From Academic Kids
The flute is a musical instrument of the woodwind family. Unlike other wind instruments, a flute produces its sound from the flow of air against an edge, instead of using a reed. A musician who plays the flute is sometimes called a flutist or flautist.
Flute sounds are typically open and hollow as a result of relatively weak upper partials. As a result, flute tones are sweet in character and blend well with other instruments. The flute's timbre, pitch and attack are flexible, allowing a very high degree of instantaneous expressive control.
Categories of flutes
from : www.flute.com.cn (http://www.flute.com.cn) A flute is an xtremely widespread instrument around the world, which can be attributed to its simplicity and pleasing sound. A flute made from a mammoth bone, found in the Swabian Alps and dated to 30,000 to 37,000 years ago is the oldest known musical instrument.  (http://www.cbc.ca/story/arts/national/2004/12/30/Arts/flute-prehistoric041230.html) At its most basic, a flute can be an open tube which is blown like a bottle. Over time, the increasing demands of musical performance have led to the development of what many people consider the flute, the Western concert flute, which has a complex array of keys and holes.
There are several broad classes of flutes. With most flutes, the musician blows directly onto the edge of the flute. However some flutes, such as the recorder, whistle, and ocarina have a duct that directs the air onto the edge. This makes the instrument easier to play, but takes a degree of control away from the musician. Usually fipple flutes are not referred to as flutes, even though the physics, technique and sound are similar.
Another division is between side-blown (or transverse) flutes, such as the Western concert flute, piccolo, fife, and bansuri; and end-blown flutes, such as the recorder, ney, kaval, shakuhachi and tonette. The player of a side-blown flute uses a hole on the side of the tube to produce a tone, instead of blowing on an end of the tube.
Flutes may be open on one or both of their ends. The ocarina, pan pipes, concert whistle, jug, police-whistle, and bosun's whistle are closed-ended. Open-ended flutes such as the concert flute and recorder have more harmonics, and thus more flexibility for the player, and brighter, more pleasing timbres. An organ pipe may be either open or closed, depending on the sound desired.
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.
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.
Because the air-stream has a lower mass than most resonators used in musical instruments, it can beat faster, but with less momentum. As result, flutes tend to be softer, but higher-pitched than other sound generators of the same size.
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.
The air-stream must be flat, and precisely aimed at the correct angle and velocity, or it will not vibrate. In fippled flutes, a precisely machined slot extrudes the air. In organs, the air is supplied by a regulated blower.
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 aperture. 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 the recorder.
Generally, the quality called "tone color" or "timbre" varies because the flute produces harmonics in different intensities. A harmonic is a frequency that's 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).
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.
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.
The Western concert flutes
The Western concert flute is a transverse flute which is closed at the top. Near the top is the embouchure hole, which the player blows against. The flute has circular finger holes, which can be used to produce high and low sounds depending on which finger holes are opened or closed.
The standard concert flute is pitched in C and has a range of about 3 and a half octaves starting from middle C. However, many professional flutes have an extra key to reach the B directly below middle C. Also commonly used in orchestras is the piccolo, a small flute usually pitched an octave above the concert flute. Alto and bass flutes, pitched a fourth and an octave below the concert flute, are used occasionally. Parts for the alto flute are more common than for the bass. Many other sizes of flute and piccolo are used from time to time. A much-less common instrument of the current pitching system is the treble G flute. An older pitching system, used principally in older wind-band music, includes D-flat piccolos, E-flat soprano flutes (the primary instrument, equivalent to today's concert C flutes), F alto flutes, and B-flat bass flutes.
The modern professional concert flute is generally made of silver, gold, or combinations of the two. Student instruments are usually made of nickel silver, or silver-plated brass. Wooden flutes and headjoints are more widely available than in the past.
The modern concert flute comes with various options. The B-flat key (invented and pioneered by Briccialdi) and the B foot joint (which extends the flute's range down one semitone) are practically standard.
Open hole flutes (where some keys have a hole through the middle resembling donuts, and which holes the player must then cover with fingertips) are standard for concert-level players, though some flutists (particularly students) select closed-hole "plateau" keys, or use temporary plugs to cover the holes in the keys until they master the more exact finger-placement open-hole keys demand. There is some belief that open hole keys permit louder and clearer sound projection in the flute's lower range. Open-hole keys are also needed for some modern "extended" avant garde pieces, including those requiring the player to play harmonic overtones, or to manipulate "breathy" sounds in addition to the traditional "pure" tone.
Open hole keys are typical of French technique, championed by the Paris Conservatoire, which dominated the 20th century. However, the century has changed, and the French school is under fire; specifically, the placement of the G-key (previously offset in student models and inline in professional models) may or may not be moving, depending on who you ask. Less controversial options include the amusingly named "gizmo key", which facilitates C7.
To play the western concert flute, you hold the flute in this position (http://personal.zcloud.net/timzart/fluteposture.htm), and blow gently across the hole in the mouth piece. To distinguish separate notes push down the keys of the flute in distinct fingerings (http://www.wfg.woodwind.org/flute/). However, there are a few alternate fingerings that will assist one in playing difficult passages.
The Indian flutes
The Indian flute, one of the oldest instruments of Indian classical music, appears to have developed independently of the western flute. The Indian god Krishna is said to be a master of the instrument. The Indian flutes are very simple instruments when compared with their western counterparts; they are made of bamboo and are keyless. The pitch of concert flutes is not standardized, and is largely left to the personal preference of the artist.
Two main varieties of flutes are used currently. The Bansuri, which has six finger holes and one blowing hole, is used predominantly in Hindustani music, the music of north India. The Pulanguzhal, which has eight finger holes, is predominantly used in Carnatic music, the music of south India. The south Indian flute had only seven finger holes till 1970s when the legendary T. R. Mahalingam introduced the eight holed variety.
- Theobald Boehm, The Flute and Flute-Playing (Dover Publications, 1964)
- James Phelan, The Complete Guide to the Flute and Piccolo (Burkart-Phelan, Inc., 2004)
- Nancy Toff, The Flute Book (Charles's Scribners Sons, 1985). The Development of the Modern Flute.