A question for subwoofer EQ gurus

Discussion in 'Archived Threads 2001-2004' started by MichelF, Feb 19, 2001.

  1. MichelF

    MichelF Extra

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    Good day,
    This is my first post on this forum...
    I have 2 subwoofers and they need some boost at 20hz and probably EQ at other freq as well (I still have to analyze the room response precisely).
    I was planning the following:
    LFE out from pre/pro
    EQ the LFE signal (with a mono EQ, I was thinking of the Symetrix 551E)
    EQ out to stereo amp in1 with the amp set to internally Y the signal to in2 (the two channels in the amp receive then the same mono signal).
    Now my question: is this the right way to do or should I equalize the 2 subwoofers independently (stereo EQ instead of mono EQ) despite the fact that I send the same LFE channel to both sub.
    In this second case, I would then use a Y cable to split the LFE channel at the output of the pre/pro and send this dual LFE signal to the stereo EQ and equalize them independently.
    Note that I am a bit reluctant to set the LR channel full range with no sub and use an external active analog crossover as the pre/pro already has an internal active digital crossover (unfortunately my pre/pro does not have dual sub out, this would probably be ideal solution for stereo sub).
    Thanks in advance for your advice.
    Cheers,
    MichelF
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    If both subs are together, EQ as one, if separated > a few feet, then individually to see if 'stereo' EQ is required. Don't sweat anything < +/-1.5dB, as our hearing down low isn't too good.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  3. Rick P.

    Rick P. Stunt Coordinator

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    Michael, I think the Symetrix is going to be WAY overkill for something as simple as sub duty. Things like wide dynamic range, ultra-low distortion and precision sound are kind of lost when
     
  4. MichelF

    MichelF Extra

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    Rick,
    I was looking at the BFD as well but my subs need subsonic filter at 20 hz and bass boost at this frequency as well (I don't have it in the sub at the moment, I have to provide it externally with the EQ). Can I do that with the BFD? From what I read and have been told this does not seem to be a good idea with the BFD and that's why I was looking at the symetrix. How does the BFD behave below 20 hz?
    Michel
     
  5. ThomasW

    ThomasW Cinematographer

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    MichelF
    Things to consider. First can your sub really deliver enough output that EQ below 20Hz is needed? Do you understand how little software there is that actually has any signals much below 20Hz?
    To answer your actual questions, the lowest frequency the BFD can EQ is 20Hz. The lowest listed frequency the Symetrix can provide is 10Hz. However the bands in the Symetrix can "ganged" and as a result the lowest EQ point ends up being about 6Hz. BUT if your're going to try this you better have a true monster sub, and a very powerful amp (and as always remember, closed road course, professional driver, do not attempt this at home [​IMG] )
     
  6. MichelF

    MichelF Extra

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    Thanks Thomas,
    Perhaps I should explain what I am trying to do. I am in fact playing with a pair of powered sub able to go down to 17hz (-3dB). For various reasons I am not happy with their internal amp (no XLR in, low flexibility of the crossover, noise from the transformers, automatic enable not working properly,...). I then asked the company whether I can use an external amp and the answer was positive as far as I can provide an external replacement for their internal -12dB/oct subsonic and +6dB bass boost filter at 20 hz.
    The idea is then to use and external amp (Crown K1 or K2 for example) and an external EQ (Symetrix) that would also allow me to EQ the subs in the room. Does that sound totally crasy?
    My main problem with the BFD would be the lack of subsonic filter... should I really care?
    MichelF
     
  7. ThomasW

    ThomasW Cinematographer

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    MichelF
    IMO unless these subs are really something special, you're on the overkill as far as equipment is concerned. Since you haven't told us what subs you are using, I have to wonder if the system can really take advantage of the very low EQ offered by the 500 series.
    Nothing short of a huge IB or something like the HE15's with multiple PR's needs the big Crown stereo amps.
    Also remember that the 551 is mono, the 552 is stereo. Don't misunderstand I think the Symetrix gear is great. I have 2-551E's, one for the HT and one for the family room. But compared to the "stereo" BFD, the Symetrix 500 series is expensive, especially if your only using it for bass treatment.
    Here's a link to the .pdf file that's the manual for the 551/2
    http://www.symetrixaudio.com/manuals/551-2-A2.PDF
    Read this and it will explain all the features that these EQ's offer. It does have a very nice low cut filter, 6Hz-260Hz range, 12db/octave of cut. It can be combined with one of the EQ bands for additional flexibility.
    As to whether or not you need the low cut depends on how well your subs behave when fed something subsonic.
     
  8. MichelF

    MichelF Extra

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    ThomasW,
    The subs are two 15" B&W ASW4000 (internal AMP is 450W: so more or less in the range of the Crown K1). As I said, I don't want to use their "decoder input" (which by-pass the internal cross) because the automatic signal detection introduces a delay when it switches the amp on and it is also very audible when it switches on and off: music starts playing without strong bass, then bass come,... delay then very audible click and the subs play bass... bass signal goes down... click again and the sub stop and so on (this drives me crazy).
    If I use their "cross-over" input it introduces an additional cross-over in the circuit and flexiblity is not its strong feature. But I must admit this works.
    Other weakness in my opinion: no XLR input.
    What I would have really like was: decoder input whithout auto-enable and XLR input.
    But I must admit that the setup I am considering can be very expensive (note that the ASW4000 are already expensive). I may try a BFD first before investing further (still using the sub cross-over input).
    Note that B&W told me that if I want to go the external flat response amp route I need a subsonic filter at 20hz (as the ASW is a ported design I guess there would be a real risk that the driver becomes unloaded otherwise).
    MichelF
     

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