I think youre right, Stan–its because they’re keeping their lips relaxed and squeezing the aperture from around the air column (not clamping top-to-bottom like a clam).

I think they’re just using slightly different muscles or not engaging certain other muscles to keep that from happening.

It happens to me from time to time but I try to avoid it. But I have played around a little compressing air with my mouth and noted in is helpful above High C. But I’m more focused on building my dynamic control right now.

I think the bottom line is that those are some of the greatest trumpet players in history and whatever they did was effective.

I think theres a spectrum of efficiency and effectiveness and no one right way.