Hi Steve:
Many thanks. I've seen references to the "Gramophone Exchange, LTD." for a number of years, and wondered exactly what it was.
Out of curiosity, I googled "Gramophone Exchange" --very little online-- but after a little digging, I spotted the following reference to a patent application for an improved horn design:
We, GEoRGE HERiBEIT RUSSELL and EVELYN JANE WINIFRED SEMEn,
both of The Gramophone Exchange, 29-31, New Oxford Street, London, W. C. 1, both subjects of the King of Great Britain and Ireland, do herelby declare the nature of this invention to be as follows: This invention relates to gramophones, phonographs, graphophones and the like known nunder the general name of talking machines, and has more particular reference to trumpets, horns or sound amplifving means (hereinafter referred to as horn ") such as are enclosed in the cabinet and located beneath the turntable and motor of so-called " hornless " machines.
SEE:
http://v3.espacenet.com/textdoc?DB=EPOD ... 174675&F=0 (Don't know if the spelling errors, etc., are a result of sloppy scanning or what.)
As you noted, it's rather a mystery why EMG would have licensed their design for others to produce, unless, of course, they did not have the in-house resources to support expanded mass-production of their components for the retrofit market, etc., or perceived that the market for this would not have justified the investment cost needed for additional manufacturing tools.
I know that during the late 1920s, in the US, there were a number of suppliers that produced components for upgrading older Victrolas, etc.--mostly sound boxes and tone arms. I've also seen a few ads for electric pickups designed to fit on the tone arm of an acoustic record player, and connect to a radio amplifier via wires (or even using radio frequency!) Interestingly, I've never seen horn retrofit packages for older style gramophones, even though some of the smaller folded style horns could have easily been fitted into some of the larger, old-style cabinets. Surely, there would have been a market for this.
All this shows that there are still a lot of mysteries to solve.