- This paper presents an H/sub 2//H/sub /spl infin// feedback controller design for active sound control in a headrest. The design method which employ an H/sub 2/ performance criterion, with H/sub 2/ and H/sub /spl infin// constraints, was formulated as a convex programming problem using FIR Q-parameterization and frequency discretization, and solved using sequential quadratic programming. The design method was found effective since various objectives and constraints which are useful for this active sound control application were readily included. A robust controller was then designed for an experimental headrest system, and the performance, robust stability, and the multiplicative plant uncertainty model used in the design are presented and analyzed. A reduced-order real-time controller was then implemented on a digital signal processing system, producing the performance predicted in the design.