这些（噪音）可以是穿透教室建筑结构的室外活动声、教学活动的声音以及室内产生的其它各种声响，这些声音都会因为房间的回声效果而被放大。
These levels come from outside activities that penetrate the classroom structure, from teaching activities, and other noise generated inside, which can be exacerbated by room reverberation.
关键是要听取打击一口气没有得到答复，一个更绝缘回声效果的时间越长，脆的说明以及！
The key is to listen to a blow in one breath with no response, an echo effect of the more insulation the longer the crisp note well!
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