How does an electric guitar hear a string without a microphone?

An unplugged electric guitar can sound surprisingly quiet, yet its connected amplifier can fill a room. Beneath the steel strings, a magnetic pickup turns their movement into an electrical signal. It does not need to listen to the surrounding air in the way a microphone does.

A common pickup contains a permanent magnet and a coil of fine wire. The magnet magnetizes the nearby steel string. When the string vibrates, it changes the magnetic field passing through the coil. That changing magnetic flux induces a voltage across the wire’s ends. The voltage varies with the motion, carrying information about the vibration.

The signal travels to an amplifier, which uses electrical power to drive a loudspeaker. The speaker moves air to produce the sound heard across the room. The pickup is therefore a translator of motion into a signal, not a source of the large amount of energy supplied to the speaker.

Pickup position changes the sound. A vibrating string moves differently at different points along its length, with several vibration patterns superimposed. A pickup near the bridge generally gives a brighter sound than one nearer the neck. Selecting pickups changes which part of that moving pattern is sensed.

This also explains why ordinary nylon strings do not work with the same magnetic pickup: they do not respond like steel strings to its field. Other pickup designs can sense vibration differently. The familiar guitar cable carries an evolving electrical pattern; the string’s sound is rebuilt as moving air at the speaker.