The present invention comprises a method and apparatus for continuously, controlling a gain of an amplifier circuit while switching between open-loop and closed-loop power control. The acoustical signal is amplified and drives a speaker of the speaker system. The sidewall defines the opening and includes at least one recess formed therein. The covering member contains a reflective material, and covers at least the side surfaces of the transparent member. Concurrently with FFT processing of the first sub-frame, butterfly operations are performed on the sub-transforms of the second and third sub-frames.