I am wondering purely threoretically, but does the lips moving have anything to do with creating vibrations? Is it possible for the venturi effect to create vibrations in a trumpet if say lips were inflexible? I know in flutes that is possible, but for trumpets. Another way of putting it would be are the lips flapping just a side effect of the compressions in the air waves, that are actually creating the sound, and the deformation of the lips dampening the sound that is produced by the venturi. I may be way off track here, but it seems plausible to me.