Any down-side to running a dual sub setup?

Discussion in 'Speakers' started by John Pine, Jan 19, 2005.

  1. John Pine

    John Pine Supporting Actor

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    I’m considering running dual SVS PB10’s for my mostly music (80/20) setup. The room is fairly large (23’x 18’ w/14’ vaulted ceiling) and the subs would be in opposite corners of the longest part of the room. The subs would be approx. 30’ apart. One sub will be in a row with the mains and center the other would be in the opposite corner underneath the left surround. The primary listening area is approx. 12’ from the sub closest to the front sound stage. Will this cause me any acoustical problems? Any other issues to watch out for? Is there a thread or a site I should check out before buying anything?


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  2. Wayne A. Pflughaupt

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    For movies you’ll definitely want two PB10’s in a room that large. For music one will be fine.

    If you’re talking about a catty-cornered set-up, I wouldn’t recommend it. I tried it once in a rectangular room like yours, and measured response was absolutely abysmal.

    You’ll probably get the best results if you co-locate them in the same corner. Any abnormalities in response you can smooth with a parametric equalizer.

    Since you’re primarily running a music system, you might want to check my recent review of the PB10. I found some things regarding its musicality that you might find interesting. The link is in my signature.

    Regards,
    Wayne A. Pflughaupt
     
  3. Bryan P

    Bryan P Extra

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    I have read your review of the SVS PB10 versus other subwoofers. It would seem that your experience with the PB10 on music without your 25Hz high-pass filter has more to do with the peak in your room response at 26Hz than it does with the musical nature of the PB10 itself. Unless John Pine has a similar peak at 26Hz in his listening room, I would not expect that he would experience the same issue. I have a SVS PB10-ISD subwoofer myself in a large U shaped room and I have not experienced any boominess or lack of tightness in the bass.
     
  4. Wayne A. Pflughaupt

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    Bryan, if there was a peak at 26 Hz in my room I wouldn’t be boosting my own subs there (apparently that escaped your notice?). And it would have shown up in some form or fashion in the other subs’ response measurements. It didn’t. What you’re seeing in the chart is purely the SVS' output.

    My readings in the small room showed a significant rise below 30 Hz (there seems to be a problem with the link, but you can see the chart in the PDF link at the bottom of the review).

    I’m not the only one to report this characteristic of the PB10. If you saw Ed Mullen’s test, the low-frequency rise shows up on his in-room chart, too. And, this recent owner reports the same thing:

    http://www.hometheaterforum.com/htfo...hreadid=223363

    As far as you personally not experiencing it, it’s probably a function of your unusual U-shaped room. The open “wing” often functions similar to a bass trap. Thus unless John has a similar room he may want to do some experimenting of his own. As is the case with anything relating to subwoofers, one person’s evaluation is only relevant to someone else if they have an identical room and sub.

    Regards,
    Wayne A. Pflughaupt
     
  5. Zack_R

    Zack_R Stunt Coordinator

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    In Ed's ground plane testing of the PB10 there is no evidence of a gently or sharp rise present between 23 and 38hz. At best there is a one dB rise from 22 to 20 hz.

    here

    This would suggest to me that your large room does have gain below 29 hz but the other subs are rolling off faster than any gain from the room would give.

    I don't think there is a peak in your large room but I do think there is room gain below 29 hz it's just that the other subs are rolling off too fast. Therefore I do not think the rise in response is a characteristic of the PB10 but the effect of peoples rooms on the PB10.

    A very well written and awesome review BTW.
     
  6. Bryan P

    Bryan P Extra

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    You may want to consider making your purchase in stages. Start with a single PB10, a sound level meter and a setup disk. That way you can experiment with subwoofer placement, crossover frequency and phase adjustment without the added complexity of a second subwoofer. You can also determine if the acoustics of your room are going to necessitate bass equalization with a Behringer Feedback Destroyer or similar device. Then you could add the second subwoofer and fine tune your setup.

