Lansing discovery- WHOA!

[moldyoldy]

I found it particularly interesting that Blackburn's patent illustration shows a threaded horn connection as opposed to stud & plate...

[Steve Schell]

Moldyoldy, thanks for linking to Dr. Blackburn's patent; I should have done this.

I have often wondered who originated the idea of the radial slit phasing plug. RCA collaborated with the MGM team during the creation of the Shearer Horn System. Lansing Mfg. Co. supplied many drivers to RCA in the mid to late 1930s, as well as to the Loews theatre owners for their new systems that were otherwise all RCA. RCA was building their MI-1428A compression driver by late 1936; it had an eight slit radial plug, and was soon replaced by the MI-1428B with its fifteen slit plug. These were very different drivers than the Wente-inspired Lansing drivers, as they used a 4.5" composite cone diaphragm and exited out the end rather than through the body of the driver. RCA had been in a pitched battle with Western Electric over what it felt was its domination of the theatre business, and evidently took pains to avoid building any design that could be considered an infringement of W.E.'s patents.

Lansing began building Blackburn's radial slit plug in 1936 or 1937 when the threat of legal action dictated the change. It was said in print at the time that the reason for the change was that the radial plug was easier to manufacture, though we know the real story. Isn't it curious though that Lansing reverted to the circumferential plug in both driver formats as soon as conditions permitted?

By about the time Dr. Blackburn's patent was granted, he had left Lansing to work on radar for the government at M.I.T. Lansing had likely reverted to the circumferential plug by then anyway, so there was no need for assignment of the patent to Lansing Mfg. Co.

Max Graham of RCA is generally credited with the design of the RCA 1400 series drivers. He worked under John Volkmann, who (as John Hilliard mentioned in an article) travelled to Hollywood to assist the Shearer team. Dr. Blackburn was of course a member of the team, who then later went to work for Lansing. Somewhere in this critical mass of brilliant minds someone originated the concept of the radial slit phasing plug. Was it Blackburn, Graham or Volkmann? They are all gone now, so we may never know for sure.

The RCA 1400 series compression drivers used a 2.5" 16 TPI attachment to the horn and a 1.5" exit, as did the Lansing 284, 285 and 284B drivers. The business between Lansing and RCA ended around 1940, and each adopted new mounting standards shortly after. The Lansing 287 driver, introduced in (probably) 1940 used a three stud mounting that was retained in the 288. RCA shifted to a two stud mounting about 1942.

Below are a couple of pictures of the RCA MI-1428B phasing plug, a Lansing large format driver with circumferential phasing plug (may be a later 287) and a Lansing 285 with the Blackburn plug.

[moldyoldy]

Beautiful, museum stuff, Steve, Thanks! I'd never seen the RCA innards before. Is it an illusion, or are the RCA exit openings slightly 'twisted' about the axis?

Thanks for the clarification of the ambiguities relating to Blackburn's patent, too. I had assumed the assignee was designated when a patent was filed, rather than later, when it was issued.

There are likely many details of "who did what, when, and why" we'll never know for sure. I've been on a patent binge recently, with the discovery of Google's patent search abilities. What started as simple curiousity, soon led to the realization that neither Lansing Mfg., nor Altec claimed any patents until fairly late in the game, while Bell, WE, RCA, and others made regular offerings. Can you shed some light on this please?

[glen]

A fascinating discovery Steve!
Thanks for sharing it with us.

I think you should be named the official PaleoAudiologist of Lansing Heritage!

[Earl K]

Thanks Steve for showing this to us .

It's great to see those pictures of such a monumental find .

[Earl K]

moldyoldy,

Thanks for the link to that Googled "Blackburn" patent , very interesting.

- FWIW / I also notice the lack of Hilliards' name anywhere on that document ( notwithstanding everything else )

[moldyoldy]

moldyoldy,

Thanks for the link to that Googled "Blackburn" patent , very interesting.

- FWIW / I also notice the lack of Hilliards' name anywhere on that document ( notwithstanding everything else )

Most welcome, Earl.

Noticed that too, didja?

Until Google opened the text on those old patents for us, it was almost as easy to invent something as to find it in 'prior art'. I've found various "duplexes" by others as far back as '29. Altec had no patents until Carrington's Duplex, filed in '47;

http://www.google.com/patents?vid=USPAT2568883

and Lansing Mfg. had none. None of either company's early "claim to fame", legacy products including VOTT were patented, unless earlier, and by others.

W.E.'s divestiture gave Altec free use of their prior art. Apparrently none of Altec or Lansing's products differed enough from that prior art to warrant their own patents until much later.