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2 Subwoofers

Discussion in 'Archived Threads 2001-2004' started by DerekB., Mar 13, 2003.

  1. DerekB.

    DerekB. Auditioning

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    I have a question about having 2 subs for HT.
    What are the advantages/disadvantages of having 2 subs in a home theatre setup? Will improper placement hurt rather than help the sound?
     
  2. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    Yep!

    STACK 'EM
    STACK 'EM
    STACK 'EM

    JKS
     
  3. Edward J M

    Edward J M Cinematographer

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    Placement can definitely impact sub performance, single or dual. In general, corner loading excites the most room modes and provides the flattest FR with the least nulls. However, this method is not set in stone and occasionally even better results are obtained by experimenting with several different locations.

    An old trick is to place the sub at the listening position walk around the room and evaluate where the bass sounds and measures the best. The best spot is where you want to place the sub.

    Really, the only legitimate reason to add a second identical sub is because the first sub is incapable of reaching the SPL levels you desire without exhibiting audible distortion or signs of obvious distress like bottoming out.

    Adding a second identical sub will not fix any sound quality problems endemic to the first sub such as poor FR, a lack of deep extension, or a high THD - you will just get more of the same sound with a second sub. If you want better sound, buy a different higher quality sub.

    Try to stack or co-locate dual subs to minimize their potential to interfere with each other. Co-locating subs generally adds 6 dB in volume. This obviously increases your headroom by 6 dB and allows you to calibrate each sub a few dB "cool". Other placement options will generally yield less of a volume increase, maybe on the order of 3-4 dB.

    If you must load them in opposite corners, an infinitely variable phase control (0-180) will help you "dial-in" the second sub so it contributes to - rather than interferes with - the first sub.


    Regards,

    Ed
     
  4. FrantzM

    FrantzM Stunt Coordinator

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    Regarding placing a sub in the corner:

    Many things some of them good (corner loading acts as a horn and allow a better coupling of the transducer to the room, the corner or horn acting as an acoustic transformer, you do get an increase in output) many of them not good occur when you place a sub in a corner. You have mentioned that it excites all the room modes, that is true and that is not something you want, YOU do not want to excite ALL your room modes at once. IT can be really bad, it all depends on your room dimensions. You could find yourself in a position where Nulls occurs. Nulls are the worst position to be as a listener, where where you can through equalization work around a peak at given room mode, you can not do anything for a null, nothing, zilch , zero. To move the position of a peak or a null with respect to your listening position you need to move the sub away from the room boundaries and that means from the walls.

    This can get quite complicated but suffice to say that room modes occur in all three dimensions ( let us not even consider the obliques modes which could best be described as the diagonal ones). Thus placing just one sub in one location creates an uneven distribution of peak and null in one of the direction ( for example the width of the room).

    Two subs are in my opinion better than one, granted you double the work you will have to do to place them properly but it is worth it way beyond the simple increase in output power.


    finally, Speaker placement is not trivial, inches do count. I refer you to the superb series of article from Floyd Toole on the subject, I do not have the URL but a search in Google for Floyd E. Toole and Speaker Placement will locate them. Required reading for any HT and/or music enthusiast.


    Frantz Mathias
    Port-au-Prince, Haiti
     
  5. steve nn

    steve nn Cinematographer

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    DerekB. Another thing to keep in mind if you should go the duel stacked approach is calibration. When doing so it is best to calibrate one with the other powered off. When finished with sub one, power it off and power up sub two and calibrate. Remember you are going to get a 5 to 6+db bump when you power up both, so you will have to calibrate each sub individually with this in mind. After you have finished this procedure you then can make any final adjustments in the duel mode._____________________________________________ _____

    I do use a third sub when we have company over. I have a null which the third sub addresses when the situation calls for it. Good luck.
     
  6. Chris Zell

    Chris Zell Stunt Coordinator

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    I disagree with theh blanket stack 'em recommendation. It is a rare room that is not better served with 2 subs located separately. usually on opposing mid-wall locations. It takes a lot of work and care to get it right (and parametric EQ helps a lot also!!!!), but it is worth the effort IMO. If you are just going to stick them in the room and be done with it, then perhaps it is best to place both in the same corner. But I would much rather research it and optimize the bass. Try the Harman white paper page - her is a link to one good paper:

    http://www.harman.com/wp/index.jsp?articleId=1003

    There is also another one there entitled "Getting the Bass Right" that is quite good. Also great stuff there about other audio topics, such as rooms.

    It is best to run mono bass to all subs also, according to industry sources I trust.

    I attended a seminar earlier this week where we set up 2 subs in a weird shaped room (so the best sub positions were not obvious at all), with EQ for each sub. Suppiled with a PC program and a mic that could take curves in seconds, we achieved incredibly flat bass at the listening position, and it actually only took minutes once we understood the concepts and program operation. I was sold - I want a second sub now!

    On other thing to remember - relatively small changes in sub locations can make big differences. For example, leaving the sub in place, but spinning it 90, 180 etc. and measring the differences can be surprising! The best locations we found actually had the subs along differnt walls, firing right at the corner (and very close to the corner - inches away!

    Cheers,
    Chris
     
  7. FrantzM

    FrantzM Stunt Coordinator

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    One more thing

    Regarding equalization. It took me a while personnally to get warm to dogital. Lately I have to say the best digital gear are way up there with the best analogs. This said there exist a rather cheap totally digital equalizer out there the Behringer DSP-8024. it cost around 300 and you can buy it on their web sites. Please do not use it for your main system, iti s far too broad and too colored but in the bass you could spend a lot more money and not get a result as good as this unit can provide. Granted this requires a lot of experimentation and a good understanding of basic acoustics but the results are well worth it.

    read Foyd E. Toole articles and experiment with the Behringer, you will be quite pleased

    Frantz

    No affiliation with Behringer whatsoever...
     

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