Common faults of exhaust muffler The principle of a car silencer is that its exhaust pipe is composed of two pipes of different lengths, which are separated before they meet. Because the difference between the lengths of the two pipes is equal to half of the wavelength of the sound waves emitted by the car, the two columns of sound waves cancel each other and interfere with each other to reduce the sound intensity when superimposed during superposition, so that the sound is reduced, so as to achieve the effect of sound attenuation.