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Thread: 2446 with SL diaphragms for 2450 or 2451. Choice?

  1. #1
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    2446 with SL diaphragms for 2450 or 2451. Choice?

    I have confused myself again.

    I am using 2446H drivers and would like to experiment with different diaphragms. The Truextent Be diaphragms are too expensive ($950 each).

    However, some you have suggested using an aquaplas coated diaphragm for a smoother response (although the high frequency extension may be a bit reduced. The impedance is not an issue since I am using DSP crossovers.

    According to Simply Speakers they have genuine JBL diaphragms (coated with aquaplas) for either the 2450 drivers or the 2451 drivers that will fit a 2446 driver.

    The 2450 driver uses a 4 inch voice coil with 1.5 inch exit (cost of the SL diaphragm is about $80 and they only have the 8 Ohm) Part # JBL D8R2450SL

    The 2451 driver also uses a 4 inch voice coil but the driver itself is a 2 inch exit (like my 2446) and the cost is about $125 and they only have the 16 Ohm version (and not currently available).
    Part # is JBL D16R2451SL

    Again, I am not worried about the impedance, so what am I not understanding? Although both diaphragms are designed for a 4 inch VC, I guess the design for a 1.5 inch vs a 2 inch exit or the phase plug must be the difference? Which is the better choice? BTW, both are smooth (not ribbed).

    Thanks,
    -Tom

  2. #2
    Senior Member edgewound's Avatar
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    Quote Originally Posted by withTarragon View Post
    I have confused myself again.

    I am using 2446H drivers and would like to experiment with different diaphragms. The Truextent Be diaphragms are too expensive ($950 each).

    However, some you have suggested using an aquaplas coated diaphragm for a smoother response (although the high frequency extension may be a bit reduced. The impedance is not an issue since I am using DSP crossovers.

    According to Simply Speakers they have genuine JBL diaphragms (coated with aquaplas) for either the 2450 drivers or the 2451 drivers that will fit a 2446 driver.

    The 2450 driver uses a 4 inch voice coil with 1.5 inch exit (cost of the SL diaphragm is about $80 and they only have the 8 Ohm) Part # JBL D8R2450SL

    The 2451 driver also uses a 4 inch voice coil but the driver itself is a 2 inch exit (like my 2446) and the cost is about $125 and they only have the 16 Ohm version (and not currently available).
    Part # is JBL D16R2451SL

    Again, I am not worried about the impedance, so what am I not understanding? Although both diaphragms are designed for a 4 inch VC, I guess the design for a 1.5 inch vs a 2 inch exit or the phase plug must be the difference? Which is the better choice? BTW, both are smooth (not ribbed).

    Thanks,
    -Tom
    The only difference between those two drivers is the exit.

    2450 has a snout flare exit of 2"

    2451 has no snout and 1.5" exit.

    Same basic motor and Coherent Wave Phase plug.

    To go further down the rabbit hole, the 2446 ceramic motor has the Coherent Wave Phase Plug and snout flare 2" exit. The 2447 ceramic motor has the Coherent Wave Phase Plug, no snout and 1.5" exit
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    I had forgotten the phase plugs were similar (at least in design). So are you suggesting either diaphragm in the 2446 would perform similarly? Since 1.5 inch horns are usually crossed at a higher frequency, I was wondering if the 2451 diaphragm was built to take the increased excursion. I am grasping at straws here .....

    In looking through the older threads, it seems that folks have used either of the aquaplas diaphragms (2450SL or 2451SL) and mated them with a 2446 or 2445 driver. Although the majority seemed to use the 2451SL.

    Thanks,
    -Tom

  4. #4
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by withTarragon View Post
    . . . Since 1.5 inch horns are usually crossed at a higher frequency, I was wondering if the 2451 diaphragm was built to take the increased excursion. . . .
    Are you saying higher frequencies require greater excursion?
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

  5. #5
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by withTarragon View Post
    . . . The 2450 driver uses a 4 inch voice coil with 1.5 inch exit . . .
    No it doesn't.
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

  6. #6
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by withTarragon View Post
    . . . The 2451 driver also uses a 4 inch voice coil but the driver itself is a 2 inch exit . . .
    No, it isn't.
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

  7. #7
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by withTarragon View Post
    . . . . so what am I not understanding? . . . .
    Well, to begin with, there's the importance of getting the model designs clearly in mind and the model numbers correct when asking questions about them.

