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PostPosted: December 16th, 2017, 11:47 am 
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Joined: April 20th, 2014, 5:21 pm
Posts: 233
Here are copy diffusers fror the Eurodyn from the same Korean guy.

https://www.ebay.com/itm/Acoustic-Lens- ... Sw0hlZL~lL

They look like a less aggressive version of JBL Acoustic Lens but these predate JBL by decades.

A similar diffuser was used on the Siemens 10" full range cone, a general purpose speaker like the Altec 755A, made from the 1950s-70s. The end result looked a lot like the 1950s General Electric 12" with the "grills," if you ever saw those.

The Eurodyn module was typically bolted into a large flat baffle, like 8' high, 4' wide for theater installations, a pre-Roscoe OB setup.

German theater gear was great equipment that never made it to the US. Most of it is in Japan and Korea now.

PostPosted: December 16th, 2017, 12:51 pm 

Joined: July 17th, 2016, 6:24 am
Posts: 589
German shop is closed today. Shall try calling again on Monday.

Found Bruce Edgar's interview with Positive Feedback.

When you talk through the exponential horn, people can hear the coloration to your voice, which is a certain resonant quality that wasn't there before. You talk through a Tractrix horn and you don't hear it. It's completely open.

The explanation goes back to the difference between spherical and plane waves. When the plane waves travel down to the end of the mouth of the exponential horn, suddenly there's a bulge where they exit into space, and that bulge is essentially a discontinuity. So, you have reflections at the mouth, which travel back to the throat and set up a quarter-wavelength resonance condition. With the Tractrix horn, since the waves are spherical going through the horn, they exit the mouth with very few reflections. When I first started building Tractrix horns, I heard this immediately. They didn't have the same horn colorations I'd heard before.


Expo is good for low frequencies and Tractrix for mids and highs.


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