This technique is usually used for HT when the subs are in mono or LFE. You can cancel certain room modes by placement with 2 subs much better than one. On our resource page there are a few articles that can be very helpful, possilbe the most helpful is one by Todd Welti and Floyd Toole of Harmon International on how many subs. For this technique to work the subs do have to be identical.Rives Resource Page
I use stereo subs to reinforce monitors. Sounds great. It helps tremendously if you have a symetrical set-up. A kick drum does sound like a kick drum. It is exponentially more difficult to set up stero subs though.
I tried 2 subs with my B&W matrix 804's and they added a depth to the soundstage that was unknown to me before. I have since switched to Legacy's Focus 20/20 which is like having 2 subs in a speaker. Definetly an improvement over 1.
Virtually all CD's are mono below 80 Hz, so I doubt there would be a significant audible difference between dual mono subs and dual stereo subs.
I do believe that dual subs offer significant room integration advantages over a single sub.
From my investigation of the subject, there seems to be two well thought-out schools of thought on dual subwoofer placement. One holds that the ideal is to place the subwoofers to the extreme left and right of the listening position. This maximizes the interaural time difference and thereby the sense of spaciousness that the subwoofers convey.
The second school of thought recommends what could be described as highly asymmetrical placement, to maximally stagger the path lengths from each sub to the room boundaries and the listening position. This results in the smoothest bass, and is the technique that I use most
In my experience 2 subs are better than one. They must be identical and in many cases should be placed at the near the midpoints of the room to help control room modes. They are difficult to set up without a tech with the proper equipment to help you,otherwise the placement is really by chance and you probably will not get the most for the money. That being said, properly setup stereo subs sound awesome indeed.
I run a pair of Def. Tech. Cube II's with my monitors to great effect, clean, fast, controled.
Hey Duke, can you expand on your "second school of thought" comment above. I run dual subs and am all ears on set-up advice. You too Sgr and Rives. My primary concern is 2-channel audio even though I have HT in the same installation.
BTW Uru975, the bottom end of the Focus 20/20s is tough to match. I was a very happy owner of a set before getting Whispers. Even for HT, there is no need for a sub with those speakers...just lots of amplifier current!
Audiogon is fabulous! Thanks for all the input, and it seems as though we have some real discussion going on.
It looks as though the subs have to be identical, eh?
A basic premise of the second school of thought is that room acoustics dominates in the bass region. So the idea is to use what inevitably happens in the room to your advantage as much as possible.
Consider the single subwoofer situation: There's a path length from the subwoofer to your listening position, and then there's another path length from the subwoofer to the opposite wall and back to your listening position. At a certain frequency, the difference between those two path lengths is equal to one-half wavelength. At that frequency you will get cancellation at the listening position. Higher up there will be a frequency where the path length difference is equal to one wavelength, and at that frequency there will be reinforcement at the listening position.
Obviously you have more than one wall in the room so the situation is more complex, but you get the idea. You can get quite large peaks and valleys in the in-room reponse at various locations depending on how the reflection patterns coincide.
Now if you put a second woofer in the room positioned such that its path lengths do not concide with those of the first woofer, the peaks and dips from their outputs will never exactly coincide (in other words, they will be "decorrelated"). So the net result will be a smoothing of the response throughout the room.
Here's an example setup: One subwoofer located near the left front corner but elevated up several feet off the floor, and the other subwoofer along the right wall a little bit behind the listening position but well away from the corner.
There may be a way to mathematically predict optimum locations for randomizing the interaction patterns of multiple subwoofers in a room, but that's out of my league.
There is great merrit to what Duke just said.
For my symetrical stereo sub set-up there are obvious peaks and nulls when playing test tones. It is possible to get things relatively flat by using the controls on the subs. But when you do this the music looses a lot in my opinion.
Judicious use of an EQ like the one from Velodyne has crossed my mind, but it does sound awfully good as is.
If space and living conditions permit I would try exactly what Duke recomends.
I've gotten great results with matched, dual subs. In addition to a fuller and more natural base, the addition of the second sub has resulted in a wider soundstage, added a bit more clarity to both instruments and voices and contributed to a smoother response in the low to mid-range. My listening room is over 3500 cu. ft. with many openings and a vaulted ceiling that climbs to 13 ft. The second sub has definitely made a difference in this large space. After experimenting with several locations, I concluded that placing both subs along the same wall, with each sub slightly outside of the LF and RF speakers respectively produced the smoothest and most natural sounding bass.
Giving credit where credit's due, my primary source for the above-mentioned first school of thought is David Griesinger, and my primary source for the second school of thought is Earl Geddes.
Just for the record, Earl recommends having more than two low frequency sources in the room, and preferably a mixture of vented and sealed. So I doubt that he'd have a problem with using two non-identical subwoofers.
Thanks for the responses everyone. I am restricted quite a bit in where I can place my subs, but I will try to turn them to see how this changes things if at all. My room too is over 3500 cu ft, but my subs seem to have plenty of oomph for it. FWIW, placing audio points underneath made an audible and measurable difference.
In light of all this excellent discussion, I now ask, would going with two smaller subwoofers give me more stable/solid bass so that the two smaller ones would equal or surpass the sound quality/volume/etc. of one larger one.
