In an early patent (together with the already mentioned connection blocks) was a blockdiagram with two microphones, a mixing unit and an amplifier:
the pasted cover (middle) is from the catalog of Deutsche Lectron GmbH, the photo to the right a replica of mine. A Lectron dynamic microphone block was never found – may be that the alternative with a loudspeaker block (connected as a microphone) was sufficient. So in several experiments and even in some Bastelsatz applications (Soundlevel Meter, Burglar Alarm, Remote Control – Clapper -) the latter version was the favorite:
Dynamic Microphones have an impedance of ~ 600 Ω, the loudspeaker block (primary transformer coil) > 1200 Ω (DC resistance ~ 300 Ω) and could also used as a “loudspeaker” but can be heard only from a short distance, so the loudspeaker version is more flexible.
This topic was modified 8 months ago by mwpeters75. Reason: Changed font and size styling for easier reading