What Is a Small-Bore Trombone?

Bore size measurements require measuring the width of the trombone slide. There are many styles of trombones, and their classification depends partly on the size of the bore. Small-bore trombones typically have a bore size of exactly 1/2-inch -- in some cases, slightly smaller. Understanding the difference between bore sizes in trombones will help you to select the proper trombone for your needs.

Tenor Trombone

The tenor trombone has a bore size of 1/2-inch. The tenor is the most common trombone in the trombone family; it has the same approximate range as a trumpet, although it sounds an octave lower. The tenor trombone falls into the largest category of small-bore trombones -- that is, it has the largest possible bore without exceeding the criteria required to be classified as a small-bore instrument. As a result of its small bore, the tenor trombone produces a clear, penetrating sound.

Alto Trombone

The alto trombone also uses a bore size of approximately 1/2-inch. Alto trombones have a higher register than a tenor trombone; although they usually have the same-sized bore as the tenor, the difference in pitch comes from the overall construction of the instrument. The alto trombone boasts a smaller slide a and more compact mouthpiece, making it ideal for alto parts in a trombone choir.

Soprano Trombone

The soprano trombone has a bore size of approximately 0.45 to 0.47 inches, similar to the bore of a trumpet. Soprano trombones have the smallest bore of any trombone, and its smaller bore makes the instrument more compact and creates more resistance against the player's airflow; this resistance makes it a difficult instrument to play well. The soprano trombone usually appears in trombone choirs playing the soprano part.

Valve Trombone

The valve trombone doesn't use a slide, instead, it employs valves similar those found on a trumpet or baritone. Valve trombones have the same range as a tenor trombone but lack the slide mechanism which allows for effective glissandos. The bore size of the valve trombone qualifies as a small bore and usually extends no larger than 1/2-inch. The valves make it easier to accurately play fast passages, but its restricted airflow changes the sound of the instrument slightly.