91久久精品www人人做人人爽-久久不卡视频经典视频-人人人妻人人妻超碰-日韩毛片在线观看.-久久 99精品久久久久-国产一区二区三区欧美激情-91中文字幕制服-欧美日韩国产激情另类-国产麻豆91精品女同性恋,伊人五月六月丁香综合久久,九色pornyav导航av,痴女 在线 播放 亚洲

Industrial boiler fan noise pollution is mainly three factors, namely: sound source, the media and the receiver. Only the three exist at the same time in order to interfere with the listener. From the three aspects of the start, by reducing the sound source, limiting noise propagation, blocking the reception of noise and other means to achieve the purpose of noise control, in the specific noise control technology, can be used sound absorption, sound insulation and muffler three Measures.