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Thread: CNC copy of an 2328 adapter

  1. #16
    Senior Member Lee in Montreal's Avatar
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    I will have a 3D model in a few days, as well as a chart displaying the progression of the cross section from throat to mouth. Adapter is 1" thick for 2" drivers. It's more in line with a Westlake style adapter than a JBL one. No "ballon" here... ;-)

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  2. #17
    Senior Member Wardsweb's Avatar
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    I was working on something very similar today. You can see the adapter block on the left of the horn. The black is spray paint I used to match the horn throat. This gets cutout to transistion to the 1" cutout. It is 1" thick. For comparison to it's left is a 3/4" adpater I got from Bill Martinelli years ago.

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  3. #18
    Senior Member Lee in Montreal's Avatar
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    Nice.

    Are you going with a 1" driver? Also, after prepping, assembling and finishing the horn, I found very easy to fit the fins from the throat. Carefully slide them in. There's just enough play for an easy slide. And as the fins are razor sharp, you won't scratch the horn by fitting the fins from the thoat.

    Can't wait to see your finished horn with the mirror-like polished fins. On the last stage of aluminum polishing, I like to use a rubbing compound called Autosol that leaves a mirror finish.

  4. #19
    Senior Member Wardsweb's Avatar
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    Yes, a 1" driver as that is what came in the C50 speakers I bought. I may go 2" later.

    I use white tripoli to polish and Happisch Simichrome to mirror.

  5. #20
    Member reVintage's Avatar
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    Of course the baloon is intentional as said earlier. The flare is 160Hz exponential. This is what the WE594 had. JBL copied it when they made their 375. For some reason they changed the flare to 180Hz.
    Also the 2328 differ significantly from the prototype according to the designer. Think we had that up to discussion in an earlier thread about the adapter a few years ago.

    http://www.audioheritage.org/vbullet...highlight=2328
    Brgds
    Lars

  6. #21
    Senior Member Lee in Montreal's Avatar
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    Hi Lars

    The ballon has now been integrated into the draft. Interestingly, I checked another set of 2328 I had and the machining at the thoat is very different. One set is smooth, one set is notchy. The notchy set is what made me think the ballon was an "error". While it is obvious wuth the smooth set it was designed in. I guess I now have a complete draft that I can use in a few years when most 2328 will have been melted or junked . That project has evolved into a 1" adapter.

  7. #22
    Member reVintage's Avatar
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    The thing you draw in post 16 is totally wacko. If you want to add a 1" to 2" adapter let it be 160Hz and something like 200mm long. If you make it 400Hz(like most 1" drivers flare) it should be something like 100mm.

    Best is to check the flare and length from a radial horn spreadsheet. 2397 is a cut radial. Yggdrasil have one and I also have one.

    Also the prototype probably was 4"*1,5". Have checked my 2328´s and it seems OK.

    The fins should not be polished as we have low airspeed. Glass blasting should be fine.
    Brgds
    Lars

  8. #23
    Senior Member Lee in Montreal's Avatar
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    Hi Lars

    You are bringing a few points that deserve to be discussed, even though I don't entirely follow you. ;-)

    1" - 25.4mm, therefore if I design a 1" adapter, it won't be 200mm. The goal is to make a compact adapter while everyone understood that the cut-off will be higher.Therefore the lower cut-oof will probably be around 1khz and not 800Hz. But it is fine with me as it is what I am after.

    As far as boundary layers caused by a polished/smooth surface, this is a well know/documented subject in automotive and aeromotive industry. Air and fluids do stick more to a perfectly smooth surface than on one with irregularities. It slows down the flow by creating unwanted friction because air and fluid will bond to the surface. But in reality, is there any airflow in a tweeter or a medium driver? Does the membrane move enough to create flow, as such is the case with a woofer? And even with a woofer, if I use a smooth ABS pipe, will it have detrimental effects?

  9. #24
    Member reVintage's Avatar
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    Hi Lee,
    You are probably right in that the air speed is so low that the flow is almost absent. Still in low speeds like in the Tornado catamaran I used to sail, rudders worked best when matted(?) down. But there speed was higher, up to 30 knots.

    About 20cm it is correct when you do the 1-2" adapter with the same flare as 2328. very simple! As I also said the 400Hz expansion would give you ca 10cm but the they don´t fit so well together. Better to do a 400Hz "2328" in that case. Hornresp. is a very good tool.

    About the bulb you get the answer when you check Altec 511 but the "bulb isn´t smothed out there. Actually it is what happens when you follow the exponential expansion rearwards you come to the point where you come to the square point. If followed rearwards the horn form would be vertical. So cut the radial at the square point to go from square to round.


