a store here: 800 Series HTM1D. When I first saw it I didn't understand at first what I was looking at, then finally my mind got a grasp on it and went holy sh*t! [​IMG] That photo doesn't convey how large it really is, epsecially its depth.

    2) I don't know all the specifics but wiring speakers in series does alter their operating behavior. To what extent will vary from speaker to speaker. This can happen becuase when wired that way, each speaker's crossover is now part of a "chain" and that can alter the way their individual resistors, inductors, capacitors, etc behave and the overall circuit they are part of (if you ever look at diagrams of a speaker's crossover, each tweeter/woofer/etc is wired in *parallel* to the input-that way each has unobstructed access to the amp). This is also why better stereo receivers and amps don't have their A and B speaker outputs wired in series, besides the fact that really cheapo models just plain can't operate very low impedance loads. I'm sure this is why Sherwood specifically points this out on their $150 RX-4105 2.0 receiver.

    3) as Phillip already said, phase problems are a real possibility when two speakers are used together in a horizontal orientation. Specifically, the further off to the side you are, the worse these get. Most reviewers call this a "combing effect" because like when two combs are slid past one another, the teeth alternately line up i.e. they're in phase then eventually slide out of position i.e. they're out of phase. With two speakers producing two sets of identical sound waves, what you get as you move from the exact center seating position is also a combing effect but this time with sound waves. This will be most noticeable at the points where individual drivers cross over to another driver (since in any crossover their will be some overlap of the two drivers' operating ranges). This is why nowadays most conventional speakers use 100% vertical driver arrays, so you don't have to point the speaker directly at the listening postion for best results.

    This is why the best dedicated center channels use a separate midrange, mounted either directly underneath or above the tweeter; and, the bigger the better so its crossover point is lower >>> because the less sound two side-mounted woofers handle, the less overall combing effect there is.

    Speakers are a lot more complicated then they look[​IMG]: when some magazines tested Bostons Acoustic centers that had one active woofer (the other "woofer" was actually a passive radiator) they reported that combing was almost non-existant sitting to one side, but when sitting on the other side combing significantly increased. So keep that in mind when laying other speakers on their sides i.e. put the comfortable chairs on the good side!

    4) Besides the fact they are usually physically smaller, I'll bet many centers very probably sound kind of thin mostly because of their placement. Most of them are placed quite far from a rear wall or especially any side walls-both of these are bass reinforcing surfaces; on CRT direct-view TVs the open grill on the top of their cabinets (to let hot air escape) probably has certain effects since bass waves can enter there; and the flat surface of the monitor itself could be causing problems (think of in-wall speakers & their problems).
     
  16. ericX

    ericX Auditioning

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    Well, based on Dolby's advice to buy identical speakers all around, I went out and did just that. The sales person's face sure lit up when I said I would take three pairs instead of just one...

    Thanks to everyone for their help! [​IMG]
     
  17. Sonnie Parker

    Sonnie Parker Second Unit

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    Well geee... what did you get... inquiring minds wanna know! [​IMG]
     
  18. Philip Hamm

    Philip Hamm Lead Actor

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    Congratulations eric, based on my experience (three identical up front, two similar non-identical in rear) think you're going to be very happy with your selection!

    And yeah, what did you end up getting?
     
  19. ericX

    ericX Auditioning

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    On a budget, but still wanting something pretty decent, I got six Energy C-200's to go into a 6.1 configuration (one in the front center for now - we'll see if I can perceive any off-center voices - I suspect not based on feedback here). [​IMG]
     
  20. Sonnie Parker

    Sonnie Parker Second Unit

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    I think you will very happy!
     

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