Natural Science Forum / Physics / Acoustics / July 2007

I am working on a project concerned with sonoluminescence,in which we
have to create standing ultrasonic waves in water inside a 250cc
flask. Testing the piezoceramics I encountered with two problems:
1. The amplitude of the waves, which have been propagated to the water
(detected by a microphone), differs when I change the pole of the
ceramic that contacts with the flask, i.e. when (-) pole is connected
to the flask, the amplitude is so much lower than the connection of
(+) pole of the ceramic to the flask.
2. The resonance frequency differs for the connection of (-) and (+)
poles to the flask as described above, e.g. for (-) pole it resonates
at around 21200Hz, but for (+) pole it happens at about 21500Hz.
Please let me know if this behavior is natural or not.
Also please explain what I can do for solving the problem.