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Thread: How to determine proper JBL polarity

  1. #16
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    Quote Originally Posted by engineerjoe View Post
    It's pretty standard now I believe, that pin #2 on a XLR input is positive. I swear when I got started years back, pin #3 was hot? I found some old adapter XLR to stereo 1/4" cords I made many years ago and I had to swap the hot wires to work with modern stuff.I just was making a new system and also found that I had some of my drivers out of phase. So this issue seems current for me. I got a pair of JBL/Selenium 2" drivers to test. Someone removed the rear cover on one and rotated the diaphragm 90 degrees. It wasn't blown just re-installed incorrectly. I got lucky there. So while inside I tested for polarity. I just used an old AAA battery very quickly to observe diaphragm movement. I've never done that before and I'm wondering if I should continue that practice? On my normal JBL cone woofers, I feel that quick pulses of low DC volts (1 volt) won't hurt them. I don't hold on long enough to heat anything up. Just to double check polarity.
    Ok, let's do the math: Assuming a fully charged AA or AAA cell, you apply a power of 1.5[V]˛/8[Ω] = 0.28 watts. That really won't hurt, even after a longer period. But, as I've never done it before with a disassembled CD: Is any diaphragm movement clearly enough to see?

    Best regards!

  2. #17
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    Quote Originally Posted by Kay Pirinha View Post
    Ok, let's do the math: Assuming a fully charged AA or AAA cell, you apply a power of 1.5[V]˛/8[Ω] = 0.28 watts. That really won't hurt, even after a longer period. But, as I've never done it before with a disassembled CD: Is any diaphragm movement clearly enough to see?

    Best regards!
    I saw it move! Most guys back in the day used a 9 volt to a 1/4" plug because it was so easy. I was warned not to use it on horn drivers for prolonged periods. So I stayed with that.
    Using that formula, I think I will continue when inside a driver of unknown polarity.
    I was going on and on about sound systems without knowing if the OP was into large sound systems, studio, or just for home stereo use! Very sorry.
    I like to ramble.

  3. #18
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    I use a 9 volt as well. It moves big cones enough that you can clearly see their direction. I doubt keeping it hooked up very long will do any damage to low end drivers, just not enough wattage.
    For compression drivers, I will unscrew the diaphragms. Hit terminals quickly with 9 volt (could probably get away with 1.5v). The diaphragm will either stay put or jump slightly. You won't see any movement of the actual diaphragm surface and I'm guessing if you did, you'd probably be in trouble. I keep it quick, DC (0 Hz) isn't anything a mid or high driver like.

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