I really like your analogy saying that the lips should ‘be’ the vocal chords for playing the trumpet and just recently starting to trust it really works just that simple.
I am just wandering, is there also an analogy between head voice (not sure if this is correct English, Falsetto perhaps?) and playing the upper register. I mean, do you know what happens in your throat when you sing with head voice (falsetto) and is that in any way similar to the upper register (e.g. playing with a smaller oral cavity?)
Maybe this is not correct nor useful at all, but I like to have the physical image and physics sorted out in my mind to check if I am on the right track.
Good question, it will be interesting to see the responses you get.
But it’s important to remember that we must not tense up or restrict our throat or body as we ascend.
The aperture must be reduced, but that could and should be done without any unecessary tension in the throat or body.
There does need to be tension in the aperture corners to reduce the aperture AND to keep it open and in the air column so the lips can vibrate freely in the air column, etc.
Less air moves through the instrument the higher we play, so there is a feeling of lighter air and there is an increase in back pressure which can cause a tendency to tense up the throat and body–but that doesn’t help us; we must resist that tendency and learn in time to stop doing that. The lips will vibrate in the air column if they’re there and aren’t overly tensed.
Leading with the air and thinking of a “heee” tends to help me up high and playing softer, but with good air, helps too.