Mufflers refer to airflow ducts that also have noise propagation. Noise reduction devices such as pipes and elbows with sound-absorbing linings or pipes that use sudden changes in cross-sectional area and other discontinuous acoustic impedance can be used to attenuate or attenuate the noise in the pipe. Reflect back. The former is called a resistive muffler, the latter is called a resistance muffler, and there are also impedance composite mufflers. Category: Plastic Muffler, Brand: SMC, Series: AN