How does a microphone work?

In a dynamic microphone, the diaphragm is attached to a small coil of wire sitting in the field of a magnet; as sound moves the coil, it generates a tiny electric current, the reverse of how a loudspeaker works. In a condenser microphone, the diaphragm forms one plate of a capacitor, and its vibrations change the capacitance, producing a signal; this type needs a power supply, often 48-volt 'phantom power' in studios. Dynamic microphones are tough and common on stage, while condensers are prized for detail in recording studios. Smartphones and laptops use tiny MEMS microphones etched onto silicon chips. Early telephones in the late 1870s used carbon microphones, whose resistance changed as sound compressed carbon granules.