?s about Behringer Feedback Destroyer

Discussion in 'AV Receivers' started by Steve Schaffer, Jan 2, 2005.

  1. Steve Schaffer

    Steve Schaffer Producer

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    I have some significant dips in response from my sub, mostly around 55-60hz and some peaks at other frequencies.

    I was considering the use of the Behringer Feedback Destroyer model DSP1124P and was tryin to educate myself as to how it can be used to equalize my sub's response.

    I downloaded the instructions at snapbug and it seems that the use of analyzing software is recommended.

    Unfortunately my computer skills are sorely lacking and the use of such software and the necessary equipment is sorta beyond my capabilities at this time.

    Would it be feasible to simply use the low frequency sweeps on AVIA and a Radio Shack SPL meter to find the dips and peaks in frequency response, write them down, and then by trial and error adjust the Feedback Destroyer to compensate?

    Am I correct in assuming that with the feedback destroyer one can choose what frequencies to boost or suppress and also the bandwidth of the correction? In other words the device is not locked into specific frequencies that can be adjusted but instead the user can choose what frequencies to adjust?

    I know this all sounds pretty naive to most of you but I was hoping that I could use this device without having to use a computer to analyze my frequency response curve.

    Thanks in advance for any help on this!
     
  2. David Judah

    David Judah Screenwriter

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    Yes, you could do it that way, Steve, but it would be awfully time consuming. You would also want to make sure you have the SPL meter correction values handy. You can download programs like ETF and use it with little difficulty and save yourself some time.

    The EQ is relatively easy to use. Being parametric, you can select the center frequency, the width you want to affect, and the amount of change for each of its 12 bands. I wouldn't try to fix dips with it, but it does a nice job of leveling out some of the large peaks.

    There is a nice FAQ about the 1124 floating around that covers everything about it. You should be able to find it with a search, but of course since many of us use one, we can answer your questions, as well.

    Good Luck,

    DJ
     
  3. Brian L

    Brian L Cinematographer

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    I think the FAQ in question is the snapbug site he mentioned. FWIW, the procedure there is based on taking measurements with a RS SPL meter. In fact, the spread sheet that is part of the write up has a spread sheet that has the correction factors built in.

    I would be the first to agree its time consuming, and not as sexy as the PC based analyzers, but it does work.

    BGL
     
  4. Steve Schaffer

    Steve Schaffer Producer

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    Thanks for the encouraging words. I'm not especially scared of time consuming calibration sessions or trial and error diagnosis of problems. My main concern is dips rather than peaks however. Perhaps just turning up the sub volume to bring the dips up to "normal" and then reducing the resultant "peaks" would work? I know I'm being naive again but maybe that would be worth a try. I'm using a Pioneer VSX-45tX and have also used a Denon 2805 with auto-eq, but those don't eq the sub and I've read in several threads that getting the sub response flat is actually of more benefit than the mains and surrounds.

    My thought was that the Feedback Destroyer is not as expensive as some other things I've done and only gotten marginal results, and that setting it up might actually be fun in a way.

    I've experimented with sub placement to cure the dips and found that the only good location is in the middle of the dining area adjacent to my family room, not exactly a practical solution.
     
  5. Andrew Pratt

    Andrew Pratt Producer

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    Steve the BFD should be able to flatten your response a great deal. If you look on my site under DIY there's a link to the before and after I applied the EQ and you'll see that I was able to fix some dramatic dips and peaks to get the nice house curve I have now. It really makes a big difference in the sound you get and using the RS meter and Sonnies excel sheet makes it pretty easy to do.
     
  6. David Judah

    David Judah Screenwriter

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    I was going to suggest experimenting with sub placement, but since you have already then using a BFD should be the icing on the cake. You could though build a DIY sub big enough to eat on and use it for your dining room table too.[​IMG]

    After taking your measurments, you'll probably have one or two big peaks and I would concentrate on bringing those down first, then listening to it with and without the BFD in the chain(it has a defeat button, so you can compare easily)before deciding if you need to set additional filters. Many times that's all you need to do. You don't want to overdo it, which is very easy to do when you get the new toy.[​IMG]

    Also, I wouldn't worry about getting the response ruler flat. You want to have a nice House Curve, as Andrew mentioned, and that will mean a rising response below 30 Hz due to room reinforcement. You don't want to equalize that out unless one of the big peaks happens to be in that range(which is rare--you'll know by looking at the graph and listening if it's a problem).

    You'll be amazed when you recalibrate how much some of those frequencies were underrepresented, because you were previously calibrating to the peak/s. In some rooms it makes a huge difference.

    Have fun.

    DJ
     
  7. Ryan Tsang

    Ryan Tsang Second Unit

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    Off topic:

    I switched over to using XLRs for in AND outs of the BFD and the bass level is noticeably higher for this, compared to the 1/4in jacks. I had to recalibate. I thought it was that "-10dbv/+4dbv" button at the back but it's not.

    I've relocated the BFD on top of the sub. I run 15ft female to male XLR interconnect to the BFD to take advantage of whatever noise eliminating feature of a balanced connection over a (relatively) long run. Then I run a short female XLR-RCA IC to the sub.

    Back to topic:

    Steve....use one of those cds with static 1/6 oct tones. Don't use the AVIA sweep. It's too fast for just pen and paper and so you have to "rewind" a hundred times to graph the whole response. Then you move the sub or apply one change and you gotta do it again. The snapbug site has one you can burn.
     
  8. Jon W.

    Jon W. Stunt Coordinator

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    If you need test tones download the NCH tone generator and make your own and burn them to a CD. This thing is awesome and I found it to be easy to use. You can make tones for what ever frequency you want and what length you want.
     
  9. Steve Schaffer

    Steve Schaffer Producer

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    Thanks again for all the suggestions. I picked up one of these last Monday evening. I didn't have enough time to really do much except halfway familiarize myself with how to set the filters. I played with it just using AVIA and hitting still frame at the lowest "dip" points per the meter then reading the frequency off the screen--very crude, I know. Anyway I set up a couple or three filters to try to bring up the dips and per the sweep have actually managed to make a bit of progress. Don't have another day off until Sunday so won't have much time to play with it more until then, but so far am having fun with it and seem to have actually improved the sound, or maybe it's placebo effect, but my reference scenes in some dvds (battle sequence in Gladiator and engine room scene in Titanic) seem to be revealing stuff I didn't hear before.
     

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