One or two subs

For your application, the single sub might be better.

Since much of the low frequency signal is essentially mono in nature, the output of two subs will likely cancel at certain frequencies unless they are fairly close together.

A friend of mine does audio and home theater installations and used Sonus Faber and REL equipment for such installations. If budget permits, he always went with multiple subwoofers. This is done not to preserve the stereo/multichannel effects, but because it is MUCH harder to get even bass response in a room with just one subwoofer. Unless the room is really big and you like to really crank it up, two smaller subwoofers would be preferable to one really big subwoofer.

Two, for best affect.

I think an important piece of information that you omitted is the size of your room? If it's a large room I'd go with two subs along the line that Larryi mentioned above. So what is the size of your room?

Unfortunately I have one of those living and dining room combos. 12x26 with 10 foot ceilings.

Two. I have three and there is bass without excessive boom. Everything blends better with multiple subs.

I think I would go with two subs separated into two different corners or sides so the room if possible.

A 50 Hz sound wave would be a bit less than 23 feet long, assuming the speed of sound is 1125 feet/second at sea level.

A half wave would be 11 to 12 feet long. If your subs are 11 to 12 feet apart, the peak pressure from one sub would reach the other sub as it is making its low pressure point, cancelling its effect at that location, assuming a mono signal.

If you are at some arbitrary listening position in the room, the sound wave cancellation would depend on the frequency and your distance from each sub. For a mono signal, the best positions would be equidistant from the two subs.

Off the center line, there will be frequencies where the two subs will have an additive effect, resulting in a fairly uneven frequency distribution.

Room resonances further complicate the situation.

I frequently read here that 2 subs are better than one. But the part about cancellation in a 2 sub setup makes a lot of sense to me.
I have 2 subs near the corners on one short wall in a rectangular room that is 13.5 x 23 x 7.5

The subs are about 9.5 feet apart. So is Jameswei correct? He states "the output of two subs will likely cancel at certain frequencies unless they are fairly close together."

Whether you have one, two or more subwoofers you will have cancellation/reinforcement from the waves reflecting off of the walls, floor and ceiling. The various nodes of either reinforcement (where the crest or trough of two waives meet) and cancellation (where the crest of one wave meets the trough of the other) are most severe with ONE subwoofer. Having multiple subwoofers creates many more such nodes so that any particular listening spot is subject to many of such interactions so that any one interaction is not as severe in effect. This is the primary reason to use multiple subwoofers--actually creating many more of such cancellations and reinforcements instead of fewer and more severe wave interations.

James' analysis - tho correct in a vacuum - has it backwards.

Reflections off of the walls of your room will cause destructive cancellation to the long wavelengths of low frequencies - whether you're using a single sub or multiple subs or a full range loudspeaker, for that matter. (You can google 1/4 wave cancellation to calculate the frequency (ies) at which this cancellation occurs.)

So, you always start out with a problem when you have low frequency wavelengths in a confined space. The trick is that - per the calculator I mention above - you can manipulate the details of the response interactions by changing the location of the low frequency driver relative to the walls.

Of course, that's tough with full range speakers. Move the woofer and you move the mid and tweeter. The best position for the woofer is usually not the best position for the other drivers - hence the first advantage of using one or more subwoofers instead of a full range loudspeaker.

The oft-cited benefit of using a second sub is that careful placement of that second sub, relative to the first one, can re-inforce the diminished frequency band created by room interaction with the first sub. That is, place the second sub closer to the wall than the first sub and the bass response trough rises in frequency. Optimal placement of a second sub will almost always result in smoother FR than a single sub, because they can re-inforce the output in each others' null area. A third sub is even better, a fourth better yet, and so on. Take a look at the Audiokinesis web cite for a good explanation.

One complicating factor is the software in the AVR. If you're using room correction software, the AVR will do much of the FR smoothing work for you and the benefits of multiple subs may be reduced. I can't comment on the gear you're using, but my general rule is: without room correction, two subs generally are better than one. With software, generalizations are tough.

Good Luck.

