Because of the intrinsic inefficiency in loudspeakers, most electrical energy is converted into heat with a corresponding rise in temperature of the driver structure. To avoid the harmful effects of elevated temperatures on the voice coil, an active heat control (AHC) process limits the electrical signal when the temperature nears the danger limit. Typical AHC using a closed-loop approach can produce oscillations and audible artifacts because of sensor delays. This paper demonstrates that an open-loop AHC can work. A bounded voice-coil temperature can be achieved using a dynamic range compressor configured as a brick-wall limiter with a threshold that is controlled by the temperature of magnetic components. The temperature of the magnetic assembly and the driving force of the loudspeaker can both be estimated in real-time by a linear quadratic observer (a Kalman filter) and an envelope follower respectively. The new AHC scheme is compared to closed-loop AHC using a simulation example.
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