I used to be all in for double horns; that is, until I saw this video. The horn players are all playing single F horns, and that is the only type of horn allowed in the Vienna Symphony. I used to go through an insane hour and 30 minute warn up. I started with the warm up in "Art of Horn Playing" method book by Philip Farkas which is all on the F horn. I found myself doing impossible things like the 5ths and octave arpeggios with 8th notes, quarter = 132. And yet, when I got to my own warm-up, I could not play with the freedom I had on just the F horn. I doubt if any high schools use singles in their bands, but they sure do in Vienna.