Hi Jutta, I am sure Greg will have a better answer, but the throat design on a trumpet mouthpiece helps create the overtones that you hear from the instrument.. a tighter throat will create roughly a brighter sound (more high overtones)(think a roger ingram lead piece with a #29 drill) and a larger throat will typically create a more broad and darker sound (bach 1.5C with a #24 drill). there are too many variables these are just the basics when talking about throats and backbores, which is what i think you are talking about. about the choking off feeling: yes you are blowing way too much air into the mpc. try this: eyes closed, then blow really hard into mpc. then same thing but blow really softly into mpc. notice the difference in feeling between the two extremes. do this a few times. then start blowing air softly into mpc and gradually increase. as soon as you feel the air backing up into your throat you have gone too far. the point where you can blow air and it doesnt back up is roughly how much air you need to be blowing into mpc at any given time based on loudness of course. any more than that leads down the windy road of too much tension.. etc.. which is why we are here! hope this helps.. and as i said Greg will probably have a better answer…