Nordlands, you forgot something. With the lips pressed tightly together, we need pressure to open them, that energy is then LOST as applied to speed! They aren't open long enough for the air to pick up speed which would be the case if we just were blowing into free space. The trumpet fights back. That is why if you are not breathing right, your air backs up and you can't get rid of it fast enough when playing high! The simplified picture based on the garden hose/venturi just doesn't hold up. That is a direct current analogy that does not resemble our playing because too many pieces are missing. If you are up to comparisons, blow up a balloon then let go of it and calculate how long it takes until it is empty. Then blow it up again, stretch the nipple until it squeals. Calculate the time until the balloon is empty (it takes longer.........) That is because of the energy required to overcome the stretched but small "aperature". Our embouchure does not work by stretching, rather by compression and that also SLOWS the time needed to get rid of our air by a substantial amount (otherwise just like stretching the balloon). When we factor the backpressure of the horn at higher frequencies, there is a further SLOWING. The trumpet is an acoustic transformer - transforming higher pressure to lower pressure. All this venturi stuff does not apply to reactive systems. Pressure is not speed in a reactive system. The trumpet/mouthpiece/embouchure is not linear in the way air is dealt with. Most everything that is "common knowledge" in this respect is not true and has no basis in physics.