    Harman International has an interesting white paper on the optimum location of multiple subwoofers at harman.com/wp/index.jsp?articleId=1003. Since the paper is based on simulations and not on real world testing, I don't think you can take the results of the paper as gospel. However, I do think it would be worth trying their setup recommendation to see how it works in your room.
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    There are two big problems with a dual sub setup that I can think of:

    a) 2 subs gets you more output, but the 2 of them gets you no better low freq extension. You need a single bigger sub for that.

    b) Unless you really know what you are doing, you can create big problems with peaks and valleys at different points in your room.

    The idea behind two subs is to get a smoother response than with just one sub. In theory. [​IMG] However, the problem with two subs is that you simply cannot get them in phase at more than one point in the room. As soon as you move away from that point (and it doesn't take much), you start to have problems with varying amounts of constructive and deconstructive interference.

    You *do* get more output from 2 boxes, but why not take the same amount of money and just get a larger SVS? [​IMG] Which *will* have more low freq extension too. Co-location works for 2 subs, but again, you just get more output with no better low freq extension. If you're going to put them in the same place, again, why not just get a larger/better one with the same money?

    I looked at getting multiple subs a few months ago. And I actually have quite thoroughly characterized my room with this: www.etfacoustic.com/ . But even with all the characterization I've done, and a certain amount of determintaion that I could succeed where so many before me had failed, I came to the conclusion that it just wasn't worth my time to try it with a multiple sub setup. For 9 people out of 10, buy the single largest/bestest sub you can, and stick it in a corner. And ... I was actually thinking about getting upwards of 4 of the PB10's, but I instead went for one PB12-Ultra/2. One of the best decisions I ever made. [​IMG]
     
  8. SteveCallas

    SteveCallas Second Unit

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    Using two co-located subs won't get you a better low frequency extension, but they will play lower than what only one sub could.

    If the -3db point of the sub is say 20hz at reference, adding a second sub would mean lowering the output of both subs so that they add up to the original reference spl. By lowering the output, the -3db point at reference is now let's say closer to 17hz. So in essence, you are gaining the ability to play lower frequencies at louder volumes.

    Also, if you co-locate the subs in the same corner, and they are both in the same phase setting, you shouldn't experience any cancellation problems.
     
  9. Kevin C Brown

    Kevin C Brown Producer

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    I think I understand what you're saying, but I will try a different way.

    There is no difference in low end extension, but 2 co-located subs will allow you to play the same low freqs with slightly less distortion at a slightly louder volume.

    But again, if you are going to co-locate them, why not just get a single bigger (better) sub that *will* go lower, for the same or even less money? Then you're only paying for 1 enclosure, 1 amplifier, 1 set of electronics, etc. In other words, if I simply compare one PB12-ISD/2 with 2 separate PB12-ISD's, you end up paying a lot more for the two boxes: $600 x 2 vs $900 (plus whatever the shipping difference is between 2 separate lighter smaller boxes vs one larger heavier box). Even better, is one PB12-Plus/2 at very close to the price of 2 separate PB12-ISD's... Better drivers and lower freq extension. [​IMG]

    I understand if you already have one sub, then buy one more to co-locate them. But from scratch, I'd personally just get the single bigger (better) one.
     
  10. John Pine

    John Pine Supporting Actor

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    Thanks guys for all the great feedback! Wayne I read your review, excellent job! Interesting, I was not aware that using two subs “catty-cornered” might create more problems than it solves. Unfortunately, I don’t have enough room to put both PB10’s side by side. The other two corners won’t work, one has a door leading outside and the other is an open stairwell down to my bonus room. Kevin, one reason I was considering two PB10’s instead of one 20-39PC+ or one PB12-ISD/2 is because of the feedback I received on the PB10 at this forum and others. But really, I’d rather just purchase one unit. The feedback was that short of the PC-Ultra, the PB10 has the tightest and most musical response of any SVS driver in my price range. They also said that the design of the new PB10 driver is very similar to the PC-Ultra. Bryan, good idea but don't know if I'll be doing a dual setup now. Guess more research is needed.
     
