Is it a Baritone or Euphonium?

Remember that old "baritone" I bought?  Well, it should be more properly called a euphonium.  "What's the difference?" you might ask.  Certainly to the layman, the baritone and euphonium look the same.  But they sound quite different.

The reason is simple -- cylindrical tubing produces bright, sharp sound; conical tubing produces round, mellow sound.  To give you an idea, a trumpet and trombone are about 2/3 cylindrical and thus, have a very bright sound.  A tuba is about 2/3 conical and sounds just the opposite--round and mellow.  The baritone horn's tubing is about half-and-half so it doesn't sound like a trombone nor does it sound like a tuba -- rather, somewhere inbetween.  Here is a comparison of the two instruments:
 

The Baritone Horn	The Euphonium
Shape: the tubing is about half cylindrical and stays about the same size ending in a quick flare at the bell	Shape: the tubing is mostly conical and gradually increases to the flare of the wider bell
Sound:  More cylindrical tubing produces sound which is bright, sharp, and distinct.	Sound: Conical tubing produces sound which is deep, round, and mellow (sim to the tuba)

However, these horns don't always look similar.  Neither of the above instruments look like the horn I used in school.  Also, don't believe anyone who tells you that "a baritone has three valves and a euphonium has four".

There are many variations of both instruments which further adds to the confusion.  Variations exist in the number of valves, position of the valves, design of the bell and so on.  Also, you will see horns in either brass lacquer finish or silverplate finish.  Front-facing bells were designed to project more sound forward to the listener or for marching bands.  Here are just some examples I've come across:

Examples of Euphonium/Baritone Horn variations

Euphonium  (brass lacquer finish) Baritone Horn (silverplate finish) Three top-action valves	3/4 size; 3 top-action valves)
Four top-action valves (The fourth valve allows playing lower notes, changing the horn's fundamental pitch from B-flat to F, just like the F-attachment on the trombone)	Three top-action valves and fourth on the side  (Fourth valve played with left hand)
Three valves on the front; bell upright (note the mouthpiece and leadpipe on opposite side as this type of horn is held differently)	Four valves front; bell upright
Three valves front; bell front Most often, the front-facing bell  was detachable and could swivel (This was typical of the style I used in school)	Four valves front; bell front
Late 19th century; oval shape; four rotor valves; made by Cerveny, Czechoslovakia	Lehnert of Philadelphia - 1870's A rare left-handed euphonium  with four rotor valves
Looking somewhat like an overgrown trumpet... this is a "marching baritone" designed for marching bands and drum and bugle corps	Presented for comparison to the Marching Baritone is the King Flugabone which you saw on the trombone page.  With its constant cylindrical tubing, it's a flugelhorn shape with a brighter, more trombone-like sound
And...the most unusual variation of all... The Double-Bell Euphonium This special type of horn was invented in the 1880's and was made through the 1900's although its popularity waned after WWII.  The last of the double-bell euphs was made by King in the 1960's.  It had a special valve to redirect the sound from the large bell to the smaller one.  The idea being that one instrument could sound like either a euphonium or trombone -- though it sounded more like a euphonium and a baritone horn.
King upright bell,  four front valves (silver finish) Buescher bell front, four front valves Conn bell front, four front valves My own 1907 Buescher upright bell with three top valves and side change-valve
1902 Conn five front valves; upright bell / swivel small bell	(close-up view of valves) In this instrument, the fourth valve performs like other 4-valve instruments, lowering the fundamental pitch to F. The fifth valve was the redirect valve, and, unless you were a six-fingered player, you depressed the special valve with the left hand.

So, how do the trombone, baritone horn, and euphonium  differ in sound?
Here are two musical examples and sound files of the same melody played on a trombone, a baritone horn, and a euphonium.

From what we know based on the shapes of the tubing, the trombone will have the brightest, most brilliant or brassy sound; the baritone horn will sound a bit softer and mellower; and the euphonium will have the softest, most round and mellow sound of them all.
 

Example 1
Trombone	Baritone Horn	Euphonium
Example 2
Trombone	Baritone Horn	Euphonium