Suggest some appropriate BFD filters...

Discussion in 'Home Theater Projects' started by Jeffrey Stanton, Sep 30, 2003.

  1. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I do not have a test disc yet but my amp has some subwoofer test tones (from 35 to 250 Hz). Will have to guess for 16-35 Hz or ignore for now.

    Here's the uncorrected rat shack numbers:

    35 Hz: 93 dB
    39 Hz: 93 dB
    44 Hz: 93 dB
    50 Hz: 92 dB
    56 Hz: 92 dB
    63 Hz: 91 dB
    70 Hz: 93 dB
    79 Hz: 93 dB
    88 Hz: 88 dB
    99 Hz: 85 dB
    111 Hz: 78 dB
    125 Hz: 78 dB
    140 Hz: 74 dB

    All speakers set to SMALL.
    LFE crossover point: 90 Hz
    Sub: Acoustic Visions 5 c.f., two 2200 gram PRs, 18 Hz tune, 1400 watt amp

    Can anyone please give me an interpretation of this curve and some likely filters to apply?

    Thanks,

    Jeffrey Stanton
     
  2. Geno

    Geno Supporting Actor

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    you are running pretty flat according to those #'s. why would you want to change anything?
     
  3. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Because I paid $110 for my BFD and by god I'm going to use it for something. Surely I'm a dB or two off somewhere!! I thought ALL rooms had resonances, & surely I do not have an "acoustically perfect" room, that would sure suck & I've never heard of such a thing.

    I MUST have some numbers to feed my BFD...[​IMG]
     
  4. Geno

    Geno Supporting Actor

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    I do not have an "acoustically perfect" room, that would sure suck????????????????


    haha i can see that upgraditis has started giving you mental problems too [​IMG]

    well im sure you will get a bit different results when you get the calibration disk.


    I actually plug an oscilator straight to my sub amp and do my readings that way. I can get down to 1 Hz [​IMG] [​IMG]

    if you HAVE to use the BFD, then id say get everything from 35Hz to the xover point at one # like 93 db's.
    again by looking at your #'s you are very very close to being flat.
     
  5. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    OK. I wondered what I was supposed do as I approach the crossover point, are things SUPPOSED to roll-off as I approach 90 Hz or am I supposed to keep that area close to the crossover point as flat as possible compared to the rest of the curve(NOT rolling off). I take it from your response that I want to keep it flat (say, 93 dB like you said...)instead of rolled off.

    What about everything under 35 Hz? Just leave those frequencies alone until I got tones to cover them.

    Thanks

    Jeff S.[​IMG]
     
  6. Geno

    Geno Supporting Actor

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    yes, depending on the crossover and all that, there should be a roll off. Im pretty sure they START to roll off @ the Xover point, so if you are flat to 90Hz then you should be fine.

    everything UNDER 35 Hz?, well yeah, just wait. there will be some point where the db's roll off, but you said its tuned to 18Hz, so it really shouldnt drop off till then.

    if im wrong in any of this, someone please correct me
     
  7. Wayne A. Pflughaupt

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    Jeffery,

    I suggest keeping the main L/R speakers on when you do your test tones. That may affect the readings around the crossover point (i.e., some equalization may be needed).

    I’m guessing you have a Yamaha? I didn’t have as much luck using their tones as I did with a disc with sine-wave signals (not to mention, the 35Hz limit).

    After you get your test disc and take readings with the mains on, I’m sure you’ll have something to equalize. [​IMG]

    Regards,
    Wayne A. Pflughaupt
     
  8. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    You're basically flat from 35 to 80 Hz and you're complaining??!! Consider yourself lucky. Get some test tones that go from 35 down to 20 or so Hz, and also apply the correction numabers to those RS meter readings. THEN you'll have your challenge laid out.
    Seriously, you are flat (depending, of course, on the corrected RS meter readings) in the frequencies where nearly all music bass is located and you are indeed fortunate.
     
  9. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Hey, what happened to the edit button? I wanted edit that post to correct a spelling, and I don't see the edit button. What gives, admins?
     
  10. Richard Greene

    Richard Greene Stunt Coordinator

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    What signals were used and where were you measuring from?

    The measurements are so good they suggest you were using pink noise or warble tones, measuring outdoors where there are no standing waves, or you placed the microphone a few inches from the subwoofer to eliminate room effects rather than locating the mic where your ears would be located!

    The signal used should be sine wave tones spaced no more than 1/6 octave apart and the microphone should be placed on a tripod where your ear would be located (and if you want to get more sophisticated, make a second measurement
    about 8 inches away and average them to simulate left and right ears combined).

    No subwoofer/room I have ever heard of or measured had an in-room frequency ressponse of +/-1dB as you measured up to almost 90Hz. The best equalized bass frequency response I have ever measured at a listening position was about +/-3dB.
    This was measured using 1/6 octave spaced sine wave tones.
    The deviations were somewhat worse using a slow sine wave sweep.
     
  11. Jones_Rush

    Jones_Rush Stunt Coordinator

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  12. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Richard:

    I thought there was something wrong with those numbers.

    I used the low frequency test tones generated by my DSP-A1 amp. I put my SPL meter on a tripod at listening postition. I figured those numbers weren't right. Guess I can't use those Yamaha test tones,huh? I have no idea specifically what kind of test tones they are, they're just referred to as "low frequncy test" tones. Hogwash. Or maybe the Tumult got fried during testing (it was not a pleasant experience), I would hate to hazard a guess right now. Need test disk. Back to drawing board...[​IMG]

    Thanks,

    Jeff S.
     
  13. Geno

    Geno Supporting Actor

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    I would assume if it said that it gave you a 40 Hz signal that it wasnt pink noise and it actually was a 40 Hz sin wav.

    "The signal used should be sine wave tones spaced no more than 1/6 octave apart"
    I think thats what came out of his receiver. And I think that he's really got that flat of a response.
    we'll see after he gets disk
     
  14. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Geno: I figure either there's something wrong with the type of test tone generated by the Yamaha or there's something wrong with the sub. What point would there be to putting test tones on an amp for low frequency testing if they weren't any good for that. I think it more likely there something wrong with the sub. During the testing it sounded like it was going to pound itself to death & shake the drywall loose in the process. As the test progressed it got louder and louder as it got down to 35 Hz. Did not sound good at all. I assumed this was normal. It may be for all I know. And then again the sub may be malfunctioning in some way as yet inconceivable to me at the present time. FUBAR'ed.

    I will get test disc and we shall see. I have no idea why Yamaha would furnish internal low frequency test tones that ONLY GO DOWN TO 35 Hz. That's ridiculous. Maybe it's because none of their subs go that low...
     
  15. Geno

    Geno Supporting Actor

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    Maybe it's because none of their subs go that low...

    exactly [​IMG]
     

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