connecting two subs in stereo: left right &... center? - AVS Forum
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post #1 of 5 Old 04-03-2014, 08:37 AM - Thread Starter
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Lots of time spent playing with REW's room sim reveals that this is the best placement option for bass in my small rectangular room.

Everything concerning the response associated with this placement has already been thoroughly investigated.  I used to sit facing the short wall.  I've done numerous calibrated measurements.  I put my sub & myself where REW said we'd get the flattest bass response & REW was right.  The sound is absolutely freaking amazing in that position.  You're just going to have to trust me. 

First problem, as you can probably guess, this setup boosts left/right axial modes (i.e. the omnidirectional subwoofer is now quite directional).  My other half is getting lonely, so I'm planning on getting a second sub for the opposite wall.. No, not that kind of other half!  The other physically attached half of my body.

Second problem, I have identical front left, right & center three-way tower speakers.  I'd like to wire the subwoofers in stereo with the front left & right (in series, respectively) for a true four-way stereo configuration, but I don't want to leave the center out of the mix. 

As far as I can tell, my best option is to split the amps center output signal & biwire the center speaker through each sub's speaker level terminals... 

Will that be okay?  I can't imagine why not...

My receiver has an LFE output.   I just don't want it crapping up my image (it is mono).

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post #2 of 5 Old 04-03-2014, 10:46 AM
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There is no *stereo* at LF.
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post #3 of 5 Old 04-03-2014, 11:05 AM
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As he ^ said. Stereo subs, meaning similar to stereo speakers with both placed on the same wall, is almost never the best or even a good idea. Unfortunately the mind likes symmetry so people often do it, but for best performance and flattest frequency response, the subs should be on opposite walls almost always. That is if you only have two subs. A small investment in the mike for REW and then you won't have any more questions. [That's a total lie, the more you know, the more questions you'll have, but at least with REW you'll be dealing with facts instead of generalities and opinions.] smile.gif
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post #4 of 5 Old 04-04-2014, 08:12 AM - Thread Starter
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I agree with you two, especially the "almost never" part.

Anyway,  I want my three front speakers to track as closely to eachother as possible!  They're identical & I want to keep it that way (impedance, anyone?).

As long as the subwoofers are crossed over at the same frequency...
Can I connect the amp's center channel through both subs & then to the center speaker without any major problems arising?

That's four wires coming out of the amp's center terminals, one pair going to each sub, being filtered, & then all four wires being terminated into two terminals on the center speaker.  I'm not sure if I'm going to have signal issues, thought I am more sure that I shouldn't have any.  I'd like to be 100% sure before I spend a small fortune on sixty extra feet of wire, a butt load of banana plugs, a pair of stands & another subwoofer.

Otherwise, the next best place to put one sub is in the ceiling corner, front or rear wall & center.

Additional Information:

Based on the collected information, I've drawn up this model with sketchup.


As you can see, the subs are positioned on opposite walls.  I simply want the bass to occupy both ears, rather than dominating one (as this is the best position (either side) for flat bass reproduction in this particular space.

From the listening position (center, 2'8" off the floor) REW's room simulator generates this graph for the subwoofer placement depicted above.


I am aware that there is no "stereo" at LF, but I did explain why this isn't entirely true for my case in particular.

I don't really want to get into the science behind why certain frequencies are perceptively radiating from the one subwoofer, placed to my right, just above ear level, which causes wide modal resonance centered at a post 90 Hz frequency. No, that's not my question. I totally understand why that's happening, but thanks anyway. :)

Using this layout, I've reduced the modal distortion caused by the room dimensions to a single frequency.  Other than this one frequency the only issue is that the bass resonates from the rear right corner & noticeably diminishes as it travels through my head, bounces off the opposite wall & back into my left ear.  Perhaps this wouldn't be an issue if I were a ghost, but spectral mass I am not & a lot of those frequencies are prevented from reaching my left ear because they are being absorbed (by me) before they have a chance to bounce off the left wall. 

This is why I am adding a second subwoofer & that is why I've decided that these frequencies should be sourced from the left & right channels.  I don't want these subwoofers playing the LFE channel.  For that, I was thinking something more like this:

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post #5 of 5 Old 04-04-2014, 01:28 PM
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Quote:
Originally Posted by morphemes View Post

Can I connect the amp's center channel through both subs & then to the center speaker without any major problems arising?
No. You will have the impedance of all three in parallel and that will be too low a load for most amps.
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Originally Posted by morphemes View Post

Perhaps this wouldn't be an issue if I were a ghost, but spectral mass I am not & a lot of those frequencies are prevented from reaching my left ear because they are being absorbed (by me) before they have a chance to bounce off the left wall. 
A sub radiates hemispherically so your mass, which is actually not absorbing much LF is only a small part of the area of the wavefront by the time it reaches you.
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