 These instruments are primarily used in marching bands so the sound comes from a forward-facing bell, as dissipation of the sound from the backward-facing bell becomes a concern in open-air environments.Many college marching bands and drum corps, however, use mellophones instead, which, with many marching bands, better balance the tone of the other brass instruments; additionally, mellophones require less special training of trumpeters, who considerably outnumber horn players.The Wagner tuba is a rare brass instrument that is essentially a horn modified to have a larger bell throat and a vertical bell.