The function of the muffler at low frequency is similar to that of the liner liner of the same length without additional insertion loss.

Sound attenuation consists of three parts: the absorption and reflection of the near axial wave in the elbow wall, and the energy of the near axial wave, which changes into the energy of the oblique wave at the turning, and is absorbed effectively by the sound-absorbing material.

In the rectangular section tube is inserted in a right angle bend muffler in the shop, and the acoustic liner elbow on both sides, the length of 2 to 4lz (LZ is the characteristic width of the tube cross section), is the high frequency insertion loss is 10dB higher than the insertion loss of the same length of the straight pipe liner.