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Crossover Schematic Speaker Polarity

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  • Crossover Schematic Speaker Polarity

    I have put together an econowave using the D220Ti and large Advent woofers in an Advent 4002 box and using the Jackgiff 3/18/08 schematic shown below. Sound is "off" and I am going to investigate how I wired the high frequency driver, as I have found another schematic (and others also) where the HF driver is wired in reverse polarity. I am wondering if one can look at the schematic and determine which would be the correct way to wire the HF driver, what is the reasoning for doing it? What is the result, soundwise, when one does this?

  • #2
    You're probably aware of the loss in bass if you hook an amp up to only one speaker (of a stereo pair) "backward" (the wrong polarity). If a bass track was mixed into both channels, and one of your speakers is wired "out of phase", and you place the speakers next to each other - as the cones move, ONE will be moving out while the other is moving in, and the sound waves (moving through the air) will just kinda teeter-totter back and forth between the woofers, rather than both of them moving together in unison - driving the wavefront forward intothe room.

    Well, a similar situation exists when 2 drivers are handing off the freq. spectrum to each other. Right at the Fc (crossover freq.), BOTH are trying to reproduce the same freq. at the same volume. Just the diffs. in physical "depth" of the voice coils (between, say, a dome tweeter and an 8" woofer - where the V.C. might be 2" behind the baffle) can cause the sound (at the Fc) to be out of phase (this is freq. dependent).

    ALSO, caps and coils (but not resistors) will "rotate" the phase (forward or backward). So if you had 2 identical drivers (say a pair of 3" or 4" FR drivers - so their V.C.s WILL physically be in the same plane) fed through 2 filters (one an HP - high pass, and one an LP), THEY could end up out of phase at their Fc due to the filters "orders" (parts count and topology) and component values.

    Their are so many variables, that there's no simple way to state whether a (or which) driver in a multi-way passively-crossed system should be wired (polarity-wise) w/respect to the others.

    Any "reputable" XO design software (like Jeff Bagby's "PCD" - and its "workalikes') uses phase data embedded into .frd/.zma files to track all these issues and calculate the phase of each driver in a system AND how the drivers will "sum". Pretty cool, eh?

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    • #3
      The crossover is 2nd order/2nd order, which results in 180 degrees total phase shift between the drivers at the XO frequency. That often requires reversing the tweeter polarity to prevent a cancellation dip centered at that frequency. It's a bit odd that a 2nd order/2nd order crossover was used. It's been pretty much standard practice for decades to use a 2nd order LP/3rd order HP, which eliminates the potential for a polarity issue and provides much better HF driver protection, for only the added cost of a capacitor.
      Reverse the polarity of the tweeter on one speaker, try them both, use the wiring configuration that sounds better.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        I had to refoam the woofers on these and am now ready to get back with fiddling with them. I know I did these within the last 10 years, they are the correct thin wall type for the Large Advent woofers, I guess they just don't hold up. Anyway, I have confirmed that the crossovers were per the JackGiff design, with the HF leads reversed. But one thing I'm not sure about is how the L-pad is wired in. Does it matter if the L-pad is wired with the 1 and 3 lead reversed in this design or does that just mean that the rotation is different with no effect on the end result?

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