Originally Posted by
BillyD
Ok, but let me put my question another way. Is it that air just occupies space in the tubes at atmospheric pressure, and that for each note the musician wants to create he needs to move all that stagnant air up to a certain speed? Or is it that the air in the tubes is held under pressure until the musician pushes it just a small amount to make a note? It just doesn’t seem possible that the human lungs can push all that stagnant air against the inherent drag of all those narrow tubes for each note he wants to play. But if so, that’s incredible.
Originally Posted by
LesterOfPuppets
You're just changing the length of tubing the air/vibrations travel through, which changes the pitch.
IIRC.
The way I understand it is that the shape and size of the tubes that make up the instrument are sized in order to facilitate resonance of the air at certain frequencies. The instrument is at atmospheric pressure on the inside, and the only real airflow that moves through is a byproduct of the moving air required to create the initial vibration with your lips. The valves just change the length of the tube that the sound waves travel through, with each valve combination tuned to resonate at a specific frequency. Most brass instruments I've tried are quite free-blowing, there is some resistance but not a whole lot. The smaller the ID of the tubes, the more resistance there is. Try blowing through a straw vs blowing through a paper towel tube.
I have played both trumpet and tuba. The tuba does require a bit more airflow, but that just seems to be a necessary consequence of the amount of air it takes to vibrate your lips at frequencies that the tuba is designed to resonate at. If you want to try a silly experiment, try to buzz your lips at a high frequency and then at a very low and floppy frequency. I think you'll find that the latter will exhaust your lungs a lot faster than the former.
TL;DR - You just make the air inside the horn vibrate from buzzing your lips, any air movement through the horn is a necessary byproduct of that.