Hi Bill,
Sorry to be so late. I worked out a simulation for you in Spice (thanks Wayne!) for your piezo series. It gives an atten. of (about) -3dB at 20KHz and a xover frequency around 10K. You get about (with a 93dB flat-simulation- speaker output)
+/- 87dB@10KHz, 89dB@15KHz and 91dB@20KHz.

Looks good on this side (of the highs). Make shure your wire wounds are not inductive or you will end with a pretty crazy bell-shaped-curve with a peack at 95 dBs.
Regards.