Problem setting BFD

Discussion in 'Archived Threads 2001-2004' started by Greg Yeatts, Apr 29, 2002.

  1. Greg Yeatts

    Greg Yeatts Second Unit

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    Can there be room modes that are too tough to tame? I have a room that is 23X13 with an open double doorway to a 14X22. My sub is placed in a corner furthest from the double doorway.

    I have a broad peak from 45-64 hertz of 10 db. I can tame most of the peak, but a peak at 46db remains no matter what. I can center a band on 46 hertz with a bandwidth of 10/60, apply 48 db of cut and only reduce the peak by 2 db. Tomorrow I will try to move the sub out of the corner. This does not bode well for WAF. Also, when I work on the broad peak, no matter how I attack it, I lose 6 to 7 db at 52-54 hertz. I have the BFD software. But it hasn't been able to help.

    Any ideas?
     
  2. Richard Greene

    Richard Greene Stunt Coordinator

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    My room has a broad peak from about 40 to 55Hz. that was significantly reduced using one BFD band.

    Frequency response deviations were reduced from +/-9dB

    before equalization to +/- 4.5dB with one band of EQ.

    Subwoofer EQ is used to reduce the SPL of frequency response peaks heard/measured at the listening position. You've got a broad peak that should be easy to reduce.

    I assume your measurements were made using sine waves with 1/6 octave (or smaller) spacing). It would be helpful for you to post the SPL at various frequencies because your description ("a broad peak") does not tell us enough to guess how to set the BFD.
     
  3. jeff lam

    jeff lam Screenwriter

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    There's gotta be something wrong. I had a 12dB peek at 40Hz in my room and tamed it with a 12dB cut just fine. Make sure all your settings are correct.

    Enable the mode to PA, center the freq, bw, and cut. Oh, and make sure you are using the correct channel the sub is on.
     
  4. Greg Yeatts

    Greg Yeatts Second Unit

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    Here is my corrected frequency response using the correction factors on Sonnie Parker's website for RS SPL meters. I can tame everything but the 45 hertz peak. I can reduce this peak some (5 ot 6 db), but I have to apply 30 db of cut to accomplish this. When I apply this much cut I reduce the 50-53 hertz by 6 db (I create a hole when I fix the peak) I have played with the center frequency, bandwith and gain. Nothing seems to work. The one problem I may have is that my sub box is tuned to low. I have a 12" Dayton DVC in a 3.1 ft3 box with a 15" pr. I may have way too much weight on my PR. This would cause ultra low extension (which I appear to have), but the low frequencies would be attenuated when compared to 40-50 hertz.

    The testing was performed from my listening seat using 1/6 octave sine waves and an RS SPL meter.

    Corrected

    Freq.DB

    1692.5

    1890

    2089.5

    2287.5

    2588

    2887

    31.591

    3684.5

    4090.5

    45100

    50101.5

    5697.5

    6395.5

    7185.5

    8083.5

    8981.5

    10081
     
  5. Shawn Solar

    Shawn Solar Supporting Actor

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    I had the same problem. I accidentally had it set at 3.2khz instead of 32hz. Or something close. Make sure the little light beside the selected frequency is hz not khz. I had a 9db peak centered at 61hz and started at rising from 59hz-67hz and found that 2 bands did a better job than one. I found one covered too wide or too narrow.
     
  6. Seth_L

    Seth_L Screenwriter

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    Not to belittle your post, but are you sure the peak isn't coming from your main speakers? I had a 10dB peak around 43Hz that wouldn't go away even with a 48dB cut and it turned out that it was coming from my front towers, not from the sub.

    Seth
     
  7. Greg Yeatts

    Greg Yeatts Second Unit

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    I took some weight off of my PR last night. It was as I had thought, I was sacrificing output from 20-30 hertz for good extension to 16 hertz. DB3 is with the modified PR and some changes using the BFD(DB1 is baseline). I am still having trouble reducing the 45 hertz peak. This peak is less of a problem now as the efficiency from 20-30 hertz has improved. The 63 hertz peak should be easy to fix (ran out of time last night). Not sure what's going on at 71 -80 hertz. After the PR mod maybe I need to change my phase switch on the plate amp.

    This should look pretty good when I am done. Is plus or minus 3 dB from 19 hertz to 80 hertz pretty good even when equalized?

    Freq.DB1DB3

    1692.585.5

    189088

    2089.592.5

    2287.592.5

    258893

    288790

    31.59192

    3684.588.5

    4090.591.5

    4510094

    50101.590.5

    5697.589.5

    6395.593.5

    7185.573.5

    8083.581.5

    8981.590.5

    1008184
     
  8. Peter Mansell

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    Greg,

    I had exactly the same problem when setting up my BFD. What little knowledge I have on the subject leads me to believe that we are simply suffering from a time related problem.

    My test disc is a series of sine waves, each five seconds long. When I'm at the frequency with the impossible to tame peak, I can clearly see the level rising over time as the signal continues.

    This is exactly the sort of problem that Tact's room correction system is designed to fix, as it is both time and frequency based equalisation.

    Try running a sweep such as the 200 - 20Hz from Avia. Even though I couldn't fix the peak in my response when using continuous sine waves, the sweep sounds much better with the BFD in place.
     
  9. Greg Yeatts

    Greg Yeatts Second Unit

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    OK, DB4 is the latest set of measurements from my sub when equalized with a Behringer Feedback Destroyer DSP1124P. I am now a true believer. The only problem I really have is that to tame the peak at 45 hertz (its still really hot at that frequency) I had to apply an 18 db cut at 45 hertz. I did this using a 1/6 octave bandwidth. Not only was the 45 hertz fully affected, neither were the frequencies around 45 hertz. My measurements are plus or minus 1.5 db from 19 hertz to 63 hertz. Plus or minus 3 db from 18 hertz to 71 hertz. The reason the measurement drops above around 70 hertz is that my sub is at a higher level than my mains and the crossover is bringing the level down.

    Freq. DB1 DB3 DB4

    16 92.5 85.5 85.5

    18 90 88 88

    20 89.5 92.5 93.5

    22 87.5 92.5 93.5

    25 88 93 93

    28 87 90 91

    31.5 91 92 93

    36 84.5 88.5 90.5

    40 90.5 91.5 91.5

    45 100 94 94

    50 101.5 90.5 93.5

    56 97.5 89.5 92.5

    63 95.5 93.5 91.5

    71 85.5 73.5 88

    80 83.5 81.5 86.5

    89 81.5 90.5 89.5

    100 81 84 85

    The sub can hit 110 db peaks on the pod race (the explosion in the tunnel) on the Star Wars Episode I The Phantom Menace with no audible distortion (that I can hear). The part I really like about the eq is that during the pod race I can now hear individual pulses when the racers come by instead of a bloated amorphous drone.

    My sub is a DIY using a Dayton 12" DVC in a 3ft3 box with a 15" Adire Audio PR using about 500 grams of mass.

    For music the sub is almost too clean. I really can't tell its there. I guess this is how it should be when your bass is well integrated. I am thinking about applying a ?house curve to my eq to get a little excitement back.
     

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