I had a little discussion recently with a horn player about using Bb horn fingerings for certain parts of the the lower register. He had never heard of using Bb horn in the lower register. If you're just learning the double horn for the first time, and you don't have an instructor to introduce these preferred fingerings, you might find this youtube clip helpful:
http://www.youtube.com/watch?v=U55zSAqJzIo If this link doesn't work, search youtube for < French Horn : Fingerings for French Horn >
It's a little confusing at first because he starts on the G one and a half octaves below middle C and works up chromatically. It goes by pretty quickly so I had to watch it several times to follow exactly what he was doing. He starts the low G on F horn with fingerings 13 then switches to Bb horn (with the trigger)from the C# through F, then switches back to F horn on F#.
The low register notes he plays on Bb horn are: Low C# is T23, D is T12, Eb is T1, E is T2, F is T0. [T means trigger.]
He stays on F horn through second space G, then switches to Bb horn G# and above to high C.
Valerie
Valerie