DIY Tempest freq resp... BFD help

Discussion in 'Speakers & Subwoofers' started by al lout, Feb 25, 2005.

  1. al lout

    al lout Stunt Coordinator

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    Hi all,

    I've just ordered the BFD DSP1124P. It will be here sometime next week. I've just measure my sub's freq response. I need help on how to flatten out my freq resp as I'm totally new on BFD. I read/printed the BFD guide on snagbug site. Here is what I've got so far. This is for my diy Tempest corner loaded, xover at 80hz. All speakers turned off except the sub of course.
    [​IMG]
    Notice: The data are raw. I haven't add any corrections yet.

    I need you guys help on what freq and bandwidth should I filter at. I just want a head start [​IMG] I can't wait for the BFD to arrive. Thanks.

    Al,

    Edit: Correction: Look like the graph from bfd guide site auto apply the corrected values to the graph.
     
  2. Max F

    Max F Second Unit

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    Dude don't turn it up so loud! I hope you were wearing earplugs...

    Thats a good FR and i would focus on getting rid of the peak at 56 hz. You might try some other filter or even go with a room curve. Actually, always just graph with corrections. With corrections you probably already have a room curve. Overall, correcting this room should be very easy.

    Nice job on the tempest. What kind of box is it?
     
  3. stephanX

    stephanX Stunt Coordinator

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    holy *$%!...

    what room is that in? what kinda power? 120db is no joke...

    Next time, just so you know, when youre doing tests with sine waves/sweeps, turn it down, the curve will be close enough at 95 db to the curve you would get at 110 db(assuming youre not reaching mech limits).

    Seeing all these plots makes me wish my atlas 15 was done [​IMG]
     
  4. al lout

    al lout Stunt Coordinator

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    It's a sealed midq tempest w/ about 45oz stuffing (site recommended 32oz). It helps to reduce the boominess lil. I had to move the sub around to 5 different locations to get these decent readings, and it wasn't fun to move +100lbs sub around the room.

    Al,
     
  5. al lout

    al lout Stunt Coordinator

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    It well worth your time and effort... I'm sure you won't be disappointed. Just so you know, when I watch "The Haunting" DTS at -8db below RL, my meter shows 117db. The sound was so lively, I thought I'm in the movie and that my house is about to come down [​IMG] I've demoed to my frnd that wants to buy velodyn sub (~$1400). He's now thinking of building one [​IMG] Good luck w/ you DIY sub, you will be glad when it's all done.

    Al,
     
  6. al lout

    al lout Stunt Coordinator

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    Here is my updated chart (1/6 Octave Frequency).
    [​IMG]
    Please help me on where to filter and bandwidth of the filter. Thanks.

    Al,
     
  7. stephanX

    stephanX Stunt Coordinator

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    wow dude, i cant believe youre getting that response out of a sealed sub with a tiny bit of boost.

    my room is 12x9 and im putting a ported (psuedo*)SBB4 atlas in it(lowq)

    Good luck with your bfd, once you get your sub set up flat youll be happy you did.

    * i found that you can slam a ported atlas into an elcosure 1 cubic foot smaller than the real SBB4 and get a very similar result
     
  8. al lout

    al lout Stunt Coordinator

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    I've measured my sub responses from 10hz to 125hz (increment by 1hz). Do any of you know where can I get corrected values for all of those freqs? Please let me know. Thanks.
     
  9. MikeDuke

    MikeDuke Stunt Coordinator

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    If you mean the corrections for the radioshack meter here they are
    10hz.....+20db
    12.5hz...+16.5db
    16hz.....+11.5db
    20hz.....+7.5db
    25hz.....+5db
    31.5hz...+3db
    40hz.....+2.5db
    50hz.....+1.5db
    63hz.....+1.5db
    80hz.....+1.5db
    100hz....+2db
    125hz....+.5db

    To find a value betweewn what is listed say 22hz, just take the 20 and 25, add them and divide by 2. so it would be around 6 for 22
     
  10. al lout

    al lout Stunt Coordinator

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    Finally got my BFD. I need help on how to determent the bandwidth (octave?)

