How to use piezo sounder "feedback" line.

Could someone point me in the right direction as to how
to wire the third lead on some piezo sounders? It seems that
this is a "feedback" input of some sort, but I can't seem to
understand how it works. I am guessing that you use
it to control the oscillation frequency, but I could be wrong.

Any thoughts?

Thx!

Chris

Take a look at **broken link removed**.