Buying a bigger sub vs. buying more subs?

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Mar 10, 2002.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Imagine this situation...

    You have a complete set of Definitive Technology bipolar speakers, a pair of Prosub (10", 125 watts) subs, and a PF15 (15", 185 watts) sub.

    What would you do? Would you try to find an extra PF15, use the PF15s as the LFEs, the Prosubs as front channel woofers, or would you buy a bigger sub?

    I know there is no definite answer to my question, but I'm trying to get an idea about what to do. From what I understand, multiple subwoofers excite different nodal frequencies in a room, so bass response should be smoother throughout, while buying a bigger sub might get me better bass response in a single point of the room.

    Would I be correct in my assumption?
     
  2. Wayne A. Pflughaupt

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    That is not correct, Javier. In most cases, the more low frequency sources you have around the room the worse response gets. Sometimes it gets so bad it is beyond the capabilities of an equalizer to correct.

    I would loose the Prosubs and get another PF-15. Put them both in the same corner and you will lower extension and increase low frequency output by 6dB. Any response peaks (and indeed many dips in response) can be addressed with a parametric equalizer.

    I find that corner placement results is acceptable response (and performance) in most positions in a room, except near the same wall the sub is against.

    Regards,

    Wayne A. Pflughaupt
     
  3. Travis G

    Travis G Stunt Coordinator

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    Wayne,

    I have heard this fallacy also. I suspected that it was not true, based on things that I have read, but I didn't have the knowledge to confidently correct the misinformation. Particularly on Home Theater Spot. There are people that say putting a second sub in another corner will help solve room mode problems. Do you have any references to literature that proves this untrue?

    Travis
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi Travis, Wayne. Thank you for your answers!

    The information I had on multiple subs came from... what is this book's name? "The Definitive Guide to High-End Audio", or something like that. It was written by a very popular Stereophile editor.

    I had my doubts about the book, though, since some of its assumptions (recommending the infamous "green pen" for CD's while duly accepting not knowing whether they work or not, for example) fly in the face of logic. But the author proclaimed that multiple subs were preferrable to smooth out the lower frequency response.

    From my limited physics background, I'd suspect it'd be impossible to determine whether the sound wave would be destructed or reinforced by the use of multiple subs. Then again, I thought the author might have a point, since I am not speaking from practical experience.

    On the other hand, I could use Room Optimizer, treat the Prosubs as woofers (with an 80-120 Hz cut-off) for the front speakers, and the PF15 to handle the LFE while I get a bigger subwoofer, since I feel my front speakers' 4 inch cones are not to the task of handling midbass.

    Thanks for your thoughts!
     
  5. Dustin B

    Dustin B Producer

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    Nousaine and Vodhanel say sticking them in one corner is better than one in each corner. I'll take there opinion on the matter over a Stereophile editor any day.
     
  6. Wayne A. Pflughaupt

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    Javier,
    If your mains have 4" woofs, then adding the Prosubs as mid/upper bass woofers would be an excellent idea.
    Travis,
    Dustin is right. Tom Nousaine tested and measured the response of multiple subs in a room in an Audio magazine article a few years ago (Placing the Bass: 2 subs in the corner beats 5 in the round, June 1996). He positioned five subs at the main right, main left, center and two rear locations and took measurements of the following configurations: Two subs at left and right positions; three subs at left, center and right positions; three subs at center and rear positions; four subs at left, right, and two rear positions; five subs, one each at all five positions.
    The best results were measured with a single sub in a corner, and were even better with two subs in the same corner. Exciting three room modes simultaneously with corner placement eliminated all nulls in response and therefore resulted in the smoothest unequalized response. Indeed, in most cases, no combination of multiple subs even exhibited a response that could be effectively equalized for linear response. The response from using one or two subs in the corner was not perfect, but a 30Hz peak his room exhibited could have been easily tamed with a parametric equalizer and resulted in smooth response to 20Hz.
    Tom Vodhannel has noted in various posts here and on other forums that in his experiments, the more subs he added the worse response got, and trying to equalizer them all as they interacted with each other was a nightmare.
    Recently I decided it was time to put theories aside and take my own tests, so I moved my two subs into a bedroom that measures 16 x 14 x 8 and took some readings. I took readings with:
    • Both subs in the same corner.
    • A sub in two corners at both ends of the same wall.
    • The subs in opposite corners (catty-cornered placement).
    • A single sub 3-ft. out both directions from the corner.
    • A single sub against the wall half-way between the corners.
    My conclusions were:
    • Corner placement gave the smoothest response and the greatest output. Extension was better than every other placement except center-of-wall. Adding the second sub to the corner predictably increased output by 6dB.
    • Separating the subs in two separate corners on the same wall resulted in a 2-3dB loss in output. Extension suffered as well, with response roll-off starting 1/3 octave higher than same-corner placement. However, overall response was acceptable, if not quite as smooth as dual corner placement. This would probably be an adequate alternative to dual corner placement in most cases.
    • Placing two subs in opposite corners (catty-cornered) resulted overall gain reduced by 2-3dB and significantly reduced extension, 1/2 octave less than with single-corner placement.
    • Moving a single sub out from the corner (3ft. in this case) creating nulls that no other placement had, and resulted in an overall reduction in output of 6dB.
    • Centering a single sub between two corners (against the wall) results is abysmal performance, with overall output down 12dB. However, this placement did deliver the best extension, but the price of admission (75% less output) makes it wholly unacceptable.
    Regards,
    Wayne A. Pflughaupt
     
