Dual Subwoofers - Good Or Evil?

nathanm · « **on:** 29 Oct 2003, 07:33 am »

I didn't wanna usurp jqp's thread even though it deals with similar stuff. I'm getting some conflicting information regarding the use of dual subwoofers, so I figure I'd open it up for debate and create more confusion for myself. I realize my square room is working against me and nothing I do will actually fix the problem, but please, entertain my delusional thinking for just a moment.

Let's say a guy has ugly, boomy peaks at 40Hz or so with a single sub. Will adding a second one make the problem worse or better? I am a symmetry nut so dual subs has a strong asthetic appeal to me for one; but I am curious if a certain kind of placement with two subs might yield a more even frequency response or not.

Any information on tuned hemholtz devices would also be cool.

MaxCast · « **Reply #1 on:** 29 Oct 2003, 11:35 am »

Double post

MaxCast · « **Reply #2 on:** 29 Oct 2003, 11:36 am »

Nathan, check out this site
It has a number of articles on speaker positioning and about three on subs and placement.

Have you thought about moving? It may be cheeper...

Wayne1 · « **Reply #3 on:** 29 Oct 2003, 01:58 pm »

Nathan,

The problem is in your room. Adding more subs will just add to the problem.

If do not wish to go the full digital EQ route, you might want to look into this Marchand piece

http://www.marchandelec.com/wm8.gif

It might help to tame your room.

See if you can rent or borrow a hanheld RTA (real time analyzer) from a pro audio shop. It will make tuning a sub to a room much easier than using a RatShack SLM.

jqp · « **Reply #4 on:** 29 Oct 2003, 03:51 pm »

Dual subs are just natural. We have two ears, right?

Dual subs give twice the spl of 1 sub. Twice the goodness or twice the badness. But you can use lower watted amps to get the same spl, assuming they are appropriate amps for your subs. If you have a problem with one sub, I don't think it would be worse with 2 subs, more likely that it would get better. With room or structural modes, you could shake your house apart twice as fast!

Theoretically would you not at least have more sucessful placement solutions with two subs? Like putting two sonotube amps in the corner to cancel out the evil waveforms.

cryotweaks · « **Reply #5 on:** 29 Oct 2003, 04:44 pm »

It is a room correction system for subs.

http://www.speakercity.com/Sos/SubwooferOptimizer.shtml

Frank at Speaker City swears by this. Yeah I know he sells them too, but I've known him long enough to know when he really likes something. Heck its cheaper than another sub...

_scotty_ · « **Reply #6 on:** 29 Oct 2003, 05:34 pm »

nathanm,if you buy a second sub with a variable phase crossover,0 to180
and anywhere in between,by placing the sub behind you you can vary the phase and almost completely null out the standing wave nodes. The idea is to cancel out the bass wave after it passes your listening position and before it hits the rear wall. Phase is time, by varying the phase of the subwoofer output you can time it so that the desired cancellation will occurr. Looking at it another way the size of the bass wavelength you are trying to reproduce won't actually fit in your room. By operating a second
sub out of phase with the first you are giving the bass wave a virtually larger room to propagate in. The rear sub doesn't have to be as big as the
front because of the attenuation that takes place in the room,it should go as low in frequency. If you set it up right, you won't even know it is operating as desired until you turn it off.

jqp · « **Reply #7 on:** 29 Oct 2003, 05:37 pm »

I think Tyson uses a Behringer Destroyer? to tame modes.

So assuming you would do this type of management, whats good for one is good for 2. It will give you and opportunity to have 2 sub amps and 2 subs, 2 of every kind of cable, 2 of every tweek for those 2 subs. I think it is worth it to get 2, but more expensive.

You could always start with one and see if you want another...

jkarhan1 · « **Reply #8 on:** 29 Oct 2003, 05:42 pm »

How would you incorporate 2 subs if your reciever only has one sub out?
What is the best configuration?

