Is there anyone familiar with the tweeters found in the base of many
birds-in-trees automatons, sometimes called "bocages"? They consist
of a small bellows with an attached thin brass plate with a small hole
in it that makes a simple tweet sound when pumped. When paired with
an alternating second bellows, they make a tweet-tweet sound.
I would like to make a replacement for a missing one but, after many
unsuccessful tries, I need advice about the theory behind them. The
diameter of the hole, taper of the countersink, thickness of the plate,
and any other pertinent information would be greatly appreciated.