A typical box speaker midbass driver employs a series inductor & maybe a shunt resistor (for baffle step compensation) & a Zobel network (to control impedance), that together provide low pass filtering. The impedance of the inductor is high for transients, so you can't take advantage of an amplifier's low output impedance, is correctly terminating the driver back EMF during transients a consideration during network design? Obviously, a poor termination (stored energy) will show up in a waterfall chart.
A high source impedance is not a poor termination, it's just different. This is an audio myth. Response may change and impedance variations may come into play, but the CSD (waterfall, or stored energy as you put it) will not be a problem if your response is as it should be.
