  We study the dissipation of diffuse ultrasonic energy in a reverberant body
coupled to a waveguide, an analog for a mesoscopic electron in a quantum dot. A
simple model predicts a Porter-Thomas like distribution of level widths and
corresponding nonexponential dissipation, a behavior largely confirmed by
measurements. For the case of fully open channels, however, measurements
deviate from this model to a statistically significant degree. A random matrix
supersymmetric calculation is found to accurately model the observed behaviors
at all coupling strengths.
