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Bfd

Discussion in 'Home Cinema Speakers' started by petrolhead, Nov 21, 2003.

  1. petrolhead

    petrolhead
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    Any advice on using and setting up Feedback Destroyer
     
  2. Steve Bate

    Steve Bate
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  3. petrolhead

    petrolhead
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    Cheers Steve.

    I already had that one and was hoping for more personal feedback from forum members.

    If I remember right Apoc had installed one
     
  4. Apocalypse

    Apocalypse
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    Many members have one now, THX1138 and Smurfin were the latest to take the plunge. That snapbug review is IMO the definitive guide on the BFD, follow that and plot a graph, from there you can get advice on how to cure it. If there is anything specific you want info on that is maybe not covered in the Snapbug review just ask away.

    As for general feedback of the BFD, I've had it for nearly a year now and it's absolutely essential in my setup, in the AV game no other £100 product can give you so much for such little outlay :smashin:

    Phil
     
  5. petrolhead

    petrolhead
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    Hmmm

    Can't wait to play with it then .....................
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    The BFD fefore you ask :D
     
  6. Apocalypse

    Apocalypse
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    Just remember this golden tip, switch on the BFD before you switch on the sub, if you could have seen my face when the HGS18 popped while my head was 1 foot away from the driver :eek: :eek: :suicide:
     
  7. petrolhead

    petrolhead
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    Ok, cheers for the tip

    I am going to have a fiddle this weekend
     
  8. Steve Bate

    Steve Bate
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    :clap: :eek: :eek:
     
  9. petrolhead

    petrolhead
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    Here is the first graph before doing anything.

    Where should I make the adjustments?

    Deleted to save bandwidth
     
  10. GaryG

    GaryG
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  11. petrolhead

    petrolhead
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    Sorry, don't understand
     
  12. petrolhead

    petrolhead
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    Now stuck with bandwidth
     
  13. Cool-hand

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    Sounds like a headf*** but a neccesary evil, oh God!

    Good luck.
     
  14. petrolhead

    petrolhead
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    Achievement to date

    Deleted to save bandwidth
     
  15. jag77

    jag77
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    Think you're getting the hang of it.

    A few more tries and you'd get a pretty good curve. The best advise I can give is to keep trying. Once you know what the bfd can or cannot do, you'll be much closer to get to the ideal curve.

    A tip thou: never ask for more than 3dB gain from the BFD.
     
  16. petrolhead

    petrolhead
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    Cheers Jag, yes I knew about no more than +3 gain, if thats what you mean.

    I assume - gain geater than 3 is ok.

    Looking at the first graph where would u start?

    I feel I am going round in circles
     
  17. Apocalypse

    Apocalypse
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    Petrolhead - The first thing you have to decide is where you want the curve to go, you have to consider if you want to just reduce peaks or if you want to increase troughs as well, the first option is preferable and should be your goal. With that in mind and looking at your first graph these are my suggestions :-

    1, Reduce the 40Hz peak to 85 Db with a fairly large bandwidth of say 15, Gain of about -12 and set the filter to 40Hz exactly (these are initial figures to see what it does, from there you finetune)

    2, Next reduce the peak at 66Hz to just below 80Db, again a large Bandwidth of about 15, Gain of about -10 and set the filter to 66 or 67 using the finetune button.

    The goal is to reduce these two peaks to form a gradual slope from 40Hz to 80Hz, beyond this figure there is not much the sub can do unless you have a high sub cut-off of about 100 and beyond. By curing those two peaks to form a straightish (is that a word :rolleyes: ) line you'll have a decent house curve that didn't require any boosts :smashin:

    Phil
     
  18. petrolhead

    petrolhead
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    You are a gem Apoc, cheers and will post result

    When I did the origional curv the BFD was not in the frame so I wonder if I should start again forst with it bypassed (Light flashing) or will it be the same....

    Here is the answer to my question:

    [​IMG]
     
  19. Apocalypse

    Apocalypse
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    The first attempt should be done with the BFD engaged but with no filters activated.

    How have you setup the amp/processor, from my own findings I now set the Processor to the THX Pro Logic mode for the sinewaves, in stereo mode the results are misleading because my centre speaker was not involved (my centre has strong output from 50Hz). If I have time later I'll do a graph using the original Snapbug frequencies, I normally use my own that don't go any higher than 80Hz.
     
  20. Apocalypse

    Apocalypse
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    Here is my current reading :

    [​IMG]

    The huge peak at 111Hz is a doubling of the Axial mode at 56Hz (my rear wall), this will be cured with bass traps soon.
     
  21. codling

    codling
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    Apocalypse,

    how do you export youR graph from excell?

    cheers carlos
     
  22. Ian J

    Ian J
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    I used a screen grab within Paint Shop Pro to "export" mine
     
  23. Apocalypse

    Apocalypse
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    It's a standalone graph that only requires you to have Excell or similar, I have the file on one of my sites :

    http://www.reviewsandnews.co.uk/subtestmodel.xls

    If you just want to input your BFD figures (pink line) simply reduce each figure in the "RAW" section to 0.
     
  24. Apocalypse

    Apocalypse
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    Is that what Codling meant, I wasn't sure :)
     
  25. codling

    codling
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    thanks guys

    i'll give it a go.
    carlos
     
  26. petrolhead

    petrolhead
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    So you mean filters set to OF (Off)?

    I just play using direct + Sub.

    I have done another plut but this time PLII with THX as you sugested -

    [​IMG]
    This will change as I add more plots


    PS To save bandwidth on this thread I have deleted some of the other images
     
  27. Jeff

    Jeff
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    What is the BFD doing at 120 and 160Hz? I find those graphs a bit disturbing.
     
  28. petrolhead

    petrolhead
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    Ist attempt

    See previous post

    What next or is this it?
     
  29. Apocalypse

    Apocalypse
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    Petrolhead - You should only be reducing the actual peaks, whatever you are doing you are also reducing frequencies that should not be reduced. Something is very wrong with the final graphs, the BFD should NOT affect frequencies at 120 & 160Hz like that.

    Can you be specific and state how the amp/processor is setup, what sub cut-off you're using and if the Xover is In or Out. When you say "Direct" what exactly do you mean because "Direct" on most amps/processors deactivates the LFE channel. Lastly can you state the exact filter settings you've used and at what frequencies you've used them.
     
  30. Apocalypse

    Apocalypse
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    Here is a crude idea of what you should be aiming for Petrolhead, easily achieved once you get used to the BFD.

    [​IMG]


    If you're lucky you can reduce the peak at 89Hz too, the sub just might reach it to have some effect.

    Phil
     

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