Flute

This article is about the musical instrument. For the sailing ship, see Fluyt. For the drinkware, see Champagne flute.

Flute acoustics

A flute produces sound when a stream of air directed across the top of a hole bounces in and out of the hole. Some engineers have called this a fluidic multivibrator, because it forms a mechanical analogy to an electronic circuit called a multivibrator.

Related Topics:
Sound - Fluid - Electronic - Multivibrator

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The stream beats against the air in a resonator, usually a tube. The player changes the pitch of the flute by changing the effective length of the resonator. This is done either by closing holes, or more rarely, with a slide similar to a trombone's slide.

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Because the air-stream has a lower mass than most resonators used in musical instruments, it can beat faster, but with less momentum. As a result, flutes tend to be softer, but higher-pitched, than other sound generators of the same size.

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To be louder, a flute must use a larger resonator and a wider air-stream. A flute can generally be made louder by making its resonator and tone-holes larger. This is why police whistles, a form of flute, are very wide for their pitch, and why organs can be far louder than concert flutes: an organ pipe's tone-hole may be several inches wide, while a concert flute's is a fraction of an inch.

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The air-stream must be flat, and precisely aimed at the correct angle and velocity, or else it will not vibrate. In fippled flutes, a precisely machined slot extrudes the air. In organs, the air is supplied by a regulated blower.

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In non-fipple flutes, especially the concert flute and piccolo, the player must form and direct the stream with his lips, which is called an embouchure. This makes the transverse flute's pitch and timbre more instantly expressive than any other instrument. However, it also makes the transverse flute immensely more difficult for a beginner to get a full sound out of than fipple flutes such as the recorder.

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Generally, the quality called "tone colour" or "timbre" varies because the flute produces harmonics in different intensities. A harmonic is a frequency that is a real number multiple of a lower register, or "fundamental" tone of the flute. When a flute sounds harsh, or whiny, it is being played to provide more harmonics. Generally the air-stream is thinner (to vibrate in more modes), faster (providing more energy to vibrate), and aimed across the hole more shallowly (permitting a more shallow deflection of the airstream to resonate).

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Almost all flutes can be played in fundamental, octave, tierce, quatre and cinque modes simply by blowing harder and making the air-stream move more quickly and at a more shallow angle. Flute players select their instrument's resonant mode with embouchure and breath control, much as brass players do.

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The timbre is also affected by the quality of the resonator. Generally, more rigid resonators (such as wood) have a "dead" sound, because they have a higher acoustic impedance, and do not resonate with the harmonics. Concert flutes are expected to produce a "brilliant" sound, with a wide range of harmonics. To help this, they are thin tubes made of hard-drawn silver or gold alloys. These are more mechanically elastic than wood, and therefore vibrate in more modes. Theoretically, flutes constructed in thin tubes of elastic but heavy metals, such as alloys of gold, tungsten, platinum or osmium sound "richer" because they vibrate to a lower, therefore more audible, range of harmonics. This effect also explains the good tone of bronze and brass flutes, which are less massive, but more elastic.

Related Topics:
Gold - Tungsten - Platinum - Osmium

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