I have the next theoretical-practical problem. I have to build a tubular bell array (like that at symphonic orchrestas) with tubes (not rods) of aluminium or copper. The principal problem I have is I don't know how to state the wave equation for a tube (I have done it for a string). How I do it? When I have the wave equation stated I must get the frecuencies to get a standing wave. Obviously this is what I want. Could you help me?