Replacing a 8 ohm Speaker with a Piezo. Will it work?
If you do a source transformation on the voltage source and resistor in parallel for the \$8\Omega\$ speaker, you get a current source which is what we care about when driving a speaker. We know that the current through the cap can be written as \$I_c=sCV\$; this means that as the time rate of change of voltage increases, current will increase, and vice versa. The result is that we've protected our speaker from passing too much current and eventually (potentially) being destroyed. Aside from this, impedance of the speaker typically comes into play when we want to maximize the power transfer between an amplifier and the load (speaker). In this case, seems like we don't care too much. A piezoelectric speaker works by virtue of the fact that an applied voltage results in a strain on the material. To my knowledge it is safe to apply the rated amount of DC to one of these, and the high resistance makes it safe to apply this voltage directly without creating enough heat to burn up the device. This circuit should work as expected IMO.