All fiberglass horns are lighter, and were originally designed for youngsters on the marching field. They lack resonance. Fiberglass horns will metal bells sound basically the same as all fiberglass horns with an attempt to look better. They are top heavy and don't sound that much better than fiberglass horns, and definitely don't compare to the sound you get from all brass horns. There is only 1 fiberglass sousaphone I would buy and actually play..a Conn 22K which is the fiberglass version of the short action 20K. It has a huge sound with the same push as a 20K but without the resonance.