A simple model of the Erhu soundbox

The erhu is a common, bowed, two-string instrument from China. Unlike the Western violin, it has received scant attention from the musical acoustics community, in spite of having comparable versatility and power. This paper outlines the structure of the erhu and a vibro-acoustic model suggested nearly 30 years ago in the Chinese literature. The model is developed and supported by admittance and acoustic pressure data. The evidence is that the radiation spectrum of the erhu is dominated by pairs of coupled membrane-cavity resonances that resemble the formants of the human voice. The power of the instrument arises from the large admittance of the membrane, and also the fact that half the membrane-cavity modes are radiation-efficient breathing modes.