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Thread: Crossover freq.which

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    Crossover freq.which

    I built a system 30 years ago with a LE 15A,LE85(both which are 8 ohm) and a LX5 network.My networks went bad 5 yrs ago and I replaced them with 3115A(which are 8ohm for LF and 16 for HF.My diaphragms in my compression drivers are 8 ohm.I have blown 2 in 5 yrs,should I replace the diaphragms to 16 ohms?

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Roadglide View Post
    I built a system 30 years ago with a LE 15A,LE85(both which are 8 ohm) and a LX5 network.My networks went bad 5 yrs ago and I replaced them with 3115A(which are 8ohm for LF and 16 for HF.My diaphragms in my compression drivers are 8 ohm.I have blown 2 in 5 yrs,should I replace the diaphragms to 16 ohms?
    Nope. As it turns out you already have 16 ohm drivers. For reasons that no one seems to know, JBL has labeled both the LE15A and the LE85 8 ohms and 16 ohms at different times even though the actual impedance never changed.


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    Quote Originally Posted by Roadglide View Post
    I built a system 30 years ago with a LE 15A,LE85(both which are 8 ohm) and a LX5 network.My networks went bad 5 yrs ago and I replaced them with 3115A(which are 8ohm for LF and 16 for HF.My diaphragms in my compression drivers are 8 ohm.I have blown 2 in 5 yrs,should I replace the diaphragms to 16 ohms?
    ( Especially in a home setting ) blowing horn diaphragms is a sure sign that something is wrong with your system ( or the way you use it ).

    The most likely cause ( of the HF failures ) is too low a crossover point . How did the diaphragm failures manifest themselves ? Were you ever shown the failed diaphragms ( if so , what did you see ) ?

    Anyways, the 3115A network ( with it's 500hz crossover point ) gives too low an X-point for that small diaphragmed le85 ( especially when the driver is mated to the 2307 horn ) . ( The 3115A was just passable when a 375/2440 was used behind the 2311 / and that was just due to the 4" diaphragm size being tougher ) .

    ( Due to the confusion over JBL impedance naming conventions ) you need to make sure that you ended up with the higher impedance replacement diaphragms.
    Do you remember what model replacement diaphragms were purchased ? What are their DCR's ?

    I'd suggest you replace those crossovers with 3110A networks ( purchased used, obviously ) to raise the crossover point, @ 1/2 octave ( from 500 hz to 800 hz )

    ( If you are handy ), you could also build a 3110A functional equivalent using the following diagram for the horn-driver section ( courtesy of Giskard ) .



    Click the pic to read the full thread ( hosting the above picture ) .


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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Earl K View Post
    I'd suggest you replace those crossovers with 3110A networks ( purchased used, obviously ) to raise the crossover point, @ 1/2 octave ( from 500 hz to 800 hz )

    ( If you are handy ), you could also build a 3110A functional equivalent using the following diagram ( courtesy of Giskard ) .



    Click the pic to read the full thread ( hosting the above picture ) .

    Good advice... the S7 driver combo with 500Hz does work, but isn't happy at abusive levels.



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    Crossovers

    Quote Originally Posted by Earl K View Post
    ( Especially in a home setting ) blowing horn diaphragms is a sure sign that something is wrong with your system ( or the way you use it ).

    The most likely cause ( of the HF failures ) is too low a crossover point . How did the diaphragm failures manifest themselves ? Were you ever shown the failed diaphragms ( if so , what did you see ) ?

    Anyways, the 3115A network ( with it's 500hz crossover point ) gives too low an X-point for that small diaphragmed le85 ( especially when the driver is mated to the 2307 horn ) . ( The 3115A was just passable when a 375/2440 was used behind the 2311 / and that was just due to the 4" diaphragm size being tougher ) .

    ( Due to the confusion over JBL impedance naming conventions ) you need to make sure that you ended up with the higher impedance replacement diaphragms.
    Do you remember what model replacement diaphragms were purchased ? What are their DCR's ?

    I'd suggest you replace those crossovers with 3110A networks ( purchased used, obviously ) to raise the crossover point, @ 1/2 octave ( from 500 hz to 800 hz )

    ( If you are handy ), you could also build a 3110A functional equivalent using the following diagram ( courtesy of Giskard ) .



    Click the pic to read the full thread ( hosting the above picture ) .

    . If I replaced the diaphragm to 16 ohm would that work?

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    Quote Originally Posted by Mr. Widget View Post
    Nope. As it turns out you already have 16 ohm drivers. For reasons that no one seems to know, JBL has labeled both the LE15A and the LE85 8 ohms and 16 ohms at different times even though the actual impedance never changed.


    Widget
    My driver says 8 ohm on it and the diaphragm I have bought says 8 ohm,but they make a 16 ohm replacement.My system worked fine with the LX5 network and was told by a JBL rep. that the 3115A was a great replacement and my system kicked ass till I pushed 100 watts at it.I was on the web and saw that the 3115A had a 16 ohm on the HF,which my LX5 had 8 ohm

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    Put a multimeter on one of your le85 drivers ( set to read DC resistance, using a lower scale for ease of reading the display >>> for example, use a 0- 20 ohms scale if available ) and then tell us what you see.



    PS : Of course one does this sort of measurement with the driver disconnected from the network.

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    Quote Originally Posted by Roadglide View Post
    . If I replaced the diaphragm to 16 ohm would that work?
    You need to ( electrically ) determine which impedance diaphragm you are currently using ( if you used bona-fide JBL replacement diaphragms & the shipping box said D8R2421 ( as one example of a replacement diaphragm type ) / then you have the wrong diaphragms in those drivers >>> and should replace with D16R2421 diaphragms ) .


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    Quote Originally Posted by Earl K View Post
    Put a multimeter on one of your le85 drivers ( set to read DC resistance, using a lower scale for ease of reading the display >>> for example, use a 0- 20 ohms scale if available ) and then tell us what you see.



    PS : Of course one does this sort of measurement with the driver disconnected from the network.
    I am reading 2.1 ohms

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    Quote Originally Posted by Earl K View Post
    You need to ( electrically ) determine which impedance diaphragm you are currently using ( if you used bona-fide JBL replacement diaphragms & the shipping box said D8R2421 ( as one example of a replacement diaphragm type ) / then you have the wrong diaphragms in those drivers >>> and should replace with D16R2421 diaphragms ) .

    I am currently using the after market equivalent of D8R2421

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    Quote Originally Posted by Roadglide View Post
    I am reading 2.1 ohms
    You've installed the wrong diaphragms .

    You need a diaphragm with a dcr reading of @ 8R to 10R (ohms) .

    The D16R2421 is the proper replacement diaphragm for your le85's.



    PS: don't feel bad , you're not the first ( or last ) to get misled by JBL's wayward labelling scheme.

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    Quote Originally Posted by Earl K View Post
    You've installed the wrong diaphragms .

    You need a diaphragm with a dcr reading of @ 8R to 10R (ohms) .

    The DR162421 is the proper replacement diaphragm for your le85's.



    PS: don't feel bad , you're not the first ( or last ) to get misled by JBL's wayward labelling scheme.
    Thanks,I thought that,just needed confirmation

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