BFD causing distortion

Discussion in 'Home Theater Projects' started by Dan_M, Jul 8, 2004.

  1. Dan_M

    Dan_M Agent

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    First of all here are some graphs of my corrections before and after. The sub is a 142.5l vented box tuned to 18hz with a 12" Dayton Titanic MK3 and 250 PE plate amp.

    [​IMG]

    Before I added the BFD I had my reciever attentuating the LFE 10db plus taking another 6db off the top of that for a total of -16db. When I added the BFD I ended up running the LFE at +5db. I also ended up having to turn the sub up from 1/8th on the amp to just over 1/3rd to calibrate it with my mains after corrections.

    Now when testing with some bass heavy material I can hear distortion that wasn't there before the BFD. What does clipping sound like versus bottoming? Identifying the distortion would probably help to know how to fix it. I was thinking it could be bottoming since I thought I'd gain amp headroom, but I did turn the amp gain up quite a bit. What can I do to minimize this?
     
  2. Dan_M

    Dan_M Agent

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    Well I think I've answered my own question. I backed off the pre gain a few db and turned up the amp volume. This cleaned things up while still giving me the output. Guess I should just let the amp do it's job.

    I'm very impressed with how much a difference a nicely calibrated/EQd sub sounds rather than just tossing it in a convenient spot and hoping for the best. My sub is much more detailed now that I tamed that 63hz peak. It was a tad boomy at times before. I also enjoy the bass in movies now at lower volumes, I found myself before cranking the master volume so I could feel the bass. The bass in music is nice and tight now too, I no longer turn the sub down to listen to cds.
     
  3. Allen Ross

    Allen Ross Supporting Actor

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    looks like you got a nice house curve right there, don't play U571 too loud [​IMG]
     
  4. Dan_M

    Dan_M Agent

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    You think that house curve is too steep? I was thinking about taking a few db off that 20hz mark.
     
  5. Wayne A. Pflughaupt

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    A house curve is room-dependant; smaller rooms need a steeper one, larger rooms less of one. So it might not be too steep if you have a smaller room.

    The way I like to check the curve is to pay attention to the tones at 100Hz and 32Hz. If they sound like they’re at the same volume, you’re on the right track. If one or the other sounds louder, try adjusting the curve accordingly.

    I also think a curve sounds better if you level it off at about 32Hz. So you might like it better if you flatten out that 20Hz hump.

    Regards,
    Wayne A. Pflughaupt
     
  6. Dan_M

    Dan_M Agent

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    I changed a few more things on my sub to help protect it from bottoming and finalized my BFD filters. Here is the end result:
    [​IMG]

    I tamed the hump at 20hz and changed the rumble filter from 11hz w/o gain, to 18hz with about 1/2db of gain @ 30hz. I added sockets on the back side of the preamp PCB for the 2 resistors that control the rumble filter and bass boost. This way I can change them w/o taking the amp apart and soldering. Everything sounds pretty good, even tho it can be hard to tell what's distortion and what's the house rattling.
     
  7. Dan_M

    Dan_M Agent

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    I'm still having issues with what I think is my driver hitting it's excursion limit. According to Unibox I should be hitting my 19mm limit at just under 16hz with a full 250W. Coupled with the rumble filter on my amp it seems to me I shouldn't be able to push the driver past this point. Did I miss something when I modeled this sub? It's 142.5l tuned to 18.1hz with a 12" Dayton Titnic MK3.
     

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