12 Volt Encyclopedia · Volume V · Article 4
Subwoofer Anatomy, Part Two: Voice Coil, Former, Spider and Motor Assembly
Inside the frame, electrical current, magnetic flux and suspension force interact. The motor generates force, the suspension controls position, and the voice-coil assembly must survive both heat and acceleration without losing alignment.
Voice-coil winding
Copper or aluminum wire is wound around a former in one or more layers. Coil diameter, winding height, wire size and number of layers influence resistance, inductance, thermal capacity and moving mass. Dual coils provide wiring flexibility, not two independent motors.
Former
The former supports the winding and transfers force to the cone. Aluminum conducts heat but is electrically conductive and can influence inductance. High-temperature composite and polyimide formers reduce eddy-current effects and mass in suitable designs.
Spider system
The spider centers the coil and supplies much of the suspension’s restoring force. Diameter, corrugation, resin, fabric and number of spiders shape compliance and travel. Multiple spiders can increase control but may also increase stiffness and moving mass.
Gap, pole and top plate
The top plate and pole concentrate magnetic flux across the narrow gap containing the voice coil. Tight geometry improves flux density but requires precise alignment. Extended poles, undercuts and shaped plates influence symmetry and usable excursion.
Back plate and magnet slugs
The back plate closes the magnetic circuit and often incorporates the pole piece. Ferrite slugs provide magnetomotive force between steel plates. Stacking more ferrite can help only when the rest of the circuit can use the added flux.
Faraday or shorting rings
Conductive rings or sleeves in the motor create opposing eddy currents that reduce inductance variation and magnetic modulation. Properly applied, they can improve upper-bass response and reduce distortion. They do not simply make the static magnet stronger.
Cooling and venting
Pole vents, under-spider vents and basket windows move air around the coil and gap. Cooling must be quiet and effective without weakening structures. A vent can also generate turbulence if area, edge shape or clearance is inadequate.
Installation and testing checklist
| Checkpoint | What to verify |
|---|---|
| Compatibility | Source output type, receiving input type and allowable voltage range match. |
| Routing | Signal wiring is protected, secured and separated from likely interference sources. |
| Termination | Connectors fit firmly without excessive force; no cable weight hangs from a jack. |
| Signal | Every channel is identified, clean and unclipped at the intended source level. |
| Final test | Polarity, channel assignment, noise floor and operation are verified with the vehicle running. |
Frequently asked questions
What actually pushes the cone?
Current in the coil interacts with magnetic flux, producing force described by BL times current.
Do more spiders always improve control?
No. Geometry and compliance matter more than count.
Why is the magnetic gap narrow?
Concentrated flux improves force, but precision and cooling become demanding.
What does a shorting ring improve?
It can reduce inductance-related response change and distortion.
Can vent noise be mistaken for damage?
Yes, but persistent or worsening noise still deserves inspection.