Who uses a BFD?

Discussion in 'Archived Threads 2001-2004' started by PaulDF, Jan 7, 2003.

  1. PaulDF

    PaulDF Second Unit

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    I have been looking into the Behringer Feedback Destroyer lately, but can't seem to understand quite what it is meant to do...

    I have read that most of you use it to flatten your in room sub response. Is that its main purpose? What about the "feedback" part? Does it help too?

    If it can flatten a subs response curve, then I would think I could also tailor the curve to my liking. Such as a bit of boost around 35-40hz. How much gain does each band have? 6db?12db??

    Any info will be appreciated! Thanks.

    Also, where can I find it in Canada?

    Paul
     
  2. MarcVH

    MarcVH Second Unit

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    The BFD is originally designed to control feedback in studio monitors ("feedback" is that noise that can be made when a live microphone is held close to live speakers; it's often heard on dial-in radio shows just before the host shouts "Turn down your radio!") Most people don't have live microphones in their home theaters, so that's useless. Fortunately, it's also a flexible parametric equalizer.

    Given a sound meter, appropriate test tones and some patience, you can dial in a desired "house curve" instead of a flat one if that's what you want. Multiple memory settings allow you to have different settings, e.g. maybe a "flat" one for listening to classical music and a "sloped up to 30 Hz" one for action flicks.

    Each of the 12 filters can apply an adjustment from +16 dB to -48 dB. Remember, though, it can just change the signal passed to your sub -- it can't make your sub any more powerful or change the point when it clips or bottoms out.
     
  3. PaulDF

    PaulDF Second Unit

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    Marc, are you saying it has 12 multiple memories?
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    No, it has 12 bands, or "filters", which you can use to flatten the frequency response of your subwoofer.

    Feedback, as defined by my UltraCurve manual, happens when a particular frequency is continuosly growing in amplitude because of bad equalization or poor microphone placement. In order to kill it, you need a particular filter which will bring that specific frequency down in amplitude. That's the reason you can use the BFD as a parametric equalizer.

    As Marc said, though, it won't make your sub more powerful. It will just change its frequency response to one of your liking.
     
  5. TimForman

    TimForman Supporting Actor

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  6. PaulDF

    PaulDF Second Unit

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    Thanks guys, lots of info there. I would like to be able to preset a few curves to switch between for music, movies, etc. I understand that it will not make my sub more powerful , but if given enough headroom, I could cut certain freq's, and leave others, right?

    Is it as complicated as it looks? Do I need it? I only have a modest system so far, compared to most.

    Will it be worth it for me, or will I just be forever adjusting and tweaking, as I can never just leave things alone!

    Also, it looks like I will not be able to adjust my receiver's sub out when I want to turn the bass up or down, is this true?
     
  7. Stephen Dodds

    Stephen Dodds Second Unit

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    You can't use thye BFD if you have a receiver unless it has both pre-outs and main amp ins, which not many do these days except Harman Kardon.

    The BFD goes between the prepro and the power amps.


    Steve
     
  8. PaulDF

    PaulDF Second Unit

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    I am only wanting to use the BFD as an EQ for my subwoofer. It of course has a pre-out.

    I do not have separates, but my receiver does have pre-outs for all channels, though no "main amp in".
     
  9. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Paul, you are OK. As long as you have a subwoofer out, the BFD will work fine. Your subwoofer will have the power amplifier.
     
  10. PaulDF

    PaulDF Second Unit

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    Whew, glad I didn't buy it and then find out it did'nt work, or get a scare anyway.

    What I want to know is, would it be worth it for me, with a fairly modest system(but big sub), to hook up a BFD? Will it make a definite audible difference to perhaps give a little more mid-bass by lowering the lower and also the higher freq's in the sub's bandwidth? To tailor for music or movies. (like an adjustable bass boost)
     
  11. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Paul, at least for me, flattening the response curve of my subwoofer has given me wonderful results. I used an UltraCurve, which actually tries to flatten the entire audio bandwidth. I have been testing it with a pair of old JBL Control LA minimonitors and a Cerwin-Vega 12" passive subwoofer.

    After listening to my Etymotic ER-4S earphones, my (Behringer corrected) JBL/CV passive system and my main MartinLogan uncorrected system, I can only say I'll be moving my Behringer to my main system. The MartinLogans sound colored and not accurate when compared to my other systems. Bass goes from bloated and exaggerated to juuuuust right. I loved the change.
     
  12. Phill O

    Phill O Stunt Coordinator

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    Having never used the Behringer Feedback Destroyer, The first thing that came to my mind when I saw the acronym BFD...
    Big F*#K'n Deal. [​IMG]
    No offense to anyone who uses this product. I am sure it does a great job for most people. Just one of them weird nights for me.
     
  13. Shawn Solar

    Shawn Solar Supporting Actor

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    All systems from a $400 to $3000 dollar sub can benifit from some equalization. Truth is unless your room is acoustically flat(unlikely) or you have room treatements or bass traps which actually address standing waves, It can make a world of a difference. Boomy bass is usually from the room. So if there is a spike at 50hz no matter what sub you have you will always have a spike at 50hz

    Now like I said bass traps are the only way to get rid of standing waves. Problem is most traps are fairly large and are required in multiples. So the next way to go is a parametric eq like the bfd. An eq does not get rid of standing waves it can only lessen the effects of them. And for only one listening postion. It can also not adress any nulls or dips in the response. So in eesense it can make the bass worse for someone sitting across the room. Bass traps are effective through out the entire room.

