gravity,stress on the surface of an inflated balloon,a stretched spring...these all have"potential" energy. if you rub your finger on the surface of an inflated balloon the sound emanates from the surface as a whole in affect amplifying the vibrations caused by your finger and the surface tension of the rubber membrane.an earth quake is an example of the same thing on the surface of the earth...the waves emanate from the center and cause destruction in a radius area on the surface.in the case of the spring the waves are longitudinal because they travel along the length of the tension.the atmosphere itself has a potential energy(atmospheric pressure).if you put 100 microphones around one source of sound the total input to all of the microphones combined would be more than the output of the one sound source.anywhere you have stress you can use it to amplify energy and do so without destroying the potential.