voicecoil

A voice coil is a coil of conductive wire that forms the movable element in many electroacoustic transducers, most commonly loudspeakers and dynamic microphones. It is mounted to the diaphragm or a moving assembly and sits within the air gap of a permanent magnet. When an electrical signal passes through the coil, the resulting electromagnetic interaction (Lorentz force) moves the coil and attached diaphragm, producing mechanical vibrations and sound. In dynamic microphones, the diaphragm moves the coil and the changing magnetic flux generates an audio signal.

Construction and materials vary with driver size and design. The coil is typically wound on a cylindrical former made of paper, polyimide, or lightweight metals. Conductors are usually copper, sometimes aluminum to reduce mass. The coil’s length, number of turns, and former geometry determine its electrical impedance and how it interacts with the magnetic field. Leads connect the coil to the rest of the circuit and must tolerate repeated bending without degrading.

Electrical and mechanical properties are intertwined. The coil has a DC resistance and inductance, which influence power handling, sensitivity, and high-frequency response. Heating from I²R losses limits output and long-term reliability, so winding and potting materials are chosen for temperature stability. The coil’s mass and stiffness affect transient response, efficiency, and distortion, while the surrounding suspension and magnetic gap define linearity and excursion limits.

Applications and considerations. Voice coils are central to most dynamic loudspeakers, from woofers to earbuds, and to dynamic microphones. They must be designed to balance lightness, strength, and thermal performance while minimizing distortion. The term can also refer to the moving coil in a microphone, though not all microphones use a voice coil.