Stereo Subwoofer Pairing

" Use of multiple subs can minimize rooms nodes so, depending on the room, it can be an excellent solution to achieving flat in-room low frequency response."

Hi cleeds,
     Strictly speaking, your statement is true and has been scientifically and independently verified and documented by multiple acoustic engineers, including Dr. Geddes and Dr. O'Toole among others.  They've both published white papers on the subject if you're interested.  However, you failed to mention some details about their findings that are important to this discussion and for rjb1101 to know about.

     These scientists, through extensive testing and measuring, discovered that room bass nodes were consistently reduced as the number of subs was increased in a given room.   Yes, 2 subs are technically 'multiple subs' but they found that the use of 2 subs, while resulting in better in-room bass response than just a single sub if properly positioned, had the least affect on reducing room bass nodes. They basically concluded that the more subs in a given room the better the bass response becomes.  Not very surprising, right?
     Of course, they realized there's a practical limit to the number of subs people will accept in their rooms.  So they further stated that 3 to 4 subs, if properly positioned, would result in the elimination of the vast majority of bass room nodes in most rooms. This is the basis for Audio Kinesis utilizing 4 subs in both their distributed bass array systems.
    There is also a precise method of positioning each of the 4 subs for optimum bass response in any room that is based on Geddes and O'Toole's scientific research.  It's detailed in both Audio Kinesis manuals and I'll describe it if anyone is interested.  

    ." stereo deep bass is a myth ...

Not exactly. Depending on the phase of the LF signals, it is absolutely possible to hear bass in stereo."

     I have no knowledge of your statement being true and Dr. Geddes and Dr. O'Toole make no mention in any of their white papers of the ability of humans to perceive bass in stereo.  Most of the research I've read actually concludes the opposite; that humans have great difficulty discerning where LF sound waves are emanating from.
     I know I don't perceive LF sound waves are emanating from any of my 4 subs even though my listening chair sits between the 2 rear subs against opposing l+r walls in my 23 x 16' room and the 2 front subs are along my front wall -one behind each l+r speaker.  I perceive the bass as emanating from appropriate instruments and voices within the sound stage illusion I perceive as in front of me. 

     I willingly concede, however, that what I perceive as bass emanating from specific spots within the sound stage illusion is actually a form of perceiving stereo bass.  So, even though I'm unaware of any scientific proof verifying it, I believe hearing stereo bass is possible with the assistance of our brains because I've experienced it in my own system.  Sorry, thinking out loud.   
     From my experience, I think a more accurate statement is that we hear and feel the bass which our ears/brains perceive and assign or interpret as emanating from the proper instruments, voices and positions within the sound stage illusion our ears/brains are also perceiving and interpreting.

Tim

I have been using (and integrating) sub woofers in my music audio systems for years, 2.1 systems in the past, my current setup is a 2.2 setup, with a pair of identical models (both purchased new at the same time).
Though low bass sounds have a very long wavelength, so long it's difficult if not impossible to sense the direction they are coming from, I have found that having a pair of sub woofers gives the "visceral" experience of directionality to the bass, so I'd recommend installing a pair of subs of the same model.

Hi ejr1953,

     I think we're stating similar but slightly different things.
     You're stating you've been able to perceive 'stereo bass' in your system through the use of only 2 matching subs.
     I'm stating I've been able to perceive 'stereo bass'  in my system through the use of 4 matching subs precisely positioned.
    I don't question your results but I'm curious about and would like to learn a few things about your system compared to mine:

How did you determine the best room position for each of your subs?

Do you have equally good bass response throughout most of your room or is the bass response optimized for your listening position? 

     My thought is that you've optimized the bass response at a single listening position which is a significant accomplishment but bass response at other positions in your room are likely not optimized since the vast majority of room bass nodes are not eliminated with 2 subs in a given room but are with 4 subs strategically positioned.  You may not be concerned about this but I was striving for good bass response at all 7 of my room's seating positions for both music and ht.
       Please don't misunderstand my intentions.  I'm not concerned with claims that my system performs better than yours but rather with providing the OP with useful information about how 2 sub systems are not able to eliminate the vast majority of bass room nodes as 4 sub system are and, therefore, are unable to provide good bass response throughout virtually the entire room.  I think it's best he receives accurate info and let him decide for himself based on his circumstances and preferences.
     I just want to make sure he doesn't get the impression that a 2 sub system will perform equally as well as a 4 sub system.
Enjoy,
 Tim  

If this is a two channel system in a reasonably conventional room and your main speakers are making a soundstage at the listening position two subwoofers effectively placed should provide more than enough node free area at the listening position to begin with. 

I'd suggest using both your existing subwoofers with the .7s in a mono configuration as a starting point. Concentrate on finding their optimum room location which reduces the most room nodes.

If the REL cabling prevents your from locating your subs at most locations in your room you might consider running them using their low level inputs and very long economical interconnects from Blue Jeans or Monoprice cable to aid in their room location.

You should be able to mitigate your concern of what you term as overlap with proper crossover and gain. Frankly, I don't think this will be an issue especially if the subs are irregularly located in the room and running in mono.

When I compared a REL Studio III it worked best sourced from a low level signal processed through a Velodyne DD Optimization program. I am not a fan of REL subwoofers.  

  

Deep bass is not directional, and that has been shown by a lot of research. Yet, as some have argued here, it may sound as if these deep bass notes do indeed emanate from different speakers. The explanation is that the human brain uses the upper harmonics from the main speakers to locate the deep bass tones. You can do two simple tests. The first is to use only one subwoofer. Interestingly, and provided the sub has been integrated properly, even with one mono sub the deep bass will seem to come from the two main speakers. The second test is to use two stereo subs, but turn off the main speakers. You will not hear stereo, because the directional information from the main speakers is lost.

So you can happily connect two subs in mono and not lose anything. However, why not connect them in stereo anywany- is there a disadvantage to connecting two subs in stereo? Indeed there is, because two mono subs will produce the same signal, and will therefore be smoothed more completely by having two subs reproducing the same signal in different locations. This is why most experts and manufacturers suggest to connect two subs in mono.

Two subs are indeed better than one because they reduce room modes. Similarly four are even better, but this is a story of diminishing marginal returns.
In principle you have four ways to deal with room modes in a given room:
1 use dipole subs (Rythmik have a kit for a dipole sub). Dipoles excite far fewer room modes, so you address the problem at source. The disadvantages are that dipoles tend to be larger and require more power.
2 install bass traps. The down side is that they are big and ugly.
3 use multiple subs. Two are a big improvement, and four brings additional improvement.
4 use dsp room equalization like the Antimode 8033. Use this with one sub and the (big) improvement is quite localized. Use it with two and the improvement applies to a much larger area.

Ideally, you may want to use all four methods. In real life, a combination of two or three will already bring vast improvements. If you have a bit of space I would opt for two dipole subs combined with room eq. If the room is small and domestic tolerance limited, I would opt for two really small subs like the SVS SB1000 plus an Antimode. If you have space and the budget, by all means go for four.

Ideally subs should be the same model, but as long as they are not too different there should not be a problem. Two identical ones but with slightly different ages are not an issue at all. Speakers do indeed need to be broken in, but this does not normally take more than a few hours. With subs, you are unlikely to even notice (but wait for a few hours with the Antimode equalization).