Marty is right that room resonances will be largely determined by the room dimensions, regardless of the number of subs. Careful placement of the sub or subs can help a bit, but the walls will still be the most important factors. (Like, it's very hard to reproduce a sound with a 30 foot wave in a 26 foot room, no matter where the sub is or even if there are multiple subs. On the other hand, the room will tend to emphasize sounds with 26 and 52 foot waves.)

Using multiple subs to try to reduce the impact of room resonances is difficult and not very effective, especially since the output of the subs will be reinforcing or cancelling at different frequencies as a function of how far apart they are and where they are relative to the listening position, as well as dealing with room resonance factors.

I use two REL Strata II subs ... more even bass response to be sure, but I can't overstate how much more effort and fiddling it took me to get two subs sounding 'right' vs. just dialing in a single sub. In my room, the secret ended up being to have one of them out-of-phase, and the other one in-phase (and it had to be the correct one, not either/or). That helped me finally narrow in on the elusive 'sweet spot', but it really took me a lot of trial-and-error effort to get there.

With two subs, neither one of them barely breaks a sweat, and you don't even know they're on until you turn them off (if that makes sense :-) and the whole 'rightness' of what you've achieved collapses.

And this probably goes without saying, but definitely run those RELs via the high-level (Neutrik) connections (i.e. off your amp's speaker outputs). Just my $.02.

Kalbi23,

You don't have to take my or anyone else's word on the subject. Just google "multiple subwoofers in a home theater" and you will find that most experts agree on the superiority of that approach. Multiple subwoofers makes it possible to have much more even bass response throughout the room.

The issue for you is whether it is wiser to spend more money for a bigger/better single subwoofer vs. buying multiple cheaper subwoofers. That is a more difficult choice. Most listeners would find that a single bigger subwoofer will give more impact (hit-you-in-the-gut effect) and deeper bass, but multiple smaller subwoofers gives more even coverage, better pitch definition and better overall sound for music reproduction. If you place a high priority on impressive home theater sound effects, the bigger badder woofer would probably be a better choice.

James wrote:

Using multiple subs to try to reduce the impact of room resonances is difficult and not very effective, especially since the output of the subs will be reinforcing or cancelling at different frequencies as a function of how far apart they are and where they are relative to the listening position, as well as dealing with room resonance factors.

Well.....

The point of adding a second sub is precisely the phenomenon James describes as a problem. The delta between the response deviations of multiple subs averages back to the norm (anechoic response) - provided you place them carefully.

As to the larger point James is making, again, overall, I'd say "true" (regarding effort, with one caveat) and "false" (regarding potential for good results):

Attempting this exercise by ear is a major PITA. I'm 100% sure that many folks will quit before they get it right.

Doing it with a real time analyzer is much easier and likelier to produce a good result (with more than negligible time required).

Doing it with a high quality automatic room EQ package is a snap and IME will certainly produce excellent results. OTOH, this approach IME often provides excellent results with one subwoofer, so..point taken.

Bottom line: If you take the time, two unEQ'd subs will almost certainly produce smoother bass than one unEQ'd sub.

Thank you all for your responses. After doing some online research, looks like I'll need to go with a one sub set up as my living room is not optimal for a 2 sub set up. If I am facing the tv, the wall is to my left and the additonal space and kitchen is to my right. The subs would go in the left front corner and left rear corner, as I've found online, thats not a good dual sub set up. Any thoughts?

WITHOUT any doubt...2 subs are better than 1. I believe it is best to have 2 of the same subs which ever you choose. Get the best subs you can afford. I use a single Rel in my 2 channel - using the Neutrik Connection. But it is barely on...the crossover is set at 25 htz and the volume is almost off. It just ever so slightly underpins my mains.
BUT<<< in the Theater I use 2 subs...(won't mention the brand)....In theater the subs play a bigger roll. They will probably be crossed over around 80 Htz and be considerable louder. Here's what I find...Having 2 subs eliminates any localization of the low frequencies as well as improving upon room modes - Much smoother response. The bass comes at you like a wave. Ever once in a while, only 1 sub will kick on and the room seems lopsided. then the other kicks on and it's like both feet planted on the ground.
Not to be a party pooper but the rel will run out of gas on some content dished out in Movies - Try the wooshe finger hold at the end of Kung Fu Panda 1- that is a great torture test...Good Luck and happy listening

For the members who have two subs, how is it positioned?

