Recorder multiphonics
R. Dean Ayers, Lowell J. Eliason, David Forel · The Journal of the Acoustical Society of America · 1983
A systematic study has been undertaken to identify and analyze all possible multiphonics on a popular brand of plastic recorder (Aulos, alto voice). The absence of a bell at the end of the recorder combines with the open-hole cutoff effect to guarantee strong, nonharmonic bore resonances, and many of the forked fingerings produce stable multiphonics when blown somewhat hard. The more stable and aurally interesting multiphonics have two strong spectral components, one supported by the fundamental bore resonance and the other by the fourth or fifth resonance. Heterodyne descendants of these components are also found, but rarely with comparable strength. The less interesting multiphonics have just one strong component, often at the third resonance, with noticeably weaker components beating against it. Some fingerings will produce more than one multiphonic, depending on the breath pressure and/or attack used. One factor that may be significant for stability is the fact that the edge tone itself goes multiphonic at the blowing pressures used, without any feedback from the bore.