Systems and methods for authenticating a passive speaker include (i) activating, by a playback device configured to drive the passive speaker, a passive speaker identification circuit of the passive speaker by providing an identification signal to an input terminal of the passive speaker, wherein the passive speaker is a particular type of passive speaker having particular acoustic characteristics; (ii) while the passive speaker identification circuit is active, measuring, by the playback device, an electrical current of the identification signal; (iii) determining, based on the measured electrical current of the identification signal, an impedance modulation of the passive speaker; (iv) determining, by the playback device, the particular type of the passive speaker based on the impedance modulation of the passive speaker; and (v) applying, by the playback device, a calibration to the playback device based on the determined particular type of the passive speaker.