Concert instruments aren't necessarily Pointed towards a audience like marching instruments are. For example, look at a concert, and marching tuba. The Marching tubas bell faces the crowd. Concert tubas bell points upward. Also on a marching instrument, it makes it easier to get a grip on it since your moving. For instance, a mellophone is the same thing as a french horn, but is easier to march with. It's always the same sound though.