耳(er)廓(kuo)外(wai)側面有許多卷部，形同(tong)(tong)一(yi)組凹面鏡，它們可以是(shi)外(wai)界傳來的聲(sheng)音發(fa)生(sheng)反(fan)射和折射，從而(er)使聲(sheng)音在麥克(ke)風(feng)(feng)位(wei)置(zhi)處(chu)的聲(sheng)壓增(zeng)(zeng)(zeng)大(da)。與(yu)耳(er)背式(shi)助(zhu)(zhu)聽器(qi)相比(bi)，耳(er)內(nei)式(shi)助(zhu)(zhu)聽器(qi)的麥克(ke)風(feng)(feng)位(wei)于(yu)耳(er)內(nei)，其(qi)助(zhu)(zhu)聽效果就是(shi)因為(wei)這(zhe)一(yi)原理而(er)增(zeng)(zeng)(zeng)強。耳(er)內(nei)式(shi)與(yu)耳(er)背式(shi)助(zhu)(zhu)聽器(qi)所占耳(er)甲腔/或外(wai)耳(er)道外(wai)耳(er)道的解剖(pou)外(wai)置(zhi)不(bu)同(tong)(tong)，且不(bu)同(tong)(tong)款式(shi)的耳(er)內(nei)式(shi)助(zhu)(zhu)聽器(qi)的麥克(ke)風(feng)(feng)位(wei)置(zhi)不(bu)同(tong)(tong)，因此其(qi)聲(sheng)增(zeng)(zeng)(zeng)益也有所不(bu)同(tong)(tong)。高建林(lin)的實驗說(shuo)明CIC麥克(ke)風(feng)(feng)處(chu)的聲(sheng)增(zeng)(zeng)(zeng)益大(da)，其(qi)次為(wei)ITC，再(zai)者ITE。