There was no flat erhu before, and the flat-pole erhu is the result of the improvement of modern erhu. I'm not sure whose patent it is.
Compared with round bars, flat bars have three advantages.
1 more convenient. Generally, the shape of the left-hand lever is oblate, which is more suitable for changing the handle and sliding the string.
2, strong tension, because the direction of the piano bar is the widest direction of the flat bar. Not easy to bend.
3, more beautiful and more exquisite.