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Thread: New Product Development - 2402/075 - Can You Help?

  1. #1
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    New Product Development - 2402/075 - Can You Help?

    I will probably join the Urban Workshop this/next week and will have access to a Professional 3-D printer in ABS plastic. I've been learning CAD using DesignSpark and have some ideas for use with JBL products in mind.

    I've already designed a set of tweeter stands and am working on a "slant plate" assembly for use with the 075/2402. 3D printing lets me create and test ideas that JBL could never have dreamed of with their technology of the time. And, with a couple keystrokes, we can change things such as the curvature of the slant plate and print a new set. This shows the slant plate and there will be an assembly that goes around the 075/2402 to mount it in front of the tweeter/baffle board (hence the rear cut-out that considers that the tweeter typically stands 1/4" out from the baffle board).

    Anyway, this post is a request for a 2402/075 for disassembly and measurement. The unit doesn't need to work nor be in good condition so long as it is not dented or bent in any way. I may also try to cast the phase plug in clear acrylic tapped for the screw. (Why should 077s get all the ooohs and aaahs? How cool would that be???) I could also do this with the 2405 phase plug if someone has one "lying around" and of course they would get a pair and return of their plug if they wanted it back.

    In exchange, I'll print you out a pair of stands, the slant plate assemblies, or what ever else I come up with, your choice.

    Thanks



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    The missing piece. These should tame the 075/2402 a bit.




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    The phase plug on the 075/2402 extends a bit beyond the perimeter so it was necessary to raise the face out a bit to compensate. Rather than just leave a "hole," I used CAD to blend the hole into the horizontal plane. I'll try to print out a set for initial fit and trial next week when I gain access to the $35K 3D printer.


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    I made it a bit curvier and into two pieces so two will fit in a small "If it fits it ships box.


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    Senior Member Horn Fanatic's Avatar
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    Quote Originally Posted by toddalin View Post
    The missing piece. These should tame the 075/2402 a bit.



    I'm curious as to what math you used to design your acoustical lens assembly.

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    In accordance with the theory, the plates have to be less than 1/2 wavelengh spacing. I used 0.35", similar to JBL, that takes it over 19kHz..., higher than the 075 can go.

    For the size, I used the HL-91 lens dimensions, but scaled them to the the diameter of the tweeter rather than the horn throat.

    I did more "smoothing" of the "vane posts" at the throat.


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    Senior Member honkytonkwillie's Avatar
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    Quote Originally Posted by toddalin View Post
    I may also try to cast the phase plug in clear acrylic tapped for the screw. ... I could also do this with the 2405 phase plug if someone has one "lying around" and of course they would get a pair and return of their plug if they wanted it back.
    Turning a 2405 into a 077 is akin to alchemy. I think you have a money-maker here.
    I control the treble.
    I control the bass.

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    We started the Urban Workshop last night with the laser etcher/cutter class and also have access to the 3D printer. The laser is great for working with acrylic, though you can/do get some minor burn spots along the edges.


    Unfortunately, while use of the printer and laser are included in the membership, the media are not. For the laser, you just bring in what you want to cut/etch, if it is on the approved list.


    For the 3D printer, they supply the ABS media in cassette spools. The media costs $10/cubic inch plus a $9 recycling fee on the empty cassettes! (I have no idea how far a cassette goes.) The pictured stands would use about 20 cubic inches of material EACH or about $200 just in materials.


    For the slant plates, each plate is ~8" x 2.5" or 20 square inches. If each plate is 1/16" thick, it uses 1.25 cubic inches and the cost is $12.50/plate (x 8) or $100 per tweeter. The mount adds another ~5 cubic inches and you're up to ~$150 in materials alone per tweeter.


    It is far cheaper (~$2/plate) to make them of 1/16" ABS. But ABS is not allowed in the laser cutter as it emits toxic fumes and the smoke clouds the lens. Acrylic works, but I want 1/16" and that typically comes in 1/8" and is not as strong as ABS.


    We'll see what happens.



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    Senior Member 1audiohack's Avatar
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    It's funny how 3D printing is always THE answer, until you actually get to it. Do they have value? Sure, but not for production.

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

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    But all is not lost. I've revised the slant plate to use laser cut acrylic, assuming the laser can cut down to 1/16" acrylic (the settings are provided for down to 1/8") and that the acrylic plates have enough strength.

    The 3D printing may still prove beneficial in making "plate spacers" out at the ends because these would use little material. On the other hand, if I can go to the craft store and find the right kind/size beads to space the plates, that would be cheaper and easier.

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    Senior Member louped garouv's Avatar
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    very neat project --

    Grainger or McMaster Carr (others) may also be a worthwhile source to check in with for any misc. fitments/gaskets/etc. that are necessary....

    very neat project!

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    "All of this and some of that's the only way to skin the cat."





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    I was able to try the laser cutter/etcher today.

    Look what I can do.




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    Senior Member Doctor_Electron's Avatar
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    Viva plexiglass ! Again.

    Hello,Toddlain, welcome.

    I have a few more questions. Is acrylic "A Go" for the slants?

    Would using plate lenses in front of stock ring radiators produce a "compound dispersion" pattern as a result of the stock pattern response (may not be correct terminology lingo) but I think you know what I mean by that) of the stock signal being refracted again by the plate lens? If so, what would you expect as a result? Ring radiator experts, and we know you are here at Lansing Heritage, please chime in.

    Will adding these to 2402's and 2405's alter their recomended low frequency cutoff values? New values?

    I have one 2402 with dead alnico from which I could provide parts for measurement. I would need it back because the driver is now a display. (Prop). If interested please PM me with details.

    Very interesting thread.

    Regards, -de-

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    Thanks,

    Yes, the slant plates are a go. I have enough scrap 1/8" acrylic to make up a set of plates to test out. If tests go well, I'll try using 1/16" acrylic, which I have located in colors/smoked.

    The acrylic mfg has a high-quality product that has a brown paper layer on either side to protect it. Though a bit more costly, this is is also the best stuff to use in the laser because the brown paper helps to keep the edges from burning as the laser cuts.

    Once I've made a set, I can use a 6 mfd cap on an original 075 (never opened) and run pink noise though it. The 6 mfd cap is used in the 2400/2600 crossovers with the D130, so is the lowest recommended value for use with the 075. The 2600 actually pads the 075 down to avoid injury at this frequency, but I can keep the volume at a reasonable level for testing.

    I have a 61-band RTA and can easily A/B the freq response with/without the lens. I also have professional sound level monitoring equipment (it's what I do), a protractor, and a piece of string 1-meter long so can measure off-axis response.

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