Question for all you subwoofer experts.

Discussion in 'Archived Threads 2001-2004' started by Chris Bone, Feb 14, 2003.

  1. Chris Bone

    Chris Bone Agent

    May 31, 2002
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    Here is my question:

    In an acoustically treated dedicated home theater and music listening room that is 30'x17'x9'I want to use dual subwoofers. I need to place them as close to the mains as possible. I am using three VMPS RM40's for the front three. The center is placed behind a micro-perf screen. Can I use two SVS B4plus subs on both sides of the center channel or do the side-firing woofers present a problem? Do I need to use front firing subs if I am going to place them on both sides of the center speaker? Remember, my center channel is a 5'6" floorstander. If I can make this work I will be able to hide all of my speakers including the subs. The center channel,left, right and the two subs would be behind acoustically transparent material.


  2. David_Stein

    David_Stein Second Unit

    Feb 13, 2002
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    holy crap, two b4s? what an amazing prospect...
  3. Edward J M

    Edward J M Cinematographer

    Sep 22, 2002
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    Bass is unidirectional. The four woofers on the B4+ fire externally at both ends and internally as well. I wouldn't worry about placement or orientation of the sub in the front sound stage - you'll be fine. Confirm with Tom V if you have any questions. Also, ONE B4 Plus in that room with a Crown K2 in bridged mono at 2500 watts will be more than enough SPL for even the most discriminating listener. I would at least TRY one before ordering TWO.
  4. John Doran

    John Doran Screenwriter

    Jan 24, 2002
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    as ed noted, the drivers in the B4 are front (and rear) firing, not side-firing.

    and i would certainly not hesitate to recommend two B4's if you have the space and money - i have one and would get a second in a heartbeat if my current budget allowed.

    the only potential problem might have to do with cancellation from the subs if you are unable to vary their position to accommodate any destructive interference between them; if it turns out that, when you place them either side of your center channel (and that's a hell of a center), you have issues with cancellation and you can't move one of the subs to fix the problem, well....

    but, again, email tom at SVS and he'll give you whatever help it's possible to give.

    but at any rate, i think you should at least get one B4 - i can tell you that mine is hands-down and unequivocally the best thing i have ever bought. period.

    good luck.

    - jd
  5. Haru

    Haru Stunt Coordinator

    Aug 9, 2002
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    from my own expereince, a single subwoofer is not adequate. I have heard all my life about how bass is non directional to the human hearing, and I believed it even though it did not match my expereinces.

    I never ever heard a single subwoofer set up where the bass was completely diffuse and directionally uniform. It's never 100% clear where the subwoofer is, but I can tell that its the left front quadrant, rather than say to my right. just as importantly, I can tell that its NOT coming from where the other sounds are.

    I cannot explain it. perhaps there are higher harmonics in all subs that, though very low in amplitude, are enough to be detected. maybe the sub sets off higher harmonics in walls, cabinets, etc that have enough amplitude to be detectable by the ear. I don't know. what I do know is that I was never satisfied by a single sub in my own system, nor in the systems of all the people I've helped set up their own rigs. Then I got myself an NHT subtwoi and then another one, and decided for a lark to place each next to one of the front speakers, set up so that the the sub and the tower act as one speaker with a split cabinet. and wow! the extension and output were not as impressive they were sticking the subs in a corner, running in mono, but now the bass became smooth and uniform across the soundstage, through out the volume of the room (as seemed from the primary listening position), and the spatial coherence between the bass and the rest of the system became PERFECT.

    I am an engineer, I scoff at people who talk about the audible characteristics of speaker cables, cd players, amps, etc, but in this case, I simply cannot go along with the "bass in non-directional" thing because in my experience it isn't. the logic that humans can't discern direction for sounds where the wavelength is longer than the distance between the ears sounds very reasonable, but I have seen no data that tells me that subwoofers do not cause (directly or indirectly) just enough higher frequency excitation for the human brain to be able process and deduce directional information.

    there is also the issue of whether bass is recorded in mono or not. If it is, the above still applies. but is it really? are the 80Hz and lower signals in stereo channels really identical, always, without exception?

    I am an awowed two subwoofer man, and will never do it any other way again. I would happily trade some extension, and some output to gain the spatial coherence that two subwoofers bring.
  6. Mark Seaton

    Mark Seaton Supporting Actor

    Oct 10, 1999
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    Real Name:
    Mark Seaton
    Hi Chris,

    Your plan is a common, and often implemented solution. There are many thoughts on bass reproduction in a room. When output is the primary goal, close coupling (less than 1/4 wavelength apart) is benficial, as well as making use of boundary loading (corners). Once you achieve sufficient, clean dynamic headroom, there is also consideration of frequency and time response and modal distribution. There are some creative options to be explored along these lines, and many are studying these effects in great detail. One interesting, yet hardly complete analysis can be found in the White Papers published by Harman. Take some time to peruse them here.

    As for your layout working with a non front firing subwoofer, this is dependent on the nature of the space behind the fabric panels and around the speakers and subwoofers. If entirely open, often referred to as a "shadowbox" construction, then you will likely have no problems. If there are cavities constructed around the speakers then you will have to take certain matters into consideration. You can certainly place a side firing subwoofer in an adequately sized cavity, yet you must confirm with the manufacturer as to how much space is required to not adversely affect the performance, as different drivers and ports all react differently to loading.

    As for "how much bass" you need, unless you are sitting entirely in the front half of the room, I hardly think a pair of B4s is overkill for such a room, especially if you are looking for headroom below 20Hz. Designers I work with would typically use a pair of ContraBasses in a room this size presuming the mains were capable.

    I will note that Anthony's pointer to the custom offerings from Acoustic Visions is quite intriguing, especially at the prices listed. A pair of anything beyond the sealed version ordered passive and not powered would be an interesting option to entertain paired with a big pro stereo amp. Comparatively, the B4 is likely higher sensitivity and I would expect to be louder overall above 25-30Hz, where below 30Hz it would be a rather interesting comparison, particularly when compared to the Everest and possibly the Denali.


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