A  trombone with a Conical Bore??  By definition, it defies all common sense as by design, a slide trombone must  be a cylindrical bore instrument for the slide to work (not so fast.... read on!!))

E.A Couturier was known as one of the top cornetists in the US at the end of the 19th century.  He also composed music and ultimately designed a new tubing system for brass instruments to achieve better tonality. In 1916, he formed a company to make a complete line of his "Conical Bore" Instruments. "Couturier Model" cornets were also made by Conn, Holton and York.  Click here for a detailed biography of E.A Couturier.

Couturier indeed made a complete line of his Concal Bore instruments from Cornet to Tuba, and was not to be defeated by the Slide Trombone.   Not only did he achieve this objective, but the result shown here is  a remarkably sweet playing trombone with a big centered voice... but how was it done??  I'll try with words to describe the process....

From the mouthpiece adapter the tubing gradually increases to the end of the slide where one encounters a 'skirt' or the sliding piece. The skirt only slides back and forth inside the outer slide casing - maintaining contact with the outside sleeve.  The bend at the end (with the waterkey) is also conical and feeds into the upper interior conical slide, which has the skirt at the bell section end. Hence  the slide bore is essentially conical in all positions.. See the bottom photo which shows the keeper screw. Perhaps it is enough to say it works- and works well!!

See also my set of other Couturier Conical Bore instruments including a Cornet,  a Trumpet, a Baritone,  a Mellophone and a Tuba!