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Thread: Is this even technically possible...

  1. #1
    Senior Member Ed Zeppeli's Avatar
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    Is this even technically possible...

    ...without some kind of notch filter?

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    I did close measurement (3") centred on the dustcap to see how my cabinet was performing. Looks pretty good I must say until the 50DB DROP @ 795 HZ!

    So is this even possible without some sort of notch filter engaged? Bad woofer? Odd mic anomaly? Something else I'm missing here? I'd bypassed all EQ and any feedback elimination within the driverack is off.


    I will continue troubleshooting and checking the other side etc but any suggestions would be appreciated.


    Thanks,

    Warren
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  2. #2
    Senior Member srm51555's Avatar
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    I just read today that if you have a dip at the crossover frequency you may need to invert the phase of one the drivers. But I am very new at this so others may chime in with a better answer.

    See step four in the link below.

    https://www.minidsp.com/applications...eo-2-way-xover

  3. #3
    Senior Member Ed Zeppeli's Avatar
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    That's the thing. I changed the crossover to about 1k and this is a single close range measurement of the 2234H driver. All other drivers muted.
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  4. #4
    Senior Member grumpy's Avatar
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    That's deep and narrow, even for an intentional passive notch filter or driver cancellation.
    This is in-box? and no crossover? I'd try moving the mic ... but that looks suspicious.

  5. #5
    Senior Member 1audiohack's Avatar
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    Quote Originally Posted by grumpy View Post
    That's deep and narrow,...
    Yeah if you don't have a hard reflection with a path length of about 8.5" like the back of an uninsulated box or a box buzz, thats a mystery.

    My measurements of standing wave notches reveal that they are only several Hz wide and deep indeed.

    Swap drivers?

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  6. #6
    Senior Member Ed Zeppeli's Avatar
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    Quote Originally Posted by grumpy View Post
    That's deep and narrow, even for an intentional passive notch filter or driver cancellation.
    This is in-box? and no crossover? I'd try moving the mic ... but that looks suspicious.
    Suspicious.

    My thoughts exactly. This is in-box, no passive crossover but it's running through the dbx Venu360, which is why I suspected some sort of feedback eliminating notch. That's what I looked for first but as mentioned I've disabled all EQs, moved the crossover point on the dbx to +1000hz and made sure no other filters were active in the dbx.

    I could try moving the mic and testing the other side under the same circumstances.


    Warren
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  7. #7
    Senior Member tjm001's Avatar
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    Quote Originally Posted by Ed Zeppeli View Post
    ...without some kind of notch filter?

    Name:  L2234Woof.jpg
Views: 260
Size:  33.0 KB


    I did close measurement (3") centred on the dustcap to see how my cabinet was performing. Looks pretty good I must say until the 50DB DROP @ 795 HZ!

    So is this even possible without some sort of notch filter engaged? Bad woofer? Odd mic anomaly? Something else I'm missing here? I'd bypassed all EQ and any feedback elimination within the driverack is off.


    I will continue troubleshooting and checking the other side etc but any suggestions would be appreciated.


    Thanks,

    Warren
    Well, it's been a long, long time since I did this kind of thing back in my apartment in Alexandria Virginia back in 1965 or so. But it's pretty much the same thing I experienced back then. There are null areas all over the place that are unexplained. The shape of the room, the shape of the dust cap, the shape of the mike. Who knows. Reality is different than theory is all I can say.

  8. #8
    Senior Member bldozier's Avatar
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    Could be an electronic condition 😐

  9. #9
    Senior Member Ed Zeppeli's Avatar
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    I'll run some more sweeps today and report back.
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  10. #10
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Ed Zeppeli View Post
    Suspicious.

    My thoughts exactly. This is in-box, no passive crossover but it's running through the dbx Venu360, which is why I suspected some sort of feedback eliminating notch. That's what I looked for first but as mentioned I've disabled all EQs, moved the crossover point on the dbx to +1000hz and made sure no other filters were active in the dbx.

    I could try moving the mic and testing the other side under the same circumstances.


    Warren
    If you suspect that the DBX is doing something odd… Try it without the DBX.


    Widget

  11. #11
    Senior Member Ed Zeppeli's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    If you suspect that the DBX is doing something odd… Try it without the DBX.


    Widget
    That...

    ...would have been my next step. Today I moved the mic over to the other cabinet at the same position on the cone and got a strikingly similar dip at 786hz. I tried a bunch of other things and then moved the mic a foot further back. Dip gone, back to smooth response.

    I was thinking there may be some oddities by measuring so close to the cone but wasn't suspecting such a steep notch.

    Lesson learned....audio is weird.
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  12. #12
    Member sebackman's Avatar
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    not close enough

    Hi Warren,

    Try moving the tip of the mic closer to the cone.

    3" is not close enough for "near field" and not far enough for "far field". That is probably why you get some weird cancellations. Maybe from the mic it selves or from the mic stat.

    When I do near field I set the mic only 5mm from the center of the woofer cone, dustcap. To get "far field" you normally need to be at least about 20" out.

    Kind regards
    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  13. #13
    Super Moderator yggdrasil's Avatar
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    If my memory serves me right nearfield measurements should be taken at 1/2 inch (1cm).
    Johnny Haugen Sørgård

  14. #14
    Senior Member Lee in Montreal's Avatar
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    Looks like a phase cancellation... What happens if you reverse the polarity of one of the drivers?

  15. #15
    Senior Member grumpy's Avatar
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    I believe only one driver is operating (post #3).

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