A compensating horn in F/Bb.
Compensating double horns differ from full double horns in that they have less tubing. When playing on the F side of the horn, the air still goes through the Bb horn tubing, but it also goes through an additional length of tubing that creates the correct length for the F-harmonic series. Since the F horn is longer than the Bb horn, there is another set of three short slides to “compensate” for the different length of the F horn.
“Compensating double horns are lighter than full doubles. This horn is a great instrument for someone just beginning horn or someone curious in compensating horns and the unique way they are built.” — Dr. Sally Podrebarac