BFD, and bandwith question?

Discussion in 'Archived Threads 2001-2004' started by Greg P, Apr 5, 2002.

  1. Greg P

    Greg P Stunt Coordinator

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    I think I understand how the BFD levels off frequencies. I have read the whole article at snapbug a couple of times, but I have a couple of questions.

    1. Since the filter comes as a slope, what is the best way to calculate where I should have the center of the filter if I have a rolloff? ( I have a BPD 1503 sealed) Anthony can you help me on this one?)

    2. Also what is the best way to filter the inductance curve once it has flattened out? One big filter or as many small ones as possible?

    3. Is there anyway to calculate these corrections?
     
  2. brucek

    brucek Second Unit

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    Greg,

    If you've read Sonnie's site, including all the links, you have all the tools needed to calculate bandwidths, so I won't bore you with that information again. It's also useful to download the BFD design software to get a visual feel for what the filters look like.

    The number of filters used and whether it's better to be wide or narrow depends on how wide or narrow the peaks and valleys in your unequalized response are.

    In that regard though, generally I may tend to go for more narrow filters than single wide ones when I'm on a crossover slope to avoid an oscillating effect on the way down.

    This is something most people do by trial and error. Usually when you're setting up your filters you will begin at the lowest frequency and work your way up, so by the time you reach the crossover slope you'll be well experienced to do a good guestimate of what bandwidths to use..

    brucek
     
  3. ThomasW

    ThomasW Cinematographer

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    Using EQ changes the Qtc of the system, it makes it higher. So the fewer filters used the better.
     
  4. brucek

    brucek Second Unit

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    Greg,

    It's fairly easy to monitor your overall and individual phase angles created as a result of one or many filters with the BFD design software I mentioned, if that's a concern. You should generally try and keep below 70 degrees at all times for the frequency range of interest. You could play around with it and see the effect on phase that the filters you choose create.

    I thought once a speaker was completed that it possessed a total speaker system Q that you designed in, and that phase differences before the power amplifier wouldn't have an effect on the Qtc itself. I'm afraid I don't know very much about speaker design, so perhaps I don't understand the question..

    brucek
     

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