TromboneChat

I have recently begun dabbling with cornet, aiming to instruct newcomer trumpet kids (and for fun, too!). After struggling with the tiny mouthpiece (I have problem even with small trombone mouthpiece), I have managed to get the sound out of it, and now can play some easy tune (Promenade from Pictures at an Exhibition and the introduction of Mahler's 5th Symphony are always amusing for the students), albeit with not so pretty intonation. Lower notes (low C and lower) and very high notes (higher than high G) are also still problematic.

However, I cannot play it for more than around 2 minutes, because I always force bass trombone amount of air through the tiny mouthpiece (the mouthpiece is around Bach 3C in size). No matter how I tell myself to breath less and use diaphragm to hold the air in, it all ends up the same: red face, strained embouchure and nerve, and putting the cornet down and goes back to bass trombone to vent my excess air, at least for a while.

How can I circumvent this problem? What training should I do? I believe a larger mouthpiece would be of not so much help because the dimensions differ only in a fraction of millimeter (the largest being inner diameter difference of 1.2mm for Bach 1C mouthpiece), and I also don't want to buy a new mouthpiece for only sporadic playing.

(I know there is another cornet doubling thread around, but I don't want to hijack it. If this thread is too repetitive, I apologize.)

The problem is most likely not that you are trying to blow too much air. It's that you are TAKING IN too much air.
Inhale only as much as you will exhale.
Learn where the resting position of your diaphragm is. Inhale, play a phrase, and aim toward ending right at your resting position. This takes practice. You don't want to have excess air that you have to exhale at the end. Always try to end at resting position.

That's the way you speak... make it the way you play.

Maybe practice switching horns on F low in the treble staff? Bass trombone playing that note should use similar air to a cornet. If your brain is thinking air as a function of partials rather than absolute pitch, maybe you can re-educate it.