Acoustic Horn Design – The Easy Way (Ath4)

Improved phase plugs may help this situation, but little to nothing is known about the flatness of driver exit waveforms. About a decade ago I showed (B&C) how this situation could be measured in a PWT, but it was never followed through.
Do you think it would be possible for a hobbyist? What would be the biggest obstacle in building such thing?
 
...the confirmation that 1,4" drivers can be used without a problem... Many of the modern ones seem to be quite good.

Alex Voishvillo has published data in the AES on the wavefront flatness of the 2430K (1.5") used in the JBL M2 monitor.
It was pretty textbook flat, so there is some data on this.
The pictures were presented without any discussion of how they were determined, IIRC.
I assume it was done in a plane wave tube by mode expansion, the basic idea is not so different from the Klippel scanner mode expansion in 3d.
There is a very informative thread on the Klippel scanner maths in Audio Science Review, after an earlier thread in DIYaudio fizzled out.

Best wishes
David
 
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Ro808

Member
2010-03-27 4:25 pm
I'd really love to play around with the JBL 2409H and the 2410H but they're not easy to buy. (Not for sale at retail.)

The 2409H is in the JBL 705P and it has a 16mm throat (21,250Hz)

The 2410H is two years newer, and it has a 25mm throat (13,600Hz)

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The phase plug of the 2410H extends all the way into the horn.

This makes me wonder if the latter solution worked better than the former solution.


These are shown and hopefully demoed at ISE, which I'll be visiting this afternoon. Hopefully I can avoid unprotected contact with farm or wild animals ;)

"The Chinese friends" offered me some drivers for evaluation, but I had to magnetize those myself. Unfortunately they didn't bring "their big guns", like those attached.

The 18Sound clone is sold under DS18 moniker with pure Titanium diaphragm, but it's also available with a Composite Aluminum diaphragm.
The grey one is more or less similar to the Denovo Audio BA-750, sold by diysoundgroup.
 

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This might also be of interest: On the Velocity Distribution at the Interface of Horn Driver and Horn
"A measurement setup was presented that allows accurate measurements of pressure and velocity distributionswithin the junction area of horn driver and horn."

"On the Velocity Distribution at the Interface of Horn Driver and Horn" Preprint Number: - 6097 - Convention: 116 (May 2004) Authors: Behler, Gottfried K.; Makarski, Michael

- So, isn't this solved already?
 
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When I saw this paper at AES I swear they were using a wire microphone which measures velocity not pressure. In theory a two plane idea should work, but I would be concerned with measurements unless the mic was extremely small.

Really there are many ways to solve this problem and which works best remains to be seen, but none have actually come to be widely used and as such there is no data on performance.
 
They mention B&K 4138 (~3.2 mm) or Sennheiser KE-4 (~5 mm). So if a 5 mm electret capsule should suffice (?), I'm quite tempted to try at least, even if I should move the driver manually on some primitive frame - that would cost next to nothing. Your technique looks most interesting and I would prefer that, I'm only scared of the math involved - not something I could cope with in a case of any trouble. This is the complete opposite - can't be any simpler.
 
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I could help with the math, let me find my notes. The biggest issue would be the matrix inversion as these can be problematic. One would likely need to use SVD, but algorithms for that are widely available these days. If you are comfortable with matrix inversion and SVD then I don't think that you would have a problem.

The Makarski technique uses a free field driver, correct? That would bother me as this is not the boundary condition that the driver would see in practice.
 
We already touched that, if that's what you mean: #394, #395

OK, why not to try (both). I already looked for some aluminum tubes around, I can get 25 and 35 mm of inner diameter, up to 6 m long. I'd start a new thread when I have it ready (one mic only for the start).

The Makarski technique uses a free field driver, correct? That would bother me as this is not the boundary condition that the driver would see in practice.
Yeah, that puzzles me as well. But neither the tube is...(?)
 
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They mention B&K 4138 (~3.2 mm) or Sennheiser KE-4 (~5 mm). So if a 5 mm electret capsule should suffice (?), I'm quite tempted to try at least, even if I should move the driver manually on some primitive frame

The latest MEMS microphones have tiny ports, pretty decent specifications and cost only a few dollars each so well worth consideration.

Best wishes
David