    What the bfd can do is bring down some peaks that can mess up the sub's fr response. For $250 canadian it does a pretty good job as I have one in my system. Most rooms can or are between +-10db. with the bfd you can probably bring that to about +-4db with some effort. now a 6db difference in spl in the critical 50hz and lower is subjectively twice as loud. Most room peaks are abouve this. So if you have one peak at 35hy and 75hz(most rooms have one large paek then one smaller peak) you can bring the level down at those frequecies so the bass is a lot smoother.

    Now what I did with mine is I used my spl metre with the correction values to set my BFD. That gives me a flat response to 20hz. I mostly use that for movies. I then created another curve with the spl metre correction values ommitted that provides a house curve.

    The reason is I watch my movies at one volume usaully close to reference level. most bassy scenes in a movie last 2-3seconds which fully excites the standing waves. Now with music I find I listen to lower levels and I watch t.v at lower volumes. At these lower volumes the bass seems very weak due to our hearing sensitivity dropping with lower volume. Specifically with bass below 50hz. Also the bass in music is very 'quick' and does not last long enough to fully excite the room modes. That is why I have a more bass heavy house curve.
     
  14. Richard Greene

    Richard Greene Stunt Coordinator

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    Good post Shawn

    The BFD is used to reduce the SPL of bass peaks at one specific listening position for a smoother bass frequency response.

    Typical subwoofer frequency response at one listening position measured using a slow sine wave sweep is
    +/- 10dB or more .... but after one, two or three bands of parametric EQ, the frequency response is typically
    +/- 5db or better.

    Troughs or nulls caused by standing waves are not affected by EQ boosts ... and I would also hesitate to boost very low bass frequencies in an effort extend the frequency response of a subwoofer (that's asking for trouble).

    A parametric EQ plus a few corner bass traps make a great combination for subwoofers. In most rooms an equalized $1000 subwoofer (even some $500 subwoofers) will provide better quality (not quantity) bass at one listening position than any unequalized subwoofer AT ANY PRICE ... with the exception of dipole subwoofers (expensive) which excite room modes less than regular "monopole" subwoofers.
     
  15. Wayne A. Pflughaupt

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  16. Shawn Solar

    Shawn Solar Supporting Actor

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    Well I guess you could try. But boosting dramatically reduces dynamic headroom. Anything more than 4-5db is not worth boosting. and I would not risk more than boosting 3db of ouput. I have two very deep dips in my reponse and actually need about 6-7db boost to level it out. I find if the dips are narrow enough it is hard to notice.
    Now with these high output subs(120db) and high power amps that are now popping up I bet it would be safe to boost response 3-6db and still never clip or bottom the amp or sub[​IMG] But maybe just music. movies at reference could still prove to be a problem.
    And Richard, I basically just copied what you've been saying for years[​IMG]
     
  17. PaulDF

    PaulDF Second Unit

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    Thanks for the good posts guys.

    I have been planning on building some bass traps for my room. I am still learning much about this, and will begin building my traps as soon as I feel competent enough to do it right. Or maybe I'll just copy how some of you members have built yours... (In the end thats what it'll be). I have done freq sweeps with my SPL Meter but haven't found a good way to chart the results yet to really give me an idea as to what my curve looks like.

    From what I have read, proper placement of a few traps in my room can make a huge increase to the clarity of the sounds eminating from my subwoofer. This sounds good to me! The wife also gave me the go-ahead, so I'd better get going on it.

    As far as the BFD, I would like to furhter use it to flatten my response curve as much as possible to be audiophylically(?) correct. Also would like to have a few more programmed curves with more or less mid-bass to suit my taste at the time. Or to show off and impress my friends who know nothing about a flattest possible response from 20khz to 20hz. The guys (like I was/am) who need the mid-bass punch.

    I have plenty of low bass for movies so I'm not looking for any boost there. I'm very curious as to whether the BDF can (simply put) act like an addable or removable boost by programming it properly as opposed to opening up my plate amp and soldering in different resistors, or whatever it takes there.

    This is my plan so far, so please tell me if I'm crazy somewhere! Thanks.
     
  18. Shawn Solar

    Shawn Solar Supporting Actor

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    Bass traps and an eq are the best way to go. The inclusion of the traps will/should take care of any nulls while also taking down a few peaks. the eq can then fine tune the response with probably one maybe two bands of equalization. My guess is you won't need to boost the response for more slam. with the fr response smooth and flat any slam that is supposed to kick you in the gut, will. bass will sound "quicker" like a sealed sub but will have the extension of a ported. The most I gather will might want to do is run the sub 6db hot from the mains. That will probly be adequete in giving you that slam.
     
  19. PaulDF

    PaulDF Second Unit

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    Thanks guys, that last post really raised my spirits...

    I will build some traps soon, hopefully, and experiment with their placement. Typically, placing them in the corners is best, right? I'm talking tube or ASC type traps. What height is best? Sitting on the floor okay or should they be higher up? What about furniture in the direct path between the sub and traps?

    I looked over my freq response figures last night, and to me(what do I know?), they don't look all that crazy. About +/- 18 db with values corrected. Biggest difference being between 20 ond 85 hz. Relatively flat but sloped up a bit.

    Should I measure with my mains connected or not? I wasn't before, but I'm now thinking I should keep them on to see how the crossovers blend.

    I will try the traps first, and see what changes that makes. If I still need/want to adjust, I'll look around for a BFD. I might even peruse some pawn shops this weekend. Who knows what could be found if I look around!

    Back to the workshop! Better get my stove going, its getting cold up here in these parts, finally.

    Paul
     
  20. Wayne A. Pflughaupt

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