See an ancient test equipment !

Hallo,
A few days ago I saw this little device and had to take a wild guess what it actually was.
After some research I found out:

It is a Siemens microphone test device. No plug and no lead is going in or out, but when you turn it over it makes a rattling noise like a rain maker with larger grains in it. Little steel balls patter on the speaker-cone-like membRane for an extended even-leveled 94 dB noise floor. You place it exactly 10 cm infront of the microphone's membRane for calibrating mics or preamps .

Do you have an old or unknown and rare gadget, too?
Feel free to post it here, as well...

:smile:

   
Siemens Eichtonquelle Click on me!