About the Avatar
This avatar is an “f-hole” used in acoustic instruments. The sound hole is an opening in the body of a stringed musical instrument. This hollow wooden resonance chamber serves to amplify the sound of the strings. F-holes are usually made in pairs placed symmetrically on both sides of the instruments such as violins, cellos, hollowbody and semi-hollow guitars, among others. The f-shape date from the Renaissance, and whether it has been designed by conscious intent or by accident, its efficiency is remarkable as demonstrated by the MIT researchers.
The research found that air flow at the perimeter rather than the broader sound-hole conducts acoustics at a much greater rate. The further into the hole the sound gets the less it permeates, meaning that the size of the hole does not necessarily impact the volume of sound whilst the edges of a sound hole allow for much more acoustic resonance.
The explanation for the efficiency of the f-hole is intimately connected to the fact that the acoustic source amplitude, via temporal changes in air flow through the sound hole, is directly proportional to sound hole perimeter length L near the air resonance frequency, rather than the area. The reason for this dependence can be seen by examining the normal velocity field in the figure 1.
Figure 1. Normal air velocity field through different sound holes (a)–(f). (Nia Hadi et al., 2015)
Reference
- Nia Hadi T., Jain Ankita D., Liu Yuming, Alam Mohammad-Reza, Barnas Roman and Makris Nicholas C. 2015 The evolution of air resonance power efficiency in the violin and its ancestorsProc. R. Soc. A.4712014090520140905 http://doi.org/10.1098/rspa.2014.0905