Conclusions
Air plays many roles in the tone production of brass instruments. This easily leads to confusion and misunderstandings. Air stream is not sound – and sound is not air stream. The situation with brass instruments is fairly complicated, because both exist in the same space at the same time.
The purpose of tone production is to make musical notes, harmonic sounds without too much noise (sizzle, hiss, sigh). The air stream is necessary, but it’s not the sound. It only excites the vibrating system. The player’s breathing organs and lips have different roles, which can’t be transferred from one to the other. Their effective and sensitive co-operation determines the final result of tone production.
The breathing system can only produce and regulate the air pressure that makes the necessary air stream. We can’t blow with our lips, but when they resist the air stream in the proper way, they start vibrating. The lip vibration is much more complicated than the vibration of a string (one- dimensional) or a timpani membrane (two-dimensional), however, the main principle is the same.
The influences of two forces in turn make the system vibrate. First, air pressure opens the lip aperture and second the elasticity of the lip tissue closes it. The lips also have a coupling with the air column, which has its own specific frequencies. The lip vibration frequency must be compatible with the air column frequency to make a good quality sound. There is also a coupling between the lips and the oral cavity, but it’s much less important to the fundamental frequency.
Terms like pressure, velocity, quantity and resistance are often associated with streaming air. The frequency and amplitude describe the fundamental properties of a vibrator. The brass players’ goal is to optimize the efficiency when transforming the kinetic energy of the air stream into the wave motion energy of the standing wave. If the tone production is effective, the amplitude (sound volume) is controlled by the amount of air stream and the frequency (pitch) is controlled by the properties of the vibrating system. Ineffective tone production can contain a large amount of air stream and noise (wind) but very little of the desired vibration (sound). If the lip aperture is too big or for some other reason a proper vibration is not possible, the result is a noisy, leaking sound. The player is wasting air without getting the wanted result. Also, a lip aperture which is too tight can be the cause of a poor coupling with the air column. In this case the harmonic partials become distorted even though the fundamental frequency is produced. In both cases tone quality is bad – leaking, tight or noisy – and out of control. In regards to the human voice, these are called hypofunctional or hyperfunctional pronunciation.
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