Shure Brothers CR81 – Vintage Microphone, High-Z CR Element

From 1942 through 1945, Shure’s factory in Chicago operated nearly around-the-clock manufacturing military mics and headphones. Wartime demand was so great that in 1942 alone, the number of employees at the company’s headquarters grew from 150 to well over 1,000. Keeping up with new contracts was not the only challenge; there were technical hurdles. Though the ubiquitous carbon microphones were able to withstand the blast pressures created by war weapons, controlled reluctance mics, preferred for their improved speech intelligibility, could not.  

The controlled reluctance cartridge is a variation of a dynamic mic. The mic diaphragm connects, via a drive pin, to a small lever made from ferrous material. The other end of this lever is positioned inside of a stationary coil of wire. Surrounding the coil of wire is a stationary magnet. As the ferrous lever is moved by the mic diaphragm, the lever disturbs the magnet field. This induces an AC signal (the audio signal) in the coil of wire.

The technology eventually made its way into consumer markets with the introduction of the Model 520 Green Bullet, Model 505 Ranger, Model 510 Hercules and Model 520 SL Dispatcher microphones in 1949.  

A secondary market emerged for Shure as home tape recording and intercom systems gained in popularity. Manufacturers needed reliable and inexpensive microphones to pair with their products. Those OEM models, often recognizable by a CR prefix, are widely available on auction sites today.

Shure advertising touted its “ruggedness, clear reproduction, and high output long needed for Public Address, Communications, and Recording – at an amazingly low price”. It was, according to copywriters, “especially ideal for general-purpose use in tropical countries and all coastal areas.” Indoors or outdoors, controlled reluctance mics were not susceptible to moisture. (It is worth noting the Shure REX Model 710, often promoted next to the HERCULES, featured an identical shell with a crystal cartridge.)

This mic was developed during wartime and the rugged composition of this microphone still holds today and is conceivable to last another 70 years.