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Thread: LE85 Polarity

  1. #1
    Senior Member Beowulf57's Avatar
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    LE85 Polarity

    Is the LE85/2420 a negative polarity transducer (as in the diaphragm moves inwards in response to a positive going signal)?

  2. #2
    Registered User paragon's Avatar
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    +-

    Yes i think so, + on the black terminal gives forward movement on dia.
    I also drive my 2441 the same.

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    The LE-85/2420 is a positive transducer.
    http://www.jblproservice.com/pdf/Stu...ries/4333B.pdf

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    Senior Member Beowulf57's Avatar
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    Oops...we have conflicting info here? Paragon says it's negative and you say positive Domino? How does that 4333B spec indicate that the LE85/2420 is positive?

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    RIP 2011 Zilch's Avatar
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    1) Negative

    2) Measure

    3) It doesn't matter

    http://www.jblpro.com/tech-library/J...eN1V12C_v5.pdf

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    Senior Member Beowulf57's Avatar
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    Quote Originally Posted by Zilch View Post
    1) Negative

    2) Measure

    3) It doesn't matter

    http://www.jblpro.com/tech-library/J...eN1V12C_v5.pdf
    Negative...thanks. The pdf doesn't seem to list the LE85/2420:

    "Compression Drivers: the following models are
    negative:
    2402H 2404H
    2405H 2426H, J
    2427H, J 2446H, J
    2447H, J 2450H, J
    2451H, J"

    It does have some significance (I think...) as I am trying to work out the phase relationships among my D130/LE85/2405H drivers using the LX5 network. The network service bulletin for the LX5 notes that the polarity of the connection should be reversed to the LE85, the network service bulletin for the 3115 does not. I do not know why...different horn lengths/and thus different driver offsets not noted in the service bulletins?

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    I'm sorry I have made a mistake. The 2420 is negative just like the 136A or 2231/2235. In my L300's the 136A woofers and the LE85 are both wired red to red and the end result, confirmed with my Cricket, is that they are negative. both moving "back" or negative with a positve signal fed to the red terminal. As you can see in the 4333 crossover diagram the woofer and midrange are hooked up with the same polarity. The 2235 is documented as a negative transducer in the JBL bulletin therefore the 2420 is also negative. Confusing!!

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    Now I'm really confused! According to the JBL polarity bullitin the 2405/077 is negative. That being said according to my Cricket hooked up to the red terminal of my L300 the readings are: woofer negative, midrange negative, 077 positive. Now according to the network schematic the 077 "red" is hooked up to "black input" and the 077 "black" is hooked up to "red input". Now shouldn't that mean that the polarity reading I get for the 077 with the Cricket be negative also?? It now appears to me that my 077 wiring is reversed somehow.

  10. #10
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    After looking at this again I think I have the wiring right all along. L300 woofer movement negative, midrange movement negative, 077 tweeter movement positive, all with positive signal input to the speaker. Sound right??

  11. #11
    Senior Member Beowulf57's Avatar
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    Thanks Zilch...the 2nd reference is useful.

  12. #12
    Senior Member Beowulf57's Avatar
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    Quote Originally Posted by Domino View Post
    After looking at this again I think I have the wiring right all along. L300 woofer movement negative, midrange movement negative, 077 tweeter movement positive, all with positive signal input to the speaker. Sound right??
    Polarity is a multi-faceted issue. The L300 has a complex crossover and the connections to the 077 may be reversed due to driver offset/crossover interactions.

    I am aware of at least three areas that bear on polarity:

    1. Absolute system polarity, i.e., from the recording to the reproduction as in when the sound wave from a trumpet moves out in a positive direction at the beginning of a note, does the speaker cone also move out. If the cone moves in, then absolute polarity has not been maintained. There is debate as to whether this makes any audible difference or not and because it is virtually impossible to determine the absolute polarity of any particular recording, I just forget about this one. If you want to experiment however, simply reverse the connections at the amp and listen to a recording both ways...you may like one way better on a particular recording, but this will not apply to all recordings.

    2. The relative polarities of different drivers in a multi-way system. This is important as all else being equal, using a positive polarity driver with a negative polarity driver will result in the two drivers being out of phase if the connections to one driver are not reversed.

    3. The phase effects of crossover networks (eg. different orders...12dB, 18dB...result in different phase shifts), driver offset and horn path lengths, etc. Calculating the effects of driver offset at any particular frequency is relatively simple, but this changes with frequency...obviously. The effects of the crossover are a matter for the experts: a.k.a. not me!

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    http://audioheritage.org/vbulletin/showpost.php?p=37580

    If your ears can't tell you then it just doesn't matter and you can hook it all up any way you want.

  14. #14
    Senior Member Beowulf57's Avatar
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    Quote Originally Posted by 4313B View Post
    http://audioheritage.org/vbulletin/showpost.php?p=37580

    If your ears can't tell you then it just doesn't matter and you can hook it all up any way you want.
    Yah, cool . And I enjoy understanding the technical explanations behind what my ears can tell me. Thanks.

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