Due to the continuing interest in the Distributed Source Horn design pioneered by Dr. Bob Hugh Smith, I thought I would post some pictures of the rare tweeters I was able to buy on ebay several years ago.
Dr. Smith was a professor at U.C. Berkeley, and was very much a part of the northern CA audio scene from the late 1940s through the 1960s. He authored several articles, made several contributions to the art, and was highly respected. As far as I know he never commercialized any of his designs, but was an audio enthusiast equipped with the skills and education to do significant work. His most lasting work is probably the DSH design, used by JBL (2397) and many others over the years.
In the late 1940s Smith was fascinated by the prospects of designing a practical tweeter to cover the top octave. At the time there had been very few real tweeters built; most notable were Leo Bostwick's Bell Labs design that was built by Western Electric as the 596A in the early 1930s for their Wide Range systems, and the Jensen model Q. Smith enlisted the help of his friend Walter Selsted, one of the top engineers at Ampex, to help with the project. After numerous prototypes, they built a small run of tweeters to use and to give to friends. They were never sold commercially. Smith and Selsted co-authored an article on the design that appeared in the January 1950 issue of Audio Engineering magazine. If there is some interest I will post the article on this thread.
Anyway, after I bought these tweeters I contacted Walter Selsted. He was surprised and pleased to hear that any of these tweeters were still around, as they had only built between 20 and 25 of them in 1949.
As you can see from the pictures, the diaphragm was spun from aluminum. The aluminum wire voice coil has no former, but is mounted directly to the diaphragm to save mass, just as in Bostwick's design. The motor is field coil rather than permanent magnet. The horn is formed from two identical cast aluminum sections. The voice coils of both of these drivers have continuity, but the lead outs need repair. I haven't gotten around to fixing them, so have not heard these units sing yet.