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Thread: JBL 2404H Low Output

  1. #16
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    Quote Originally Posted by 1audiohack View Post
    Just to back up a bit, the magnet/motor assemblies including the top plate and pole geometry are all the same on all 13 of mine. I bought two of them new when these first came out in the mid / late 80's if I remember correctly, and the last one out the door of JBL not to long ago on the etent sale sight.
    I bought seven of them new in all and got three variations. There are two different size phase plugs, one is 1.600" at the base, the other is 1.715". Then of course there is the D8R075 and the D16R2405 diaphragms for a possibility of four combinations, one of which I have never seen from the factory in my new stuff, which is the 1.600" plug withe the D16R2405 diaphragm.
    Do any of your combinations need masking tape to work?

  2. #17
    Senior Member 1audiohack's Avatar
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    Just to back up a bit, the magnet/motor assemblies including the top plate and pole geometry are all the same on all 13 of mine. I bought two of them new when these first came out in the mid / late 80's if I remember correctly, and the last one out the door of JBL not to long ago on the etent sale sight.
    I bought seven of them new in all and got three variations. There are two different size phase plugs, one is 1.600" at the base, the other is 1.715". Then of course there is the D8R075 and the D16R2405 diaphragms for a possibility of four combinations, one of which I have never seen from the factory in my new stuff, which is the 1.600" plug withe the D16R2405 diaphragm.

    Two of the used ones I bought had aftermarket diaphragms in them and the sounded different than all my others and measured not good. The times I have seen low output
    (without obvious reasons) have been voice coils partially un bonded from the radiating element or coils/formers in cotact somewhere in the gap, that just knocks the efficiency and fidelity right out of them. They don't move far enough to click and pop from the stiction like a 2 or 4 inch drive will so you are unlikely to hear it.
    If you can take a good hi resolution impedance measurement these have a well defined peak at Fs if they are not dragging in the gap.
    If you don't have all the stuff to measure and test, just bite the bullet and send them somewhere that does, look for a shop that can give you a proof of performance sheet when they hand you the bill.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  3. #18
    Senior Member 1audiohack's Avatar
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    No masking tape required! All four combinations require no such buchery.

    Sorry I am on the road doing this from an IPhone, I don't know why it sent it out twice partially. No I'm not driving at the moment.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  4. #19
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    deafbykhorns

    Perhaps your 2404s are fraudaulent copies ( knockoffs carrying a bogus JBL label ), as the poster in this 2445 thread discovered .
    - Copies often use lighter weight magnets to reduce costs // resulting in less output .

    - "Fraudaulent" ( if they aren't OEM JBL ) but have been stickered with a JBL label .
    - Here in North America a seller can be brought up on charges for knowingly selling knockoffs as originals .
    - The referenced buyer ( from Serbia ) isn't likely going to get "Interpol" too interested in his case ( unfortunately ) .

    Perhaps you could post some pics of your 2404s ( as well as their weights ) so that others can help you make a determination .

    <> cheers

  5. #20
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    They look like the real deal to me except for the diaphragms





  6. #21
    Senior Member 1audiohack's Avatar
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    Those look like real 2404's to me.

    Looks like a 2405 diaphragm (by dimensions) with a 1.600" base diameter phase plug, the combination which in my experience gives the best frequency extension.

    All bets are off with those diaphragms however.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  7. #22
    RIP 2010 scott fitlin's Avatar
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    It is the aftermarket diaphragm. I know those numbers, matter of fact I pulled an aftermarket fram I have out, to look at it, and mine says 31.09 8ohm, same size gold ring. Your 2404 cores are real JBL, get real JBL frams, you should be good to go!

    I have two aftermarket frams, I bought a while back, because at that moment I couldn't get a real JBL, and after I tried it, took it out and waited and spent for the real parts!

    IT IS WHAT IT IS!
    scottyj

  8. #23
    Senior Member ratitifb's Avatar
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    Quote Originally Posted by scott fitlin View Post
    It is the aftermarket diaphragm...IT IS WHAT IT IS!

  9. #24
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    Quote Originally Posted by hjames View Post
    Well, JBL replacement parts are speced to perform the same, the other brand is just an unknown. Its hard to say for sure - but that'd be my guess.
    Its hard to know what the specs of the aftermarket product is.
    They may look similar, but you pay for the sound, not for the looks.
    Dang - didn't we start here, days and days ago!
    You get what you pay for, and someone bought a cheaper replacement diaphram ...
    2ch: WiiM Pro; Topping E30 II DAC; Oppo, Acurus RL-11, Acurus A200, JBL Dynamics Project - Offline: L212-TwinStack, VonSchweikert VR-4
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  10. #25
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    Yes, someone bought a cheaper diaphragm but I wouldn't expect it to be 10db down in sensitivity. I would call it cheap chinese garbage, but look at the bright side, it may have a higher power handling rating or maybe not.
    I ordered the original diaphragms

  11. #26
    Senior Member louped garouv's Avatar
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    Quote Originally Posted by deafbykhorns View Post
    it may have a higher power handling rating or maybe not.


    how much power were you thinking of running through them?

