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Old 10th July 2011, 09:42 PM   #11
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I had toyed with the beam splitter idea with some glass plates directly behind the panel with the apex touching the panel in the center and on the ends this seemed to work very nicely.

I have been thinking that a cylnderical refelction surface may give good or better results and a more even dispersion pattern than the two flat surfaces I had originaly tried.

I will explore this more once I get going and set up a measuring system outside to eliminate the room refelctions.

As my test were mono and while I was working on my drive electronics last year.
So I haven't done alot since July of last year.

So Stay Tuned,I am getting there but slowly !!!
jer
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Old 11th July 2011, 12:04 AM   #12
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Quote:
Originally Posted by CharlieM View Post
It would be interesting to see the lens you have in mind. I haven't seen your lens of course, and I assumed that it would work in a manner similar to the highly curved multi-element lens used by Harold Beveridge.
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I still believe flat panels sound better within their restricted sweet spot but I'm definitely not against curved panels or lenses. In fact, I am seriously considering building a pair of curved ESL's for myself. Then I could listen to my flat panel ESL's when I'm home alone and switch over to the curved panels when company comes over
I think that Kontra is probably trying to describe the slanted plate acoustic lens as popularized by JBL.
See attachment #1 for an idea of how well it works, providing very uniform off axis coverage up to 10kHz.
Unfortunately design formulas are difficult to come by, although there is an AES paper on their design.
AES E-Library Acoustic Lens, Their Design and Application

In general terms, the lens provides an acoustic path length that increase as you move off axis.
This delays the sound and bends the projected wavefront. See Attachment #2
1) the spacing of the plates determines how high in frequency the lens will work.
2) the angle of the plates determines vertical dispersion limits
3) the cut out determines horizontal dispersions limits and variation with frequency. JBL research showed that the hyperbolic cutout shape gave the most uniform dispersion trends. Hard to argue, looking at the data in Attachment #1.

For ESL use, the slanted plates with hyperbolic central cutout would be placed from top to bottom of the ESL line source. The JansZen Z-40 used this concept.
JansZen Z-40 electrostatic speaker

The Soundlab minisat incorporates the lens into its grill frame. See Attachment #3
Looking at the Soundlab lense, you can see that they did not use the hyperbolic cutout that JBL and JansZen did. Rather, a simple 90 degree notch was used.

For your purpose, you could keep the flat panels you prefer for personal listening and build a lens/grill frame that you could attach when company comes over. When using the lens, you would need to EQ up the high frequencies since the lens takes what had been an on-axis flat response and spreads it out over more space. The result would be a drooping HF if you didn't correct it.
Attached Images
File Type: jpg JBL_lens_measurements.jpg (133.7 KB, 401 views)
File Type: jpg slant_plate_lens.jpg (24.0 KB, 397 views)
File Type: jpg SL_lens.jpg (10.7 KB, 400 views)
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Old 11th July 2011, 12:27 AM   #13
markusA is offline markusA  Sweden
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Very interesting.
How wide can you make the flat panel before the directivity issues become to much?
As alway the trick seems lie in finding the best compromise between spl and dispersion?
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Old 11th July 2011, 12:40 AM   #14
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Yes,I remember those and I have seen and heard the JBL ones that Ted Nugent used on his stage PA cabinets he used through the 70's,up close.
But that was way before I knew anything about speaker design.
I saw those cabinet's way back when they were built at Al Nalli Annex in Ann Arbor Michigan when I was about 14 to 16 years old.
I believe it was Technic's (I think ) used them on a set of home speakers aswell.
I have been wanting to try them on my panels aswell,But like you said the design info is scarce.
It would be great if anyone has acsess to a set to post the dimensions so that it could be tried on a planar tyoe driver such as an ESL.

jer.

Last edited by geraldfryjr; 11th July 2011 at 12:48 AM.
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Old 11th July 2011, 08:02 PM   #15
Kontra is offline Kontra  Russian Federation
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Quote:
Originally Posted by bolserst View Post
I think that Kontra is probably trying to describe the slanted plate acoustic lens as popularized by JBL.
L. D. Rozenberg "Sound focusing systems" Publishers of the Academy of Sciences USSR 1949 but sorry on a russian lang
flat hyperbolic lens without any JBL
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Last edited by Kontra; 11th July 2011 at 08:24 PM.
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Old 12th July 2011, 08:56 AM   #16
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Quote:
Originally Posted by Kontra View Post
L. D. Rozenberg "Sound focusing systems" Publishers of the Academy of Sciences USSR 1949 but sorry on a russian lang
flat hyperbolic lens without any JBL
I have found fomula for hyperbolic lenses - no need for AES $20 charge.
Later...
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Old 12th July 2011, 08:59 AM   #17
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I think the real question is: how should a loudspeaker behave off-axis? Which brings in the aspect of psychoacoustics. Our hearing is quite an amazing system, ignoring it's properties in speaker design is a fatal error.

IMO, Sanders talk is indeed a sales pitch. All speaker manufacturers have one :-)
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Old 12th July 2011, 09:27 AM   #18
markusA is offline markusA  Sweden
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alexberg> If your findings are relevant, please share.

arend-jan> Thanks for chiming in. I was just contemplating that exact issue which you mention. What is the goal? What off-axis behaviour is the target?
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Old 3rd August 2011, 02:16 PM   #19
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I found the paper on JBL's acoustic lens!
As well as radiating pattern to a driver size with respect to wavelength of the radiated frequency.

jer

ACOUSTICAL LENS

http://www.lansingheritage.org/image...tor/page02.jpg
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Old 9th August 2011, 02:24 PM   #20
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Default Curved panels can be great if well designed - e.g. Soundlabs

Hi - I'm new to this Forum but thought I would drop my 10c in.
I love ESL's. Had Quad 57's years ago.
I own and still love my Heil ribbon speakers (cone woofer, does Ok ish).
But I now own a pair of Soundlab M1's - they are very large !!! And curved.
Contrary to what someone said earlier in the thread, Soundlabs are not multiple cells. It is all one large diaphragm, stretched over multiple cells. The cells are arranged in an arc and the cells are varying in size to break up resonance peaks.
Big curved panels can give fantastic imaging and depth. I walk in and around mine just to enjoy the experience of walking up to the artist.
I love mine so much that I am upgrading to the biggest model the Majestic - 9ft tall !
Try to build a curved panel. The actual construction is the same if you look at how Soundlab have achieved it.
Another possibility is to make a multi-panel system ala Quad 57 - using a thinner esl panel in the centre, and two large curved panels on each side. So it would look like a Soundlab type panel but with a line source (wider) centre strip.
Have fun. If you build it, send me a message and a photo !
Peter from Perth in Western Australia
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