Edge Tone

When air is directed at an edge, it does not divide smoothly, but tends to move to one side and form a swirl or vortex. Predisposed toward vortex formation by the flow through the slit, the resulting undulating flow may take the stream below the edge. As noted below, the behavior of an edge which is associated with a pipe is quite different from that of a free edge. 当空气 directed 到边缘时，它不会平滑地分开，而是倾向于向一侧移动并形成旋涡或涡流。由于流经狭缝的流动倾向于形成涡流，因此 resulting 的波动流动可能使流体流到边缘下方。如下所述，与管道相关的边缘行为与自由边缘的行为 quite 不同。

The pressure created by this interaction with the edge feeds back to the area of the slit, tending to push the stream upward. The reverse happens when the stream moves to the top side of the edge and then the process repeats itself. As a result, a periodic flipping of the airstream from side to side can produce a sound called an edge tone. More efficient edge tone instruments can be created by coupling a slit, an edge, and an air column. When such an instrument has been produced, the frequency is determined primarily by the air column resonant frequencies which will control the rate of oscillation of the air across the edge. The edgetone effect in such an instrument serves to help initiate and sustain the tone, and can help make the transition to a higher harmonic of the air column.

The difference between the "edgetone" as envisioned in the sounding of a flute, recorder, organ pipe, etc. and the tones produced by directing air over an edge which is not coupled to an air column has been a subject of considerable discussion and investigation. Benade comments "Until recently there has been a tendency ... to confuse the sounds produced by blowing a narrow air jet against a sharp edge when the edge forms part of a flute or an organ pipe (air reed behavior) with those produced when the system is run in isolation (edge-tone behavior). In the latter case a type of repetitive eddying called vortex shedding takes place on alternate sides of the air jet, and a sound is produced if a sharp edge is used to separate the two sets of vortices. Vortex phenomena have only a secondary influence on flute-type sound production; moreover, at ordinary musical blowing pressures the edge-tone frequencies are so high as to be nearly inaudible.

Some of the literature which addresses the differences between the free edgetones and the behavior of the edges in flutes and organ pipes:

1. Coltman, John W., "Sounding Mechanism of the Flute and Organ Pipe", J. Acoust. Soc. Am. 44 (1968)
   Coltman, John W., '管风琴与管乐器的发声机制', 《声学学会杂志》44 (1968)
2. Fletcher, N. H., "Nonlinear Interactions in Organ Flue Pipes," J. Acoust. Soc. Am. 56 (1974)
   弗莱彻，N. H.，《风琴管中的非线性相互作用》，《声学学会杂志》56（1974）
3. Bouasse, H., Instruments a' Vent, 2 vols., Paris: Librairie Delagrave, 1929,1930.
   布瓦塞，H.，《风中的仪器》，2卷，巴黎：德拉格雷出版社，1929，1930年。
4. Cremer, L. and Ising, H., "Die selbsterregten Schwingungen von Orgelpfeifen," Acustica 19, 143-153,(1968)
   Cremer, L. 和 Ising, H., 'Orgelpfeifen的自激振动,' Acustica 19, 143-153,(1968)
5. Elder, S. A., "Edgetones versus Pipetones," J. Acoust. Soc. Am. 64, 1721-1723, (1978)
   Elder, S. A., 'Edgetones versus Pipetones,' J. Acoust. Soc. Am. 64, 1721-1723, (1978)

Slit, Edge and Air Column

Air Oscillations from Slits

When air is forced through a small opening or slit, the fast-moving airstream moves through slower air. It's edges meet resistance from that slower air and tend to peel back and form vortices. These vortices interact with the stream, exerting a sideways influence on it and causing it to move in an undulating path. This undulation can actually produce a substantial amount of sound, as when you whistle. An even greater amount of sound can be produced by coupling the slit to an edge. 当空气被强制通过一个小孔或狭缝时，高速流动的气流会穿过较慢的空气。气流的边缘会遇到较慢空气的阻力，从而向后卷曲并形成涡旋。这些涡旋与气流相互作用，对气流产生侧向影响，使其沿波动路径移动。这种波动实际上可以产生相当大的声音，就像吹口哨时一样。如果将狭缝与边缘耦合，可以产生更多的声音。 The undulations in the stream move along the stream at something less than one half the speed of the air in the stream ( about 0.4 V according to Backus). Then the faster the airstream speed, the faster the oscillations of the stream when it hits an edge. 溪流中的波动以小于溪流中空气速度一半的速度沿溪流传播（据Backus称约为0.4V）。当溪流遇到边缘时，空气流速越快，溪流的振荡越快。

Slit and Edge

For a slit and an edge, not coupled to an air column, the frequency of the edgetone tends to be about 对于不连接到空气柱的狭缝和边缘，边缘音的频率通常约为 for the first main edgetone regime. 对于第一主边缘态区域

This regime, referred to as Region I of the edgetone behavior, is the main operating mode for organ pipes and presumably also for the flute. Note that the pitch can be made to go up by either increasing the airstream velocity, or by decreasing the distance from the slit to the edge (both applicable to playing the flute). Because of the feedback mechanism to the slit, the effective diameter of the edge does not figure directly in this pitch relationship as it does in the case of aeolian tones.