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Discussion Starter · #1 ·
I just have a question for anyone who has used 2 smaller bookshelf speakers to be used as a center. I have two extra bookshelf speakers currently and thought about how it would be great to just bond the speakers end to end... of course they would be symetric as well and this would create a fairly decent size center. I heard where some people do use a bookshelf as a center by just laying it down on its side but I'm going to be using two speakers instead. I would connect the speakers in "Parallel" instead of series to keep the same impedence. What would be the drawback of this design? I mean... isn't it pretty much the same as having a center with many woofers and tweeters? Crossover would function the same and both speakers will be connected to the center channel output. I guess I'm just wondering if this has been done before and if it actually works well. Any thoughts and recommendations would be appreciated. Since you are connecting two speakers to one source and have to share the power... would this cause the sound to be too weak? I have hard time believing this method wouldn't work. Anyone... please chime in.


Cy
 

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When you connect them in "parallel" you actually half the impedance (if they are the same speaker). So if you have 2 8-ohm speakers, you will be running them "paralleled" at 4 ohms. This will put basically a 2x strain on your amp's center channel. What kind of speakers are they and how are you powering them?
 

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If they don't match your mains, then you're better off without a center speaker altogether. It's fine to use bookshelf speakers as center speakers. In fact, if you can align them so that they're in line with your mains, using a matched bookshelf speaker is preferable to a horizontal center speaker.


However, there are two factors working against using bookshelf speakers -- 1) the bookshelf speakers are typically not magnetically shielded to prevent TV interference, whereas dedicated center speakers are shielded; and 2) the TV usually sits exactly where the bookshelf speaker should go, and their vertical design is not easy to integrate with the TV. A horizontal center speaker is a compromise design necessitated by where the TV usually sits.
 

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Discussion Starter · #4 ·
I just realized that you do instead a get 4ohm load with two 8ohm speakers in parallel... yikes! I guess that's why no one has really done it unless you want your center channel blown out. I guess there really isn't anything you can do to combine two bookshelf speakers rate at 8ohm to get just one 8ohm speaker. Oh well.. that's why I asked.
 

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Not a good idea. You will get comb filtering that's worse than the typically bad woofer-tweeter-woofer design of most center channels.


Check out the question in the middle of the page with the measurements:

http://www.hometheaterhifi.com/qa/qa2002/qa324.html
 

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Discussion Starter · #6 ·
wow... that's pretty nice link and answers my question... thanks Kevin! It doesn't mention anything about the change in impedance though... oh well... at least it's not a good idea to do that anyway. Case closed.
 

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CY2354- Hee, hee. :) Just to confuse the issue even a little bit more... There actually is a 2-center channel scheme that will work: one above and one below. No lateral comb filtering, *and*, because you get sound from above and below the screen, the *image* is actually directly pinned to the screen. But most people have a hard time making that work in their rack/TV stand...
 

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4 Ohms isn't a killer for a good receiver or amp, many center channels are 4 ohms anyways.


Balancing the DIS-advantages listed above, this setup does have potential advantages:


1. You can have the exact same speaker all around for timber matching.

2. A nice sized center channel

3. Inexpensive.


You can try your theory ( the over/under combination above sounds interesting) and, if 2 of them doesnt work, try just one!.


You could also try them on top of the TV, upside down, with the tweeter closer to the screen.


None of these setups are probably ideal, but hey how many of us can afford ideal setups?


5 good bookshelf speakers can make a pretty good HT.
 

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No lobing if the two speakers are above and below the display.
 

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Kevin,

You will definitely get lobing with two speakers one above and one below. At some point in front of their radiation, the output of the two speakers will interact and cause cancellations. This cannot be avoided.
 

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I have an Infinity setup with two RS5's up front, two RS4's in the rear and one RS3 bookshelf I use as a center (oriented vertically, tweeter down). I tried using both but it sounded terrible. Using just one sounds great.
 

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Scott- Don't think so. Here's the typical case: horizontally configured woofer-tweeter-woofer center channel. You get lobing in the *lateral* dimension because of the distance between the two woofers which are reproducing the same signal, as you move laterally off-axis to the center line of the speaker.


For the case of the 2 centers above and below the display, the lobing can only occur in the vertical direction. But this is a non-issue, because the proper placement of a display is that the center of the screen is at about eye level. So that means that both speakers are about the same exact distance from your ears. Which means ... no lobing. And even if your screen is offset (probably up, not down), as long as you don't go *vertically* off-axis of the center of the screen (or the midpoint of the two speakers) by more than about 15 deg, also, ... no lobing.


It's easy to get the typical horiz lobing, for example, just have a few people sit across a sofa. But vertically? The angles just don't support that.
 
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