Hello all, it's been a long time but I'm finally back in a position where I can think about cutting again.
I've recently acquired this piece of Presto-branded equipment, which I believe to be a horn speaker driver from the late 1920s - early '30s.
It certainly has the old logo, and a Brooklyn address, which makes me think this was a product of the Presto Machine Products Co. - the predecessor of Presto Recording Corp. We know that they produced add-ons and attachments for radios and phonographs, and I believe this is one of them.
Other early horn drivers and headphones have an iron diaphragm that is set in motion by an electromagnet, but this is built a little differently, more like some early loudspeakers I've seen. There is still an iron plate present, but it is much smaller, and is sandwiched between the two poles of the large magnet. This is attached, via linkage, to what appears to be a mica diaphragm - much as you would find in a phonograph reproducer. There is also another possibility - that this was intended to replace the soundbox on an acoustic phonograph, turning it into the sound system for your radio receiver.
The fascinating thing is, while I was checking the coil with my multimeter, I realized that it was generating voltage from noise in the room - it was functioning as a microphone! With the help of modern electronics, we can hear it quite clearly:https://www.mediafire.com/?7qo2as49ydyyxa6
Has anyone else come across early Presto pieces like this? I would love to be able to reconstruct the horn, or at least find out more information about it.