Measuring Method to Derive the Lumped Elements of the Loudspeaker Thermal Equivalent Circuit
A measurement technique is described to study the thermal behavior of loudspeaker systems. From the temperature time curve of the voice coil the lumped element values for the thermal equivalent circuit for loudspeaker systems are derived. Thermal behavior of loudspeakers is investigated under varied power and frequency conditions. The thermal equivalent circuit was improved, to be applicable not only for loudspeakers under open air conditions but also in cabinets. A computer controlled measuring method was developed, to enable long term measurements with constant input power. The lumped elements are calculated from the measurement data using a two-step approach, which in a first step uses polynomial fitting based on the Laplace transform of the step response function of the equivalent circuit. These initial values of the lumped elements are enhanced using curve fitting between the measured temperature curve and the step response function. Different loudspeakers were used in varied conditions (in free air, in cabinet, or clamped) for experiments.
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