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BFD EQ Help

Discussion in 'Speakers & Subwoofers' started by Cameron Yee, Aug 10, 2004.

  1. Cameron Yee

    Cameron Yee Executive Producer
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    Thanks for the advice Lee. Flipping the phase switch to 180 made a big difference in that 89 Hz dip. I had to make a couple adjustments to the filters as a result, but here is the latest:

    [​IMG]
     
  2. Cameron Yee

    Cameron Yee Executive Producer
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    It looks like I owe you another thanks Lee. I switched my mains to 60 Hz crossover and the response looks even flatter. This is a composite of the graph above and the graph with the 60 Hz crossover.

    [​IMG]
     
  3. Wayne A. Pflughaupt

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    Hmm, I would have expected a change in crossover point to make more of a difference than that. A change that slight could have other causes, such as a difference in ambient room temperature occurring between the two readings.

    If the sub sounds a little “thin” to your ears, it’s probably because response is too flat. If that’s the case you might want to implement a house curve. Here’s a couple of old posts of mine that talk about house curves. The first is succinct, second goes into more detail.

    http://www.hometheaterforum.com/htfo...81#post1975881
    http://www.hometheaterforum.com/htfo...958#post464958

    You can dial in a house curve by overlaying an additional filter. Here’s a link that shows how you can do this with the BFD:

    http://www.hometheaterforum.com/htfo...187#post576187

    The parameters given (center frequency, bandwidth, value of cut) should serve only as a guideline. You’ll have to tweak the filter for your room and system.

    As you will note in the first link, I usually recommend reference points of 100Hz and 30Hz for determining a house curve slope. However, in your case, where you have a -5dB dip measured at 100Hz, I’d use 90Hz instead.

    Regards,
    Wayne A. Pflughaupt
     
  4. Cameron Yee

    Cameron Yee Executive Producer
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    Ugh. In looking at how to dial in the higher frequencies for the house curve I discovered one of my filters was set to 250 not 25 Hz. So I remeasured everything and had to add a few more filters. The good thing is I was able to EQ out the previous problem areas at 63 and 100 Hz. I'll listen to this setting for awhile and decide on the house curve. Thanks again for the advice!

    [​IMG]
     
  5. PaulDA

    PaulDA Cinematographer

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    Are you using any bass traps to augment the BFD to achieve this flat response?
     
  6. Cameron Yee

    Cameron Yee Executive Producer
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    Nope, no bass traps. I did decide to remove a filter at 125 Hz, which didn't really do all that much for the measurements from that point on but made things sound a bit off. After doing a bit more listening I may experiment with a house curve, but as it is I have no complaints with it sounding thin.
     
  7. Lee Carbray

    Lee Carbray Second Unit

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    That line is so flat it's PHLAT!! Good job. How do you find the difference in sound from before and after?
     
  8. Cameron Yee

    Cameron Yee Executive Producer
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    Yeah, it's kind of crazy how flat it is. I did another set of measurements as I was trying a house curve filter and there was some deviation from the original numbers but only +/- 2 dB. Also, with the removal of the last filter I mentioned, the curve at 111 Hz and up is matched to the non-EQed response.

    The only issue now is a hum that I've never been able to remedy is now amplified because of (I'm deducing) my 63 Hz filter. Of course I don't notice the humming when I'm listening to music, but it's kind of annoying when the music is off. Who knows? Maybe it's providing some boost to the 63 Hz dip? I have some isolation transformers to attach to my satellite and HDTV coax, though the last time I used them they didn't seem to help.

    As far as before/after the increase in the upper bass is noticeable and nice. Still experimenting with a house curve, but haven't found the magic combination yet. I may put that off for a time as I'm getting a bit EQ'ed out.
     
  9. PaulDA

    PaulDA Cinematographer

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    I'm VERY impressed with that response, sans bass traps. Puts a few things into perspective and makes me want to run out and get a BFD now. Sadly the room is still under construction and it'll be a couple more weeks before I can set things up.
     
  10. Matthew Todd

    Matthew Todd Second Unit

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    Cameron, how many filters did you end up using? I've got a BFD, but just need to tackle what you've already done.

    Matt
     
  11. Cameron Yee

    Cameron Yee Executive Producer
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    Before I realized I had a 250 Hz filter on I was only applying about three filters to deal with the more obvious peaks and troughs. It looked like dips at 63 and 100 Hz were null areas, so I just left them alone. Once I realized the error I went back and tried filters at those points. All told I wound up with eight filters, though I may try narrowing the bandwidth on some to see if I can reduce that number.
     
  12. Matthew Todd

    Matthew Todd Second Unit

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    Thanks for the info on the number of filters Cameron!


    I downloaded this, but I'm having some trouble figuring out how to get my measured info (as measured before any EQ)into the sheet. Can anyone give me some help as to how I get this info into the sheet?

    I assume I could write it in another xcel sheet and then import it with one of the buttons there? What format should it be in and which button do I use (or is this totally wrong)?

    Thanks in advance!

    Matt
     
  13. Cameron Yee

    Cameron Yee Executive Producer
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    I played with that a bit and here's what I did:

    On the worksheet labeled "Measured Response" select "RS Calibration" (which I assumed was for Radio Shack Calibration). The frequencies there start and end lower than on Sonnie Parker's spreadsheet, so I just filled in for the values I had, which amounted to every other value starting at 15.8 Hz. For the frequencies in between the values I just split the difference so the slope would be balanced between measurements. Once that was set I went back to the worksheet labeled "BFD" and set the filters.

    EDIT: I didn't actually use this for the actual EQing as much as for getting a visual idea of the effect of various filters.
     
  14. PaulT

    PaulT Supporting Actor

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    That's about what I did with it as well. If you want to use the 1/12th Octave test tones you will get a higher resolution plot and catch any peaks or dips you might miss at 1/6th Octave.

    The ultimate way to do it would be to find your approximate peaks and dips and play tones in 1Hz increments to find the exact centre frequency to dial in for the filter on the BFD. A lot more work, however.

    Here's a good tone generator for creating your own test tones:
    http://www.nch.com.au/tonegen/index.html
    Burn them to a CD in whatever Octave Range you like.


    As Cameron noted, check the other Worksheets (bottom of the spreadsheet) for instructions, input page, etc.

    PaulDA - best 189CAD I ever spent. Also note that Behringer dealers will not discount, but hey, it's 189 bucks....
     
  15. Matthew Todd

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    Thanks guys. For some reason I missed the other tabs on the bottom of the sheet. Duh. I think I've got it now.

    Matt
     

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