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Thread: JBL 2405 issues

  1. #1
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    JBL 2405 issues

    Hello! I recently purchased a pair of 2405, i check visual the diaphragms and the dcr of each driver. The dcr in both diaphragm was the same and the diaphragms visual looks
    In ok condition. After taking them home i hooked them on my system and i realize that the one plays lower than the other and also with less detail. The diaphragms looks original and the one driver with the issue looks like never been opened before. Whats the problem could be?
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  2. #2
    Senior Member bldozier's Avatar
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    polarity maybe

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    Quote Originally Posted by bldozier View Post
    polarity maybe
    What has to do with polarity?

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    Senior Member 1audiohack's Avatar
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    Hi Soulman!

    I have seen this a couple of times and found the diapragm not quite centered and or being preloaded (pushed or being slightly distorted) by the bullet or the outer horn.

    When you get them free from coil contact with a surface in the gap and external forces they come alive.

    I don't know what you have for test equipment but one can usually see this with a high resolution impedance test where the motional impedance peak will be abnormally low if there is any coil to motor contact. Note that these don't have enough excursion to sound broken if there is coil contact, they just sound weak.

    On the other hand if the coil is separating or the diaphragm is broken the impedance peak will be very high.

    In the absence of test equipment, swap diaphragms in the drivers and see if the issue follows the motor or diaphragm. Usually careful re-assembly is the fix.

    Off subject, my family is in your beautiful country and loving every minute of it.

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

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    Senior Member RMC's Avatar
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    Hi Soulman,

    Diagnostic based on a picture is always an adventure... That being said, IF we disregard faulty connection (e.g. intermittent) and polarity, then the following MAY be issues seen on the second picture presumably the problematic one (dated 6-30-89) since you didn't say.

    These are guesses. Comparing both pictures, on the top one there is a "R" which suggests repaired or replaced? On the bottom picture, the small yellow ring appears to show a larger space (top left) than the other tweeter could that mean "off center"? Also the diaphragm appears to show some dent or bump (bottom left) as well as something on the right hand side. Could these explain the output level difference? I don't know.

    I did have a similar level problem many years ago with an "original" Motorola piezo tweeter. When I opened it and compared it to other real originals I have, I realized the one with the level issue had a noticeably smaller diaphragm than the real originals. That meant this particular unit, I had purchased used, had been repaired with other than original part even though it did say Motorola on the tweeter... But that story doesn't APPEAR to be your case here. Regards,

    Richard

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    The problematic one is the bottom one!

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    So maybe the best is to remove the diaphragm and maybe clean also the vc gap

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    Senior Member 1audiohack's Avatar
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    I brlieve a physical inspection is in order.

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

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    Judging by the marks in the aluminum...these diaphragms have been somewhat...abused.

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    Senior Member christo's Avatar
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    Quote Originally Posted by Tim Rinkerman View Post
    Judging by the marks in the aluminum...these diaphragms have been somewhat...abused.
    I would agree, I had the same issue - low output and there was a dent in the diaphram
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  11. #11
    Senior Member RMC's Avatar
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    Hi Soulman,

    Well I'm glad and old man's guesses , like me, in post # 5, weren't that off the track, even though I don't own nor have opened any 2405... Reading Barry's post re "off center" and Christo's and Tim's posts re "dent" tells me close observation and logic can go some way re diagnostic.

    That certainly doesn't make me yet a sage man nor a smarter guy, but I sure am working on it. Regards,

    Richard

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    Senior Member bldozier's Avatar
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    Honestly I was mentioning your connections
    but, maybe it's the diaphragm
    ok bye.

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    Also the "good one" has worst dents but it plays great! Also it doesn't look off centered. Im a little afraid to remove the diaphragm to be honest.

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    Senior Member RMC's Avatar
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    Hi Soulman,

    Worst LOOKING dents don't mean automatically more damaging. Those of the weak unit may impair the tweeter more than the bad LOOKING ones. Not much else you can do but to follow Barry's advice in post # 4. Unless he has more tricks up his sleeve... The guy knows 2405 details much better than I do.

    Richard

  15. #15
    Senior Member 1audiohack's Avatar
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    Quote Originally Posted by retro soulman View Post
    ... Im a little afraid to remove the diaphragm to be honest.
    I understand, that's perfectly rational. As it is though it's not performing properly so your possible losses should you ruin it are small no?

    If you choose to take it apart the first real trick is in the unsoldering of the leads. These are very fragile as you can see. I use a wood tooth pick as the tool to carefully coax the lead out of the terminal loop while the solder is melted. Wood wont melt nor will anything stick to it.

    After the leads are free, if the diaphragm wont lift out easily you may have to get under it with a thin sharp blade.

    Jbl currently does not have any D16R2405's in stock. The due date for more is 09/30/2017.

    The pictures taken from on center make it harder to tell but it looks like these are the ferrite versions?

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

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