Couesnon B♭/A "Quick-change" (1924)

This instrument showcases a striking visual design known as a long cornet—a model built with an elongated body that stretches forward like a trumpet, while retaining the tight, conical loops of a traditional cornet. It is designed as a dual-key instrument, functioning in both B♭ and A.

To shift keys, the instrument features a specialized slide that can be physically extended outward. This extra length adds more internal space to the air column, dropping the entire pitch from B♭ down to A without requiring a separate horn.
The mouthpiece receiver on this specific horn sits in an unusual acoustic grey area—it is too large to accept a standard cornet mouthpiece shank, yet too small to receive a modern trumpet mouthpiece shank. Comparison with a matching, un-displayed sister model reveals that this model line was originally designed to take a normal mouthpiece. This suggests that this specific leadpipe has an isolated factory defect or suffered damage that altered its internal dimensions.
The horn is currently in good playing condition with tight compression. However, because of this isolated leadpipe distortion, its acoustic response would be significantly improved if paired with a custom or transitional mouthpiece shank that matches its unique shape.