why subwoofers cancel each other?

Discussion in 'Archived Threads 2001-2004' started by itai, Aug 26, 2002.

  1. itai

    itai Stunt Coordinator

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    how come 2 subs placed like the two front mains (frontaly, spaced apart) are said to be cancelling each other, while all other stereo speakers do just fine?
    is it due to the mono signal? mains can play mono with no problem.
    are the mains phased out allready, from the factory?
    a whole different reason? [​IMG]
    thanks
     
  2. John F. Palacio

    John F. Palacio Supporting Actor

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    They won't really totally cancel each other.

    Depending on the separation some frequencies will be out of phase or partially so resulting in decreased output. Some will be in phase or partially so and will result in increased output. This can cause uneven output.

    This happens with regular speakers as well. It is more of an issue with subs because of the non-directionality of the lower frequencies.
     
  3. John Garcia

    John Garcia Executive Producer

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    The waves of low frequencies are quite long, depending on the room, they may actually be longer than the room itself (I think 40Hz was something like 8 feet crest to crest?) (thus the less directional sound). These waves bounce around in the room, and even with a single sub, can give you localized cancellation, depending on placement. This is compounded when you add a second sub, especially if placed in a symetrical location in the room, in a farily symetric room. With these waves bouncing around the room, eventually in and out of phase frequencies cancel eachother out. With a setup like this, placement is the key.

    In my fairly large room (14'x25'x10'), with my sub corner loaded on the right, I get a very localized null just to the right of my couch.
     
  4. Jason Wilcox

    Jason Wilcox Supporting Actor

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    it does happen with regular speakers....that's why it is necessary to have all your speakers in phase. try putting one speaker out of phase and stick it face to face with its matching speaker....the output drops considerably. that's why a phase switch on a sub is a good thing to have. lets you get your subs in phase with eachother.
     
  5. itai

    itai Stunt Coordinator

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    thanks!
    [​IMG]
     
  6. Neil Joseph

    Neil Joseph Lead Actor

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    It all goes back to your high school physics class. Remember when you have that pool of water, introduce a point of impact with the water and you get circular ripples (concentric circles). Introduce another such point of impact and you get 2 sets of concentric circles. At various points, those 2 circles will cancel each other out and at other points they will actually add to each other. It is all about standing waves and sound acts the in the same manner like those waves.
     
  7. Larry B

    Larry B Screenwriter

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    John:
     
  8. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    What about the biggest towers? those which play flat from 18Hz to 20,000Hz. Why doesn't anybody mention that they will have cancelation issues? Why does a manufacturer will want a speaker going that low if there are such known problems?
     
  9. John Garcia

    John Garcia Executive Producer

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  10. Pete Mazz

    Pete Mazz Supporting Actor

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    Stereo towers are not playing the exact same signal. Most subs are fed a mono signal, which aggravates the situation.

    Pete
     
  11. itai

    itai Stunt Coordinator

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    "you can afford room treatments to minimize standing waves and reflections."
    John, what are those treatments?
    thnks
     
  12. John Garcia

    John Garcia Executive Producer

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    Parts Express carries a variety of basic room control treatments, most notably in the case of bass/corner/standing wave reduction are the corner cylinders and wedges.
    I have noticed that at most of the high end stores in my area, they have at least cylinders in the corners of the room. though they often do not have much or any furniture (besides other gear) in the room also, unlike most home theaters.
    http://www.partsexpress.com/webpage....up_ID=333&SO=2
     
  13. Larry B

    Larry B Screenwriter

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    I recently put two Bass Busters in my listening room. They have helped smooth out the bass but they are not a panacea (YMMV). I also use absorptive panels but they help only with the high frequencies.
    Larry
     
  14. Chris PC

    Chris PC Producer

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    I mentioned this issue a while back. If two subs are bad, then two stereo speakers are similar. I say similar because they don't go as low and as loud and they also don't have a mono bass signal. I think bass can be very problematic with a subwoofer if you don't set your system up right. Look at it this way. You want the bass to blend with your main speakers, but you don't want to localize the bass. So on the one hand, you don't want the bass to go too high on your subwoofer because you might localize it, but on the other hand, if the bass goes too low on your mains, you've got potential cancelation problems when placing 3 speakers (2 mains and your one subwoofer) in the room which are producing the same low frequencies, at least in and around the crossover point.
     
  15. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Chris,

    Yes. It is a complex subject. Thankfuly, more and more audiophiles (whatever that means) are aware about the room and speakers location. I expect to see soon computer programs with several mics that can help us to locate our speakers and improve our room, in order to get the best possible results from our equipment.
     
  16. Larry B

    Larry B Screenwriter

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    Manuel:
     
  17. Michael Roderiques

    Michael Roderiques Stunt Coordinator

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  18. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Michael,

    Thanks on the ETF recomendation, Larry Chanin is testing it with another equipment and Im still waiting his results in order to see if it is really accurated or not.

    Larry,

    The TacT audio gear certainly looks impressive...
     
  19. Geno

    Geno Supporting Actor

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    One experiment I have tried is to set two raw sub drivers on the floor facing up. I hooked both to the same signal. [1 channel per 2 channel amp]. They sat one foot from each other. with my head directly above, the low low freq were nonexistant. I probably got 100Hz and up [didnt have any way to know] but as soon as I turned one down, the LLLFE came out. if you have two subs, try to test them with only the subs on. if you dont want to move one, just turn one off. I used the balance control to go from one speaker to another. I used a SS stereo preamp with matching SS stereo amp to drive my subs.
     
  20. itai

    itai Stunt Coordinator

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    thanks all for the info, for the time being, i'm sticking to one sub, as i dont have a dedicated ht room, and live in an apartment...:b
    its really intresting, with all the waves flying around, i learned a litle from this thread!
     

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