The Knopf family have been in the horn making business for over 150 years, creating revolutionary designs that have influenced horn makers worldwide. The Model No. 13 is a compensating double as opposed to a full double. This means that rather than having full length F and B-flat slides, it only has a full length B-flat side. The F side of the horn is achieved with the air moving through the B flat slides, then going through F extension pipes (shorter than "regular" F slides) to generate the right key.
This Model 13 is made with lacquered yellow brass and has a fixed bell. It has a high valve compression at 5.5, and with a proper valve rebuild the horn has extreme potential. All valves and slides move with ease. There is lacquer ware on the bell tail but nothing that would effect the sound. Comes with a hard fixed bell case.