Mechanical distorters in the kantele

This Wednesday instrument builder Jyrki Pölkki  (Soitinrakentajat AMF) came for a visit at the university to talk about musical instrument making. The thought that struck me the most was that unlike violin or piano, the kantele is not yet fixed in sound or shape, and thus it is easy to develop and introduce new features  that the players are likely to accept. This is why this spring I have been supervising a Master’s thesis on mechanical distorters in the kantele that Jyrki devised.

The mechanical distorters are essentially additional surfaces that the string touches while vibrating. They literally distort or limit the string vibration. The end result is a buzzy sound which very typical in some Asian instruments like biwa, shamisen, or sitar. In general, the distorters in the string, make it sound louder or more irritating. Why are these distorters more typical in Asian music? The master student found out an interesting speculative thought on this matter: in Europe amphitheaters were common places to perform music. These have a rising stall with seats, and this kind of structure can decrease the level of low frequencies. For example, wind noise is typically a low-frequency phenomenon. The high frequencies would thus be emphasised at amphitheaters. The Indian sitar, or the Japanese biwa were both played outside where they had to compete with low-frequency noise. In order to do this, adding distorters would produce more high-frequency components to the sound. Interesting speculation indeed. As soon as I find it, I’ll add the reference here.

In the experiments we conduct, the distorters are made of paper clips and pieces of leather. We have already made some measurements in an anechoic room. There is a possibility to use a high-speed camera to extract the waveform in the time-domain. In practice, with this device we can see that the vibration of the string that meets a flexible termination is not sinusoidal, but it has some discontinuities.

All in all, the string vibration is a fascinating and a difficult topic, when the boundary conditions become complicated. In the kantele string, the flexible pins make the sound more interesting, because they generate nonlinearities in the string vibration. For example, the twang you hear when you pluck the kantele string powerfully, is a result of this nonlinearity.


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