In England a very popular small ensemble is the brass quartet. There is a standardized instrumentation (related to the brass band world) for the brass quartet: 2 cornets, Eb horn, Euphonium. It is very similar/parallel to the standard string quartet of 2 violins (=cornets), viola (=horn) and cello (=euphonium). We Americans are used to hearing brass quintets, but we don't hear this particular 4-part mix very often. Compared to a brass quintet the quartet can sound a little thin ...