    Brgds
    Lars

  10. #25
    Member reVintage's Avatar
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    Found the pic´s of a conversion I did for fun to the 511, 2328 and 2" driver. Still haven´t tried them though.

    It is not completely correct as the 2441 is 180Hz, the 2328 160Hz and the 511 270Hz.I actually cut the 511 where it had exactly the same opening as the 2328.
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    Brgds
    Lars

  11. #26
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    no need for common cutoff frequency

    You can join segments of any flare (exponential, hyperbolical, conical) and of any cutoff frequency. The segment with the worst properties determines the behaviour of the combination. If that segment is short compared to the wavelengths involved, then it's a simple discontinuity.

    If You wanted to achieve plane waves so that You could more easily design an acoustical lens, then You would pick a very low cutoff frequency.

    Ruediger

  12. #27
    Member reVintage's Avatar
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    Hey Ruediger,

    Off course you can mix but to get an optimal result an uniform flare all the way is the way to go. About 2397 style horns I think it is a big mistake to addd the driver directly to the hornthroat. There must be a adpter with a"bulb" to change the flow from round to radial.

    So if wanting to go 1" and a crossover of 800Hz, a flare in the ballpark of 400Hz all the way should be great.

    But it can pose problems when a driver like 375, 2441 etc. has the built in horn with a flare of exponential 183Hz.

    I designed and custom-ordered Le`Cleach horns 200Hz/T=0,8 from Auta-Tech as that was very close to the initial flare of the 2441.
    Brgds
    Lars

  13. #28
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    yes & no

    Quote Originally Posted by reVintage View Post

    ... to get an optimal result an uniform flare all the way is the way to go ...

    ... There must be a adpter with a"bulb" to change the flow from round to radial ...

    ... So if wanting to go 1" and a crossover of 800Hz, a flare in the ballpark of 400Hz all the way should be great ...

    ... But it can pose problems when a driver like 375, 2441 etc. has the built in horn with a flare of exponential 183Hz ...
    Hi reVintage,

    1st statement: disagree.

    2nd statement: that's what the designer had in mind. Room for educated guesses.

    3rd statement: flare frequency = 1/2 * lowest frequency to be transmitted holds for exponential horns in general, not just for adapters. But the adapter cannot cure what the horn spoils.

    4th statement: disagree.

    Ruediger

  14. #29
    Member reVintage's Avatar
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    Hey Ruediger,

    Hi reVintage,

    1st statement: disagree.

    2nd statement: that's what the designer had in mind. Room for educated guesses.

    3rd statement: flare frequency = 1/2 * lowest frequency to be transmitted holds for exponential horns in general, not just for adapters. But the adapter cannot cure what the horn spoils.

    4th statement: disagree.

    Ruediger
    1st So a horn shouldn´t have the same flare from throat to mouth? Totally disagree or is this a missunderstanding?

    2nd Would have been interesting to see the original prototype mentioned in the other thread. Did measure(long ago) at two points except mouth and throat and and they indicated 160Hz.

    3rd. Yes, 1/2 lowest in general is correct and I even speak of the horn inclusive driver by choosing this frequency. Both Altec and JBL has ca 400Hz flare inside. The adapter is a part of the horn and should be counted in as part of it. So it should of course have the same flare(st1 above). This is what is ment with "all the way".

    4th. JBL published figures about 160Hz flare. Probably they got that from the sketch made by JBL around 1950. It was the a direct copy of the WE594 flare. For some reason the internal flare where made ca 2cm shorter(with same At and Am) in the 375. So if you take apart the driver it is easy to measure and do some math to find out it is 180Hz with exponential flare. This is a fact and can easily pe proven. It is no problem to measure from outside too. Ballpark figures are L=69mm, Am=20cm2 and At=11cm2.

    About the 2328 one must remember that the first part of the radialhorn(2397) is in the adapter. So doing a 1" adapter based on guesses is not the best idea from my point of view.

    Using Yggdrasils spreadsheet for a 160 exp radial the figures aren´t to far away for the adapter. From Lees nice drawing it isn´t clear if the bulb is at five or six cm´s from the throat. Haven´t mine available as I am at work.

    http://www.revintage.se/160.xls

    EDIT: Some second thoughts. If making new 1" adapters for 2397, why not go for 2397 flare?
    Brgds
    Lars

  15. #30
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    Never sayed it that way

    Hi reVintage,

    I did not say the horn should have a varying flare, but rather it may have a varying flare.

    See the Altec Manta Rays, and the JBL true Biradials. It gives You some freedom in designing.

    I wrote "educated guess", not "guessing".

    Ruediger

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