GT4 round exhaust head has two basic silencing modes: sound absorption and reflection. The sound-absorbing muffler reduces the energy of waste gas through the friction of waste gas on sound-absorbing materials such as glass fiber, steel fiber and asbestos; The reflection muffler has several series resonant cavities, which are connected with porous structure reflection pipes of different lengths. The exhaust gas reduces pressure, vibration and energy through reflection, collision, swelling and cooling for many times.