Nice choice, the euphonium is Buzz's favourite!
The euphonium is a tenor voiced instrument and is the second biggest brass instrument behind the tuba.
Interesting euphonium facts
The euphonium is the tenor member of the tuba family.
The name "euphonium" comes from the Greek word for "beautiful-sounding".
It is a valved brass instrument whose bore constantly increases in size from the valve section to the bell - this is called "conical bore", as distinguished from "cylindrical bore" instruments which maintain a constant tubing diameter for a greater portion of the instrument's total length.
The euphonium plays in the same range of pitches as the trombone, but its cylindrical bore gives it a more mellow, "rounder" sound compared to the "brassier" sound of a trombone.
Invented by Adolphe Sax, the euphonium is thus a saxhorn.
The euphonium is often used by symphony orchestras as a tenor tuba. Its main venues are various wind bands, military bands, and brass bands where it is frequently featured as a solo instrument.
Photo credit Daisuke Hayashi