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 pre-amps. 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!