Percussion

If you're talking about High Hopes

they use a tubular bell tuned in C flat

The tubular bell is a percussion instrument, where you hit the very top edge of the tube with a hammer. It's best to strike it at an angle. There is also a pedal to sustain the sound.

To produce various notes, the tubes is cut to match the pitch.

frequancy decrease damping due to viscosity

Sound is vibration (of air ... as we humans perceive it).

If a bell, tubular or otherwise, is made to vibrate then it will cause the adjacent air to vibrate ... and we call it sound.