page_title: Physics of whistles
section_title: Flutes, recorders and piccolos
hierarchical_section_title: Physics of whistles / Monopole-dipole whistles / Flutes, recorders and piccolos
caption_attribution_description: English: Hope flute
context_page_description: A whistle is a device that makes sound from blowing air. The physical theory of the sound-making process is an example of the application of the science of fluid dynamics. Knowledge of the geometry, dimensions and fluid properties can allow prediction of the properties of the whistle. The principles relevant to whistle operation also have applications in other areas such as fluid flow measurement.
context_section_description: A number of musical instruments, other than the pipe organ, are based on the edge-tone phenomenon, the most common of which are the flute, the piccolo (a small version of the flute), and the recorder. The flute can be blown lateral to the instrument or at the end, as the other ones are. A native end-blown flute is shown in the figure.
  They are all subject to frequency jumps when overblown, suggesting the dipole–monopole relationship. The monopole aspects are relatively fixed. The characteristic dimension L₂ of the tube is fixed; the characteristic speed c₀ is fixed. The effective length of the tube is fixed, since the radiation impedances at each end are fixed. Unlike the pipe organ, however, these instruments have side ports to change the resonance frequency and thus the acoustical Strouhal number.
  The dipole aspects are also relatively fixed. The jet orifice dimension and the distance h to the edge is fixed. Although the jet speed U can vary, the fluid-mechanical Strouhal number is relatively constant and normally operates in stage I. When there is phase-coherent gain of the two aspects, they operate as class III monopole sources. The efficiency of the monopole radiation is considerably greater than that of the dipole, so the dipole pattern is noticed, The details of system gain and interaction between these two dynamic systems is yet to be fully uncovered. It is a testimony to the skills of early instrument makers that they were able to achieve the right port sizes and positions for a given note without scientific measurement instruments.
caption: Native American style flute
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