Fig. 2: Schematic & block diagrams of the most used control strategies.
p refers to the pressure (subscripts f and b refer to front and back respectively), v to the particle velocity, G and K to a constant proportional gain, and Θ to the control law (transfer function between p and i). a Direct impedance control with a single constant gain applied to the sensed pressure (a-1) and with constant gains applied to both the front pressure and the diaphragm velocity (a-2). b Feedback controller based on error minimization between the sensed velocity and the target velocity (obtained using the target impedance to be synthezised): P-V feedback using a microphone and a velocity sensor (accelerometer or laser vibrometer) b-1 or P-only feedback where the velocity is estimated from the measured pressure gradient across the membrane b-2. c Hybrid sensor/shunt based control (feedforward type), requiring only the measurement of the front pressure pf. d PID (Proportional, Integral, Derivative) type control, which uses two pressure measurements to synthetically tune the mechanical properties of the loudspeaker independently with only three real constant gains. e Mixed feedforward and feedback control scheme that combines both strategies to improve the stability of the controller.
