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Thread: JBL 476MG Diaphragm Issue

  1. #31
    Administrator Robh3606's Avatar
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    Found the Truextent measurements pos did them in a 2450SL core you can see the roll off. Similar to the 476Be


    http://www.audioheritage.org/vbullet...s-measurements


    http://www.audioheritage.org/vbullet...hp?33761-476Be




    Rob
    "I could be arguing in my spare time"

  2. #32
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    FWIW, I consider Giskards measurements to be the definitive ones for the Truextent//Be diaphragms ( no offense meant to POS or sebackman or 1audiohack or Rob or anyone else who has provided their measurements for our perusal ).

    ( Click the pic for his thread )



    They are of much greater resolution than most others.



    PS;


  3. #33
    Administrator Robh3606's Avatar
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    Hello Earl

    Great thanks for posting them. That gives us a more complete picture of what to expect.

    Rob
    "I could be arguing in my spare time"

  4. #34
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    Quote Originally Posted by Mr. Widget View Post
    I wouldn't expect to be able to see a problem by looking at it. Sometimes you can, but often an out of spec driver looks perfect.


    On diving in and playing Rambo with your drivers.

    Let's say you have a pair of identical Rolexes. If one was keeping poor time, would you pull the main spring out of one to test the other? Even if you are quite handy, I would expect you would end up with two watches that were not quite right or perhaps worse.

    In the past JBL sold replacement diaphragms that trained repair facilities could swap out. Today the drivers are less forgiving so most do not offer this as an option and the repair procedure is a driver swap. Yes, out of warranty it is expensive, but if you own a "finished goods" JBL speaker you are entitled to have access to replacement drivers.

    On the warranty.
    In the US the warranty begins with the first sale to the end user and not the date of delivery to the dealer. I assume it is the same in your country.

    If I bought a pair of new or demo JBLs and had issues I would be on my dealer and demand satisfaction regardless of the "bargain" he may have struck with me at the time of sale.



    Widget
    Thank you all the time that you have shared with me, it's much appreciated having information from people that has deep knowledge, if is not with the drivers or the crossover, and I can't be able to change the driver, so what can cause this tonal difference between the speakers? Have you ever came across with these situation before? Can it be a simple fault? Or maybe I have to check other parameters? Let's imagine that all the enviroment of the speakers are same but we still have a sound difference between two drivers, what parameter would you check?

  5. #35
    Senior Member HCSGuy's Avatar
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    Quick recap - you are in the UK and your speakers are a “few” years old. First, what is the JBL warranty for the UK - you may have to call the UK importer of JBL to find out. Second, as Widget said, the JBL warranty starts from when a current model speaker is invoiced to the final user - it does not matter if the speaker was used as a dealer demo for 2-3yrs. I am sure, however, that JBL would balk at a warranty repair on a speaker that has been out of production for quite some time, e.g. a speaker that was discontinued 10yrs ago cannot reasonably still be under warranty, just as JBL can’t still be held responsible for the speakers my father bought in the 60’s that had their old “Lifetime” warranty. The worst case in this scenario is that your dealer did not sell you Demo speakers, but instead resold you speakers he had bought back from someone else towards an upgrade - either originally purchased from him, or elsewhere. Either way, he can pursue a warranty claim on your speakers until it is rejected by JBL. I think you have much further to go on pursuing your claim here.

    How do you know the problem is the driver? First, you need to carefully re-assemble your driver and listen to it. If that speaker still sounds off, make sure the alignment of the driver to the horn does not have any way to be shifted off, then swap just the 476mg from that speaker to the other speaker, then listen to them both again - did the bad sound follow the suspect driver (Driver is bad), or did it stay with the original (crossover may have a problem). Above all, as Widget said, DO NOT pull the diaphragm out of the good driver. If the bad sound stays with the driver, and you exhaust your efforts with JBL, then I would talk to Guido or find a really good speaker tech in UK or EU to send both drivers to, and have them test the bad driver and see if the diaphragm to driver fitment can be improved. If all that fails, which it shouldn’t, PM me about a replacement pair of drivers.
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

