The muffler's noise reduction principle involves the appropriate combination of cavities and tubes to achieve two functions for noise suppression:

Firstly, by utilizing the abrupt change in pipe cross-section (i.e., the change in acoustic impedance), the sound waves propagating along the pipe are reflected back towards the sound source, thereby causing the sound energy to reflect back to its original location.

Secondly, by utilizing reflections across several interfaces, the original forward-traveling sound wave returns to its starting point, then bends back forward again. This point merges with the two other forward-traveling sound waves that have not yet been reflected. The amplitudes of both waves are equal, and their phases differ by odd multiples of 180 degrees, resulting in their mutual interference and cancellation.