Smith Selsted Tweeters

Hi group,

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.

I would love to give it a read!!!

those sure are pretty Steve...
thanks for sharing:)

those look rather interesting. i would love to hear how they sound

Okay John, here is the article:

Thanks for that, Steve. That looks like an idea worth fooling around with. A copy of the article posted or by PM would be appreciated.

Thanks,

David

Edit: You must have been posting while I was writing my response. Thanks.

Where do you find these things Steve? Amazing!

They probably will sound terrific, Baby Smith Horns.

So cool!

Fix em, and give a detailed report, please!

:applaud:

Awesome work Mr Schell, can you post some dimensions on those horns.
Very informative article thanks for the knowledge. Boy you are very lucky to find something this rare still around. Thanks Dave:)

Pellys, I agree. I should be shot for not repairing them before now.

I'm pretty sure that this work by Smith and Selsted was influential in the design of many later commercial tweeters. During the 1950s there were dozens of tweeter designs introduced. The Jensen RP-302 is another noteworthy early effort, likely designed at about the same time as the SS tweeter or slightly after. Two Jensen project engineers wrote an article on the RP-302 that was published in Audio Engineering in 1952 (I think). It was marketed as an add-on tweeter, and was also part of the Jensen G-610 Triaxial system.

You never cease to amaze me Steve!. Thank you for a glimpse of rare and INTERESTING technology. :applaud:

Thanks for posting Steve. I look forward to getting some time to read the whole article carefully.

Those would have to take the award for the rarest horn & drivers know to man and complete with documentation!

Very nice!
Mike Caldwell

What have I been saying for a year? If they ain't Smith, they ain't horns. Thanks Steve.:bouncy:

is anyone else thinking what im thinking..... a new lens for ring radiators

Steve, you do never cease to amaze!

Thanks for sharing.


Widget

Steve , Wow! What a great posting ! Thank-you so very much for this !

- The insights into the actual construction of the driver ( and diaphragm ) are just priceless & of course the pics .

- I do hope you get your tweeters going sometime / though I understand given these units rarity, if it's a one time happening .

- Don't field coils benefit from smoother DC than what can be provided by 1/2 wave rectification ( or have I missed mention of other smoothing components ? )

Cheers :) ( I love the formulas for the derived mechanical constants )

ps : I wonder if Tool & Die workers these days still offer the better "one-off" approach by being able to use "spun" product soft-pressed into a die / as compared to hydro-forming or heat-pressing . Of course , I would have liked to know the gauge of the wire used for the voice coils and the total length of the windings as well as the gap width ( but I'm just a junky for that sort of info ).

How did they end up at your house? I've been looking everywhere for my lil' smith tweets. "Here smithy smithy"
...not in the basement...or the garage...and wouldn't you know it: Right here on the forum! Ok, Steve- can I have 'em back now.....Steve..(?)....(crickets chirping)....

Seriously- those are insanely cool. I can't wait for more updates! Thanks so much for sharing!
:applaud:

Earl, in theory the DC fed to a field coil should be as smooth as possible, as any AC components can modulate the audio signal as the field strength varies. In practical terms, I have found that it takes very gnarly DC to make an audible difference. Perhaps this is because the field coil itself is a large inductor and accomplishes much smoothing on its own. Most field supplies from the old days were simple affairs with power transformer, rectifier, choke and a couple of filter cap sections.

I used to run the field coils in my system from marine batteries, with much hassle involved in hooking the batteries up and keeping them recharged. I switched to a Radio Shack 13.8VDC, 15A switching power supply about a year ago, and noticed no change in sound quality. The supply is small, runs cool and quiet, and energizes the coils with the flip of a switch.

Hapy, I bought the Smith Selsted tweeters on ebay. I was amazed to see them show up there, and they were won for about $800.

Hi Steve Thanks I Really enjoyed the article. As well I am glad you found them and they did not end up taking a flight to Japan.:(

We need to preserve some of this stuff in the U.S.A. where it was designed.:bouncy:

And where one day I might see and hear them. :applaud:

Wonderful find! Could those be redesigned to go on 2405's ???

Thank you for sharing the article and the speaker images, Steve!

Quote:

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Originally Posted by hjames

Thank you for sharing the article and the speaker images, Steve!

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And thank you, Heather, for reviving this interesting thread. I'd not seen it before. Very cool.

Interesting cast of participants in the thread as well!

:window:

Yes, thank you Heather for reviving this oldie but goodie thread. I did a quick search and was sad to find that Walter Selsted died in 2011. He was so nice to me on the phone years ago, explaining the history of these tweeters and expressing surprise that any were still any around. I never did get those tweeters going, but sold them to my speaker guru friend Robert. Not sure if he has yet fixed them up. Robert knew Harold Lindsay (another Ampex alum and the "L" in Emilar) in the 1980s at Emilar in Anaheim, CA. Lindsay had a permanent magnet example of the Smith Selsted tweeter which lived on the shelf at Emilar for a while. Thanks to this thread and this site, a bit of this strange history is preserved.

Hi Steve;

Funny that we were talking about these just the other week!

Off subject, I have on my desk something long overdue to send you. I blame a terrible memory!

Call you tomorrow.

All thr best,
Barry.