Audio transducer with etched voice coil

Abstract

An audio transducer having a voice coil formed by an etched, flexible circuit having an elongated, oblong spiral loop and rolled into a cylindrical tube. The coil cooperates with a magnetic structure including a circular, central magnet having a front north pole plate and rear south pole plate sized to fit closely within the cylindrical coil, and an annular outer magnet having a south front pole plate and a north rear pole plate aligned with the pole plates of the central magnet. The aligned magnets define annular front and rear magnet gaps between the respective front and rear pole plates with front and rear radial magnetic fields of opposite polarity formed across the respective magnet gaps. The spiral pattern etched on the coil is configured so that current flowing in the front portion of the coil within front gap magnet flows in an opposite orbital direction from current flowing in the rear portion of the coil within the rear magnet gap. Consequently, the forces acting on the coil act in concert to create the desired transducer motion.