    Then there's the fact that Edgewound has answered your question.

    Finally, there's the possibility that you may be about to get in over your head. Installing diaphragms can be tricky because they are very sensitive to subtle details and knowing you've done it well usually requires the ability to run sweeps and test them.

    I think your real question may be, is getting aqualplas dusted diaphragms worthwhile. The general sense around here is that it is, and I can attest to that as well, but they need to be installed correctly; you should have a pro do it for you. I used them in a pair of 2450's on 2311/2308's in my 4345's and they were a big improvement over the old 2421's, although compared to new ones, I don't know. The dusted 2450's eventually gave way to small format TAD Be.

    Be of the TAD variety is worth the money if you can swing it. Caveat: buying new has become expensive and difficult; buying used can be dangerous because discontinued models are not supported by TAD.

    I haven't tried the true tempter.
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

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    Even further down, there is the 2450SL driver that is a 1.5" exit/no snout - looks like a 2451 except different bolt pattern. With the coated diaphragms having the -SL designation, it makes things even more confusing (a 2450 with an SL diaphragm isn't a 2450SL, for instance).

    That said, really the only difference that I think most people concern themselves with between the D8R2450SL and D16R2451SL is the impedance, pick the one that suits your need and have at it.

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    Quote Originally Posted by speakerdave View Post
    Are you saying higher frequencies require greater excursion?
    No, I am saying the lower frequencies require greater excursion. So normally one would use a 2 inch driver (not the 1.5 inch) if you wanted to cross lower. If all other things are equal (seldom true), but you already know this.

    I saw in my original post that I swapped the exit dimensions between the 2 drivers (it should read that the 2451 is 1.5 inch and 2450 is 2 inch). This was my mistake, but I am not allowed to correct this now.

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    Quote Originally Posted by speakerdave View Post
    No it doesn't.
    You are correct and I made a cut and paste typo.
    Let me set it correctly

    The 2451 is 1.5 inch exit and a 4 inch voice coil.
    The 2450 is 2 inch exit and a 4 inch voice coil.

    I will try and correct the text in the original question

  11. #11
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    Quote Originally Posted by speakerdave View Post
    Well, to begin with, there's the importance of getting the model designs clearly in mind and the model numbers correct when asking questions about them.

    Then there's the fact that Edgewound has answered your question.

    Finally, there's the possibility that you may be about to get in over your head. Installing diaphragms can be tricky because they are very sensitive to subtle details and knowing you've done it well usually requires the ability to run sweeps and test them.

    I think your real question may be, is getting aqualplas dusted diaphragms worthwhile. The general sense around here is that it is, and I can attest to that as well, but they need to be installed correctly; you should have a pro do it for you. I used them in a pair of 2450's on 2311/2308's in my 4345's and they were a big improvement over the old 2421's, although compared to new ones, I don't know. The dusted 2450's eventually gave way to small format TAD Be.

    Be of the TAD variety is worth the money if you can swing it. Caveat: buying new has become expensive and difficult; buying used can be dangerous because discontinued models are not supported by TAD.

    I haven't tried the true tempter.
    ---------------
    Thanks, I am clear on the models and exit dimensions. I should have proofed what I wrote yesterday.

    You bring up and interesting point about swapping diaphragms. I read a number of posts on the this forum that stated swapping diaphragms on the 2445 and 2446 was a simple task ("just pop them in"). Others advised caution, you may have been one of them.

    Recently, I replaced the diagram on a 2445 with the current JBL replacement. Yes, it certainly did require several sweeps and re-adjustments. The symptoms were 3rd harmonic distortion when driven with a 500Hz tone as a well a general decrease in output and an overall low pass filtering. After much back and forth and a shim, I was able to get it working properly.

