From bruce@ashbysolutions.com Tue Jul 11 20:28:46 2006
Subject:RE: Kind of OT: to diffuse or not to diffuse ?

Hi All,

The Leslie treble horn is a conical design, and therefore extremely directional. The diffuser takes the edge off the directionality, and in the process produces a number of reflections that add to the FM effect. This is a great article that delves into the diffusers and what they do --

http://theatreorgans.com/hammond/faq/mystery/mystery.html

>Early Leslies with treble horns were in open air and did not have
>diffusers.
>When an enclosure was built around the horn in later Leslies, the
>diffusers were added.

If so, then they were prototype models, used in the lab to prove the design. The first production "Leslie" was the Vibratone/30A (which did not use the Leslie name), which had a full enclosure. It was followed by the 31H, the 21H, the 22, etc. -- all with enclosures. I have never seen a production Leslie that did NOT have a cabinet.

For the most part, the practice of removing the diffusers came in the '60s, in an effort to make the Leslie louder, and thus more suitable to rock music.

Regards,

-BW

--
Bruce Wahler
Design Consultant
Ashby Solutions™ http://consult.ashbysolutions.com
978.386.7389 voice/fax
bruce@ashbysolutions.com

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