Left & Right Front corners...

For my 2 channel I have 2 F-113 subs. I believe it sounds better with 2 over 1.
But for my Home theater I have 5 subs.

With my 2 channel F-113's. I have those subs outside of my main speakers near the left/right corners. But, they are out into the room a couple feet both at the back wall and the sidewall. This will limit bass boom.

All things equal, more subs equals more efficiency and output capability. Smaller rooms have a problem both absorbing bass energy, however, for proper RT60, and long bass frequencies don't support well in diminutive dimensions. So I like small single subs in small spaces, multiple 8's placed together or single 10" sealed woofers in medium spaces, and maybe 12" dual's or better stacked together, or flanking each channel as stereo subs in large spaces.
Problems you run into with spacing multiple (in this case, two???) subs, spaced 1/2 way points along the wall boundaries: PHASE CANCELATION at different seating locations! Sit closer to one sub vs other in a room with subs run in mono, and you'll have a good ol time trying to not get phase cancelation issues between the two! It's simple acoustics.
Pick the sealed subs in small and medium sized rooms, and go multiple subs for more output and dynamic range from full on HT duty applications! ..but keep em together, say, in center of front of the room, near the main center for best crossover, easier integration, and lack of phase issues from seating locations. Blends best, I tell ya.

When it comes to subs, two is always better than one in terms of better and more consistent sound quality throughout the room, the caveat though it may take longer to get two subs mixed in optimally compared to one.

The more, the merrier in general, though with diminishing returns of course. Even 4 or more is not out of the question in some cases.

Once the bass levels are right no matter where you listen from in the room that you might care about, you are done.

If you listen from one location only, and bass levels are fine, then one sub may suffice just fine.

With one sub (ie no stereo), its more beneficial than otherwise to configure so sub fill in solely in lowest octaves that mains cannot handle otherwise in that sound becomes more directional at higher frequencies.

I had two subs and used a Dspeaker 8033s ($400.00) to control the room nodes. I'm now using the Dspeaker Dual Core 2.0 and can't believe how good the bass sounds.

Just my 2c

I've been using my two Velodyne HGS-15s with an SMS-1. Since I acquired a second SMS-1, I have been reading the manual about daisy chaining them so each sub can have its own acoustic room correction. I think I'll give it a try.

db

Guys, thank you for all your responses. Ive decided to go with two Rel T7s. My pre is the yamaha cxa5000, has dual sub outputs but the second output saids for rear sub, should i just plug into that or get a RCA splitter, thanks and will update once i set everything up.

See "SWFR Layout" settings, page 108 in the owners manual.

I'm going to ALWAYS advise against some recommended loudspeaker location recommendation layout in an owners manual, as there's simply too many unacounted for variables to consider for best results. Each layout and seating situation is different. Bottom line is loudspeaker / subwoofer placement in the room for any given room layout and seating locations, acoustics, etc, is going to vary greatly. And while some owners manual or recommended setup in a book can give you a rough idea, you still need to find the main seating location, and set speakers and subs according to those first, and then plot other seating after that. Then measure and listen for all, and maybe make tweaks and adjustments.
Never follow some random piece of literatures setup instructions for your space! Your ears are final judge - but measurements will always need to fall somewhere near accurate for good sound and performance. -especially when it comes to bass response! EQ the rest...

Hey everyone, just wanted to give you guys an update. Finally got the Rel T7s and started the dial in process. I must say, i couldn't be happier, the balance, soundstage is something i never thought was possible. I would always recommend dual subs for anyone who has the budget. For music i used, Royals by Lorde, Seven Nation Army by White Stripes and for movie used Dark Knight and Frozen.