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

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  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 Doctor_Electron's Avatar
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    Sorry if I "Horn In" to your thread...

    Quote Originally Posted by toddalin View Post
    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.
    OK, the HL-91 or a flat-front biradial or a CD horn are the acoustic "transformers" to match, within physical constraints, (horn diameter and length) the diaphram's acoustical impedance with the air mass of the listening area.

    For example, excluding the crossover network, the mid-range subsystem of the JBL 4350 Studio Monitor :

    Midrange Driver: 2440 2" Compression Driver

    Midrange Horn: 2311 2" Short Exponential Horn

    Acoustic Lens: 2308 Slant Plate

    Point being, in the midrange subsystem cited above, the 2440 compression driver "needs" the 2311 short exponential horn for impedance matching, and "needs" the 2308 slant-plate lens for impedance matching and to define the horizontal and vertical pattern characteristics.

    But the 2402 and 2405 ring radiators are designed and manufactured with their acoustic impedance matching and pattern control built in, by way of their throat and phasing element geometries.

    My question is, what will be the effects on the horizontal and vertical patterns due to the interaction of their intrinsic elements, and the slant plates? A lens is a lens. Something(s) will change. I know it can be worked out mathematically
    and I wish I had those skills but do not.

    How else could one predict the outcome? I think your RTA equipment will tell the tale. Ultimately, how will it sound ?

    Regards, -D_E-

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    Ultimately, the bean counters win out.

    If the slant plates were truely "engineered" to the individual horn/driver combination, one would expect that the plates for the HL-91, 92, and 93 could all be optimized to that combination..., but they're not. Furthermore, each plate measures 10" across x 3" deep. Do you think that these values are based in "audio physics," or the ability to make them in production at some cost?

    Similarly, the big oval horn came without a lens (Paragon) an BIG slant plate, like Keith Emerson used, a wavy slant plate (Hartsfield), and a midsized slant plate (maybe more?). If "one design" is superior for that horn, why bother with the others (maybe different throw for different venue?) BTW, the wavy plates were a nightmare, and I can't tell you how many were tossed out at VOX because of bends and dents.

    Without the slant plate, the HL 91, 92, and 93 will have a circular dispersion pattern (like a ring radiator). I don't know how many degrees of coverage you get, and I've never seen a published number. I would expect the lens in front of a ring radiator would have a similar effect. We'll see.

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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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