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Subsonic filter

Discussion in 'Archived Threads 2001-2004' started by Drew Eckhardt, Jun 7, 2001.

  1. Drew Eckhardt

    Drew Eckhardt Stunt Coordinator

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    I have a (passive, separate power amplifier, cross over in my preamp/processor) ported sub, currently limited so it doesn't bottom if (when) it receives subsonics (like those present in the limiter configuration test tones on my preamp/processor). Getting rid of the lowest frequencies and raising the limiter to just shy of amp clipping seems a better idea.
    Contrary to urban legend, my BFD has no problem passing tones < 20Hz, so that doesn't work for me.
    Fortunately, I'm a professional geek with soldering iron, box of passive components, and a couple of opamps.
    A 24dB/octave filter is trivial, but I haven't a clue as to
    how I should pick a -6dB point. Suggestions?
     
  2. David-alexander

    David-alexander Stunt Coordinator

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    Hi!
    I too have the BFD but I have a subsonic filter on my amp.
    So, you're sure that even by cutting twice at 20hz, by 6 or 12dB/octave ( Berhinger recommends twice 1/2 cuts instead of one full cut to lower distorsion), the BFD still let pass the sub-20hz frequencies?
    It is rated for 20hz-20khz bandwith.
    thanks
    ------------------
     
  3. Drew Eckhardt

    Drew Eckhardt Stunt Coordinator

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    10dB below reference is the comfort limit for me with movies, making my target 105dB in the 20-120Hz LFE range.
    Measured in room response at my college couch is a just a bit better than that at 20Hz, so I don't want a BFD filter centered at 20Hz and therefore haven't played with one. For that matter, a wide filter centered even lower (can I set a filter for 20 - 20/60ths using the fine adjustment?) would have frequencies > 20Hz in its band and would still be undesireable.
    That said, without a filter at 20Hz, the BFD most definately passes sine waves down through 10Hz (the limits of my test CD; my signal generator only goes down to 20Hz) although I haven't measured the attenuation.
     

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