Juergen was full of ideas that reflected his excellent understanding of the limits of technology and science. At first many of his ideas seemed impractical, but in my experience, he was usually right on target and got the results or data he was after. I learned many practice things from him in the lab; almost every encounter brought a new point of view or idea that had a long-term impact on my work. The most important project he introduced me to was that of measuring the eardrum impedance, with progressive damage to the cochlea and middle ear. I will describe this impedance measurement system, which is a one-microphone method, and discuss Juergen's and my results for the cat. The measurement system is presently the most accurate and quickest known method of measuring acoustic impedance in cavities, and it works to frequencies limited only by transducer bandwidth. The method uses four calibration cavities to find the source pressure (or velocity) and source impedance (or admittance) as a function of frequency. The losses in the cavities are included in the calibration calculation, and the method recovers automatically, using a minimization technique, the acoustic lengths of the four calibration cavities.