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Need Crossover/high pass filter...

Discussion in 'Archived Threads 2001-2004' started by Jones_Rush, Mar 10, 2001.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

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    I have just found out a disturbing fact.
    I was sure that when using my speakers as "small"
    with my Denon AVD-2000, I was getting only above 80hz signal to my speakers (that's what the manual say), apparently not, the roll off of the Denon is very slow, and I am still getting +6db at 42hz (due to room mode, but still), I figured out that it won't help much to use the Behringer to EQ the sub below 80hz when my main speakers are giving me +6db at 42hz when running in "small" mode.
    Is there a cheap crossover/high pass filter which I can use to completely KILL their SPL below ~75hz ? without hurting too much the above 80hz frequencies. I know I can use some FMODS high pass in-line filters of 150hz, but wouldn't they hurt SPL levels too much at the 80-140hz frequencies ?
    Btw, are sine waves effective enough to accurately measure a room ? I am getting 9db differences between 1khz and 1.5khz, also, I just measured my 5.5" woofer (scanspeak revelator) to do 19hz -3db at 80db at the listening spot (without using correction values), how can a 5.5" woofer be flat to 19hz -3db ? what is going on? are the sine waves "fooling" me ?
    (If I will add the correction values, then I am getting 19hz +4db!!!)
     
  2. Timmy

    Timmy Stunt Coordinator

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  3. Jones_Rush

    Jones_Rush Stunt Coordinator

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    "I agree this sounds weird. I would tend to question the test setup and tone generation. What was the source of the tones? Was your sub getting some "directed" bass?????"
    The source of the tones was a computer software named "Marchand Function Generator".
    I have no sub, I used my bookshelf speaker (with a 5.5" revelator driver) to emulate a sub performance, I knew that my bookshelf can extend very low, but when I measured it placed on the floor, where I will eventually place the sub (when I'll have one) it was -3db at 28hz. When I placed it back on it's stand, suddenly I got -2db at 19hz. I always thought that a speaker on the floor will give more bass than a speaker on a stand...
    "To sharpen the roll off of FMods, you can place 2 in series."
    If one FMOD gives me a slope of 12db per octave, will 2 in series give me 24db per octave ? also, won't two FMODs in series muddy the sound too much in comparison to 1 FMOD or none at all ?
     
  4. Richard Greene

    Richard Greene Stunt Coordinator

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    If you send a 20Hz. test tone to a small driver, you'll
    probably be hearing and measuring the harmonic distortion
    at 40/60/80Hz. rather than the original sine wave tone of 20Hz. -- the sound meter measures all noises and doesn't care what frequency they are at (including room noises when the sub makes things rattle).
    I don't believe you can place two FMODS in series for a 24dB/octave slope -- I tried that many years ago when I first bought a few pairs of FMODS and it did not work -- sound quality was awful. (If I'm wrong, I'll be a
    happy guy because I own four pairs of FMODS.)
     
  5. Timmy

    Timmy Stunt Coordinator

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    I think Richard has the answer, harmonics distorting the SPL reading.
    Series'd FMods should not "distort" anything. Whatever is left from the crossover point's rolloff on the first one, the second one will roll off the roll-off-leftover another 12db. (man; try saying that 3 times fast [​IMG] )
    I know someone using series'd FMods that is not having the described problem; but it may be dependant on specific equipment and connection methods.
    ------------------
     
  6. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Richard said:
    "If you send a 20Hz. test tone to a small driver, you'll
    probably be hearing and measuring the harmonic distortion
    at 40/60/80Hz. rather than the original sine wave tone of 20Hz. -- the sound meter measures all noises and doesn't care what frequency they are at (including room noises when the sub makes things rattle)."
    Then Timmy said:
    "I think Richard has the answer, harmonics distorting the SPL reading."
    Well, a simple test can prove exactly what I am measuring.
    I intend to use "Spectra Plus" analyzer to analyze exactly which frequencies are being measured when I play a 20hz sine wave signal. If the 5.5" woofer produce above 20hz signals and misleading me, the program will easily show it.
    I will post the info when I'll have it...
     
  7. Patrick Sun

    Patrick Sun Studio Mogul

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