How does a speaker turn a signal into sound?

A speaker can reproduce a whisper, a drumbeat and a trumpet note using the same thin moving surface. It does not need a different miniature instrument inside for each sound. Its cone follows a changing electrical signal, turning that pattern into tiny changes of air pressure that travel to our ears.

In a common moving-coil speaker, a coil of wire sits in a permanent magnet's field. An amplifier sends changing current through the coil. Current in the magnetic field produces a force on the wire. Reverse the current and the force reverses; change the current's size and the driving force changes. The amplifier supplies energy for this motion. The permanent magnet provides the magnetic field, rather than being a fuel that is used up.

The coil is attached to the cone. Flexible supports let this assembly move back and forth while helping keep it centered. When the cone moves outward, it slightly compresses nearby air. When it moves inward, it creates a region of lower pressure in front. The air's elasticity and inertia pass these pressure disturbances onward as a sound wave.

The disturbance travels across the room, but individual air particles mainly move back and forth near their own positions. A sound wave is therefore not a stream of speaker air arriving at the listener. A useful comparison is a message passed along a row of people: something reaches the far end even though the people remain near their places. Air passes the disturbance by pushes and motion, not by understanding a message.

For a simple repeating tone, frequency tells how many cycles occur each second. A 200-hertz tone repeats 200 times per second. Greater vibration amplitude at the same frequency gives stronger pressure variations without increasing their repetition rate. Pitch is closely connected to frequency, while perceived loudness also depends on the listener and the sound's frequencies.

Real music combines many changing frequencies. The cone's motion combines their patterns, so one surface can carry the details of several instruments at once. A speaker cannot reproduce every pattern perfectly: its mass, supports and shape affect its response. Nevertheless, the journey from electrical current to magnetic force, cone motion and moving pressure explains how a quiet wire can deliver the sound of an entire orchestra.