  7. Travis G

    Travis G Stunt Coordinator

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    Thanks Wayne and Dustin,
    Some of T.V.'s posts is actually what made me doubt the claims. I know that misinformation in audio literature is not uncommon and I trust T.V.'s and T.N.'s word over anybodys (except maybe Dickason or Linkwitz [​IMG]).
    It's also nice to see that you actually tested it yourself Wayne.
    Travis
     
  8. Frank_S

    Frank_S Supporting Actor

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    I have a question for Wayne as far as his readings are concerned.
    My conclusions were:
    "Corner placement gave the smoothest response and the greatest output. Extension was better than every other placement except center-of-wall. Adding the second sub to the corner predictably increased output by 6dB."
    I completely agree, I have proven this also, however I question the results below since I don't know that phasing was correct. [​IMG]
    "Separating the subs in two separate corners on the same wall resulted in a 2-3dB loss in output. Extension suffered as well, with response roll-off starting 1/3 octave higher than same-corner placement. However, overall response was acceptable, if not quite as smooth as dual corner placement. This would probably be an adequate alternative to dual corner placement in most cases."
    "Placing two subs in opposite corners (catty-cornered) resulted reduced overall gain by 2-3dB and significantly reduced extension, 1/2 octave less than with single-corner placement."
    "Moving a sub out from the corner (3ft. in this case) creating nulls that no other placement had, and resulted in an overall reduction in output of 6dB.
    Centering a sub between two corners (against the wall) results is abysmal performance, with overall output down 12dB. However, this placement did deliver the best extension, but the price of admission (75% less output) makes it wholly unacceptable."
     
  9. Wayne A. Pflughaupt

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  10. Frank_S

    Frank_S Supporting Actor

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    Thanks Wayne but that is'nt necessary. You did a real nice job of explaining your point, I just wanted to make sure the phasing was correct. [​IMG]
     
  11. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Wayne,..

    Thanks for the info on your testing. Very helpfull. I am at the point of building a couple new DIY subs for my new room, and have really been worried as to how to set up the two units for best performance. There is so much oppinion out there. Without printed sourses to refer to, and the time to find it, I was in a pinch. A quick search found your coments and results, to be right on the head. So in case anybody else is working on this problem right now. I hope bringing this to the top will help them as well.

    Thanks again,....>>>--->
     
  12. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Wayne

    "Centering a single sub between two corners (against the wall) results is abysmal performance, with overall output down 12dB. However, this placement did deliver the best extension, but the price of admission (75% less output) makes it wholly unacceptable."

    If Im reading you well, you are saying that a centered sub is able to get lower extension than in a corner? How about twice subs centered? The lowered 12dB output is for all frequencies?

    And a last question, do you happen to have graphs for all your testings?
     
  13. Chris PC

    Chris PC Producer

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    Very cool and interesting tests. I am also curious about the center of the wall deal. First, Wayne, when you mention the differences in the last four placement options, are you saying their dB is in reference to the #1 placing of two subwoofers in a corner??

