Best Sub Woofer Location - AVS Forum
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post #1 of 8 Old 04-23-2012, 09:15 AM - Thread Starter
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I am trying to find a good start position for three sub woofers in a home theater room that is 25' W x 12' H x 50' L. Someone told me to use an oscilloscope to find the locations. Any one know how to do this?

Regards,
Mike
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post #2 of 8 Old 04-23-2012, 09:34 AM
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Quote:
Originally Posted by mikesorensen06 View Post

I am trying to find a good start position for three sub woofers in a home theater room that is 25' W x 12' H x 50' L. Someone told me to use an oscilloscope to find the locations. Any one know how to do this?

Regards,
Mike

I would start with three across the front all equally distant to the listener.

If room modes were really bad then two up front(corners maybe) and one behind the listener. Still try to keep them equidistant.

Download REW and get and/or get an SPL meter and measure the right place to put or else your shooting in the dark.

Not sure about how to use the O-scope.
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post #3 of 8 Old 04-23-2012, 01:03 PM
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There is no reason to be equi-distant from the listener (which one) if you have variable phase control on each sub or a PEQ.

Three across the front is not a good idea at all...mid point side wall, midpoint back wall, midpoint front wall. Alternative, between the L and C, between the C and R and 1/3 the width of the back wall or 1/3 the length of the side wall.

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post #4 of 8 Old 04-24-2012, 06:10 AM
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How about subwoofer underwear?
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post #5 of 8 Old 04-26-2012, 10:27 AM
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Mike,


You're already ahead of the game by having three sub-woofers. Now to really take advantage, you must optimize the three and minimize the room's negative impact on what you hear. The science involved is very well understood, and quite well documented.

Three subs is a fantastic tool,...you've got to use it. It's actually reasonably easy. Here is a good, well explained paper, that's not very long, and not too difficult to grasp. Toole really explains the manner in which you can implement selective mode cancellation, by proper placement of subs to really dampen the modal effects at the LP. This is very effective and not too difficult.

Dennis gave great advice above in pursuing the midpoints of three walls, and the two in the front wall (@ 1/4 to 1/3 widths), and the third somewhere along a wall behind you,... wherever measures/works best is perhaps where I'd start. The axis in which you spread the sources is the direction of modal control you're addressing. For example, spreading the two along the front, from the 1/4 points, to the 1/3 points in from the sidewalls addresses the room's width modes. Subsequently, the rear sub addresses the front to back modes.

It's very easy in real-time to measure modal effects with REW, or OmniMic. One can clearly see the peaks and valleys in response by moving front to back, or side to side,....thus you'd know which axis is most problematic. It's not uncommon to have big wide peaks of 15dB, and nulls of 20-30dB. If you leave all your subs along one wall, you'll need to rely solely on EQ to knock down the peaks to minimize the effects of the nulls. Spreading the subs around oftentimes allows you to use dramatically less EQ, and with proper delay/phase adjustments per sub, you'll retain ideal localized and integrated bass with the mains, in an entirely coherent subwoofer system.

Now for three subs, ideally you'll need individual delay for each sub. There's many products out there, the Behringer DCX2496 is inexpensive, and very popular for duty such as this. Also, you'll have plenty of signal shaping options, both individually, and globally across the three subs too.

If you only have an Audyssey based rig, a good one like a two channel capable (MultEQ XT32), then you'll only have two locations to use. You'd need to co-locate two subs, then place the third one where is does the most good modally. Then allow the PrePro and Audyssey perform the freq and time domain EQ'ing. IMO, this is easy, however dramatically much better results may be had by implementing the DCX2496 and rolling your own.

I know that's a lot of info, however optimizing an HT with a multi-sub approach may be one of the biggest values, producing tangible results in this entire hobby. Also, be mindful that the time domain is where you'll find the gold. A strong measure of bass trapping, without negatively affecting the room's liveliness, or system envelopment, will take a good multi-sub system to the next level.

Addressing the time domain behavior of the LF, damping any ringing will add a level of delineation and detail to the bass, that no amount of equipment could ever add. Bass traps and lots of them,...if needed they can have a ~6mil plastic (or equivalent) covering to allow them to be reflective above a few hundred hz., yet entirely absorptive from that point and below. Anyway, I only bring up bass trapping because a multi subwoofer system such as yours has the potential to approach sub-woofing nirvana,...just sayin'


Best of luck



Two other links of precise interest;
The Geddes method for a multi sub approach.
This Toole paper is truly superb.

Those are focused on the task at hand, if you're interested further on the time domain, bass trapping,.. etc., PM me.

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post #6 of 8 Old 05-07-2012, 06:47 PM
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I have a question about another aspect of subwoofer placement. Let's say that we're talking about a front-firing unit that is going to go against the front wall and let's say it is moderately large, 20"w x 28"d. Is it better to face outward from the front wall (woofer 28" from the wall) or alternatively face along the wall (woofer 10" from the wall)? Or maybe even woofer pointed at the front wall??
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post #7 of 8 Old 05-08-2012, 03:44 AM
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I am soon to add a second sub with only two WAF placement options available. My current sub is between my R and C speaker (1/3rd from the right wall).

I have a choice of placing the second sub between the C and L speaker (1/3rd from the left wall) or along the left wall (1/3rd from the front wall).

Which is my best option?
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post #8 of 8 Old 05-08-2012, 05:35 AM
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Quote:
Originally Posted by eric9090 View Post

Sub woofers position if diagonal gives out best sound!

Just so I understand this correctly, you are recommending the side wall for my second sub?
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