Wolfton
The wolf sound is a howling, flickering, or floating sound on string instruments when playing a particular note. In severe cases, the attempt this leads music playing softly, for soundless wiping over the string or decay as exclusively overtones ( harmonics ), while a courageous use of the arc a stuttering roar produces. It is said that the instrument has a wolf at this tone . More good-natured instruments just sound a bit rougher at this point, as if they were being played sul ponticello , although the bow position is normal.
In the case of the large string instruments cello and double bass , high-quality specimens are also often affected, while a wolf on a violin is considered a mistake by the violin maker . The difference has to do with the fact that the body of a cello is not three times the size of a violin; that would correspond to the frequency ratio of their mood . To compensate for the relatively small size of the cello has a good sound , the ceiling be relatively thinner, which interactions between their natural oscillations favors and string vibration. In the cello, the wolf lies at the F or F #, seldom lower down to the D. It occurs when this tone is played on the G string or in high register on the C string. In the double bass, the G is usually affected.
A simple wolf killer can help if it succeeds in matching the natural frequency of the tailpiece to the disturbing natural vibration of the body and thus increasing the dissipation . Safer, but far more complex, is a separate, precisely coordinated vibration absorber that is glued to the inside of the ceiling - at a point that just promises the right amount of damping .
root cause
Playing the note concerned is problematic because its fundamental frequency lies in the case of a slightly damped natural oscillation of the body, in whose natural shape the bridge over which the strings are stretched performs clear transverse movements. Both the presence of the resonance and the participation of the bridge in the direction in which the string is excited by the bow leads to a particularly effective transfer of vibration energy to the body. That explains the difficult playing of the wolf tone. The tendency towards the harmonics is also evident, because the increased damping only applies to the fundamental vibration of the string, not to the overtones.
The flutter effect, on the other hand, has been interpreted controversially. A long-standing explanation was that the string and body represent weakly coupled oscillators between which the vibration energy alternates back and forth, combined with a corresponding change in volume. According to this explanation, the speed of the flutter should be given by the difference frequency, similar to a beat . In particular, the flutter should only occur in the flanks of the resonance curve, but should disappear in the maximum of the resonance, recognizable by the strongest tendency towards the flageolet. The flutter should occur regardless of the bow pressure and the set bow tension, provided that the fundamental tone sounds at all. The amplitude fluctuation of the fundamental tone should dominate, the overtones should be affected only secondary. The amplitude of the fundamental should fluctuate even when it fades freely. But all this is true not to. In particular, the flutter frequency hardly varies and varies more with bow pressure than with pitch. Apparently the coupling of the string and the body is so close that there is a common, mean natural frequency in the area of resonance, without the possibility of beating.
The fact that the modulation depth of the flutter can also be influenced with the bow, up to the suppression of the flutter at high pressure (with loss of sound), draws attention to the details of the vibration excitation. Under normal conditions there is a long phase of sticking (the string on the string of the bow) and a short sliding phase . This requires a certain phase relationship between the fundamental and the harmonics so that their superposition near the web results in a sawtooth-shaped movement. This phase relationship is disturbed by the body resonance, because the energy flow is associated with a phase difference of 90 ° between the excitation (fundamental vibration of the string) and the vibration of the resonator . As long as the resonator is not yet vibrating strongly, the excitation works normally, so a kink runs back and forth on the string between the bridge and the finger. As soon as the reaction exceeds a critical level, the string briefly slips through during the sticking phase and a second circumferential kink occurs, which (initially) draws energy from the resonator and grows quickly due to the reversed phase position. In addition, it competes successfully with the other kink for excitation power, so that it disappears quickly. With a time delay that corresponds to its quality , the resonator adjusts to the new excitation phase, whereupon the process is repeated.
Each time, the sound emission of the instrument drops far on the fundamental, so that its spectral line splits by a few Hertz - like a beat, except that there are not two resonators causing it.
See also
literature
- H. Dünnwald: Attempts to develop the wolf in violin instruments. In: Acustica. 41, 1979, ISSN 0001-7884 , pp. 238-245.
- Ian M. Firth, J. Michael Buchanan: The Wolf in the Cello. In: Journal of the Acoustical Society of America. 53, 2, 1973, ISSN 0001-4966 , pp. 457-463.
- Wernfried Güth, Florian Danckwerth: The string instruments: Physics - Music - Mysticism , Franz Steiner, 1997, ISBN 3-515-07031-1 , page 199ff, limited preview in the Google book search.
- ME McIntyre, J. Woodhouse: The Acoustics of Stringed Musical Instruments , Interdiscipl. Sci. Rev., Vol. 3, 1978, pp. 157-173 ( online ; PDF; 1.7 MB).
Web links
- Martin Schleske: Modal analysis (animated natural forms of a violin).