Well, using an ultrasonic transducer - I'm not aware of any that go up into the RF spectrum - not saying they don't exist, but by the same token they probably wouldn't be cheap. 3.26MHz is pretty low for RF, but mighty high for ultrasonic.
Besides, you'd have a time trying to get audio distributed around between plates that were choked with sulfate crystals. If the plates themselves were delivering the energy, it would surround all of the crystals at once.
Besides, you'd have a time trying to get audio distributed around between plates that were choked with sulfate crystals. If the plates themselves were delivering the energy, it would surround all of the crystals at once.