BFD filter help

Discussion in 'Home Theater Projects' started by Bob Bartlett, Aug 27, 2003.

  1. Bob Bartlett

    Bob Bartlett Stunt Coordinator

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    Here are my numbers:
    Freq Raw Comp
    16 75 86.5
    18 72 80.0
    20 75 82.5
    22 84 90.5
    25 84 89.0
    28 78.5 82.5
    31.5 80.5 83.5
    36 91.5 94.0
    40 97 99.5
    45 102.5 104.5
    50 108 109.5
    56 83 84.5
    63 104 105.5
    71 89 90.5
    80 94 95.5
    89 96 97.5
    100 90 92

    As you can see I have several peaks and dips. Where should I begin? I tried to make it flat but ended up needing more than 12 filters.
     
  2. ThomasW

    ThomasW Cinematographer

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    You start using cut to pull down as many of the peaks as possible. Only use boost at the very end of the EQ process to fine tune your curve. Use very small amounts of boost if possible

    Follow the 'how-to' instructions from Sonnie Parker's website

    SnapBug BFD Site
     
  3. Wayne A. Pflughaupt

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    Bob, this is really poor response. I suggest first trying some different locations, if that’s an option, to get a better starting point.

    I suggest starting with a corner, one with the longest distance of uninterrupted wall length in both directions. Most of the time this is the best location. Also, if the sub has a variable phase control, it is usually helpful in smoothing response. If these readings were taken in a corner, then move on to some other locations.

    The readings should be taken with both sub and mains on. This will allow interactions between subs, mains and crossover to be taken into account.

    Regards,
    Wayne A. Pflughaupt
     
  4. Allen Ross

    Allen Ross Supporting Actor

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    Bob, if i play my tempest really really loud, can you hear it way up there in Presque Isle?
    [​IMG]
     
  5. Bob Bartlett

    Bob Bartlett Stunt Coordinator

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    Wayne, the location isn't the best because it is behind the listening area under a shelf that the couch goes up against so the sub is completely hidden. I am using a 150 liter tempest. The only location change I can do is flip it so it fires toward the couch which it is doing now or towards the wall. I'll try facing it toward the wall and run some more numbers. I'll make sure to leave the mains on.


    Allen, try it and we'll see. I don't think anyone up here even knows what a tempest is.
    Here are the new numbers with the sub facing the wall.

    16 75 86.5
    18 73.5 81.5
    20 78.5 86.0
    22 87 93.5
    25 86 91.0
    28 80.5 84.5
    31.5 84 87.0
    36 94 96.5
    40 99 101.5
    45 104 106.0
    50 109.5 111.0
    56 93 94.5
    63 104 105.5
    71 93 94.5
    80 93.5 95.0
    89 99 100.5
    100 91 93

    Comparing the two graphs using Sonnie's excel program this look to be better. I figure anything is better than what I have.
     
  6. Rich X

    Rich X Stunt Coordinator

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    Bob,
    Thanks for starting this thread. I'm about to start setting up a BFD for a dual Tumult system as well. I'm very interested in how you work this out. Please keep posting your progress.
     
  7. Wayne A. Pflughaupt

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    Bob,

    Try these filters. I’m going to give bandwidth in octaves – you’ll have to translate that to “BFD-speak” – i.e., 1/3-octave = 20/60.
    • Center frequency 89Hz, BW 1/6-octave, cut 6dB.
    • Center frequency 63Hz, BW a little less than 1/6-octave (like maybe 1/8, if you can do that), cut 10dB. Keep your eye here on the reading at 56Hz. It should be the same value (94dB) after you’ve applied the filter. If 56Hz drops, then reduce the bandwidth of this filter until it stays at 94dB.
    • Center frequency 45Hz, BW 1/3-octave, cut 12dB. Once again, keep your eye on 56Hz. If it drops below 94dB, then reduce the bandwidth of this filter. Note: This filter will still leave the peak at 50Hz, but it will be reduced somewhat. I’ll decide what to do about it when you post your new figures.
    • Center frequency 28Hz, BW 1/4-octave, boost 10dB.
    Be sure and post your new readings.

    Regards,
    Wayne A. Pflughaupt
     
  8. Bob Bartlett

    Bob Bartlett Stunt Coordinator

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    Ok Wayne here they are:

    16 79 90.5
    18 77 85.0
    20 80 87.5
    22 90 96.5
    25 91.5 96.5
    28 89 93
    31.5 88 91.0
    36 94.5 97
    40 96 98.5
    45 93 95
    50 105 106.5
    56 91.5 93
    63 91 92.5
    71 88.5 90.0
    80 88.5 90.0
    89 92 93.5
    100 89.5 91.5
    Here are the filters I ended up with:
    28Hz BW 15/60 +10 Boost
    45Hz BW 8/60 -12 Cut
    63Hz BW 4/60 -10 Cut
    89Hz BW 10/60 -6 Cut
    I did have to keep cutting the bandwith on the 45 and 63 filters, but now I see what you are trying to go for. I'll keep experimenting until you give some more suggestions.
    Thanks.

    Bob
     
  9. Bob Bartlett

    Bob Bartlett Stunt Coordinator

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    After playing around some more here's what I came up with:


    16 78.5 90.0
    18 77 85.0
    20 83 90.5
    22 87.5 94.0
    25 88.5 93.5
    28 87 91.0
    31.5 88 91.0
    36 92 94.5
    40 92 94.5
    45 90 92.0
    50 93 94.5
    56 89.5 91.0
    63 92 93.5
    71 89 90.5
    80 91.5 93.0
    89 92 93.5
    100 90.5 92.5

    Not to shabby. I ended up using 8 filters:
    20Hz 6/60 +3 Gain
    23Hz 4/60 -8 cut
    28.9Hz 15/60 +10
    38Hz 5/60 -5
    45Hz 8/60 -12
    50Hz 4/60 -14
    63Hz 4/60 -8
    89Hz 4/60 -6

    Haven't had a chance to listen yet.

    Bob
     
  10. Jacques C

    Jacques C Stunt Coordinator

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  11. Wayne A. Pflughaupt

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    That’s certainly a dramatic improvement, Bob.

    Response is pretty flat now – perhaps too flat. I suggest playing test tones at 100Hz and 36Hz. They should subjectively sound like they are at the same level (although not necessarily measure the same).

    If you find that 36Hz sounds weaker, you are going to find that your bass does not sound flat, even though it measures flat. If this is the case you’ll probably want to dial in a house curve, using a shelving filter.

    You can find out how to effect a shelving filter here.

    Other information on house curve here and here.

    Regards,
    Wayne A. Pflughaupt
     
  12. Bob Bartlett

    Bob Bartlett Stunt Coordinator

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    Thanks Wayne I'll check it out. I will say that is sounds much better. All the boominess is gone and I don't have to run it hot like I used to to get the same effect. Thanks for getting me started in the right direction.

    Bob
     

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