Loudspeaker impedance meter

EE September 1986 by K. Rohwer LOUDSPEAKER IMPEDANCE METER A simple, yet interesting and useful, instrument for measuring the resistance and the inductive reactance of a loudspeaker. It may be argued that a loudspeaker impedance meter is something that is needed only once in a blue moon, but to many dyed-in-the-wool audio constructors it could be a godsend. Loudspeakers are frequently offered for sale at very low prices by various retailers, but often there is no indi- cation as to their characteristics. The present circuit will at least enable the impedance to be ascertained with a good degree of accuracy. A multimeter will, of course, only give some idea of the resistance. A useful aspect of the present circuit is that the resistance and the inductive re- actance can be measured separately. The only limitation of the meter is that all measurements take place at a frequency of 1000 Hz. This is an ex- cellent value for woofers and broad- band drive units, but on the low side for m...