I'm in the office now with four books in front of me on the physics of musical instruments. (All overdue by the way - better do something about that.) I definitely don't qualify as an expert in this, so let me separate some of the things that are clear to me, from what is a bit fuzzy while replying to Jeremy. The speaker demonstration shows that point 1 (while true) doesn't mean much in the production of sound. The speaker replaces lip buzzing as the driving generator of vibration. There is a lot of vibration going on because you are forcing the system at a resonant frequency. There is just no flow of air through the horn. Flow is an irrelevant byproduct of using lip bus to drive the internal vibration of the air column. All of the books I am looking at (and as far as I can tell, Lawson's calculations as well) treat the vibrating column of air as the only factor in determining the basic notes and overtone series of the horn. The lip buzz drives the notes, but the shape of the mouthpiece, tube, and bell determine the notes and the overtones. In fact, the calculations assume the walls of the horn are rigid (though some of the books talk about adding minor correction terms to make up for the fact that this is only approximately true). The role of the bell in coupling the vibrating column of air to outside air is crucial, but the books are far less clear on how this works. The bell is referred to as an "impedance matching device" but they don't say how much is related to its shape and how much to it's vibration characteristics. There is a good deal of material on bell design, and the info is probably in there, but it would require a good deal of study for me to understand this. That the shape of the bell is crucial is clear from the original calculations which assume the bell is rigid. How much the vibration of the bell contributes to the projection of the sound is much less clear to me. What is clear from my reading is that the vibrations of the column of air is the single greatest factor determining the fundamental notes and the overtone series. The primary factors determining this are the shape of the horn (all parts) and the driving frequency. The factors involved with transferring the energy of this vibration to the surrounding are far less clear to me. I think it is a very common tendency of musicians to take the basic physics of their instrument for granted and focus on the aspect that determine the fine details. You can make a valveless horn with a mouthpiece, a length of plastic tube, and an appropriately shaped tin funnel. Yes it would sound awful, but it would produce the proper notes and overtone series. You have always been able to take that as a given and focus on factors like the metal used in construction which produces the fine differences between instruments. Has that affected your ideas about the basic factors that produce sound?