耳(er)廓外(wai)側面(mian)有(you)許多卷部，形(xing)同(tong)(tong)一(yi)組凹面(mian)鏡，它們可以是(shi)外(wai)界傳來的(de)聲(sheng)音發生反射(she)(she)和(he)折射(she)(she)，從而使(shi)聲(sheng)音在麥克(ke)風(feng)(feng)位置處(chu)(chu)的(de)聲(sheng)壓(ya)增(zeng)大。與(yu)(yu)耳(er)背(bei)式(shi)(shi)(shi)(shi)助(zhu)(zhu)(zhu)聽(ting)(ting)器(qi)相比(bi)，耳(er)內式(shi)(shi)(shi)(shi)助(zhu)(zhu)(zhu)聽(ting)(ting)器(qi)的(de)麥克(ke)風(feng)(feng)位于(yu)耳(er)內，其(qi)(qi)助(zhu)(zhu)(zhu)聽(ting)(ting)效果就(jiu)是(shi)因(yin)為這一(yi)原理而增(zeng)強。耳(er)內式(shi)(shi)(shi)(shi)與(yu)(yu)耳(er)背(bei)式(shi)(shi)(shi)(shi)助(zhu)(zhu)(zhu)聽(ting)(ting)器(qi)所占耳(er)甲腔/或外(wai)耳(er)道(dao)外(wai)耳(er)道(dao)的(de)解剖外(wai)置不同(tong)(tong)，且不同(tong)(tong)款式(shi)(shi)(shi)(shi)的(de)耳(er)內式(shi)(shi)(shi)(shi)助(zhu)(zhu)(zhu)聽(ting)(ting)器(qi)的(de)麥克(ke)風(feng)(feng)位置不同(tong)(tong)，因(yin)此其(qi)(qi)聲(sheng)增(zeng)益(yi)也有(you)所不同(tong)(tong)。高建林的(de)實驗說明CIC麥克(ke)風(feng)(feng)處(chu)(chu)的(de)聲(sheng)增(zeng)益(yi)大，其(qi)(qi)次為ITC，再者ITE。