Section: Science Life
ETH Zurich physics student helps instrument-maker |
The hammered dulcimer surveyed
Last year the dulcimer-maker Werner Alder built a new concert hammered dulcimer with help from ETH Zurich researchers, among others. While searching for new development opportunities he met an ETH Zurich physics student. The two recently made the first ever systematic measurement of the resonance properties of a hammered dulcimer at ETH Zurich.
The scene is like that of a doctor’s surgery. The patient suffers from defective balance and is now being systematically checked out by doctors. The difference here is that the patient is a hammered dulcimer and the medical team consists of the dulcimer-maker Werner Alder from Urnäsch and ETH Zurich physics student Urs Grob (1). The consulting room is in the basement of the CLA building at ETH Zurich.
But what led to this examination? First there was the passionate hammered dulcimer player Urs Grob. The physics student recalls that “I became increasingly aware that individual notes were unsatisfactory, especially when I played classical music.” He began to search for the reasons but found nothing in the literature. Then careful listening led him to suspect that the resonance characteristics must be very different for the various notes. The problem seemed to lie mainly in the lower registers.
Access to suitable measuring instruments thanks to an engineering course
That surprised Grob only partly: “A hammered dulcimer must be relatively stiff to be able to vibrate better at high frequencies.” The result is that the harmonics in the lower registers lie relatively high up in the spectrum, whereas the fundamental is hardly transmitted at all. He was unable to find a general explanation for the other qualitatively unsatisfactory notes. As a natural scientist, he had an idea that was obvious, even in this situation: he wanted to measure a hammered dulcimer systematically.
Grob soon realised that the appropriate measuring apparatus was too expensive for him. So he looked around to see where there was one already in existence. He found what he wanted at ETH Zurich. Grob, the hammered dulcimer player, enrolled for the Engineering Tools course “Experimental Modal Analysis”. The contacts he was able to make there subsequently allowed him to measure his old hammered dulcimer himself.
The question of the sound holes
The first data that was obtained confirmed Urs Grob’s suspicions. They showed that the hammered dulcimer’s wooden case amplified different frequencies at different places. The low notes also lacked resonance. The physics student concluded that this could be improved significantly by modifying the resonator box or through sound holes. The smaller they were, the better the air resonance in the instrument’s low registers became.
When Werner Alder then gave a lecture about hammered dulcimer construction and posed the question about the function of the sound holes, Urs Grob, who was present, had the appropriate explanation. The instrument builder pricked up his ears and decided to act on Grob’s knowledge for his own work.
Werner Alder had himself already been in contact with an ETH Zurich team. In the previous year he had built a prototype of a new concert hammered dulcimer at the suggestion of the musician Fredi Zuberbühler. For this he had used a slightly arched resonance box. This contains a correspondingly shaped frame which ETH Zurich researchers from the Chair for CAAD had optimised with their software and for which they had prepared a digital design. The latter enabled the frame to be manufactured using a computer-controlled milling machine (2).
Werner Alder’s comment on his new development is “The tonal characteristics are probably better, but even this instrument is capable of improvement.” That’s why he wanted to use the opportunity to measure this hammered dulcimer. His literature search had revealed that there are probably hundreds of studies of the resonance properties of violins, but not a single one for his instrument.
Diagnosis first of all
That’s what led to the meeting that took place recently in the basement of the CLA building. Alder spent a day with a percussor, tapping the upper and lower sides of his new hammered dulcimer at about 130 points. Urs Grob controlled the measurement from the computer and monitored the recording of the spectrograms. The physics student comments “As far as I know, this is the first systematic measurement of a hammered dulcimer.”
Both “hammered dulcimer researchers”, Werner Alder and Urs Grob, are aware that their measurements can only provide a diagnosis for the time being. Whether this will lead to a therapy or will reveal new routes in the instrument’s design remains to be seen. Werner Alder’s calm comment: “Even if perhaps in practice I cannot derive any direct benefit from this day, I will still gain a new insight into the instrument. And I can also say that I have at least tried to make an improvement.” Urs Grob can also see clearly that there will probably never be a fully computable hammered dulcimer. He says the system is too complex for that. “However, the good thing is that in this way my theoretical knowledge is not tested simply on the basis of end-of-term examinations.”
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