Anomalous low frequencies from a bowed violin string
Roger J. Hanson, Frederick W. Halgedahl · The Journal of the Acoustical Society of America · 1998
With a bow force greater than the Schelleng maximum and careful bow control, it is possible on a violin to produce sounds of definite pitch ranging from approximately a musical third to as much as two octaves below the normal pitch. [Hanson et al., CAS J., 2, Series II, 1–7 (1994)]. The pitch is in agreement with the fundamental frequency of the observed harmonic series. The fundamental itself is very weak if the sounds are produced on the open violin G string. These anomalous low frequencies (ALF) occur when the bow force is great enough to prevent the Helmholtz kink from triggering the normal release of the string from the bow hair. The bow serves as a quasitermination point of the string so that there are pronounced bow-nut and bow-bridge reflections yielding at the bow a very complex waveform, some portion of which triggers the slipping of the string. The ALF can also be produced on a bowed monochord where the motion at several points is detected optically, and the sound is generated from the resulting signal. Some musical applications of the effect will be discussed.