耳廓外(wai)側面有許(xu)多卷部，形同(tong)(tong)(tong)一組(zu)凹面鏡，它(ta)們可(ke)以是(shi)外(wai)界傳來(lai)的(de)(de)聲(sheng)音發生反射和折射，從而(er)使聲(sheng)音在麥克(ke)風(feng)位(wei)置處的(de)(de)聲(sheng)壓(ya)增(zeng)(zeng)大(da)。與(yu)耳背式(shi)(shi)助聽器相比(bi)，耳內(nei)(nei)式(shi)(shi)助聽器的(de)(de)麥克(ke)風(feng)位(wei)于(yu)耳內(nei)(nei)，其(qi)助聽效果就(jiu)是(shi)因(yin)為這一原理而(er)增(zeng)(zeng)強。耳內(nei)(nei)式(shi)(shi)與(yu)耳背式(shi)(shi)助聽器所占耳甲腔/或外(wai)耳道(dao)外(wai)耳道(dao)的(de)(de)解剖外(wai)置不(bu)同(tong)(tong)(tong)，且不(bu)同(tong)(tong)(tong)款式(shi)(shi)的(de)(de)耳內(nei)(nei)式(shi)(shi)助聽器的(de)(de)麥克(ke)風(feng)位(wei)置不(bu)同(tong)(tong)(tong)，因(yin)此(ci)其(qi)聲(sheng)增(zeng)(zeng)益也(ye)有所不(bu)同(tong)(tong)(tong)。高(gao)建(jian)林的(de)(de)實驗說明CIC麥克(ke)風(feng)處的(de)(de)聲(sheng)增(zeng)(zeng)益大(da)，其(qi)次為ITC，再者(zhe)ITE。