query: When was the first microphone invented?
passage: Microphone
The condenser microphone, invented at Western Electric in 1916 by E. C. Wente,[19] is also called a capacitor microphone or electrostatic microphone—capacitors were historically called condensers. Here, the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. There are two types, depending on the method of extracting the audio signal from the transducer: DC-biased microphones, and radio frequency (RF) or high frequency (HF) condenser microphones. With a DC-biased microphone, the plates are biased with a fixed charge (Q). The voltage maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation (C = ​Q⁄V), where Q = charge in coulombs, C = capacitance in farads and V = potential difference in volts. The capacitance of the plates is inversely proportional to the distance between them for a parallel-plate capacitor. The assembly of fixed and movable plates is called an "element" or "capsule".
passage: Carbon microphone
Early AM radio transmitters relied on carbon microphones for voice modulation of the radio signal. In the first long-distance audio transmissions by Reginald Fessenden in 1906, a continuous wave from an Alexanderson alternator was fed directly to the transmitting antenna through a water-cooled carbon microphone. Later systems using vacuum tube oscillators often used the output from a carbon microphone to modulate the grid bias of the oscillator or output tube to achieve modulation.