I was told, I think it was this past summer, it's generally a good idea to tune everyone to a low (written) F. I think the reasoning behind this was it's a natural overtone of Bb, so if you can get that note in tune, and get the intervals in the quartet tuned, then generally the horn will set better for everyone.
We tune multiple times before we start quartet (A, Ab, Bb, Eb) and then we always start with a chorale to listen around to eachother.
We tune multiple times before we start quartet (A, Ab, Bb, Eb) and then we always start with a chorale to listen around to eachother.