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mabat 14th February 2020 07:41 AM


Originally Posted by gedlee (
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?

Dave Zan 14th February 2020 10:44 AM


Originally Posted by mabat (
...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

Ro808 14th February 2020 11:20 AM

3 Attachment(s)

Originally Posted by Patrick Bateman (
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)

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.

mabat 14th February 2020 12:37 PM

I would have something like this in mind - seems like a nice project, relatively simple but interesting enough: Acoustic Vector Network Analyzer

gedlee 14th February 2020 02:09 PM

That system could probably be adapted to the task with some different software. The set-up is exactly what one wants, although a longer more damped tube would be better.

mabat 14th February 2020 02:15 PM

Is it necessary to use several mics simultaneously? Using only one mic sequentially could simplify the hardware a great deal.

gedlee 14th February 2020 03:14 PM

It's possible to do what you suggest, but not as stable of course.

mabat 14th February 2020 03:28 PM

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?

gedlee 14th February 2020 03:45 PM

Behler used a unique and expensive microflown and a complex scanner. My technique would be much cheaper and I suspect higher resolution.

Remember that the wavefront will be mostly planar until very HF, so resolution is a big issue.

mabat 14th February 2020 03:54 PM

The technique described in the paper used just a small pressure microphone and took the difference in pressures measured at two distances. They say the error is still the same so the resulting shape of the wavefront is not affected.

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