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I hope I am posting this in the correct stack exchange,

I am currently researching on musical instruments, particularly the Erhu and Shamisen, and have come into 2 interesting constructs. I have noticed that on the "drum" part of the instrument there are special carvings , supposedly to improve sound quality. I am not sure what it is referred as in the Erhu, but on Shamisen it is called ayasugi bori.

To me a layman, the Erhu one seems to make sense, I 'm a bit dubious on the Shamisen, but I would like to know do they actually improve column or sound quality of some sort?

The first image is the Erhu, and the second is the Shamisen

Erhu inside

Ayasugi Bori

  • I think your quickest way to an answer on this is to find someone who actually makes these instruments - they would be able to tell you immediately. – Mark Jul 25 '19 at 3:48
  • I tried, but most people I've asked are very much fans of the traditional building method, they don't really have a solid base for indicating that it is better or why it is better they just say it does, and to me it sounds like a placebo. They see the groves are there so they may think it sounds better. – Ehesh Zoumi Jul 25 '19 at 12:21
  • very good point. To be honest, the only rigorous way around this is to pay someone to build two of them - One with grooves and one without. Then test the living daylights out of them both until you can come to a solid conclusion. Then publish. – Mark Jul 25 '19 at 12:46
  • I agree, someone with both and audio equipment to test them out – Ehesh Zoumi Jul 25 '19 at 23:03
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Only a non-answer for now:

I searched on this issue for weeks, and found no research or publication that investigate what Ayasugi or other sound box patterning actually do (in English at least). In some translations from Japanese or Chinese, it is simply stated that this feature improves the sound. I searched mostly for the instruments Koto and Gu-Qin.

An old but good theoretical work by M.A. Biot, "Reflection on a rough surface from an acoustic point source" DOI: 10.1121/1.1908741

Current possible theories (many...):

  • The rough surface causes friction for the moving air; thus the air cavity modes (es. Helmoltz resonance) dissipate more, thus the response near the resonance frequency has a lower but broader peak.

  • The ayasugi works as a diffraction grating, reflecting high-frequency sound waves at odd directions, thus making the air cavity modes (sound waves bouncing in the soundbox) more complex.

  • Again as diffraction grating, but for the acoustic waves in the wood (mechanical vibrations).

  • Increase the wood-air surface, so wood vibrating longitudinally can move the air more efficiently.

  • Increase the wood-air surface, increasing the heat conduction away from the air compressed by sound wave, increasing the sound dissipation.

  • Increase the wood-air surface, hence sound absorption due to local wood porosity.

  • Slow down the "surface sound wave" and mix it with the central portion of air; that should give a cleaner wavefront, stronger resonance peak.

  • Decrease the Stiffness/Mass ratio of the instrument body, so the mechanical resonance frequencies of the body are lower, hence better response at low frequencies.

Stay tuned! I'm carving dummy soundboxes to test that out. enter image description here

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