If you played a trumpet like you play a cymbal, by striking it, then this discssion on variations in alloys would be really appropriate. What the brass on a trumpet does is to form a closed-end tube (when your lips are on the mouthpiece), which becomes a resonating chamber for the vibrations which you introduce when you buzz. This is the most important concept at work here and the composition of the metal is a minute factor by comparison. Not that it is of NO consideraton, but references to tapping the horn are somewhat ridiculous. The shape, length, contour, bends, surface quality, and taper of the interior, bracing and bell shape and flare are the chief factors in sound production. Brass is used mainly because of its maleability. More or less copper does make it more or less maleable. More maleable means easier to bend (even after the horn is built). Less means more resistant to bending (and more resistant to abuse). My copper belled flugel is easy to injure. It does sound different, but I am not sure if it is largely due to its material or its shape and size. It seems like it wouldn't ring like a harder alloy.