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JBL L100 A Polarity Question

tonefoto

tonefoto

AK Subscriber
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Please excuse the question that is asked so often. I could not find a suitable answer, and checked the specialty hertige forum first. I have a pair of JBL L100A speakers, I think they're A models since the JBL logo is red and the serial numbers end in A.

My question; I have 2 different Woofers, one is 123A-1 (positive polarity) the other is 123A-3 (negative polarity). When I opened them up, both had black leads to the red woofer post and green leads to the black posts.

Do I need to reverse the positive polarity 123A-1 to have the green lead to the red woofer post and leave the negative polarity 123A-3 black to the red woofer post?

I'm confused about the polarity difference ramifications on these drivers and appreciate anyones' help in sorting this out.
 
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tonefoto said:
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My question; I have 2 different Woofers, one is 123A-1 (positive polarity) the other is 123A-3 (negative polarity). When I opened them up, both had black leads to the red woofer post and green leads to the black posts.

Do I need to reverse the positive polarity 123A-1 to have the green lead to the red woofer post and leave the negative polarity 123A-3 black to the red woofer post?
Click to expand...

Determining polarity for two different woofers in a pair is dead simple. Just use a 1.5V battery to the box's input terminals and see which way the cone moves. Make them both the same.

Determining which way they _should_ move is a little tougher. Which one should have been in that vintage L100? Make the other one the one that gets switched and I think you will be as "correct" as can be, given the age and lack of documentation of those. (Assuming that the pair are from the same version.)
 
test polarity in the box

Thanks for your reply, I did find the polarity difference by testing each woofer out of the box. The newer version woofer (123A-3) is reverse polarity, or negative, the other is positive. I'm uncertain as to which one is original. That's why i posted the question, but it sounds like you're saying I could bypass the confusing wire connections (one version of this speaker uses green for positive the other uses black) by just testing polarity while they're hooked up to the crossover in the cabinets by testing at the speaker inputs. I should then connect the corresponding woofers so that both push in the same direction. Does it matter whether they're pushing in or out? The 123A-1 pushes out when its tested to the 1.5V + side, the 123A-3 pushes in.
 
tonefoto said:
Thanks for your reply, I did find the polarity difference by testing each woofer out of the box. The newer version woofer (123A-3) is reverse polarity, or negative, the other is positive. I'm uncertain as to which one is original. That's why i posted the question, but it sounds like you're saying I could bypass the confusing wire connections (one version of this speaker uses green for positive the other uses black) by just testing polarity while they're hooked up to the crossover in the cabinets by testing at the speaker inputs. I should then connect the corresponding woofers so that both push in the same direction. Does it matter whether they're pushing in or out? The 123A-1 pushes out when its tested to the 1.5V + side, the 123A-3 pushes in.
Click to expand...
The problem occurs at the crossover frequency between the woofer and midrange. If the polarity between the two is incorrect you will get a hole in the response curve.
 
Polarity Problem

So, there may be a problem with the crossover messing with the midrange? Can anyone help in connecting these speakers correctly? I appreciate the explanations, but would like to listen to them as they were intended to operate. I don't have the expertise to dig deep into this, but if anybody could simplify a remedy it would be greatly appreciated.
 
As you will discover over at Heritage, a definitive answer is unlikely. Your ears are smarter than you think. In any case, it's entirely possible JBL reversed polarity between the mid and woofer deliberately for a desired effect. They may actually sound better the other way.
 
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Here's a comparison of the crossovers for each.
 
Jeffery said:
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Here's a comparison of the crossovers for each.
Click to expand...
As you can see, in the original crossover, the low (black) input goes to the high (+) side of the woofer. On the later crossover, the low input goes to the low (-) side of the woofer so the reverse polarity of the -3 woofer makes the phasing of the woofers the same.
 
It looks like I have a pair of L100A Late Models. The 123A-3 is original and the 123A-1 must've been replaced at some point. Is it correct to assume that the black woofer lead is positive and the green is negative, and both should have the positive leads attached to the positive posts on the woofers?
 
Black is always considered low or (-). I am beginning to go nuts following these phases. For the -1 woofer put the black wire on the red (+) woofer terminal.
 
Thanks all for the illumination on this. I'll connect the 123A-3 to the black lead and the same for the 123A-1 and try it.
 
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