The Bowed String On the Development of Helmholtz Motion and On the Creation of Anomalous Low Frequencies
Knut Guettler · 2002
Of the many waveforms the bowed string can assume, the so-called “Helmholtz motion” (Helmholtz 1862) gives the fullest sound in terms of power and overtone richness. The development of this steady-state oscillation pattern can take many different paths, most of which would include noise caused by stick-slip irregularities of the bow-string contact. Of the five papers included in the thesis, the first one shows, not surprisingly, that tone onsets are considered superior when the attack noise has a very limited duration. It was found, however, that in this judgment the character of the noise plays an important part, as the listener’s tolerance of noise in terms of duration is almost twice as great for “slipping noise” as for “creaks” or “raucousness” during the tone onsets. The three following papers contain analyses focusing on how irregular slip-stick triggering may be avoided, as is quite often the case in practical playing by professionals. The fifth paper describes the triggering mechanism of a peculiar tone production referred to as “Anomalous Low Frequencies” (ALF). If properly skilled, a player can achieve pitches below the normal range of the instrument. This phenomenon is related to triggering waves taking “an extra turn” on the string before causing the string’s release from the bow-hair grip. Since transverse and torsional propagation speeds are both involved, two different sets of “sub-ranged” notes can be produced this way. In the four last papers wave patterns are analysed and explained through the use of computer simulations.