Reasons why a violin plays like it does

Certain characteristics of the eigenmodes of vibration are critical in determining the playability of a violin. As objective properties of the instrument, these eigenmodes of vibration shape the acoustic functioning of the violin.

The sound radiation as well as certain characteristics of the instrument's playability such as the response and the perceived "resistance" are due primarily to the modes (eigenmodes of vibration) of the instrument. The reason is that the sound production is based on an extremely complex chain of effects and reactions: The player excites the string so it vibrates, and a series of harmonic overtones associated with the bowed fundamental note is produced. In other words, at very specific frequencies (meaning what is known as the "harmonics"), the string will begin to vibrate very strongly. These vibrations exert a force on the bridge of the instrument: The violin is excited periodically via the bridge at the frequencies which are produced while the bridge will "dance about" perpendicularly to the top plate of the violin.

If the frequencies of these exciting string forces hit upon resonance in the corpus of the instrument, this will have a strong effect. The corpus will then begin to vibrate with these resonances. The resonances are the frequency ranges in which the corpus has the largest "natural vibration mobility". Here, a small excitation force will lead to the greatest vibration responses on the part of the top and back plates. As we have seen above, these vibration responses are very welcome on the one hand since they can be very effective "sound radiators" depending on how they are construed. On the other hand, the strong vibration response of the top plate will feed back to the bridge and thus also to the still vibrating string. The string vibration is "disturbed" to a certain extent by this feedback. These "disturbances" are sensed by the musician as the "response behavior". In this context, musicians will say how easy or hard it is to "get into the sound" or how much or how little they can "push" the string.

With some notes, this "disruption" can be so large that the musician can no longer control the vibration of the string. This is the case with wolf tones. Here, the corpus will shake to such a great extent due to the extremely high dynamic mobility of one of its main resonances (main corpus modes) that its feedback to the string via the bridge causes the "controlled" vibration of the string to break down. The vibration immediately builds up again due to the continued bow pressure but it will simply break down again if the corpus is sufficiently "shaken up". The fast interplay produces a howling wolf tone which is all too familiar to many string players. The wolf tone is due to the particular nature of a mode of the instrument and is easy to detect with modal analysis.

A violin's acoustic properties can be characterized in terms of its eigenmodes of vibration, i.e. individual regions of strong dynamic mobility. Each mode is characterized by its eigenfrequency, mode shape and damping. Since the sound and playability differences, similarities and idiosyncrasies of violins can be traced back to the different modes, we think that there is hardly a more effective acoustic tool for violinmaking than modal analysis.