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Thread: Upgrading from 2421B to 2425J

  1. #16
    jbl
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    [QUOTE=4313B;352925]The LE85/2420/2421 with aluminum diaphragm is a very desirable compression driver.

    And plenty of people have put the D8R2421 or D16R2421 aluminum diaphragm into a ferrite 2425/2426 core.

    Conversely, plenty of people have put the D8R2425 or D16R2425 titanium diaphragm into the LE85/2420/2421 alnico core.


    Grass is always greener.

  2. #17
    Senior Member martin2395's Avatar
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    Does the 2421B 'suffer' from JBL's inverted polarity madness?
    I tested a 2121 midbass yesterday and it turned out to have the positive signal on the black terminal....

  3. #18
    Senior Member Mostlydiy's Avatar
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    I believe they do, page 2, specs 2/3 down

    http://www.jblpro.com/pub/obsolete/2421ab.pdf

    /Mostly

  4. #19
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    If you want to upgrade you will have to look for even more modern JBL drivers which are unobtainable, or look for other brands. TAD 2001 or 2002 are better but also much more expensive.

  5. #20
    Senior Member martin2395's Avatar
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    Quote Originally Posted by Mostlydiy View Post
    I believe they do, page 2, specs 2/3 down

    http://www.jblpro.com/pub/obsolete/2421ab.pdf

    /Mostly
    I tested the 2421 yesterday with a 1.5V battery and noticed that the diaphragm actually moves upwards with positive voltage applied on the red terminal so it looks like it has de "modern standard" connection. Or should it move to the other side?

    So far the conclusion is: 2121, 2235H, 2405H = Black(+) at least in the 4343. Now i rewired them so that i can normally connect the 4343 to the amp with the red terminal being the (+).

  6. #21
    Senior Member Mostlydiy's Avatar
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    If it moves "upward" with positive to red then It moves towards the phaseplug when positive is to black, so its reversed as the pdf says. If I caught your meening with upward that is.

    /Mostly

  7. #22
    Senior Member martin2395's Avatar
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    Quote Originally Posted by Mostlydiy View Post
    If it moves "upward" with positive to red then It moves towards the phaseplug when positive is to black, so its reversed as the pdf says. If I caught your meening with upward that is.

    /Mostly
    It's exactly as you say - positive signal to the red terminal makes the diaphragm move upwards = towards the back of the driver.

    That would mean that the 4343 is fully negative, all units having the positive signal on black connectors.

  8. #23
    Junior Member JMD's Avatar
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    D16R2425 missing thin spacers / metal strips under the three mounting screws

    Hello, help me please.
    I need to replace diaphragms D16R2421 in the speakers JBL2421B in my loudspeakers systems 4345 from JBL.


    I found an expensive genuine parts D16R2421 with an aluminum diaphragm from JBL. I also found a newer and cheaper titanium diaphragm D16R2425 genuine from JBL. These titanium diaphragms are also available in unbranded version and are very cheap.


    When I see the images the new titanium diaphragms well, so there missing thin spacers / metal strips under the three mounting screws. These spacers shall ensure an air gap, and thus the air permeability between front and rear wall diaphragm. Air permeability in original parts is very small but it is there. I do not know why it matters. IMHO I think that this permeability is undesirable. Please, whitch replace diaphragms should I chose?

    Thanks very much

    Bohdan

  9. #24
    Senior Member 1audiohack's Avatar
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    Rudy Kleimann and I have tested more than a few inexpensive aftermarket diaphragms on a proper plane wave tube and have yet to find any that are even close to the JBL's. At the very least buy the genuine JBL Ti's if not the Al's.

    My two bits.

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  10. #25
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    Quote Originally Posted by 1audiohack View Post
    Rudy Kleimann and I have tested more than a few inexpensive aftermarket diaphragms on a proper plane wave tube and have yet to find any that are even close to the JBL's. At the very least buy the genuine JBL Ti's if not the Al's.

    My two bits.

    Barry.
    Did you test the Radian Al phragms? I keep thinking they might work nicely for me.

  11. #26
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    Did you test the Radian Al phragms?
    I have those in 2420 and they sound good. I have not measured them.

  12. #27
    Junior Member JMD's Avatar
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    D16R2421 vs. D16R2425

    I did measure JBL2421B. The result was very good. The curve at the end of the spectrum is smooth. I assume, that titanium dome will not be as smooth. Break up can cause hard sound.

    Bohdan

  13. #28
    Senior Member 1audiohack's Avatar
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    We did measure a couple of Radians in the small format drivers and they were decent. Without pulling up the data and going by memory they (more than one/all that we measured ) had a dip in the frequency response with a corresponding wrinkle in the phase response around 7kHz. Not major but non of the JBL's exhibit this. I attributed this (correctly?) to a surround resonance.

    I do not really lump the Radian's in with the cheap replacements as they are better and significantly more expensive than the crap that simply makes noise and looks the part. I have no long term listening experience with them. Right or wrong I still bleed orange.

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  14. #29
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    The Radians are ok replacement diaphragms, but not an upgrade to a JBL aluminum diaphragm. If you want to upgrade get an Altec driver. JBL did not do anything with the one inch phase plugs for 50 years or so. Altec have worked with the phase plugs a lot.

  15. #30
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    Altec 808s with Radian phragms

    I have Altec-Lansing 808-8As with 811B horns and Radian diaphragms.
    They sound great but need to be crossed over at 1.2k.
    I use a bi amp system with a DBX crossover.
    They have also proven to be very durable with a 3B Bryston driving them sometimes to clipping they haven't failed in over 20 years

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