help with bfd filters

Discussion in 'Archived Threads 2001-2004' started by Steven Hen, Apr 11, 2002.

  1. Steven Hen

    Steven Hen Stunt Coordinator

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    Could any of you bfd pro's give me some suggestions for filters to use to even my curve out? I just can't seem to get rid of that 50hz peak, I've tried a bunch of filters but I'm not sure about what freq and bandwidth I need to be looking at.
    http://www.villagephotos.com/pubimage.asp?id_=210288
     
  2. Richard Greene

    Richard Greene Stunt Coordinator

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    I'm not sure I'd qualify as a BFD expert because I consistently underestimate how much correction is needed and it usually takes me three iterations to reduce a frequency peak sufficiently.

    Here's my wild guess based on a ten second glance at your frequency response chart (this is just a starting point --

    trial and error will get the right answer for you):

    -12dB

    at 50Hz,

    1/3 octave (20/60)
     
  3. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    I agree with Richard that I would start with a single filter on that dominent peak, but I would center it at 49 and make it narrower 10/60 of an octave. I would then generate another curve to choose the next filter(s) or a modification of that first one. I would also from here on out generate the curves with the mains playing. The rolloff above 60 Hz suggests to me that this is the sub playing alone. Also, get the overall level of the sub matched to the mains before proceeding with the next iteration. Depending on what happens with the mains on, you very well may only need that single filter to ger +- 5 dB.
     
  4. brucek

    brucek Second Unit

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    Steven,
    Keep in mind that, you are entering into the BFD, an absolute bandwidth at the 3dB points above and below the center frequency.
    So for example, a 20/60 BW entered with a center frequency of 50Hz would effect an absolute bandwidth of 40/60 2/3 octave at the 3dB point from its zero effect. So a 12dB cut would still be reducing by 3.5dB at 1/3 above at 63Hz and 1/3 below at 40Hz. Then the frequency that it hits zero effect would be much wider than this and certainly would encompass the valley you have at 38HZ. Bad news.
    My suggestion would be to start somewhere around 5/60BW at 48Hz with a cut of -8dB and work from there after a remeasure... [​IMG]
    brucek
     
  5. Steven Hen

    Steven Hen Stunt Coordinator

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