Anyway to use the BFD to boost frequencies below 20hz?

Discussion in 'Archived Threads 2001-2004' started by Anthony_Gomez, Feb 27, 2002.

  1. The BFD has a limit of 20hz (center frequency).

    Is there any trick to boost a center frequency of say 15hz?
     
  2. ThomasW

    ThomasW Cinematographer

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    Tom Nousaine is using 2 bands of EQ set at the same frequency to force a boost in the lowest frequency of his Symetrix 551 from 10Hz down to 8Hz. This doesn't drop the center but does boost below the lowest frequency.

    I imagine that somehing similar can be done with the Behringer. Or wait until the QSC DSP-40 comes out it will boost as low as 10Hz
     
  3. jeff lam

    jeff lam Screenwriter

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    Can't you just use the lowest frequency(20Hz) and increase the bandwidth till you get the propper boost down below that, then use another filter or two to bring back down the higher frequencies above 20Hz that got boosted.

    Do you understand what I mean?

    That's the only thing I can think of...
     
  4. ThomasW

    ThomasW Cinematographer

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    Jeff

    Yup that's it.

    Have to be careful making the bandwidth too wide though. Could be some problems cleanly cutting the higher frequencies
     
  5. Sonnie Parker

    Sonnie Parker Second Unit

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    If you centered the boost at 20hz and used a wide bandwidth you might very well increase the area below 20hz. But your center point is 20hz and you are going to have the largest boost at that point that you probably won't need. Then you'd have to use a narrow bandwidth cut to lower the 20hz boost back down and the filters would just be fighting each other. No telling what kind of response you would get. If you have other problems in your response you may run out of filters trying to fix what the wide bandwidth boost did above 20hz.

    Boosting frequencies that low will most likely eat up a bunch of your amp's headroom as well. Personally I would use caution in doing this. You could try it and see what happens. I'd be very interested in knowing if it worked out for you.
     
  6. Thomas/Jeff:
    What would happen if I did this? (thought experiment). used one eq -16db at a given bw and frequency, then used another eq to do +16 at the same bd and freq to bring it flat...and repeated this oh....3 more times.
    the end result should be a flat responce, but what about distortion and phase?
    ...does the BFD modify the signal one eq channel at a time or does it use the net eq responce?...you know what I mean?
    Sonnie Parker:
    I have plenty of amplifier juice=)...crown K2
    ...as is I am using a large boost (14db at 20hz iirc) and still have plenty of amp remaining=)
    btw, this is a sealed/EQed sub...bpd1503
     
  7. John A. Gordon

    John A. Gordon Stunt Coordinator

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    Regarding the DSP-4, due to time contraints, the cut-off will remain at 20Hz, sorry. At a later time, we may ad it which you will be able to download via our website.
     
  8. jeff lam

    jeff lam Screenwriter

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    Anthony,

    Don't know about the phase thing, I'm kind of wondering about that myself.

    What is your response like down low? Why do you need to boost so low, I would imagine that 20Hz is low enough. Maybe you should consider cutting higher frequencies and using more amp gain. Can you get us some current numbers and your desired numbers?
     
  9. ThomasW

    ThomasW Cinematographer

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    Anthony

    Using EQ changes the "Q" of the system. The more EQ used the higher the "Q" rises. So try it and see if you like what you hear.
     
  10. TerryC

    TerryC Stunt Coordinator

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    I don't mind boosting the 20hz region. Our hearing at those frequencies is already so poor its not an issue boosting them slightly imho. Heck most will likely prefer it.
     
  11. Thanks for the comments guys. I'll toy around with it a bit and see how it goes.

    As for the Q....well...I am pretty much looking for a flat responce down to atleast 20hz (in room)...so I wouldn't really be hearing any rolloff of any particular Q.
     

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