Air stream - loudness
The air stream begins when the air pressure in the lungs and oral cavity rises higher than the threshold pressure needed to overcome the lip resistance. Human vocal cords react the same way to the air pressure. It is a common belief that increasing the speed of the air stream makes the lips vibrate faster and thus creates higher notes. In fact, the speed of the air stream inside the instrument is different at almost every point of the tubing because of its conical shape. For example, inside a trumpet the air speed can vary from about 0 to 20 m/s (bell corner, mouthpiece throat). Low, loud notes have the fastest air speed and high, soft notes have the slowest air speed. It’s easy to understand, because the former need much more air per time unit than the latter ones. In the lip aperture the air speed is constantly varying because the size of the aperture is varying. A crescendo on a long note makes the air stream faster but the pitch doesn’t change; only the vibration amplitude increases. In a diminuendo things happen the opposite way. The air stream speed has no influence on the fundamental frequency (i.e. the pitch) – otherwise crescendos and diminuendos would be very unstable. Breathing, blowing, and the so called “use of air” are very important for brass playing, but the only thing the breathing organs can do is regulate the air pressure. The air stream is a result of pressure differences. It’s not possible to move the role of vibrating lips to the breathing muscles.
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