Question

R5.3 Discuss the physics of an acoustic musical instrument that is capable of playing a variety of distinct note. How are the notes chosen and controlled? harmonics be controlled when a note is played? How is the sound coupled to the atmosphere? Using an instrument, or a recording of the instrument, estimate the Q of the instrument as a resonator.

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Answer 1

R5.3) Consider a flute for this example. It can be thought as a hollow tube closed at one end. This ensures that a node is formed at the closed end of the flute and an antinode is formed at the open end. The fundamental note (largest wavelength) will be such that quarter of a wave fits into this tube satisfying the above node-antinode condition. This case is satisfied if all the holes in the flute are shut.

If any of the holes is kept open, an antinode is forced at the location of the hole. This, along with the boundary node gives a note which will be different than the previous note. Likewise, different open holes produce different set of notes.

The holes in the tube control the wavelength but the frequency of the note is also dependent on the speed of sound (and the wavelength). The speed of sound is dependent on the temperature and humidity of the atmosphere. This way, the sound is implicitly coupled to the atmosphere.