The muffler does not use the resistant material, the shell is connected by the galvanized steel plate, and the inner cavity uses different perforation rates and different rear cavity double holes, which has a good noise reduction effect in a wide audio frequency range, and is widely used in clean air conditioning systems. The inner wall is a special perforated plate with a diameter of 1mm and a spacing of 100mm. The central layer is an air layer with a thickness of 200mm. The smaller holes and thicker air layer make it difficult for the sound waves entering the micro-perforation to return to the original air duct, forming countless acoustic "black holes" to achieve noise reduction.