Well, MPM, I think you're getting close to an explanation. The horn is a resonance tube---and I think this is where the effort comes in. You're right, it's easy to get a sound (squeek, blat or whatever), but the work is in trying to get the right note to play. Why?
Did you folks see the resonance patterns posted on another thread using a silver belled King trumpet? How much effort does it take to make the bell 'ring' properly? How efficient is the bell at changing the vibrations to form a different note? How efficient is the bell at shedding the previous vibrations?
Think about the great horn makers----Reynolds, Siggy Kanstul and John Duda. Every single one of them is a master at making bells. If the bell is the key that also would explain why, every so often, what should be an ordinary horn winds up with extraordinary sound. I have a little Conn Director cornet that resonates like a dream when most of these horns didn't. And, if it is the bell that makes us work, that would explain why Tony Scodwells approach works so well----match up the resonance of a bell with a leadpipe/tuning slide combo that feeds the air at the right speed and flow for the resonance of that particular bell.
Anyway, that's my theory of what's going on. Something creates a 'back pressure'---and MPM, I disagree that you aren't experiencing it. I'd say that you are experiencing it, but at a level that is comfortable for you. I worked as a Respiratory Therapist for twenty years and did a lot of lung volume tests. What I and other therapists have found is that we could always tell the woodwind/brass players because they average lung volumes twice as great as what was predicted. What all of the wood and brass instruments have in common is resonance. All of these instruments take air, convert it into a wave and make the instrument vibrate. The lungs adapt by becoming more efficient (maybe larger?_) through pushing against this resistance. If you're blowing a horn that is low resistance for you, you won't feel the backpressure. I can be comfortable with a PEEP of 5-10 cwp, but above that, I'm not comfortable. This is where the human variable part comes in by matching up your physiology with a horn.
And yes, we're a bit off topic, but it's interesting to try to figure out what makes the beast work!
