Wolf tone

The wolf tone is a problematic reaction of a stringed instrument while playing a certain note. In severe cases, an attempt to play it quiet, toneless for wiping over the string or to resonate exclusively overtones ( harmonics ), while a spirited use of the arc produces a stuttering roar. It is said that the instrument was in this sound a wolf. Docile instruments sound just a little rough on the spot as if they were sul ponticello played, although the sheet position is normal.

For large strings cello and double bass also quality copies are often affected, while a wolf is a failure of the luthier at a violin. The difference is due to the fact that the body of a cello not three times as large as that of a violin; which would correspond to a frequency ratio of their mood. To compensate for the relatively small size of the cello, the ceiling must be relatively thin for a good sound, which favors interactions between their natural oscillations and the string vibration. When cello the wolf lies with the F or F #, rarely deeper, down to the D. It occurs when this tone on the G string, or in a high position is played on the C string. When the bass G is mostly affected.

A simple Wolftöter can remedy the situation, if it is possible so to tune the natural frequency of the tailpiece to the interfering natural vibration of the body, thereby increasing the dissipation. Safe, but far more complex is a separate and precisely tuned mass damper that is stuck inside the ceiling - on a site that promises just the right amount of cushioning.

Cause

Playing the affected note is problematic because their fundamental frequency is a little muted natural vibration of the body, in its own form, the bridge over which the strings are stretched, carries significant lateral movements. Both the presence of the response and the participation of the bridge in the direction in which the string is excited by the arc, resulting in a particularly effective transfer of vibrational energy to the body. This explains informally the difficult playing the Wolftons. The tendency for the harmonic is seen as the increased attenuation of the fundamental mode is only valid string, not the harmonics.

The flutter effect, however, was interpreted controversial. A long held explanation was that string and body represent weakly coupled oscillators, between which the vibrational energy changes back and forth, connected to a corresponding change of volume. After this statement, the speed of the flutter should be given as a beat by the difference frequency similar. In particular, the flutter should occur only in the flanks of the resonance curve, the maximum of the resonance, recognizable disappear at the strongest tendency to harmonics, on the other hand. Flapping should be independent from the bow pressure and the set arc voltage occur, provided the keynote sounds at all. The amplitude variation of the root should dominate, the overtones be at most secondary affected. The amplitude of the fundamental should also vary the free decay. But all this is not true. In particular, the flutter frequency varies little and rather with the bow pressure than with the pitch. Apparently, the coupling of string and body is so tight that there is a common, medium natural frequency around the resonance, without the possibility of a beat.

The fact that the modulation depth of flutter can be influenced with the bow, to the suppression of flutter at high pressure ( with sound loss) draws attention to the details of the vibrational excitation. Under normal conditions, there is a long phase of adhesion ( the string to the stringing of the bow ) and a short glide. This requires a certain phase relationship between the fundamental frequency and the harmonics, so that their superposition results in a sawtooth-shaped movement near the bridge. This phase relationship is disturbed by the body resonance, because with the flow of energy, a phase difference of 90 ° between the excitation ( fundamental frequency of the string ) and the oscillation of the resonator is connected. As long as the resonator vibrates is not strong, the excitation functions normally, so it runs between the bridge and the finger on the string a bend back and forth. Once the reaction exceeds a critical level, slips during detention phase, the string briefly and it creates a second -round kink which the resonator (initially) extracts energy for the reverse phase and growing fast. He also competes with the other kink successfully excitation power, so this is rapidly disappearing. With a time delay corresponding to its quality, the resonator is adjusted to the new excitation phase, whereupon the process is repeated.

In this case, each time reduces the noise level of the instrument on the root far away, so that the spectral line splits by some Hertz - like a beat, just that no two resonators are responsible here.