Both the flat octagonal erhu and the flat round erhu belong to the high-end professional improved erhu. The size of the piano barrel is highly compressed and the width is elongated, which increases the horizontal amplitude, so that a loud volume can be obtained, and the improvement of the volume can be achieved. Compared with the hexagonal erhu, the volume Larger and more penetrating. Because the flat octagonal erhu and the flat round erhu have certain differences in the appearance of the piano barrel and the production of the grooves in the amplification, the two have their own characteristics in terms of timbre. The flat octagonal erhu drum has a flat octagonal shape on the front and an oval shape on the reverse. The inner wall has a groove for amplifying sound. Compared with the oval shape before and after the flat erhu, the front of the drum has a thicker wall and a larger volume. It has the characteristics of deep and deep, which makes the overall timbre of the erhu have a very "thick and solid" feeling, and the penetrating power of the timbre of the high position has also been improved.

Since the front of the flat-round erhu is milled into an oval shape, the wall of the tube becomes thinner accordingly, so the grooves in the amplifier cannot be made, so that the bass is slightly attenuated, and the overall sound is bright and crisp, which is very suitable for playing. For example, "Horse Racing" and other lively and relaxed repertoires, piano friends can choose the corresponding improved erhu according to their own preferences.