How Speaker Components Work: Voice Coils, Diaphragms, Cones & Compression Drivers Explained

The voice coil: where electrical signal becomes motion

The voice coil is a cylindrical winding of copper or copper-clad aluminium wire, wound around a former (the cylindrical tube it's bonded to), suspended inside a fixed magnetic field created by the driver's magnet assembly. When the amplified audio signal — an alternating current — passes through the coil, it interacts with that magnetic field and produces a force (per Lorentz's law) that drives the coil, and everything attached to it, back and forth along the driver's axis.

Voice coil diameter, wire gauge, winding height, and impedance all affect power handling and how efficiently the coil converts electrical energy into mechanical motion without overheating. This is also the single most common failure point in a heavily used PA speaker: sustained high power drives coil temperature past the adhesive's or former's tolerance, causing the winding to deform, rub against the magnet gap, or open entirely.

Cone, spider, and surround: turning motion into sound

The cone (or diaphragm, in a compression driver) is rigidly bonded to the voice coil former and moves with it, pushing and pulling air to create the pressure waves we hear as sound. Cone material — paper pulp, coated paper, polypropylene, or aluminium — trades off stiffness, damping, and weight, which together shape frequency response and distortion characteristics.

Two suspension components keep the cone moving in a straight line without rocking or rubbing: the spider (a corrugated fabric disc mounted between the cone's neck and the frame) centers the voice coil in the magnetic gap, and the surround (the flexible ring at the cone's outer edge, sealing it to the basket) allows excursion while sealing the cone to the frame. Both degrade with age, heat, and UV exposure — a cracked or hardened surround is a common cause of buzzing or reduced bass response in an older speaker.

Compression drivers and diaphragms: high-frequency reproduction

A compression driver is the horn-loaded high-frequency counterpart to a woofer's cone-and-coil assembly, but with a critical difference: its diaphragm — a thin dome, usually titanium, aluminium, or polymer film — moves a tiny distance compared to the acoustic energy it needs to produce, and a horn couples that small, high-pressure motion efficiently to the room. This compression is what allows a driver a few centimetres across to project clearly over a large PA system's low end.

Diaphragm failure is common and usually specific: overpowering (from an underpowered amplifier clipping, which sends more high-frequency energy than a clean signal would) burns out the voice coil bonded to the diaphragm's neck, and a damaged diaphragm must be matched by exact model, throat diameter, and impedance — a mismatched replacement will either fail again quickly or perform far below spec.

The magnet assembly: providing the fixed field

A ferrite or neodymium magnet, together with the top plate and pole piece, creates the fixed magnetic field the voice coil moves within. Neodymium magnets deliver the same field strength at a fraction of ferrite's weight and size — the reason modern touring and line array cabinets are dramatically lighter than equivalent designs from a few decades ago — at a materials cost premium that shows up in driver price.