Time for a new "blogging season"!!
Sometimes I get a student to play out more and receive the complaint: "I don't like the way I sound."
It's true that, when you start to use more air, the lips need some time to get used to it.
Compare this to learning to ride a horse. If all you do is sit on a slow-moving horse, how will you learn to ride at a full gallop?
On trombone, however, we don't have to worry about falling off and breaking our necks. So jump on, play out, and get used to refining your sound AS YOU CONTINUE TO PLAY WITH A FULL SOUND.
You don't learn to gallop unless you gallop.
You don't learn to play out unless you play out.
(hmm, I wonder if that same thing is true with high notes)