Just caught the tail end of this conversation, but thought you might
find this of interest:

http://www.hpfriedrichs.com/rr-pzphone.htm

73
Pete
AC7ZL

Arv-K7HKL wrote:
Go to http://www.allelectronics.com and do a search on their
website for "piezo".
They have a number of Piezo elements available at reasonable prices.
Arv K7HKL

On 15 Jul, 22:07, telcodev wrote:
On Jul 13, 11:30 pm, lw1ecp wrote:

I guess a look at the guts of an old piezo tweeter could give you a
hand.
I had never heard of a piezo tweeter before your post. They sound like
a different type of device than what I am pursuing. I need an earpiece
with very high impedance, one that can work off of the nominal
potential a crystal radio circuit can produce.

But hey, thank you for the feedback, my world is ever so slightly
larger than before...