Sad to say, many people still confuse the Baritone Horn* with the Euphonium. Safe to say, if you are in the U.S, you are dealing with a Euphonium. Only in the rare instances of British-style brass bands will you have a true Baritone Horn.
*Note: I always use the term Baritone Horn and not simply Baritone. I do this to make sure I am as clear as possible in which instrument I want. Baritone is an ambiguous term. Properly, it means a male voice between a tenor and a bass, but it can refer to a size of saxophone, a size of ukulele, a size of flute (in new nomenclature – see my post on flute species), or a string instrument (Baryton).
A true Baritone Horn is a narrow bore, slightly conical instrument that is closer to the Cornet in structure. A Euphonium is a wide bore, hugely conical instrument that is closer to the Flügelhorn in structure. The Baritone Horn, Alto/Tenor Horn, and Cornet form a cohesive family, while the Flügelhorn, Euphonium, and Tubas form another cohesive family.
There are even manufacturers who get this difference wrong. The American maker King has an instrument in their catalog (model 623) that they state is a “Baritone,” but upon inspection, these instruments are actually compact Euphoniums.
Both the Baritone Horn and Euphonium stem from Sax’s family of saxhorns. The problem lies in that Sax himself created two families and united them under one name, so that the soprano through baritone members were one family and the bass and contrabass members were another. The only pitch that overlapped the two “families” were the two members in 9-foot B-flat. Sax called these the Baritone and the Bass. Today, their descendants are the modern Baritone Horn and Euphonium respectively.
What I’ve found is a series of YouTube videos by the Euphonium virtuoso David Werden who demonstrates three different instruments: a Euphonium, a Baritone Horn, and a Double-Belled Euphonium. A Double-Belled Euphonium is a Euphonium that has a second, smaller bell (smaller than a normal trombone bell) that will give an echo effect. It is basically two instruments built into one and can be changed between as simply as pressing a valve.
Mr. Werden plays the same piece (“Neapolitan Dance” by Tchaikovsky) on all three instruments. Note how much smaller the Baritone Horn is than the Euphonium.
After watching these videos, note the drastic sound difference between the smooth, mellow Euphonium and the bright and bouncy Baritone Horn. These instruments should never be confused for one another.