Technology
Speaker Systems
Quick fact
The first practical loudspeaker, invented by Ernst Siemens in 1877, used a moving coil in a magnetic field—exactly the same principle used in most speakers today.
Why this is interesting
You press play on a song, and sound fills the room. But how does a tiny electrical signal from your phone become a thundering bass or a delicate whisper?
Read the full explanation
Understanding Speaker Systems
Imagine a speaker as a miniature piston. Inside the speaker box is a driver—the core component. The driver has a strong permanent magnet, a voice coil (a coil of wire), and a cone (the diaphragm). When an electrical audio signal flows through the voice coil, it creates a magnetic field that interacts with the permanent magnet. This forces the coil to move back and forth. Because the coil is attached to the cone, the cone moves with it, compressing and rarefying the air in front. That alternating pressure travels as sound waves. The faster the signal alternates, the higher the pitch; the stronger the signal, the louder the sound.
A deeper explanation
The mechanism is based on the Lorentz force law: a current-carrying wire in a magnetic field experiences a force perpendicular to both the field and the current. In a speaker, the voice coil is placed in the radial magnetic field of the permanent magnet. As the signal current alternates direction, the force on the coil changes direction, causing it to vibrate. The cone amplifies this motion and radiates sound efficiently. The speaker's impedance (typically 4 or 8 ohms) determines how much current it draws from the amplifier. The frequency response—how evenly the speaker reproduces different pitches—depends on the size, mass, and stiffness of the cone, as well as the enclosure design. Understanding this helps in choosing speakers for different purposes, from subwoofers to tweeters, and in troubleshooting audio issues.