SHURE MODEL 450 MICROPHONE
From the Shure 1972 Microphone Catalog:
The new modern design of this rugged omnidirectional Dispatcher Microphone fits every decor for dispatching and paging use, and features a telescoping height adjustment (approx. 2 1/2″) for maximum convenience. The case is made of rugged gray Arnio-Dur*, which won’t crack, peel. rust, or dent. The patented Controlled Magnetic Cartridge incorporates an impedance switch for low or high impedance. The push-to-talk switch bar activates both microphone and relay circuits, and has an optional locking feature to lock microphone in On position. The relay switch is normally open and the microphone switch can be normally open or normally shorted, as required. Seven foot tour-conductor (two shielded) cable.
Frequency Response: 100 to 10,000 Hz.
Impedance and Output Level: Dual:Low (25-250 ohms), -53.0 db (0db= 1milliwatt per 10 microbars);
.225 millivolts/ microbar.
High, -54 db (0 db=l volt per microbar);2.00 millivolts/ microbar.