    What about one subwoofer in a corner and one subwoofer centered along the wall? I imagine not very impressive performance, but just curious if someone has done this.

    Also, not sure what you mean by "A single sub, 3 ft. out, both directions from the corner". Do you mean, 3 feet out from the corner along one wall, then out 3 feet from that point?

    I have a single subwoofer in a small room. So I should avoid putting my single subwoofer in the center of a wall, and put it as close to a corner as I can? I don't have an eq, so I guess this involves trial and error?

    Also, further to what Manuel suggests, if you get more extention at the center of the wall, what about one subwoofer or two subwoofers at say 1/4 or 1/3 the way along the wall? (With two, side by side, or stacked)

    What about subwoofers and tower speaker interaction around the crossover? Like I mention elsewhere, if you have a subwoofer that goes to 16 to 18 hz nearly flat and two towers that go to 32 hz - 3 dB, even with a crossover of 50 to 100 hz, won't there be interactions going on not much unlike having 3 dissimilarly placed subwoofers? To a lesser degree, obviously, but still, its going to be there, right?
     
  14. Wayne A. Pflughaupt

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    Kevin,

    Happy you found the info you needed.

    Manuel,

    To break things down a little more, in my room the centered sub was an average of 7dB higher between 20Hz and 28Hz compared to a single sub in the corner. However, from 32Hz to 63Hz, the cornered sub delivered 13dB higher output on average. That’s why I concluded the improved extension for the centered sub wasn’t worth the severe penalty in output.

    In addition, the cornered sub delivered much smoother response; the centered sub’s response was much more ragged and uneven.

    Adding a second sub in the center location will of course deliver greater output, but it will not nearly equal the output of two subs in the same corner, nor address the poor response issues of the former.

    Yes, I made crude documentation on graph paper. If I can fix a glitch with my scanner this weekend I'll be happy to shoot you a j-peg.

    Regards,

    Wayne A. Pflughaupt
     
  15. Chris PC

    Chris PC Producer

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    Wayne,

    Sorry, but what testing methods did you use? SPL meter with individual tones? Or software?

    I guess my biggest curiosity is in the 1/3 or 1/4 placement along the wall. Is that worse or better than in the center of the wall. I'm guessing that if you place a sub 1/4 or 1/3 the way along a wall, it should be better than the center of the wall for loudness, but not as good as the corner, and perhaps more extention than the corner, but not as much as the center of the wall. With two subs as an option of course.
     
  16. Wayne A. Pflughaupt

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    Chris,

    I used test tones, an SPL meter and graph paper. Crude but effective.

    I only tested centered between the two walls, not asymmetrical, so I really can’t speculate about what the results of that would have been.

    Regards,

    Wayne A. Pflughaupt
     
  17. Dennis B

    Dennis B Stunt Coordinator

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    Wayne,
    Have you read this 5-page article?
    http://www.tubetrap.com/articles/ht-1.htm
    It pretty much explains the results you observed.
    I was wondering if you ever tried mid-room configs, like 1/4 of the width and 1/4 of the length. I know this would turn you sub into a table unless you have a dedicated HT room, but just for the sake of experimenting, I found those positions had good overall responses. My sub ended up to the right side of my room, between the FR and the RR speakers, closer to the wall for the best curve. I used ETF, BTW.
    Of course if you choose the corner+BFD approach, you're OK anyway.
     
  18. John Gregory

    John Gregory Auditioning

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    How about a sub in a dormer on the same wall as the TV? Even if you haven't tried it, any thoughts?
     
  19. James Bergeron

    James Bergeron Supporting Actor

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    Hmmm this is making me think, I was thinking of upgrading my Velo CHT-15 for an HGS-18 but after reading some measurements on the CHT-15 I found it basically is just missing the high volume output below 20Hz, it can still do 90DB up to 20Hz, so If I were to just stick another CHT-15 on top of my current one I could expect a 6db boost up to 96DB at 20hz and so on.... hmmmmmmm.

    Definitely A LOT less expensive to go with another CHT-15 even 2 more, 3 stacked now that would be some tower of subs hehe.
     
  20. Wayne A. Pflughaupt

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    John,

    Corner placement usually gives the best all-around sub performance, especially after equalization. The location of the TV has no bearing on this.

    Dennis,
     

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