Brass is used for some musical instruments because it can be used.
Experimental effort has been expended on the effect of construction
material on the sound of brass and woodwind instruments, and the
differences seem to be undetectable to physical instrumentation*.
In one experiment a brass trumpet was packed on the outside with
modeling clay and the sound was unaffected! Silver, gold, and even
platinum are used to make the same instruments that are made of
brass in cheaper versions. Instruments made of precious metals are
often made with greater craftsmanship than their brass congeners,
and that may affect relative sound.
I have a Dolmetsch descant recorder made of plastic that sounds
every bit as good as a wooden recorder. The material does not
vibrate significantly, it seems; the shapes of the boundaries are
likely the only important factor in producing sound. Wooden flutes,
oboes and clarinets do sound different to me (I think) from their
metallic counterparts, but I don't know if that has anything to do
with intrinsic differences in the materials. It may be that the
shapes of the cavities are different for wooden than for metal
instruments.
Leigh
* Of course some audiophiles believe that there are differences
in acoustic stimuli which cannot be perceived except by the
discriminating audiophile. They call these "audible differences"
and are quite mystical in their beliefs. These people buy, for
example, Monster brand cables for their speaker wires.