  6. #36
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    Quote Originally Posted by HCSGuy View Post
    Quick recap - you are in the UK and your speakers are a “few” years old. First, what is the JBL warranty for the UK - you may have to call the UK importer of JBL to find out. Second, as Widget said, the JBL warranty starts from when a current model speaker is invoiced to the final user - it does not matter if the speaker was used as a dealer demo for 2-3yrs. I am sure, however, that JBL would balk at a warranty repair on a speaker that has been out of production for quite some time, e.g. a speaker that was discontinued 10yrs ago cannot reasonably still be under warranty, just as JBL can’t still be held responsible for the speakers my father bought in the 60’s that had their old “Lifetime” warranty. The worst case in this scenario is that your dealer did not sell you Demo speakers, but instead resold you speakers he had bought back from someone else towards an upgrade - either originally purchased from him, or elsewhere. Either way, he can pursue a warranty claim on your speakers until it is rejected by JBL. I think you have much further to go on pursuing your claim here.

    How do you know the problem is the driver? First, you need to carefully re-assemble your driver and listen to it. If that speaker still sounds off, make sure the alignment of the driver to the horn does not have any way to be shifted off, then swap just the 476mg from that speaker to the other speaker, then listen to them both again - did the bad sound follow the suspect driver (Driver is bad), or did it stay with the original (crossover may have a problem). Above all, as Widget said, DO NOT pull the diaphragm out of the good driver. If the bad sound stays with the driver, and you exhaust your efforts with JBL, then I would talk to Guido or find a really good speaker tech in UK or EU to send both drivers to, and have them test the bad driver and see if the diaphragm to driver fitment can be improved. If all that fails, which it shouldn’t, PM me about a replacement pair of drivers.
    Thank you for the detailed answered, sorry for the late reply, I have been dealing with health issues, for the JBL warranty issue, unfortunately I can't be able to take any action so I have cut my own rope.

    I have tried swapping the drivers, same result, I have measured all the crossover capacitors - the crossovers give the same ratios, I have measured all the drivers - they gave the same ohm ratio, I have tried listening all the drivers seperately together - same result, I happen to hear a tonal difference between two HF drivers, I also believe the driver is ok but then the problem will be with the crossover, I think I need to check the crossovers with a good technician, I need to find the problem but unfortunately I couldn't so far

  7. #37
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    Quote Originally Posted by Robh3606 View Post
    Here is a brand new DR82450SL and mine looks almost the same. You have to remember that you are dealing with a flat ribbon that gets twisted from the opposite side and gets twisted again to make a solder connection. One side is coming from the opposite side of the coil and that's the one I have a picture of. The other side looks much better because you only have to twist it 90 degrees to make the solder connection. Granted either one of them are not pretty but they pull this of in what a .025 gap!

    You might just have a simple alignment issue/screw torque. When you took out the diaphragm did you notice if some of the screws were easier to break the torque on?? I once have a driver where one of the screws was "loose" and once I retightened it was fine again. JBL should help you with this.

    Rob
    Maybe it is from the crossover what do you think? I had k2 S5500's before and had a similar problem, it happen to be the crossover, but as far as I know I need to pull out all the capacitors from the crossover board in order to have the correct measurement, right?

  8. #38
    Administrator Mr. Widget's Avatar
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    I guess we all assumed you followed basic trouble shooting 101 before deciding to jump into opening up the drivers.

    Did you try swapping your left channel 476Mg with the one on the right? This will immediately tell you if you have a network/wiring issue or a driver issue.


    Widget

  9. #39
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    Quote Originally Posted by Mr. Widget View Post
    I guess we all assumed you followed basic trouble shooting 101 before deciding to jump into opening up the drivers.

    Did you try swapping your left channel 476Mg with the one on the right? This will immediately tell you if you have a network/wiring issue or a driver issue.


