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Thread: Measuring compression drivers. Questions.

  1. #16
    Administrator Robh3606's Avatar
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    I have to ask you have a good pair or Aluminum 2440 diaphragms so why are you changing out to 2441's? You have 2405's up top no? The biggest difference between the 2440 vs 2441 is the increased HF extension. I don't see what you are gaining by the switch.

    Rob
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  2. #17
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    Quote Originally Posted by Earl K View Post
    I'd recommend ( since you have measuring capability ) that you play around with the diaphragms fitment to see if you can adjust the FR of that diaphragm ( by re-torquing the 8 screws wth various amounts of pressure and changing-up the sequential pattern used for the 8 screws ) .
    - Do you know how to torque down a head-gasket ( or even a car-tire for that matter )?
    Thanks for the time you are taking to reply. Its appreciated.

    I will have a go at shimming and apply varying amounts of torque to the screws. Strange that changing the sequential pattern for the screws would make a difference. I did notice some of the screws are magnetized and some are not?

    Head Gasket? No. Car Tire? Yes. Odd question, I'm not completely useless just have no experience in changing diaphragms and want to have a go.

  3. #18
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    Quote Originally Posted by Robh3606 View Post
    I have to ask you have a good pair or Aluminum 2440 diaphragms so why are you changing out to 2441's? You have 2405's up top no? The biggest difference between the 2440 vs 2441 is the increased HF extension. I don't see what you are gaining by the switch.

    Rob
    I should have mentioned. I have built Giskards charge coupled networks for my 4350's. The 2440 doesn't reach the now required 10k.

  4. #19
    Administrator Robh3606's Avatar
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    OK makes sense now!

    Rob
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  5. #20
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by kelossus View Post
    Thanks for the time you are taking to reply. Its appreciated.

    I will have a go at shimming and apply varying amounts of torque to the screws. Strange that changing the sequential pattern for the screws would make a difference. I did notice some of the screws are magnetized and some are not?

    Head Gasket? No. Car Tire? Yes. Odd question, I'm not completely useless just have no experience in changing diaphragms and want to have a go.
    Having done a few myself and taking factory tours at JBL (pre departure from Northridge) and at Meyer Sound, it is obvious that properly installing a diaphragm is not trivial. I doubt 80-90% of the drivers that have been serviced by someone not at the factory ever gets the originally specified performance.

    If your diaphragms are sound they should be MUCH closer that yours currently are. That said, even with a pair of perfect diaphragms, without shimming and accurately measuring and comparing with a known target there is no way to get theses precision devices set up correctly.


    Widget

  6. #21
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    Quote Originally Posted by Mr. Widget View Post
    Having done a few myself and taking factory tours at JBL (pre departure from Northridge) and at Meyer Sound, it is obvious that properly installing a diaphragm is not trivial. I doubt 80-90% of the drivers that have been serviced by someone not at the factory ever gets the originally specified performance.

    If your diaphragms are sound they should be MUCH closer that yours currently are. That said, even with a pair of perfect diaphragms, without shimming and accurately measuring and comparing with a known target there is no way to get theses precision devices set up correctly.


    Widget
    I am getting the impression that most believe it is the diaphragm that is faulty more then the installation. I am happy enough to spend time playing with shims with the hopes that proper alignment inside the gap may fix things.

    Unsure if a pair of used 2440 diaphragms would be worth anything but considering an attempt at a sale to fund a pair of radians. I should have just bought the Radian's in the first place and waited for a NOS pair of 2441 diaphragms to surface.

  7. #22
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    Had a bit of a play and this is where I'm at. I did try to keep the microphone to driver distance the same but they may have been out by a few cm here and there. I think this result is good enough? Would you be happy to call it a day with these sweeps?

    Strangely enough I could not get a consistent distortion curve. For whatever reason these last sweeps I took today look worse then my initial sweeps. Even on the driver that hasn't been touched.

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  8. #23
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    Quote Originally Posted by kelossus View Post
    Had a bit of a play and this is where I'm at. I did try to keep the microphone to driver distance the same but they may have been out by a few cm here and there. I think this result is good enough? Would you be happy to call it a day with these sweeps?

    Strangely enough I could not get a consistent distortion curve. For whatever reason these last sweeps I took today look worse then my initial sweeps. Even on the driver that hasn't been touched.

    Name:  Final Sweep.jpg
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    I'd recommend that you now stop fiddlin with diaphragm fitment ( those 2 are as matched as anyone else might achieve ). So, Congratulations!

    Distortion specs won't be reliable until measurements are made above a certain level of background room noise ( iow; the "room noise" makes the results unreliable when the drivers distortion is below that level ).



    PS; typically one displays the frequencies in a logarithmic scale ( you've chosen linear ).

  9. #24
    Senior Member 1audiohack's Avatar
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    I would also say you're done.

    What made it happen for you?

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

  10. #25
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    I shimmed the diaphragm with some sticky tape. Also there was a bit of debris in phase plug slit.

  11. #26
    Administrator Mr. Widget's Avatar
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    Congratulations, your results look very good!


    Widget

  12. #27
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    Nearly ready to go.

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  13. #28
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    Up and running. Everything works as it should. Will do some system measurements tomorrow and dial them in via the l-pads.

    I do believe in capacitor burn-in and they sounded a little closed in for the first hour. Starting to come to life now. Haven't put the woofers in yet in case I need to change something.


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  14. #29
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    Going through old posts I can see a few members mention balancing the HF and LF sections by measuring with an SPL meter.

    Can someone please detail what the process is?

  15. #30
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    Bloody hell I have no idea whats going on.

    Noticed one of the diaphragms buzzing this afternoon. Measured the driver and its back to shit again? WTF!!!!

    Can anyone advise what exactly the tolerance markings on the top plate mean? My compression driver top plate has +2 +2 +2 +1 and my Diaphragm is a -2. My diaphragm comfortably clears the phase plug and further shimming completely ruins the already shit measurements. I feel like the coil might be rubbing somewhere in the gap. Is there a way to sweep these drivers without having to put the back cap on?

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