耳(er)廓外(wai)(wai)側面有許多(duo)卷部(bu)，形(xing)同(tong)(tong)(tong)一(yi)組凹面鏡(jing)，它們可(ke)以是外(wai)(wai)界(jie)傳來的聲音發生反(fan)射和折射，從而(er)使聲音在(zai)麥克風(feng)(feng)位置處(chu)的聲壓增(zeng)大。與(yu)耳(er)背式(shi)助(zhu)聽(ting)器(qi)相(xiang)比，耳(er)內式(shi)助(zhu)聽(ting)器(qi)的麥克風(feng)(feng)位于耳(er)內，其助(zhu)聽(ting)效果就是因(yin)為(wei)這一(yi)原理而(er)增(zeng)強。耳(er)內式(shi)與(yu)耳(er)背式(shi)助(zhu)聽(ting)器(qi)所(suo)占耳(er)甲腔/或外(wai)(wai)耳(er)道外(wai)(wai)耳(er)道的解剖(pou)外(wai)(wai)置不同(tong)(tong)(tong)，且(qie)不同(tong)(tong)(tong)款式(shi)的耳(er)內式(shi)助(zhu)聽(ting)器(qi)的麥克風(feng)(feng)位置不同(tong)(tong)(tong)，因(yin)此其聲增(zeng)益(yi)也有所(suo)不同(tong)(tong)(tong)。高建林的實驗說明CIC麥克風(feng)(feng)處(chu)的聲增(zeng)益(yi)大，其次為(wei)ITC，再者(zhe)ITE。