If the voltage polarity is reversed back and forth at a high rate (frequency),
there will be a violent ion movement inside the tube which will generate
high intensity pressure waves (ultrasound waves) throughout the tube tht
will be transmitted through the tube wall into the room air. Also, the
electric fields generated by oscillating net charge densities in the tube
will deform the tube walls and thereby generting the pressure waves in
the room air (ultrasound).