Album of pictures of the unknown object: https://imgur.com/a/5cM7SrE
Like I said, I've asked all kinds of different subreddits about this object already, including /r/whatisthisthing, /r/ww2, /r/amateurradio, etc. They're pretty much all stumped. So, I figured I'd ask historical experts in hopes than one of you may know something about it.
There are actually two objects in the imgur album I linked to. The darker gray one and the lighter silver one are two of the same thing, but the silver one has been polished and as a result the VOICE, TONE, and RECEIVE cast onto the bottom of it has been worn off. Those 3 words are the only bits of writing on the things. Both of them were found around the early to mid 1980's in California, more than likely at an electronic surplus yard such as Apex Electronics. Both objects are made of aluminum and weigh about two pounds. Outside of that, there isn't much else information on what they were prior to being found.
Out of all the posts I've made, I've only gotten two answers that confidently said "this is what it is." One of them said it was a "sound powered inter-compartment intercom" from a warship, the other said it was "part of a WWII cryptography radio used by the allies in the Pacific Islands." Both of these posts did not provide any definitive or visual proof, and despite my best research I couldn't find any information to confirm either of them either. (I did ask several experts on sound powered technology though and they all said they've never seen anything like it, so it's unlikely that it actually was the first option)
If you guys have any ideas on what this object was before it was found in the 80s, please let me know!
My father is a radio enthusiast who served as a 1st class radio operator during military service in 60ties' Czechoslovakia. Nowadays he likes to repair 20ties-40ties radios as a hobby.
He says that he's never seen anything like this in a radio and that he is sure that those objects were NOT a part of a radio. Since there is a robust VOICE/TONE switch, his guess is a siren/megaphone combo.
It looks like there was some kind of handle that selected between "Voice" and "Tone". The CAD files don't show that detail. Does that mounting seem to do anything inside?
I tried looking with:
And got a lot of theoretical papers and the term "Helmholtz chamber" seems to be related to those as well.
I tried adding in "cylinder", "cylindrical", "double cylinder" and aluminum, but got nothing.
EDIT:
Does it look like the voice/tone/receive switch connects to anything internally?
I wonder if the tone somehow transmits a pure tone that is used to calibrate some sort of array (or to annoy people). As a tone is a fairly distinctive sound and has excellent signal-to-noise properties, it makes for a good calibration mechanism. That said, it is terrible for transmitting information (except simple Morse or On Off Keying) because it has a low bandwidth (theoretically 0, but practical affects might give it some wander.
Does it look like there is a plug anywhere?