Fine-tuning and measurements of a sensorless motional feedback subwoofer

In his earlier article, Robert Munnig Schmidt described a subwoofer system with an electronic solution to adapt and control the subwoofer mechanical-dynamic behaviour. One reader commented observed a anomaly in the system transfer function, a small 90Hz response peak. One thing lead to another and resulted in this article focusing on the nature of the driver inductance and its variance from a pure inductance. The article also addresses fine-tuning the system and the distortion reduction that can be achieved.