Dual Subwoofer Question

Is it OK for me to have 2 subs that are not matching in a music/HT system? i.e. have a 10" & 12" of different make together or should I have identical subs?
I don't think it's a good idea. It's definitely something you would want to audition before putting any money down. However, I'm not optimistic.

If it was strictly for HT effects like bombs blasting or car crashes, you could probably get away with it.

However, you stated that you will use it for music too. If it's crossed over anywhere above 35-40Hz, I would be very surprised if it wasn't noticeable.
I don't see any reason why you "must have" identical subs...should work fine as long as you have independent control over each sub.

Several technical issues could arise
Can they both x-over at same frequency?
Do they both have full adjustability on phase?
Do they both have same x-over slope?

Assumming answers to all of above are yes, then IMO, its possible, but unlikely that it would be successful. First of all, I assume you would be using one for each channel, which would make balancing the system very difficult. If each sub has different room modes (likely if different sizes), you could end up with double the number of peaks. OTOH, in the unlikely possibility that they have opposite modes, you could eliminate peaks. HIghly to extremely unlikely, but possible. Audition before you buy, for sure. The only scenario where I could conceive that it has a reasonable chance of being successful is if you used the smaller sub to supplment the L&R and the larger for the LFE channel. You would probably need to set your processor for large L&Rs, and take a high level signal from the speaker outs of your amp, and then high pass that to the L&Rs.
Thanks for the replies guys, you are guys are so smart.

Ok, my listening is 80% music, 20% HT. I prefer tight musical fast bass as opposed to deep & slow.

My 1st sub and 2nd potential sub will both have Xover frequency, phase adjust and of course volume controls.

Also, my 1st sub has both RCA L and/or R outputs to feed signal to 2nd sub.

Give me a few more opinions for and against this 2nd sub, cause I'm itching to buy it off Ebay for a great deal
I have 2 subs, one on either side of my couch, set off a couple of feet out. Hidden under plants, they are also mostly invisible. One is an Adire Rava- which is a front firing 12" sealed sub and the other is a Hsu VTF-2- with a 10"downward facing driver. They are both quality subs and play without problems together. They are both dialed about halfway up in volume and the crossovers are also set the same. The sound is room filling, tight and they can't be localized. During movies they tranfer vibrations and slam to the couch which always brings suprise and joy to friends and family. Use quality subs, find the right place for them and you will be fine, as long as your room is not difficult.
I have a system very much like Swampwalker described. I use a pair of 10's (RBH 1010SE) driven off my L/R channels - and an SVS dual 12" behemoth (PB12 Plus/2) for HT. I love it.

When I'm in 2-channel mode the SVS is silent and I get the extremely tight bass which I wanted - yet I also get gut wrenching bass when it's needed. Best of both worlds IMO.
2 subs will give more bass and "potentially" better bass. The most important thing is how you manage them. A lot of things come into play: placement,settings etc. Even when I set up one sub I use "tools" to maximize results. Someone mentioned the need for the same crossover settings which is not neccesary. Most subs can be set at the same frequency and may or may not have the same slope. However there may be a small dip or peak that setting one of the crossovers differently may improve. All rooms are different as are the subs we use. Take the plunge and enjoy. There is a lot of info on tools and how to use them.

Good points, ET. I have been thinking that with 2 subs, they would be run as monos. As many have found, there is some differential (stereo) information at these low freq and with two diff subs with two diff settings, x-overs, slopes, etc., I can see problems for music but probably not for HT. It is true that the two could make the bass more even, cover up for anamolies in the other, but if I was buying a stereo pair then I would buy a stereo pair. You would not use 2 diff speakers for L & R for full range or monitors. If you have access to a second at no cost, give it a whirl for sure, but if you have to buy the 2nd, why not get a matching sub.
I have two matching subs, and I have found it difficult to get really useful info on how to set them up. Dual subs should work well for music and for movies. I run mine in stereo. I have been playing with advice written on the RANE website on how to set things up [see the manual for the AC 22B crossover - it has timing (phase) and level setting instructions]. Their focus is more for setting up sepatate speaker cabinets for live performances, but the same problems exsist in our homes. Check it out to see if it helps.

As for two different subs...I am not so sure that would be great for music. Not that it would be bad, but I just don't know. For movies though, I always thought two were better than one to help get an even response from multiple listening locations once they are set up correctly.
I've got two subs - my older one is a Sunfire True 10" and my new one is the Vandersteen V2W. The V2W is more musicly sound (three down firing 8" and a passive front firing 12") and I use that for the LFE channel. My older Sunfire is now being used to give the rears a FULL range ability. WOW there is a lot of rear surround bass in movies (i.e. U571). I am getting a new house and I will finally have a theater room - which means that I will eventually by one more V2W - one on the left side and one one the right side for LFE and the Sunfire still for the rears.

My point is if you try the 2 sub set and use them as I have you won't be disapointed. Just choose which of the two is more musicly sound as your main sub and the other as a rear channel sub to give you full range when doing movies.

And to think I almost got rid of the Sunfire because I thought there just wasn't enough full range sent to the rears in movies - WRONG! And the rear channel bass doesn't really get set to the main sub in LFE or just standard bass info...didn't discover that till I tested it.

Happy Listening!
It's going to be difficult, and not ideal if it can be avoided.
First of all, you need to know how to set up a subwoofer correctly in the first place, let alone 2!!!!
For instance, I recently did a 15 year professional custom installer friend of mine a huge favor by re-engineering and calibrating his home theater system for him. Things were so bad, he called me to see if I could help him. He had 2 subwoofers of different brands in his personal home system, that were most definitely "ill-set up". When I went through his system, everything was off (namely 3 mismatched brands of speakers in system!!!, speakers obscured behind furniture/couch!!!, speakers mis-aimed for tonality, frequency response out of whack, crossover settings off, "dead short" in one of his rear channels, volume levles off between channels, EQ settings all way off, overlapping frequencies between subs and mains, and out of phase, including the subwoofer setup and integration with the rest of the system). Needless to say, his system sounded AWEFUL!
In respect to this post, yes, it was a challenge getting both brands of subs to integrate into the system efficiently. Namely however, the possitioning of the subwoofers in relation to the rest of the system and seating possitions, was a challenge. I ended up having to move the subs into a possition where they coupled with the mains in relation to the seating possitions, for proper crossover and phase parameters. When I got to the system, the two subs were placed on opposite sides of the room, causing phase challenges from different seating possitions in the room. You'd get it close in one seat, then the two subs would cancel each other out from another possition-not good.
My experience and knowledge finnaly got things integrated for tight accurate bass, but it wasn't easy. I noticed both subs exhibited diffent bass quality, when switching between them. I think, even from a "noise/distortion cancelation" viewpoint, having two subs that respond and are engineered exactly the same makes things much better potential-wise. I'd recommend matching dual subs, perhaps set up in stereo, depending. Still, yeah, two matching subs better than mis-match, IME.
Not that you haven't heard this a dozen times already, but try at all cost to have the subs match. Size, IMO you can fudge a bit, ie 10" and 12" or 12" and 15". However, stick to the same manufactor if possible.