The utility model is characterized in that the end surface of the air cylinder body is provided with an arc-shaped air groove, both ends of the air groove are shallow and the middle is deep.

By varying the groove spacing, the diameter of the single or double diameter hole, and the rear air cavity depth and content, one can obtain absorption over a wide variety of frequencies.

The fanned air discharged toward the opening is then introduced into a groove in fluid communication with the opening.