Loudspeaker driver anatomy
A conventional moving-coil driver contains a motor, moving assembly, suspension, and supporting structure.
Diaphragm
The diaphragm is the main radiating surface. It may be a cone, dome, flat membrane, or another shape.
An ideal diaphragm would be light, stiff, well damped, and free from resonances. In practice, these goals conflict. Geometry often provides much of the required stiffness.
Voice coil
The voice coil is wound on a former and positioned in the magnetic gap. Current flowing through the coil creates the driving force.
The coil must be light enough for good sensitivity but strong enough to handle heat and mechanical stress.
Magnet and magnetic circuit
The permanent magnet provides magnetic flux. The pole piece and top plate concentrate that flux in the narrow gap containing the voice coil.
Ferrite and neodymium are common magnet materials. Neodymium can provide strong magnetic performance in a smaller package.
Surround
The surround connects the outer edge of the diaphragm to the frame. It allows axial motion while helping control and restore the diaphragm’s position.
It can also absorb or reflect waves travelling through the cone, so its geometry and material can affect high-frequency behavior.
Spider
The spider supports the moving assembly near the voice coil. It centers the coil in the magnetic gap and contributes much of the suspension’s restoring force.
A poorly controlled suspension may become nonlinear at large excursions.
Dust cap
The dust cap helps prevent debris from entering the magnetic gap. It may also contribute to high-frequency radiation.
Basket or frame
The basket holds the magnetic assembly, suspension, and diaphragm in alignment. It should be sufficiently rigid and should allow rear radiation to escape without excessive obstruction.
Terminals and flexible leads
The terminals connect the driver to the amplifier or crossover. Flexible lead wires carry the current to the moving voice coil.
Optional features
Some drivers also include:
- Pole-piece vents
- Under-spider ventilation
- Copper or aluminum shorting rings
- Phase plugs
- Demodulation rings
- Heat sinks
These features may improve cooling, reduce inductance variation, control compression, or modify radiation.