Example, would two Hsu 10" subs be "better" than one Hsu 12" sub (the exact model numbers escape me right now? Same with two Rel Stratas as opposed to one Rel Storm?
Thanks, as usual, in advance!
In addition to Rusler's question, when running two subs do people here like to run them in stereo or mono?
I run mine in stereo, though mono may work better. I don't have nearly as much free time to play with set-up as I would like. For my pressent room configuration my guess is that mono will work better. Also the crossover point would help dictate this.
Two smaller subs can do more work than one larger sub. mine is set up with three 8" woofers for each side. There is no problem with getting lots of bass. A room of 3,500 cu/ft is fairly large. Finding a high output sub that is also detailed can be difficult. There is a guy selling a pair of NHT Sub2i's right now. I know that these are VERY high output and would fill your room. It is just a question as to personal taste though.
Im using two identical 8 subwoofers with custom long-throw drivers and custom high-power class AB amps rated at 150 watts continuous and 400 watts + peak. I also own a 10 sub from a well known manufacturer that cannot compare with the 8 sub. The reason is that although the 8 sub is smaller, it uses a better amplifier and a higher quality driver which translates into more musical and a better performing subwoofer. Components used in this sub were selected for performance reasons without cutting costs to increase profit margins as manufacturers often do.
Recently, I auditioned a system that included four Peerless woofers (not active subwoofers) in a dipole setup with two per channel. The bass reproduction was awesome and the best I have ever heard. Using this a reference, the bass reproduction Im getting from my two 8 subwoofers is remarkable by comparison considering their size vs the fact that there were four 12 woofers total in the dipole setup driven by amps with 250 watts per channel into 8 ohms. So in answer to the above
Two smaller subwoofers can provide more stable/solid bass that would equal or surpass, etc. BUT, it depends on the quality of your subwoofers to begin with. In my case, two subwoofers have taken the sound to a higher level in every musically meaningful way: deeper, more robust bass that is more evenly distributed across the listening room; wider and deeper soundstage; improved clarity and definition of instruments and voices especially from the lower-mid through upper-mid ranges; overall the sound is more dynamic and alive.
Stereo or mono? Both of my subs are run in mono.
I agree with Bignerd, two smaller subs can do more work than one larger sub. Bass reproduction also seems to be more effortless with two. Two subs have no difficulty in
providing more than enough sound pressure to fill over 3500 cu. ft. of space in my listening room.
How does one go about hooking up two subwoofers?
Any companies known for the quality of their amplifiers?
Two subs can't go lower than each's ratings, though, can they? I know the 10" Hsu goes to 25 Hz and the 12" goes to 20. Does the qualitative difference end at how low the subs can reproduce the deepest bass? In other words, is the biggest advantage in clarity, stability, tightness, musicality?
I run two Rel Storm IIIs with my Audio Physic Virgo IIs. I ran a test CD to set up my Cross over point on my Rels. I found in my large room my Virgos roll off at about approx 38 Hz. Higher than the 34 Hz rating. My Rels at about approx 22-24 Hz. Again not as low as rated. I have my Rel cross overs set at 36 Hz. So every room becomes part of a complex setup problem to maximize the intergration of the subs with the the speakers. All of us who do not have dedicated sound rooms must compromise. Just find what works best in your room and situation. I run my Rels high level inputs off the speaker posts (most Subs do not have high level inputs). That way I get Left and Right channel subs...works best in my room, I have a very cohesive union of sub & speaker. Tight articulate base that seems to work magic all the way into the mids. I used Stereophiles first test CD and a well known setup CD the sound track to the movie Sneakers. The track is called "Cosmo...Old Friend"
Good luck, Greg
So, can someone list ways to set up two subs to run in stereo, or does this just mean that you connect the subs via rca or xlr into your pre-proc and then eq them.
With active subs, you can connect a Y cable to split the sub output at the pre/pro or receiver. Or you can connect one sub at the LFE output, and wire the 2nd sub w/ speaker wire as the left/right front speakers and connect those speakers to the sub.
Hsu Research has earned good marks for its subwoofers. I have never auditioned one nor researched the amplifiers used by Hsu. Sunfire (Bob Carver) makes outstanding active subwoofers with powerful high quality amps. Some others in this group: Sonance, M & K, Velodyne, NHT, Martin Logan Descent, Vandersteen, Definitive Technology Supercube and Orb Audios Super Eight. All of these subs reach deep into the low range (to 14 Hz) and can move a lot of air. The specs dont tell the whole story. A sub should be matched to the other speakers in the system to achieve the best performance. Ultimately, performance should be evaluated in your home not in a store or a lab. In some cases, I couldnt tell the difference between subs rated lower (Hz) from ones whose bottom was a few Hz higher. Some 8 and 9 subs like the Sunfire SuperJunior and Orb Audio Super Eight outperform and sound much better than some 10 subwoofers. For music vs Home Theater use, I prefer a subwoofer capable of longer excursion for higher frequency reproduction especially in a sub/satellite system. For an in-depth discussion of subwoofer design check out Bob Carvers White Papers at Sunfire.com under technology and Sunfire True Subwoofer Whitepapers.