    I am starting to think that some of those diaphragms that were "just popped in" are causing all sorts of problems. It really is worth taking the time to do it correctly.

    I will end up going with the 2450 diaphragm (coated) for my 2446.

    Thanks,
    -Tom

  12. #12
    Dang. Amateur speakerdave's Avatar
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    The diaphragms are made for the same frequency ranges.

    The long throats in legacy compression drivers are based on a design created at the beginning of movie theater sound, when the goal was a crossover frequency of 300Hz. That became almost entirely moot a long time ago. A few decades ago Emilar (I think, may have been first) and then JBL and others decided that the legacy throats were getting in the way of improving horn designs for the crossover frequencies most commonly employed. especially in home hifi. The higher crossover frequencies permitted modern snoutless CD exits in the 2447, 2450SL and all subsequent drivers of that type for better dispersion of the higher end of the treble range.
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

  13. #13
    Senior Member edgewound's Avatar
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    Quote Originally Posted by withTarragon View Post
    ---------------
    Thanks, I am clear on the models and exit dimensions. I should have proofed what I wrote yesterday.

    You bring up and interesting point about swapping diaphragms. I read a number of posts on the this forum that stated swapping diaphragms on the 2445 and 2446 was a simple task ("just pop them in"). Others advised caution, you may have been one of them.

    Recently, I replaced the diagram on a 2445 with the current JBL replacement. Yes, it certainly did require several sweeps and re-adjustments. The symptoms were 3rd harmonic distortion when driven with a 500Hz tone as a well a general decrease in output and an overall low pass filtering. After much back and forth and a shim, I was able to get it working properly.

    I am starting to think that some of those diaphragms that were "just popped in" are causing all sorts of problems. It really is worth taking the time to do it correctly.

    I will end up going with the 2450 diaphragm (coated) for my 2446.

    Thanks,
    -Tom
    That's a good choice.

    Maybe I can simplify the differences between all these different diaphragms...and drivers.

    Regardless of diaphragm impedance...The later 375, 2440, 2441, 2445, 2446, 2447, 2450, 2451 are all physically interchangeable with each other. The ceramic 2445, 2446, 2447, Neodymium 2450, 2451 all have a machined relief in the top plate 180 degrees apart make room for the the voice coil lead out wires to prevent rubs and buzzes. They also have a recess machined into the top plate to help with self centering of the diaphragm. The AlNiCo 375, 2440, 2441 drivers do not have either of these features and rely on centering pins to mount the diaphragm. Sometimes the pin is larger that the mounting holes in the later titanium drivers and will require reaming of the mounting hole to allow it to fit. Many times I've had to ream out the hole because it required to much force to get it to fit the pin. After mounting, it requires a live tone to position the diaphragm cleanly and sometimes even tapping the top plate with a mallet to center the pole piece/phase plug.

    The diaphragms: "SL" means it been coated with aquaplas. 2450 diaphragms have a ribbed or embossed dome to help with rigidity, no aquaplas coating.

    The 2450SL diaphragm is a D8R2445 smooth dome diaphragm with aquaplas coating. The 2451SL diaphragm is a D16R2445 diaphragm with aquaplas coating.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    Quote Originally Posted by JeffW View Post
    Even further down, there is the 2450SL driver that is a 1.5" exit/no snout - looks like a 2451 except different bolt pattern. With the coated diaphragms having the -SL designation, it makes things even more confusing (a 2450 with an SL diaphragm isn't a 2450SL, for instance).

    That said, really the only difference that I think most people concern themselves with between the D8R2450SL and D16R2451SL is the impedance, pick the one that suits your need and have at it.
    I think SL stands for Snout-Less. 2450SL was the first JBL driver without the snout if I'm correct.

  15. #15
    Administrator Robh3606's Avatar
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    SL stands for a coated diaphragm you are thinking of 2425S that had a threaded snout,

    Rob
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