Sentence:  In trumpets for assisting the hearing, all reverbation of the trumpet must be avoided. It must be made thick, of the least elastic materials, and covered with cloth externally. For all reverbation lasts for a short time, and produces new <WSD>sounds</WSD> which mix with those which are coming in. 
Meaning of the word marked with <WSD> tags:  A vibration capable of causing such sensations.