This paper presents techniques and examples for computing the peak current that a complex loudspeaker load can draw when driven by a signal with well-defined voltage limits. This peak current can be characterized by a nominal resistance Rn. The theory for Rn of Preis and Schroeter, valid for infinite bandwidth, is applied to finite-bandwidth impedance data acquired from an FFT analyzer. Some theoretically calculable loads and their respective Rn values are presented. Simple test data are analyzed which show that the impedance data must be real at the band edge. Complexities involved in the processing are discussed and illustrated for real loudspeaker impedance measurements, and phase tilting or use of the cyclic minimum-phase impedance is necessary to provide consistent results. It is not unusual for the nominal resistance Rn of a loudspeaker to be less than half the minimum impedance value.
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