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Thread: 2451h installation of 2450SL diaphragms, centering

  1. #1
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    2451h installation of 2450SL diaphragms, centering

    Hey guys,
    I just got a pair of Aquaplas 2450SL (made in Mexico) diaphragms from Speaker Exchange, to try on my 2451h. The note for the diaphragms says "non-centering" and must be installed by a specialist, whatever. Okay. Can I do this myself?
    I can install carefully, run a sweep. What am I testing for? Suggestions? Is this note to be taken seriously? Has anyone here done this?

    thanks,
    Herman

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    Senior Member 1audiohack's Avatar
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    Hello Herman;

    They are kind of self centering. The aluminum rings on the bottom of the diaphragms locate into a machined recess in the driver top plate. They usually fit in snug to tight. Sometimes / often you need a bit of movement to get them properly centered though.

    I usually end up filing them down a bit to make alignment possible. Usually by the time all the anodizing is filed off both aluminum rings since they are never perfectly aligned, that’s enough. Often the diaphragm is slightly protruding in between the rings so that gets smoothed up also.

    Try them as is first.

    I buzz them at 300 Hz with a small amp you trust with the screws in just snug and push them around until no buzzing is detected.

    If everything is right, you can briefly put just over 10 volts to them at 300 Hz before the diaphragm hits the phase plug.

    So, yes you can do it. if you have more specific questions, ask away.

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

  3. #3
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Herman Chigrin View Post
    Hey guys,
    I just got a pair of Aquaplas 2450SL (made in Mexico) diaphragms from Speaker Exchange, to try on my 2451h. The note for the diaphragms says "non-centering" and must be installed by a specialist, whatever. Okay. Can I do this myself?
    I can install carefully, run a sweep. What am I testing for? Suggestions? Is this note to be taken seriously? Has anyone here done this?

    thanks,
    Herman
    Factory sweep test specs is 500-1200hz @2.83 volts for 8 ohm, 3.5 volts for 16 ohm. I actually go 200Hz to 20KHz to make sure there is no weirdness. You can damage your hearing with too much long term exposure to a 118dB driver, so be careful.

    Make sure you line up the terminals to the reliefs in the top plate 180 degrees apart to eliminate possible rubs at the lead out wires. The countersink in the top plate makes it "somewhat" self centering. Put the mounting screws in loose, apply the test voltage while holding down the diaphragm mounting ring when you find zero buzzes or rubs, then snug down the screws in a "star" pattern. Old AlNiCo model drivers don't have this feature...they have mounting pins. Sometimes modern replacement diaphragms need the mounting holes reamed out a bit to fit the locating pins.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    Thanks guys. I will try this over the weekend. Great advice! Resistance measurement is 4.2 and 4.3 ohms for the pair. Guess that's the normal tolerance.
    I would have ordered 16 ohm but they only sell the 8 ohm now

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