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Impedance sweep results on sealed box

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  • Impedance sweep results on sealed box


    So in theory a sealed box should have only 1 impedance spike, correct?

    But for the life of me, i can't figure out why i have 2. Both left and right side have identical impedance sweep results

    The cabinets are all air tight, foam gaskets checked and reapplied extra weather stripping tape just in case. The tweeters and woofers are very well fastened (birch ply) with good locking strength; no screw spin-out problems like in typical MDF

    Has anyone measured their sealed air tight cabinets and got a similar result before?

    I searched past links about the driver cones themselves leaking air (?) - is that true?

    Is there anything else i should check. Thanks for chiming in

  • #2
    Is this sweep done with just the woofer connected? This looks like it is the full system impedance.

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    • #3
      Yup it's the full system impedance

      I think I made a mistake

      Once i removed the port plug, i saw 3 spikes. Plugging back the port gave the 2 spikes. Seems to be normal, right?

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      • #4
        Correct. The second spike is from your tweeter.

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        • #5
          More precisely (while your tweeter might not hand off acoustically to your woofer at just over 1kHz), this is where the rising impedance of your filtered (low passed) woofer hands off to the filtered (high passed) tweeter. SEEMs a bit low, but fairly typical.

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          • #6
            It is unusual to see the woofer impedance rising that fast. My guess is the Le is pretty high, at least 4.0
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              There's a crossover in that sweep, I wouldn't speculate on the woofer Le.

              The important bit for the box is below 100Hz, center of the peak is Fb sealed, the lowest point of the dip between the peaks when ported is your ported Fb.
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music
              Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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              • #8
                S o l u t i o n ! ?

                Why not just tell us your drivers and XO components, and a sim will verify your Z-sweep?

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                • #9
                  A plus, it looks relatively free of wrinkles, other than a small one around 150hz.
                  http://techtalk.parts-express.com/fo...khanspires-but
                  http://techtalk.parts-express.com/fo...pico-neo-build
                  http://techtalk.parts-express.com/fo...ensation-build

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                  • #10
                    Add more stuffing (damping) inside the enclosure and watch the woofer impedance at resonance shrink.

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