Marconi-Reisz Carbon (c.1925/6)

The first mics used for broadcasting were Peel-Conner carbon-granule mics manufactured by GEC. They were virtually identical to those used in telephones of the time and were very noisy and of very poor quality with a spectacular resonant peak at 1kHz. Placed close enough to a speaker with a powerful voice, they could output 1mW to the line feeding the transmitter, which was essential as there was often no amplifier between the mic and the transmitter.



The Marconi-Reisz mic was developed c.1925/6. It originated in Germany but was manufactured in the UK. It consisted of an octagonal block of marble hollowed out on one side to form a cavity into which carbon granules were placed and held in place with a diaphragm initially made of rubber and later of mica. The mica diaphragms had an unpleasant peak at around 5kHz and eventually rice paper was used. All carbon mics need a polarising voltage and this was provided by an 8-volt supply in BH in 1932.

The Marconi-Reisz was a vast improvement on the Peel-Conner mics and although it could be easily overloaded and tended to produce an increase in hiss if the carbon granules packed together, the later versions had a response that was within 2dB from 100Hz to 8kHz. It continued in use until the introduction of the Type A ribbon mic in 1935.

Below are pictures from Frank Brockman of a probably slightly later mic, with double ended slinging lugs. The suspension springs and frame are all original.