Background noise question

[Elavionic]

I need to design a circuit that controls the level suplied to a piezo in respect to the ambient level sound or background noise.
So if the ambient noise raises the piezo should also raise the sound an vice-versa.
Thus anyone have any ideas?
Thanks in advance.

 

[flatulent]

One thing to keep in mind is to stop measuring the background when your piezo emits sound. One simple way to measure the background is with a cheap microphone, op amp amplifier stages, half wave rectifier stage feeding a RC network with a large time constant. This will produce a DC level proportional to the background noise. You can shunt one of the AC amplifier stage inputs with a FET or BJT to cut off the background measurement when the piezo sounds.