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BFD Problem. Is mine faulty?

Discussion in 'Home Cinema Speakers' started by Mark Ward, Aug 24, 2003.

  1. Mark Ward

    Mark Ward
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    I'm having difficuly with my BFD and suspect it may by faulty.

    Attempting to tame my currently rather live room I finally got around to playing with my BFD.

    Temporary Room problems
    12,500 cubic/ft
    42ft x 20ft
    Partially Carpeted
    No Drapes (boarded up windows)

    BFD Graph here

    I'm pretty sure I understand how to set the BFD's filters, here's what I've done so far.

    With the sub level on the preamp turned up to just below clipping level in bypass mode and then re-calibrated to +3db using the sub's volume levels I get the Blue Line.

    Very messy results, but I knew that. The prominent frequencies that are prevailing are the reason it seems so quiet once they are tamed but I can re-calibrate again once I've "tuned" the room.

    I've turned OFF all filter presets in 1 to 3 and 5 to 10. I've set all active filters in Presets4 to "PA" and turned OFF those I'm not using.

    Lots of trial and error and I'm at the stage with the Pink line.

    I'm having difficulty making any impact at all on the frequencies above 45hz.

    I've tried setting a wide bandwidth filter covering the entire plateau, lots of little filters. I've even tried -40 gain setting individual "10" bandwidth filters at50, 56, 63, 71 & 80. Nothing has any affect what so ever on this frequency range.

    Anyone have any ideas what's up? or anything else I could try?

    Thanks,

    Mark.
     
  2. Apocalypse

    Apocalypse
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    Hi Mark, I've looked at your results and the filter settings you've used and I'll post my thoughts as to what is IMO different about your setup.

    You say you did the test with twin Servo 15s, if that's true and the initial unfiltered tests were showing db levels above 100db then IMO the room is creating extra noise caused by the pressure levels of 2 huge subs played that loudly. Can you try the unfiltered test again with the amp volume set to a level that shows about 80-90 as an average, this might also save the foundations of your house :laugh:

    Check the "Operating Level" button at the back of the BFD, normally it should be depressed for home use but dunkyboy said he got far better results with the button left alone, as you are using 2 huge subs this could be an avenue to go down.

    You're using some quite extreme settings on your filters I noticed, the highest bandwidth setting I've ever needed was 13 but you're setting at the 22Hz mark is set to a whopping 25, that's over 1/3 of an octave and would have a dramatic effect on the surrounding frequencies. I only mention it because you still have filters set at 23Hz and 30.9 respectively which have allready been filtered with the 22Hz mark setting, was the peak that huge :eek:

    Here is a review of a BFD used with 2 subs if you haven't allready seen it.

    An average filter for me would be something like :

    Freq = 50
    Bandwidth = 10
    Gain = -6

    For really huge peaks I've been known to use a gain of -10 but one of your filters has a gain of -16, that just doesn't seem right, again I think the room is interacting with the subs and causing extra noise.

    Hope any of the twaddle I wrote helps :rolleyes:
     
  3. Mark Ward

    Mark Ward
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    Thanks for the input

    Test results are accurate, remember this a massive room. M&Ks Professional website shows recommendations for big rooms up to 6000cubic/ft. Mine is more than twice that size. The subs are now placed together centrally under the centre speaker for practical reasons.

    Will happily try again but I know they're correct. It may sound strange but -10dB is normal listening levels in such a massive room, it really doesn't sound THAT loud.

    Button is in, though happy to try it with the button out.

    I felt that dramatic problems needed dramatic settings.

    The top of the first peak is 25hz, I decided to tryto bring down the 22hz range first, remeasure and add extra filters as needed.

    Setting a 2nd filter at 25hz had too severe an affect on the 28hz range but moving the filter forward to 23hz and changing bandwidth by trial & error tamed the tail of the peak and got me a pretty flat line to 25hz.

    Yes, it was. The 30.9hz filter was again trial and error, I couldn't seem to remove the +2db "peak" at 28hz created by the 23hz filter without dramatically affecting surrounding frequencies, but was happy with the results up to 45hz.

    BTW. Are you sure that 30.9 would be affected by the 22hz filter? My understanding was that 1 unit in bandwidth was a 1/60th octave, so 10 units would be 1/6th Octave on the bottom line of the graph. By this reckoning I figured this range would affect just below 20hz to just above 25hz.

    I will check it out now:)

    Seems reasonable to me, as I said before I have BIG peaks to tame.

    This is what I think too. Pitched roof in a massive space with no sound dampening on the walls, no curtains and only some old carpets thrown on the floor was always going to be a problem.

    When I can afford it I'll fit drapes, carpets dampening but for now I'm stuck with what I have.

    My major concern is that having reasonably tamed up to 45hz, I can't seem to affect above this frequency what-so-ever.

    I have had one idea to try.... I'm going to swap over to the right channel from the left and see if that has the same problems above 45hz. If not, I'll try a different preset (perhaps preset 1) as I don't know why the recommendations in the snapbug feature say to use preset 4.

    Thanks for your time and help,

    Mark.
     
  4. Apocalypse

    Apocalypse
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    It's pretty clear that your large room and my tiny room have very different results, if I played tones that showed a db level of over 100db I'd be experiencing a metabolic change by now :eek:

    If you own AVIA can you do another check if possible, there is an LFE sweep from 100Hz ~ 20Hz that is counted down onscreen, can you try this with your sound level meter and BFD, it's all I use now when I reposition the sub.

    Here is a thread in which I go into it in further detail if you're interested, just scroll down a bit.


    And on another completely different note, why does the software for forums not allow you to add more than one character space, it ruined the effect of my post :clown:

    Phil
     

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