But the question is still - why is it relevant? If you intend to use it for music, then the power at 10kHz is very, very much smaller than the power in the bass range. And if you intend to kill dolphins, then we are talking about special hardware, in which case there exists datasheets with the relevant information.

The normal way to use this kind of tweeters in a sound system is to have a series resistor to reduce the possibility of a high-frequency fedback loop. But you normally don't a filter to strip off the low-frequency sound since a piezo horn has a very high impedance and works capacitive. It basically ignores the almost-DC signals for the bass.