    1. I want to set a boost of +2db at 22hz (from 21hz to 23hz). What is that bandwidth or how many octave is that?
    2. Set boost of +2db at 33hz (range from 31hz to 34hz). What is that bandwidth?
    3. Cut of -9db at 55hz (range from 52hz to 58hz)? What is that bandwidth?

    Can someone show me how to calculate the bandwidth? Really appreciated. thanks.

    Al,
     
  11. Max F

    Max F Second Unit

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    Make sure you read everything on the snapbug site:
    http://www.snapbug.ws/bfd.htm

    Also read the manual and look at p.20. All your answers are in those two sources.

    Most of this is trial and error anyway. Try bandwidths of 5 (1/12th) and 10 (1/6th) and see if they work. Or you can start smaller. Most of mine were fatter peaks.

    You'll get the hang of it!
     
  12. PaulT

    PaulT Supporting Actor

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  13. al lout

    al lout Stunt Coordinator

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    Thank you, all.

    I was playing around w/ the BFD. Here is my chart after I applied 6 filters. I took the measurements on increment of 1hz. It took me a long time but I was able to pinpoint which freqs I need to apply the filter.
    [​IMG]
    For some reason, at 47hz - 51hz I was not able to add boost. It doesn't matter how much gain I added, the responses are the same. Any tips on how can I make it more better? Thanks all. Time to insert some movies and let it rips...

    Al,
     
  14. PaulT

    PaulT Supporting Actor

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    that will be a null from the room response - probably nothing you can do aside from moving the sub - that would mean starting the measurements again and possibly having another dip or peak somewhere else.....

    In all honesty I would cut your peak at 56Hz and search this Forum for 'House Curve'- see my response below.

    You have a good start on a pretty flat response, you may like it better with a rise in response as you go lower in frequency. Listen for a while as you have it, then enjoy the tweaking [​IMG]

    [​IMG]
     
  15. al lout

    al lout Stunt Coordinator

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    Thanks PaulT for the tip. After reading more about house curve, I decided to tweak some more. Here is what I come up with.
    [​IMG]
    It's not quite smooth yet. Noticed that I measured the FR in 1hz increment. I've used 7 filters to get to this. Wonder what else can I do to improve without using too many filters.

    Al,
     
  16. JasonCI

    JasonCI Stunt Coordinator

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    al lout-

    Working in 1-Hz increments is overkill. Its only benefit is finding the center frequency to set the filter. In addition to being very labor intensive it emphasizes negligible volatility IMO. It also looks like you're introducing more volatility by using too many filters or filters that are too wide and close together.

    Using frequencies in 1/12th octave intervals is more than adequate. Just use the whole frequency closest to each 1/12th octave frequency. As PaulT recommended, get the PEQ spreadsheet. Then, concentrate on peaks and nulls that deviate more than +3 dB or -3 dB from the normalized level. Cut the peaks that deviate more than +3 dB's. Boost severe nulls sparingly, no more than +6 or +7 dB's.

    One more thing. I advise turning it down a lot. You can over heat your driver by playing them so loud. Your highest SPL comes at 56 Hz and your lowest is around 88 Hz. Before you take your readings play a 56 Hz sine wave and lower your master volume until you get an SPL around 100 dB's. This will give you an SPL of approx 65 dB's at your most severe null at 88 Hz.

    PS-SPL values for EQ'ing should be recorded with only your front right/left speakers and your sub active. AFTER correct phase is determined.
     
  17. al lout

    al lout Stunt Coordinator

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    Thanks, JasonCI. Here's what I've got after applied 6 filters. Measured at RL -25db with Sub+Mains turned on.
    [​IMG]
    I can't seemed to get the peak at 56hz to go away unless I applied the gain of -12db. I still need a cut at 42hz. Anyway, I'll play with it some more in the weekend. Now is the time for some movies. Thanks all.

    Al,
     

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