The criterions of parameter selection for a tuned frequency muffler are proposed. The experimental results show that the radius of a cylindrical perforated tube dissipative muffler meets the criterions. Based on the conclusion, through installing the rotatable circumferential separate plates, an actuator of the tuned frequency muffler is designed to realize automatic adjustment of the radius, which is available for two kinds of working conditions of acoustic attenuation and can both attain the optimal acoustic attenuation performance. Utilizing the finite element analysis and the experiment test, variation rules of transmission loss versus the muffler’s radius is further investigated. The results show that the variable-radius method used in the tuned frequency muffler can shift the frequency band of acoustic attenuation and optimize the acoustic attenuation performance, which expands the application fields of mufflers and has a great engineering value.