  11. Kevin C Brown

    Kevin C Brown Producer

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    John- I thought the PB10 uses an ISD-style driver?

    I.e., the TV-12 driver (Ultra) is better than the dB-12 driver (Plus) is better than the Improved Standard Drivers (ISD)?

    A PB12-ISD/2 is 2x12" vs 2 x 10" for two PB10-ISD subs, but in one box and at about the same price. And then if you could swing a PB12-Plus/2... [​IMG]
     
  12. Wayne A. Pflughaupt

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    Bryan, I think I could have responded to you a little more politely and diplomatically. [​IMG] I apologize profusely. Still hope we’re buddies, but if I’m on your black list now, I understand. If it helps, I'm not above shamelessly groveling... [​IMG]

    Zack,
    They can always be stacked. However, good as the PB10 is, if you need “more power” and have limited space, it would be best to just get one sub that will do the job – as I’m sure you’ve figured out.

    Regards,
    Wayne A. Pflughaupt
     
  13. Michael Brand

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    I beg to differ with some of the previous posts, with all due respect. I have been very pleased going to two SVS PC+ 20-39 subs. When I had one sub it was locatable, and my room response was uneven, ie one side of the room had more bass than the other. Two subs will not only get you more even response and more SPL, if they are tunable, as the PC+ line is, you CAN also get more low bass response. I tuned my 20-39's to 16 hz., and with two subs I have plenty of headroom.

    Here is a great article with links that discusses this very issue. From Rivesaudio.com

    Subwoofer placement and number of subwoofers
    This can be the most difficult speaker to place. There are a variety of reasons for this, but in general, bass frequencies are most affected by their placement in the room. First let's examine placement with one subwoofer. This is actually the most difficult. Subwoofers can either be placed in corners, where they have the benefit of sound reinforcement from adjacent walls. This means less amplification is required and less distortion on the sound the woofer is producing. However, this comes at a price. While many subscribe to the thought that bass is omni directional, a woofer placed in one corner can usually be detected as being in THAT corner. Omni-directional does not necessarily mean it can not be detected as a sound source. The other expense is that corner placement excites room modes and generally delivers less than a flat frequency response.

    When we calculate room response curves theoretically, we do it to find out how flat a response we can achieve. This usually yields a subwoofer placement that is slightly off center in the room and fairly far out into the room. This gives us a good idea of how flat we are able to achieve, but inevitably this is not the best overall sound for the subwoofer. It is for this reason that we do not even specify subwoofer placement, rather we give a location where we found the flattest frequency response.

    There really are two potential locations, near center and near the rear wall (within 1/8 of a wavelength of highest frequency the subwoofer is set to produce*), or in a corner and within 1/8 of a wavelength of that corner. We recommend that you try both of these locations. If you can not distinctly detect the subwoofer when it is in the corner, then this is a good place for it. Otherwise, move it to the center.

    If you have two subwoofers, corner placement behind the main speakers is almost always the best placement. These should be within 1/8 of a wavelength to the corner they are placed in. If you can afford a second matching subwoofer, this is generally preferred to a single more expensive subwoofer.

    Getting the subwoofer in phase can be a little tricky for a novice. The best way is to use a test tone at the crossover frequency of the subwoofer. Play this tone and adjust the phase so that the tone is the loudest at the listening position. Using an SPL meter can be a great help here. When it is at the loudest the subwoofer is in phase.

    * Note: 1/8 of a wavelength (in feet) = 1130/wavelength * 1/8

    Thus for a 80 Hz wavelength = 1 foot 9 inches

    Author: Richard Rives Bird of Rives Audio

    Resources and education in Acoustics: www.rivesaudio.com/educate

    Rives Audio website: www.rivesaudio.com

    Contact Rives Audio: [email protected] or 800-959-6553
     
  14. Kevin C Brown

    Kevin C Brown Producer

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    Michael- Have you looked at the freq response you get with two subs? Either manual measurements with a test disc (at least 1/10th octave), or with TrueRTA or ETF5?
     
