As a newbie, can someone explain the do's and dont's of piezo encasement? I cant quite figure if the whole thing is completely encased in contact with its 'encaser' (probably not the correct terminology lol) , or if the piezo should sit in a cavity so its encased, but with nothing touching the face?
One possibility is you may have a resonant enclosure problem.
For instance the RS 273-0073 is spec'd to have a resonance of 2500+/-500Hz. The center frequency of 2500hz has a wavelength of 1100f/s / 2500/s =0.44ft = 5.28". The range is 2000Hz to 3000Hz, so the range of sizes can go from 4.4" to 6.6" .
If this piezo transducer is placed in the center of a 5.28" wide box there is a strong probability it will squeal at 2500Hz if it gets enough feedback from the amp.
The solution is to move it off center. This has the unfortunate side effect of changing the tonal response.
What is the size of your cigar box?