Problem: locatable LFE... Solution: ????

Discussion in 'Speakers & Subwoofers' started by Adam.Heckman, Sep 17, 2004.

  1. Adam.Heckman

    Adam.Heckman Second Unit

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    I recently finished a Mid Q sealed tempest w/ 250w pe plate amp. Seems to be a staple design in the DIY community.

    The sub sits around 5-6 feet from my listening position, on the other side of an end table that is adjacent to the couch. This is it's second position I've tried and the ONLY one with ANY GFAF (live in girl). When the sub was in it's old position it worked great (for a while), it was up front beside one of the mains. Then one day I started to be able to pinpoint where the LFE was coming from. So, in order to finally appease the girl, and (hopefully) help the locatable bass, I moved it to its current position. Didn't help the locatable bass at all. Girl is happier.

    My crossover at the Denon 1604 is set to 80Hz. XO on the sub is cranked up to 140.

    My understanding was at these frequencies I shouldn't be able to locate the position of the sub due to the length of the bass waves being longer than my room. Now, the room opens up to a hallway and kitchen/dining area (to the right). So, it's a big room to fill with noise, hence the large woofer.

    So, I ask all the older, wiser, more experienced sages around here to please give me any advice or counsel that they have. Thanks in advance.
     
  2. Rory Buszka

    Rory Buszka Supporting Actor

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    Well, even the electronic filters in your reciever and subwoofer are not perfect cut-offs, but instead have a rolloff with a certain slope. As a result, there is always some out-of-band noise. Setting a lower crossover should help minimize the amount of out-of-band noise that is in your localizable range.
     
  3. Brian L

    Brian L Cinematographer

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    I had a similar situation, having moved the sub behind the couch. I ended up enabling the crossover on the sub amp (in conjunction with the 80Hz 12dB/Octave in the ICBM), and dropping it to an indicated 60 Hz.

    I initially tried running the steeper slope setting on the ICBM (but still at 80Hz), but that did not solve the problem.

    I am actually knee-deep in getting a two-sub set up sorted out, so there may be other things at play, but without dropping the sub closest to me to about 60Hz, I could tell where it was.

    BGL
     
  4. John Garcia

    John Garcia Executive Producer

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    Ability to localize has more factors than just what your x-over is. Your room is a factor, in that room modes may be the biggest problem and because of those modes, you will be able to localize the sub in certain positions no matter what volume. The first thing should be at least a basic level calibration to see if that helps with the localizing, if you haven't done this already.
     
  5. Adam.Heckman

    Adam.Heckman Second Unit

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    I have calibrated with white noise and the RS SPL meter. This is very unfortunate. I guess I'll have to build another for the other end of the couch!

    Anyone else want to chime in and help me out? Thanks again!
     
  6. Brian L

    Brian L Cinematographer

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    Well, there was a thread a while ago about using the crossover in the AVR along with the one in the sub. It would probably not be helpful in all or most cases, but its easy enough to try, right?

    And while you are doing that, using test tones to take basic FR measurements would also help (you already have an SPL meter, so just dwonload some tones and see what you are dealing with).

    BGL
     
  7. Paul_Wright

    Paul_Wright Auditioning

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    At least one of the PE 250 watt plate amps (794 I think) has only a 12db/octave xo which can result in a bass signal that's very easy to locate, especially with an xo frequency that high. Try using the Denon sub-out with and without the sub xo. Phase & frequency controls on the plate amp may help you get the slopes in reasonable alignment.
     
  8. Matthew Todd

    Matthew Todd Second Unit

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    The problem may not be the sounds that the sub is supposed to be making from about 80Hz and below (although the LFE track itself can go up to I think 120Hz).

    What you're hearing may be the mechanical sounds of the sub like the cone slapping the air, or the sub causing other things to rattle. You might try just rotating the sub in the same position and pointing it in a different direction. That may or may not help.

    Matt
     
  9. Adam.Heckman

    Adam.Heckman Second Unit

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    Thanks everyone for all the input.
    I have tried rolling it so it's forward facing. Not doing anything.

    Truth is, on better mixed soundtracks it evens out a bit more. Just watched A New Hope and Empire and the sub wasn't nearly as locatable as on other sources.
     

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