An application note from Analog Devices about AD5933, this provides a low cost substitute to expensive test equipment like signal generators, oscilloscope and voltmeters in getting the speaker’s impedance profile. Link here (PDF)
This application note describes a circuit architecture using the AD5933 that allows the system designer to measure the impedance profile of the loudspeaker and integrate this circuitry into the audio signal chain. This offers many benefits. Upon system power-up, for example, the circuitry provides the ability to measure the impedance profile and thus the acoustic properties of the loudspeaker, enabling direct comparison to a factory calibrated profile stored nearby. Any changes in the impedance profile are detected and further diagnostics are carried out, preventing premature damage.
