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Thread: LE5-12 Polarity

  1. #1
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    LE5-12 Polarity

    Hi everyone, first post and hope you can help me. I own a pair of 4312's which I've had from new since 1984. Only today I downloaded a speaker polarity test app on my phone and out of curosity tested my speakers. I was surprised to find that the midrange drivers tested negative whilst the tweeter and woofer tested positive. This was the same for both left and right.

    According to this manual the white wire is the +ve connection to the midrange driver https://manuals.harman.com/JBL/HOM/Technical%20Sheet/4312%20ts.pdf

    The image is my arrangement. The connectors are male and female so obviously can only go one way but I can't see which is +ve or -ve. Is there a way of determining which speaker terminal is +ve and -ve? I can't see any colours or markings.

    Name:  LE5-12.jpg
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    Thanks

    Don

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    Senior Member RMC's Avatar
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    Hi Don,

    Welcome aboard the Lansing Heritage.

    Your link to 4312 didn't work for me, computer tells me some security issue involved...

    First pic see my arrow, isn't that a red dot indicating polarity?

    Name:  JBL LE5-12_LI.jpg
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    Second pic is a JBL document indicating polarity conventions for transducers, see arrows for relevant info.

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    Third pic is the wiring for the 4312A version (i don't have it on-hand right now for 4312 without A) but the midrange driver seems to be wired the same as your LE5-12, see the underlined white wire and the + mention on the driver (the white/black wire being for the negative).

    Hopefully this will help you. Regards,

    Richard

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    Hi Richard,

    Thanks for the welcome and your reply. Iíll have to have a closer look at that terminal in the morning to see if itís indeed a red mark or just a rusty spot. Itís late here in Sydney. If it is a red mark and the positive wire is correctly connected I wonder why the speaker polarity app detects it as negative and the tweeter & woofer as positive? Strange!

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    I found this document on another thread which gives me a clue. It says a positive signal to the male terminal gives forward cone motion. It seems mine may indeed have been wired incorrectly from the factory?

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  5. #5
    Senior Member RMC's Avatar
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    Don,

    Don't neglect the possible crossover effect on driver wiring.

    Not necessarily miswired at factory. Polarity may have been inverted intentionaly on mid since this is a 3-way system and/or because a 12 db/oct. crossover is used, as this would allow the signals to add properly at the crossover frequency. Regards,

    Richard

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    Thanks for your input Richard. Iíve got no complaint with the way the speaker sounds as it is. However, I am curious about what they might sound like with the polarity switched. Is there any possibility of damaging the drivers if I try?

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    JBL made a lot of systems with what would seem like weird polarity - it's driven more than a few folks insane trying to replicate the systems from scratch. Not only do the crossovers use what appears to be reverse polarity on certain drivers (for the reason RMC alluded to previously) but also produced drivers that had + signal produce both forward and rearward cone motion. That there are male and female spades on the wires, to make hooking the driver up with the wrong polarity more difficult, is likely a hint or clue.

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    Quote Originally Posted by JeffW View Post
    That there are male and female spades on the wires, to make hooking the driver up with the wrong polarity more difficult, is likely a hint or clue.
    A big hint Iíd say and one that Iíll take. Thanks for your input gents.

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    Senior Member grumpy's Avatar
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    ... and no, it will not harm the driver to try, but it is by design:

    4312LR.pdf

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    Iím still confused by the engineering standard document I posted earlier which contradicts the cone movement Iím seeing.

  11. #11
    Administrator Robh3606's Avatar
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    The LE5 is connected reverse polarity with the other drivers. If you look at the wiring diagram posted for the system it makes sense. The male terminal on the driver is connected to the White/Black which in turn goes to the black in the speaker system.

    Rob
    "I could be arguing in my spare time"

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    Thatís right but it does make you wonder why they use the language they did in the engineering standard document for the LE5-12.

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    You are here->
    Quote Originally Posted by JeffW View Post
    JBL made a lot of systems with what would seem like weird polarity - it's driven more than a few folks insane

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    Senior Member DavidF's Avatar
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    Quote Originally Posted by DonR View Post
    That’s right but it does make you wonder why they use the language they did in the engineering standard document for the LE5-12.
    JBL models of this era (generally) wired the leg from the crossover to the drivers in a consistent configuration. The solid wire to the driver connected to the positive terminal of the driver, the black stripe or solid black connects to the negative terminal. Green was used for the woofer, white for the mid, yellow for the high, and orange for the ultra high in 4-ways. Likely keeping this wire configuration consistent was needed for the assembly lines.

    If you follow the "positive" leg of the three drivers in the Tech Sheet you will see that the polarity inversion was made back at the connections at the speaker input. The woofer and tweeter positive terminals are fed from the speaker black input, the midrange from the speaker red input.

    Once you can get comfortable with this wiring configuration you need to allow for JBL's standard whereby a positive signal applied to the "positive" terminal of the drivers actually results in an inward movement of the cone/diaphragm. Contrary to expectations, of course.

    There are characteristics of certain crossover slope designs that result in a phase shift in a narrow band around the crossover point. The phase shift can cause significant response variations due to the two drivers operating across this frequency point. Wiring one of the drivers in opposite polarity can mitigate some, but not all, of the response variations. So wiring the mid in opposite polarity won't harm the driver but will affect the response of the system as originally designed.
    David F
    San Jose

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    Senior Member RMC's Avatar
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    Don,

    RE "Iím still confused by the engineering standard document I posted earlier which contradicts the cone movement Iím seeing."

    I think your confusion can be remedied from the following non-technical explanation, where you have to distinguish between two situations.

    First, the polarity indicated in the Engineering Standard is for the LE5 mid driver alone. If you took it out electrically from the system and tested it for polarity you would get the same result as in the Engineering Standard.

    Second, when used in a system (e.g. 3-way) the LE5 polarity may be changed by the design engineer for technical reasons related to the crossover (such as having the signals add properly at the xo frequency). The engineer determines what's best in terms of actual polarity, in view of xo used.

    Some speaker systems have driver polarity inversion and some don't, there's nothing wrong per se either way. It all depends on the cicumstances of each particular case. So the cone movement you see may be different than what you see in the Eng Std because one has been spec as a driver alone, while the other's polarity spec is as driver used in a system which in that case requires driver polarity inversion to perform best.

    Hopefully the above will help you understand better. Regards,

    Richard

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