Oscillations and Waves > Sound Reproduction > Microphones
 DCS# 3E30.xx
CARBON MICROPHONE

APPARATUS
carbon microphone
 202-19-B6
1.5 V battery
 202-02-D1
audio transformer
 214-01-D
amplifier/speaker or digital video recorder
 202-20-B2

DESCRIPTION
This is a model of an early microphone invented by David Edward Hughes.

The carbon rod rests between brass contacts.  As the rod vibrates in response to sound, the resistance and thus the current varies.  The signal can be sent to the speaker/amplifier or recorded and played back.  The audio quality is not good but spoken words are discernible.

NOTES

The quality of the sound is very sensitive to how tightly the rod is held.