Abstract: In an active loudspeaker, a bridge rectifier generates an unregulated DC voltage from the AC mains power supply voltage. A self-oscillating pulse modulator generates a pulse-modulated switch signal that is controlling a power switch stage which is switching the unregulated DC voltage. The power-switched signal is low-pass filtered and driving a high-impedance speaker element. The amplifier is compensating fluctuations and noise in the unregulated DC voltage by feeding a reference signal back to the pulse modulator which is derived by voltage-dividing the power-switched signal. The audio volume is regulated by adjusting the voltage divider ratio of the feedback signal. The loudspeaker provides galvanic voltage isolation of the speaker inputs through an audio input stage to comply with safety regulations. This invention eliminates the regulated switched-mode power supply in active loudspeaker applications and thereby reduces cost and weight.

Abstract: In a digital wireless audio transmission system, a transmitter section includes a local oscillator and frequency modulator to modulate the local oscillator signal with a periodic transmitter spreading signal in order to generate a frequency-modulated radio-frequency signal. An amplitude modulator amplitude-modulates this signal with serial digital data that is generated by an audio interface and a channel encoder. This amplitude-keyed signal which is spread in frequency is then transmitted via a transmit antenna as electromagnetic waves. A receiver section receives these electromagnetic waves via multiple antennae and amplitude-modulates the signal of at least one antenna with antenna modulator signals that have the same frequency as the transmitter spreading signal and a fixed relative phase deviation. All of these antenna signals are then added, and the sum signal is amplified and detected by a small-signal detector.