耳(er)(er)廓外(wai)側面有(you)許多(duo)卷部，形同(tong)(tong)一(yi)組凹面鏡(jing)，它們可以是外(wai)界傳來的聲(sheng)音(yin)發生(sheng)反(fan)射和(he)折射，從(cong)而使聲(sheng)音(yin)在麥克(ke)(ke)風(feng)位置處的聲(sheng)壓增(zeng)大。與耳(er)(er)背式助(zhu)聽器(qi)(qi)相(xiang)比(bi)，耳(er)(er)內式助(zhu)聽器(qi)(qi)的麥克(ke)(ke)風(feng)位于耳(er)(er)內，其(qi)(qi)助(zhu)聽效果就是因為這一(yi)原理而增(zeng)強。耳(er)(er)內式與耳(er)(er)背式助(zhu)聽器(qi)(qi)所占(zhan)耳(er)(er)甲(jia)腔(qiang)/或外(wai)耳(er)(er)道(dao)外(wai)耳(er)(er)道(dao)的解(jie)剖(pou)外(wai)置不(bu)(bu)同(tong)(tong)，且不(bu)(bu)同(tong)(tong)款式的耳(er)(er)內式助(zhu)聽器(qi)(qi)的麥克(ke)(ke)風(feng)位置不(bu)(bu)同(tong)(tong)，因此其(qi)(qi)聲(sheng)增(zeng)益也有(you)所不(bu)(bu)同(tong)(tong)。高建林的實驗說明CIC麥克(ke)(ke)風(feng)處的聲(sheng)增(zeng)益大，其(qi)(qi)次(ci)為ITC，再者ITE。