  12. #27
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    Well, my username might be misleading but just the typical 1-20watts thru a network. I blow out the cob webs about every 2 months and hit it with about 300w thru a MC352 for about 30 seconds. Enough to piss off the wife when all the knick knacks go flying off the entertainment center. The output is not good enough with the current diaphragm for normal listening but would probably be fine in a PA system.

  13. #28
    RIP 2010 scott fitlin's Avatar
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    Quote Originally Posted by deafbykhorns View Post
    Yes, someone bought a cheaper diaphragm but I wouldn't expect it to be 10db down in sensitivity. I would call it cheap chinese garbage, but look at the bright side, it may have a higher power handling rating or maybe not.
    I ordered the original diaphragms
    I agree, 10db is REALLY excessively low. My after markets, which are the SAME as what you have are NOT 10db down, either. They just don't sound like GENUINE JBL, and not good enough, either.

    However, when the after market diaphragm was installed in the 2404, if it isn't sitting in precisely the right spot in the gap, there goes the sensitivity down the tubes. a millimeter or two will do it, small though this amount may seem. Or perhaps, when the person installed the diaphragm, they weren't careful, and nicked the windings in the gap, causing a short, where the VC is still conducting some signal, but very very low. And, as someone else had suggested, if the adhesive bonding the VC former to the diaphragm has let go, and part of the VC former is just flopping in the gap loose, THAT would definitely do it. I had a 2402 bullet tweeter with it's original diaphragm from 1983 with this exact condition a few years back, and IT PLAYED, just at an unacceptably low level. When I disassembled the 2402 I found half the VC former unattached to the diaphragm, and I was surprised it worked at all.

    On another occasion many years ago, back in the 1980,s my system had ALTEC 15,s. And I had a couple of woofers reconed, I run a commercial system, and occasionally we blow a woofer. So I had the pair reconed at the service center we use to use in Manhattan, NYC, and the recone kits were genuine ALTEC, but whoever did the work must have had a bad day, or whatever, and one woofer of the pair I had serviced just was dead sounding. Since both woofers were in ALTEC 816 cabinets, side by side, it was easy to hear. And I put my fingertips on the cone of the woofer that played very low, particularly in the midrange response, and ever so slightly pressed the cone back a bit, while music was playing. RIGHT AWAY THE LOW MIDS CAME BACK! And when I say I pressed the cone back EVER SO SLIGHTLY, I really mean SLIGHTLY! So, one of two things, the person who did the work did not shim and install the recone kit correctly, or the kit was a defective kit. But, moving the cone back, maybe a nnth of a degree put the VC where it was supposed to be, and the difference in output was astounding! The store/service center reconed the woofer, again, no extra charge to us, and this time, it came back correct. But, YES a few tiny millimeters made all the difference in the world.

    Now, your dealing with a JBL device, and a NON JBL part, and my guess, which most have already said as well, is the NON JBL part is NOT made to the exact size specification as the real JBL part. When you purchase genuine JBL diaphragms there is a small pamphlet enclosed in the packaging. The pamphlet says " Centering of the voice coil within the magnetic gap requires specific test equipment and training and is critical to the performance and reliability of this product. The enclosed part is made to critical tolerances. Damages resulting from improper installation by anyone not authorized by JBL will not be covered by the JBL warranty.

    This tells it to you verbatim, Centering and alignment of the voice coil in the gap is critical to the performance of the unit! There are a few more sentences in the pamphlet, but I posted the part I feel is MOST relevant to the issue at hand, PERFORMANCE! JBL says the positioning of the VC in the gap is critical.

    So, when you get your JBL parts, and either have it installed professionally, or DIY, and it is done correctly YOU will definitely hear two things. One is as long as the VC is where it is supposed to be, your 2404 will produce the proper amount of output, and two, you will DEFINITELY hear the magic of the JBL sound.

    And after this, you will probably say the same things WE say on this forum, USE JBL PARTS IN JBL PRODUCTS, PERIOD!

    It's CRITICAL!
    scottyj

  14. #29
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    Well, received my replacement JBL parts today, all I can say is NIGHT AND DAY difference. These things sound sweet and measure right at 105db at one watt as specified. I don't believe for a minute it was alignment issues, conclusion: chinese parts SUCK!

  15. #30
    pocketchange
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    2404H JBL OEM Diaphragm

    If you are looking for OEM replacements...
    Check Ebay
    2404H OEM JBL Diaphragm
    $36.00 per w/free shipping from TX.
    21 available (i got my 2)

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