Learning from the DQ-10 piezo arrangement.

[jackfish]

I am interested in adding a piezo tweeter to my Large Advents to exclusively handle frequencies 17 KHz and above and would like to understand how the super tweeter was employed in the Dahlquist DQ-10. From looking at the available crossover schematic can someone explain to me the characteristics of the piezo tweeter crossover, what each component does, roll off, etc? Thanks.