Loudspeaker driver (moving-coil)
The transducer that turns an electrical signal into sound. The dominant design is the moving-coil (dynamic) driver: a lightweight cone suspended at its rim by a flexible surround, with a voice coil wound near its apex sitting in the gap of a strong magnet. Alternating current through the coil makes it (and the cone) move back and forth, radiating pressure waves loudspeaker-primer-hackaday.
Anatomy
- Cone / diaphragm — the radiating piston; its area is Sd in the T/S model.
- Voice coil — the wire in the magnetic gap; its length × the flux density is Bl (motor strength), and its DC resistance/inductance are Re/Le. This coil-in-a-gap motor is the entire sound-making mechanism: drive a bare hard-drive head actuator (also a voice coil) with an audio signal and it plays music — badly, with no cone or box (hdd-speakers).
- Surround + spider — the two-point suspension that centers the coil and provides the restoring spring (its compliance is Cms, restated acoustically as Vas).
- Magnet / motor — supplies the field the coil pushes against.
Driver types
Split by frequency band, then recombined with a crossover (an LC filter network):
- Woofer — large cone, bass.
- Mid-range — the middle band.
- Tweeter — small, high frequencies.
Why it can’t work alone
A bare driver in open air sounds thin: the wave off the back of the cone cancels the wave off the front (phase cancellation). That is why a driver needs a enclosure — and why the T/S parameters exist, to predict the driver-plus-box system.
Related
thiele-small-parameters · loudspeaker-enclosure · loudspeaker-primer-hackaday · synthesis