Using all 24 BFD filters ?

Discussion in 'Archived Threads 2001-2004' started by Sankar, Feb 21, 2001.

  1. Sankar

    Sankar Second Unit

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    Got to play with my BFD today finally ! Boy was that fun !
    I used SpectraPlus along with the Radio Shack SPL meter (as a mike) and fed a pink noise signal directly into the sub input jack of my receiver's 8 ch analog inputs (Denon 3801). That way the pink noise was heard only thru the sub.
    Tamed the peaks, eliminated some troughs and ended up getting a reasonably flat response (within a db or two) .. didn't read the manual carefully and lost ALL the settings ! Fortunately, I had written them down on paper, so was able to re-program them ! In any case, at the end I had used ALL 12 filters (maybe I can go back and be more parsimonious the next time around) !
    In my current setup, only the left channel is being used .. i.e. signal goes into the left input and the left output goes to the sub ...
    Question :
    Why not pass the left out to the right channel in and then send the right channel out to the sub ? This should permit one to access all 24 filters right ? Has anyone tried this ? Any complications ?
    Thanks
    Sankar
     
  2. Sankar

    Sankar Second Unit

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    Tried this today !
    All 24 filters can indeed be used if the 2 channels are connected in series. This allowed me to go in and smooth out all the "little peaks" as well ! Fed a pink noise signal directly to the sub (all other spkrs shut off) and tweaked till the resulting spectrum was flat to within about 2-3 db. I ended up using around 19 filters though (yes, this may be an overkill, since many of the filters were just 3-4 hz wide and with a 1 db boost/cut.).
    I guess that there is always the issue of measurement accuracy once one gets to this level (i.e. the "mike", the source/quality of the pink noise, etc, etc) ... but hey, it was fun ! I have not had a chance to play any music thru the calibrated settings (will do that this weekend .. the "ear" test).
     
  3. FrankD

    FrankD Stunt Coordinator

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    Great, I always wondered if you can connect the left and right side in that fashion to double the filters available. I have a few questions to anyone that has the technical knowledge.
    Is that just too many filters to use for such a small frequency span (ie. under 80 hz)? What does it do to the sound? Are you losing anything significant?
    Now it appears that the signal will go from analogue to digital to analogue to digital to analogue and finally to the speaker. How much harm does this do if any?
    I am presently using 5 filters on my 1100pro BFD but would not mind using more filters to get an even flatter curve.
    Regards
    Frank Dodaro
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  4. Sankar

    Sankar Second Unit

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    Frank .. my thoughts exactly ! I also wonder if we screw up the phase of too many adjacent freqs ?
    I did do some minimal listening last night .. it sounds pretty good though.
    Anybody with some technical feedback ?
    Cheers
    Sankar
     
  5. Timmy

    Timmy Stunt Coordinator

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    One thing to keep in mind that your sub is only spec'd at plus/minus 3db anyway.... for a reason; and getting it any closer/tighter in response gains very little, if anything "hearable" to the ears.
    So graph out your rooms LFE response; then create a 6db wide "path" on your graph (which equals plus/minus 3db) and then make a judgement as to what peaks need tending to. If you want to get picky; then mark a 4db wide (plus/minus 2db) path. IMO, to get any more specific only pleases ones eyes, not their ears.
    Also, "valleys/dips" are almost certainly caused by cancellation waves. Which means by adding db to a "dipped" freq usually does not help matters, since you are increasing the cancellation wave at the same time. Plus, cancellation waves are like "cooridors", only effecting narrow spots in the room. Move your SPL metet two feet ahead or behind where you have it and you might be amazed the -6db dip becomes a 2db peak just 18" away. If you try and counter a cancellation dip by adding DB, then those sitting elsewhere may experience a "boominess" at those frequencies since it wasn't being phase cancelled at their sitting location to begin with.
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  6. Sankar

    Sankar Second Unit

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    Timmy, that's an excellent point about dips becoming peaks! So, for a starter I suppose that we should take measurements at a variety of locations and average the readings.
    With an RTA such as SpectraPlus, I suppose one could take the "infinite" average and move the mike to the various locations for equal amounts of time .. or take the different measurements, save each overlay, then go to the files and manually average the numbers ... phew !
     
  7. Geoff L

    Geoff L Screenwriter

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    Playing with our new toys is always fun , but isnt the general idea to tame the area of seating. The sweat spot as they say. As we all know moveing as little as 1 foot can change a null to a peak. And running dual subs in different locations, well things just get worse in most rooms, especialy doubleing as liveing space and HT-room. What I belive the majority of us have, double duty rooms.
    Wouldnt one think that trying to average the entire room to flat responce would be like catching a falling star. One would chase it and never catch it. The idea of flat responce everywhere.
    Maybe Im misunderstanding what you ment by that.
    I think trying to tame the prime seating area would provide the least work and best results.
    Of course all rooms are not equal and some would drive a sain person insain.
    Im awaiting the arrival of my BFD and find the threads pertaining to it excellent groud work.... Thanks to all that are posting their expermentation.
    Looking forward to attemps and results of room averageing. Just how close can one get.
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    Smoothe
     
  8. Sankar

    Sankar Second Unit

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    Admittedly one cannot average across the whole room .. however trying to average a circle of radius of say 2 feet around the sweet spot may not be such a bad idea.
     
  9. Geoff L

    Geoff L Screenwriter

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    Sankar,
    Yes total agree! I was out in left feild there. Sorry I totaly missed your boat on that one. [​IMG]
    Let us know how this aproach works for you....
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    Smoothe
     

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