question about piezos...

Hi I was wondering if someone could help me figure out which resistor to put on this piezo tweeter that I am running with an 8 in dayton classic woofer.

This is the woofer: Dayton Audio DC200-8 8" Classic Woofer 295-310


The piezo: Goldwood GT-400CD Bullet Piezo Horn Driver 270-069

I put a 4.7 on the piezo and it soundfine but im not sure if im getting the midrange frequencies. What would be a good resisitor to use in this setup? and how do the resistors affect piezos?

thanks