    Widget
    Of course I have tried that, I also tried swapping the speakers in order to see acoustic defects but still the same, one hf is playin %10 lower than the other one

  10. #40
    Senior Member HCSGuy's Avatar
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    Please, please, please, start with Widget's advice. Put the speakers together, take a listen. One of the speakers sounds better. Put a piece of tape on the 476Mg in that one and mark "Good" on it, or something, so you know not to mess with that one. Then swap the 476Mg's from one speaker to the other, and listen again. If the bad sound is still coming from the same speaker as before, it is not the 476Mg (***See below***). If the other speaker now sounds bad, it is the 476Mg, and you can move on to the next step.
    Name:  476Mg3BadPlots.jpg
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    Which one of these is correct? Which one would you rather have? These are all simple 476Mg frequency response plots, with no horn, 5ms gate, in a 4'x2'x2' "tunnel" made of stacked acoustic panels, with the driver at one end, firing towards the mic 1M or so away at the other end. The conditions are not perfect, so do not judge the plots for their flatness. Instead, note that at some frequencies, they deviate by almost 8db from each other - yeah, it's at 4khz, but that would make one speaker sound alot brighter than the other. These three plots are the same 476Mg, with the same diaphragm, but I have adjusted the diaphragm fitment a little for each curve - before tightening the screws, I put a little pressure on the diaphragm outer ring towards the positive terminal, then the negative, then towards the driver label. So you see, installing a diaphragm is not quite as simple as putting a spare tire on your car. Which one is correct? In my case, it's the one that best matches the Frequency response plot I took first of the other 476Mg. *** It would be the same for you, as long as you don't remove the diaphragm on the good driver. If you have corrupted both drivers, you will have to figure out how to best measure what is a "Flat" response.
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

  11. #41
    Senior Member HCSGuy's Avatar
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    Btw, I was typing my last reply while you posted yours, so sorry if I'm a little behind. So, you have determined that it is one of the 476Mg's, right? Also, you state that you are "On your own", implying you have no recourse with your dealer or JBL. If this is the case, you are going to need to spend a little money. First, you will need a calibrated microphone. I have been playing with the Dayton Audio OmniMic2, which we get here from Parts-express.com - I don't know what is available to you, but this one is about $300, and you need a PC and to download their test tracks. I would also get some acoustic foam and build a test "Tunnel" like I have so that you can make repeatable measurements with as little outside interference as possible. Then, you can take frequency plots of both your drivers, and adjust the bad one closer to the good one. Without all the test equipment, you could also try the diaphragm adjustments I did - just loosen the screws, push the outer ring one direction, tighten the screws, put the thing back together, and listen to see if it's better. Why do I think this would help? Here's my two 476Mg's before I adjusted one:
    Name:  FRCurve(1Red)-1.0.jpg
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    And Here's after:
    Name:  FRCurvePostAdjust(1Red)-2.jpg
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    I could hear the difference going back and forth between them before, but cannot now.
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

  12. #42
    Senior Member 1audiohack's Avatar
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    Awesome work HSCGuy!

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

  13. #43
    Administrator Mr. Widget's Avatar
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    A bit off topic, but a forum member told me privately that he purchased a pair of JBL’s replacements for the 476Mg. They are called 877Mg and appear to be Radian drivers with JBL built diaphragms. Apparently the 476Be will also be replaced by the 877Be.

    My guess is that due to the small numbers of systems being built and sold that use these drivers it no longer made financial sense to continue producing these high end drivers. I am not familiar with Radian’s 4” drivers, but I imagine they are not built at as high a level of precision of the former TOTL JBLs.

    I would expect to hear about the updated Everests and K2s soon.


    Widget

  14. #44
    Administrator Robh3606's Avatar
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    They must be changing the throat diameters on the Radians to 1.5" They are 1.4" and 2" available for stock drivers. Unless they drop a sleeve into the horns throats can't imagine them redoing the throats but it is possible.

    Rob
    "I could be arguing in my spare time"

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