Various aspects of dedicated pulse-width-modulation (PWM)-based amplifiers for active loudspeaker systems are addressed. A new amplifier concept, dedicated to woofer and mid-range (0-4 kHz) loads, has been developed to provide a high-fidelity solution with minimum energy consumption in both analog and digital active loudspeaker systems. The concept is based on a novel feedback topology, a modulation strategy that is dependent on bandwidth, and the use of a switching frequency as low as 44.1 kHz without compromising the sound quality. Detailed measurements on two 200-W example implementations (700-Hz and 4-kHz bandwidths) are given, showing THD + N < 0.1 % and an unweighted dynamic around 110 dB. A new efficiency measure termed energy efficiency is defined, based on investigations of consumer behavior. The amplifier examples are shown to provide reductions in energy consumption of more than 90% compared to conventional principles, mainly because of a total idle power consumption of only 1.5 W, and power-stage efficiencies approaching 96% at higher output powers.
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