  15. BruceD

    BruceD Screenwriter

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    Michael,

    I'm sorry to say that if you use the Rives 1/3rd octave test disk to measure low frequency speaker/room response you are likely to miss the actual frequency of the peaks and nulls caused by the room (room modes).

    You need 1/12th octave or 1Hz steps to identify problem low frequecny standing waves. I'm sorry to say this doesn't give me great confidence in the Rives methodology. I haven't spent any time on their site so I can't actually comment on the effectiveness of their solution.

    Typically 2 subs located in different positions will both cancel and reinforce various frequencies, but ultimately produces a lower total SPL (because of the cancellations) than 2 subs located together.
     
  16. SteveCallas

    SteveCallas Second Unit

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    A couple comments - I agree that 2 co-located subs will yield better frequency response and I have also heard that the driver for the PB10 is more similar to an Ultra driver than an ISD or Plus driver. However, even with that said, if your budget and space requirements allow, I would definitely go with a PB2-Plus over 2 PB10s - you get tunability, two bigger drivers, lower extension, and more spl. But if 2 PB10s can't fit in one corner, I doubt a PB2-Plus would.
     
  17. John Pine

    John Pine Supporting Actor

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    Ok guys the PB12-ISD/2 was definitely not an option. Didn't realize the unit was such a beast! It's 28"+ deep and would extent into a window and partially cover an HVAC floor register. It's not much smaller than my Natuzzi reading chair. Soooo, I went ahead and ordered a PB10. The PC-Ultra is really what I wanted but it's tough to rationalize spending $1200 on a sub. I'll try out the PB10 for a month or so and then make a final decision. Thanks for all the great feedback!
     
  18. Michael Brand

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    I used 1/6th octave test tones to equalize both subs with a Behringer 1124P. Most people feel that this is adequate, but I may try 1/12th octave tones some day. Wayne was pretty helpful in the equalization process, thanks again Wayne. If I get time I will post my response curves, both flat and house curve. I just wanted to show that there are people who feel that two non-located subs works better FOR THEM, and some of these people are pro's. I'm sure this is not the case in every room, or for every listener.
     
  19. Kevin C Brown

    Kevin C Brown Producer

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    1/6th octave doesn't give you enough resolution.

    I caution you though. [​IMG] I was happy as a clam with my 1/6 octave measurements. Then I used ETF5, which gives you 1.5 Hz resolution all the way up to 160 Hz. I definitely did not like what I saw. But I improved my setup from there. The point being, if you do subjectively think you have good sound quality, even using the 1/6th octave tones, you might not *want* to look any finer to see how bad it possibly really is.

    For example, here's my 1/6th octave measurements: http://img.villagephotos.com/p/2004-...freqStryke.jpg And here's my better than 1/10th octave measurements: http://img.villagephotos.com/p/2004-...owfreq10th.jpg See how the graph does get worse for the finer resolution?

    Perhaps, you are that 10th person though. But I doubt it. [​IMG]
     
  20. Michael Brand

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    You make some good points on getting finer resolution in your measurements. I downloaded more test tones to chart 1/12 octave measurements, and see what it looks like.

    I really think my room is a challenge and a bit different than most. The right side of my room seems to just soak up bass and function as a bass trap, probably due to bookshelves at an angle in the right front and rear corners, and a protruding brick fireplace in the center of the right wall. Adding the sub to the right front corner really helped even out my room response. Before the left side of the room was boomy, and the right side sounded weak. I also have limitations where I can put the subs in my room, and co-locating them in the right front corner is not an option. Yes, I am probably giving up some SPL, and maybe more even frequency response, but nothing the BFD has not been able to tame yet.[​IMG]
     

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