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Thread: CNC copy of an 2328 adapter

  1. #1
    Senior Member Lee in Montreal's Avatar
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    CNC copy of an 2328 adapter

    I have started drafting a 2328 from an actual unit I have in hand. I understand there might be inconsistencies between units and that castings can vary widely. This is a work-in-progress and I am trying to understand the progression rate from throat to mouth.

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  2. #2
    Senior Member 1audiohack's Avatar
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    Here's some dimensions to add to your pool of averages.

    I have two with an exit width of 3.915" and three at 3.850" and one with a vertical exit at 1.370", three at 1.390" and one at 1.400".
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Senior Member Lee in Montreal's Avatar
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    Thanks for the info.

    Looks like the average width could be 3.875" (3-7/8") and height could be 1.375" (1-3/8")

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    Administrator Mr. Widget's Avatar
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    Your drawings don't seem to show the greater negative draft of the "balloon" portion just after the round entry. I believe this detail is significant and not at all considered on the simple throat plates used by Westlake on their later horns and by others.

    I think your averages seem correct.


    Widget

  5. #5
    Senior Member Lee in Montreal's Avatar
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    That "balloon" irregularity is what puzzles me. I want to transfer the drawing into Solidworks and measure the area progression.

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    Pics of the Balloon, please

    Quote Originally Posted by Lee in Montreal View Post
    That "balloon" irregularity is what puzzles me. I want to transfer the drawing into Solidworks and measure the area progression.
    Can You post a few detailed pics of the balloon?

    Ruediger

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    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Ruediger View Post
    Can You post a few detailed pics of the balloon?

    Ruediger
    Here it goes. The horizontal progression is smooth and makes sense. The vertical progression shows the Ø 2" machining ending into a cavity (with a bad step). I believe that this "balloon" is only the result of the mass production at reduced costs where minimal machining must be involved. Considering the wide tolerances in many units, precision and accuracy were probably not the first target.

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    Guessing the mind of an unknown engineer

    Quote Originally Posted by Lee in Montreal View Post
    Here it goes. The horizontal progression is smooth and makes sense. The vertical progression shows the Ø 2" machining ending into a cavity (with a bad step). I believe that this "balloon" is only the result of the mass production at reduced costs where minimal machining must be involved. Considering the wide tolerances in many units, precision and accuracy were probably not the first target.

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    Maybe the designer had an idea similar to the following one.

    Perhaps You have seen the weird folds in the Klipschorn, where the horn gets wider in the vertical direction, and narrower in the horizontal direction. It opens more rapidly in the vertical direction than it should, and as a compensation gets narrower in the horizontal direction.

    The 2328 gets wider more rapidly than it should, and it gets narrower from the middle of the balloon towards the slot.

    Let's check the dimensions. Upper frequency bound is 10 kHz (2440 driver), with a wavelength of 3.4 cm. The dimensions of the 2328 (magnitude-wise) are roughly 3.4 cm.

    Upper frequency bound of the Klipschorn is 400 Hz, but let's calculate with 340 Hz, which is about the same (magnitude-wise). @ 340 Hz the wavelength is 1 meter, which is roughly the dimension of the Klipschorn.

    So at the slot it's a "Klipsch-style" horn expansion. If a Klipschorn makes sense, then this adapter must do as well.

    At the round entry to the adapter You can't do much to transform or guide wavefronts. Any expansion is wrong. The sudden change from the entrance to the balloon is a discontinuity which does no harm. But the balloon itself paves the way for the "Klipsch-style" expansion.

    Weird idea? May be

    Ruediger

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    Senior Member Lee in Montreal's Avatar
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    I am currently looking at all the possibilities for that "ballon". BTW I measured the height at 2.35" in both units of a paired set I have. I shall compared to anothr paired set currently in use. 2.35" was measured by cutting small wood sticks inserted in the ballon. From an older 2004 thread by widget, I understand he measured 2.55" on his own units. I suppose that perhaps using an average height would work.

    Next step is to borrow a bore gauge and take measures from the inside at specific intervals and model a curve.

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  10. #10
    Senior Member 1audiohack's Avatar
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    I would wager that the "balloon" is intentional. A transitional form to help manipulate a plane or spherical wave front into a fan shape. Also used on more than the 2397 so it is anyones guess to what if any particular horn it is optimized.
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    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Lee in Montreal View Post
    I shall compared to anothr paired set currently in use. 2.35" was measured by cutting small wood sticks inserted in the ballon. From an older 2004 thread by widget, I understand he measured 2.55" on his own units. I suppose that perhaps using an average height would work.
    Two things to consider:

    A) I don't remember measuring the "balloon".

    B) I won't vouch for the accuracy of any such measurement.

    OK, and a third thing to ponder... if I recall correctly (use an alphabet salad for the phrase if you like) doesn't the Altec 511 horn have a similar "balloon"? I know some horn I was once checking out did, but I can't remember which one... then again, I don't remember posting a measurement in 2004 either.


    Widget

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    Senior Member Lee in Montreal's Avatar
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    I don't know how to thank you, Widget. Sacrifying a 2328 to chop it up was brave ;-)
    From the the cuts in the picture, I was able to faithfully retrace the horizontal and vertical paths. Thanks again.

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    The balloon is probably just to transition from the circular driver entry point into the square exit point.

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    Senior Member Wardsweb's Avatar
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    [QUOTE=Allanvh5150;316237]The balloon is probably just to transition from the circular driver entry point into the square exit point.[/QUOTE
    If anything like fluid dynamics, so the sound bubble exits on both the vertical and horizontal at the same time.

    You see the bowl cut a lot in head porting for race applications. It is just the reverse, square or rectangle to a round valve.

  15. #15
    Senior Member Lee in Montreal's Avatar
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    I forgot to mention that my intent, unlike what the title suggests (my bad), is not to produce copy of a 2328. I am doing the exercise of redrawing a 2328 in order to better understand its principle. My goal is to design a 1" thick aluminum adapter as I seem to understand that the shorter adapter will be a bit better at higher frequencies. That adapter will work on 2350 and 2397 horns. I will make a few units for personal consumption for 2" throats, but the design can be adapted for 1" and 1,5" throats.

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