When amplifier current capability and loudspeaker loading are discussed it is often said that it is possible to devise special waveforms that cause a loudspeaker to draw more transient current than would at first appear to be possible. This is perfectly true. The issue was raised by Otala et al[13], and expanded on in Otala and Huttunen[14]. The effect was also demonstrated byCordelli[15].

The effect may be demonstrated with the electrical analogue of a single speaker unit as shown in Figure 7.26. Rc is the resistance of the voice-coil and Lc its inductance. Lr and Cr model the cone resonance, with Rr controlling its damping. These three components simulate the impedance characteristics of the real electromechanical resonance. The voicecoil inductance is 0.29 mH, and its resistance 6.8 ?, typical for a 10 inch bass unit of 8 ? nominal impedance. Measurements on this circuit cannot show an impedance below 6.8 ? at any frequency, and it is easy to assume that the current demands can therefore never exceed those of a 6.8 ? resistance. This is not so.

The secret of getting unexpectedly high currents flowing is to make use of the energy stored in the circuit reactances. This is done by applying an asymmetrical waveform with transitions carefully timed to match the speaker resonance. Figure 7.39 shows PSpice simulation of the currents drawn by the circuit of Figure 7.26. The rectangular waveform is the current in a reference 8 ? resistance...