_scotty_ · « **Reply #9 on:** 29 Oct 2003, 05:55 pm »

Use a Y connector or tapeout. This might be the only way to do this.

doug s. · « **Reply #10 on:** 29 Oct 2003, 07:31 pm »

nate, if ya use two subs, and have their distances to the side & rear walls slightly different, this will help smooth out room nodes...

running a second one out of phase in the back is also something to try - yust switch the speaker wire connections if the sub doesn't have phase control...

eq, as mentioned above w/a coupla different options, may also work if yer room is really problematic.

doug s.

nathanm · « **Reply #11 on:** 30 Oct 2003, 01:50 am »

Everything's already in place for using two, I've got the crossover, two EQs and the amp, plus I got a preamp with dual pre outs so it wouldn't be terribly expensive in that way, I'd just need the speaker cab. My crossover has a phase reversal switch but it is not variable, though that sounds interesting. I didn't know there was such a thing.

Putting one behind me would be rather tricky as I am already sitting against the rear wall more or less.

I downloaded some program called Real RTA which is pretty cool, but then I'd need a good measurement mic. For the time being I hooked it up with my Shure Beta SM57A but as you can see by the frequency response it works for crap on bass at a distance. Still, even so I measured big differences between the lowest bass notes. Mic aside, just listening to it there's major db variations there. Hmmm.

_scotty_ · « **Reply #12 on:** 30 Oct 2003, 02:40 am »

Here is the link to a variable phase sub-woofer plate amp, http://www.partsexpress.com/pe/showdetl.cfm?&DID=7

Piece-it pete · « **Reply #13 on:** 31 Oct 2003, 07:11 pm »

I was just passing through & noticed this post.

I run twin Hsu tubes in stereo. There is no doubt they effect width of soundstage.

Some of the nodes are worse, some better. I am about to pick up a Behringer Feedback Destroyer to take care of this once & for all. Everything you wanted to know about BFDs':

http://www.snapbug.ws/bfd.htm

For $120 it's probably the best bang-for-buck piece of audio equipment out there. For verification of this statement go to audioreview.com & do a discussion search on BFDs'.

As far as run two out of phase, wow that's a tough one to wrap your brain around! But my concern would be this: Will it cancel everything, or just the peaks?

I'm also planning on chucking my plate amps and go over to a high & low pass filter with a professional amp for the subs. Anyone know anything about balanced/unbalanced inputs & how this would affect my system?

Pete

nathanm · « **Reply #14 on:** 31 Oct 2003, 08:46 pm »

I read the article linked by Maxcast and it is very interesting. Their findings indicate that it will take between 50 and 5000 subwoofers for the theoretical ideal response!

But the practical suggestion is either two placed front and back center or four subwoofers front back and left\right in the center of each wall. Only problem is that if I sat dead center in the room the speakers would be only 3 feet away - ugh. Unless you've got a huge spacious room it feels goofy sitting in the middle IMO. Also, the article assumes all subs are running with summed mono signals. I was thinking of stereo bass signals, even though one could argue that most LF energy on CDs is pretty centered anyway. Hmmm.

Indeed, moving to a different house would make the most sense, but then I wouldn't be able to buy any hifi toys now would I? *sigh* Catch 22! My apartment would be great if it weren't for some of these annoying interior walls!

ehider · « **Reply #15 on:** 31 Oct 2003, 09:12 pm »

For what it's worth to this topic: Last year there was a presenter at Cedia who presented a 20 page study that outlined the concept of utilizing either 2 or 4 subwoofers. His measurements fo dual or quad subwoofers seemed pretty conclusive that this was the way to go (if you could afford it). In his study he took 7 different listening rooms and showed that 2 or 4 subwoofers excited less room modes and presented the listener with much better bass response (as compared to 1 or 3 subwoofers). Perhaps symmetry in subwoofers matters after all?

Poll

Dual subwoofers are: