耳(er)廓外(wai)側(ce)面有許多卷(juan)部，形(xing)同(tong)(tong)(tong)一(yi)組凹面鏡，它們可以是外(wai)界傳來的(de)(de)聲(sheng)(sheng)音發生反(fan)射和折射，從而使聲(sheng)(sheng)音在麥克風位置處(chu)的(de)(de)聲(sheng)(sheng)壓增大(da)。與(yu)耳(er)背式(shi)(shi)助(zhu)(zhu)聽(ting)器(qi)(qi)相比(bi)，耳(er)內(nei)(nei)式(shi)(shi)助(zhu)(zhu)聽(ting)器(qi)(qi)的(de)(de)麥克風位于耳(er)內(nei)(nei)，其(qi)助(zhu)(zhu)聽(ting)效(xiao)果(guo)就是因(yin)為這一(yi)原理(li)而增強。耳(er)內(nei)(nei)式(shi)(shi)與(yu)耳(er)背式(shi)(shi)助(zhu)(zhu)聽(ting)器(qi)(qi)所(suo)占耳(er)甲腔/或外(wai)耳(er)道(dao)外(wai)耳(er)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(er)內(nei)(nei)式(shi)(shi)助(zhu)(zhu)聽(ting)器(qi)(qi)的(de)(de)麥克風位置不(bu)同(tong)(tong)(tong)，因(yin)此其(qi)聲(sheng)(sheng)增益也有所(suo)不(bu)同(tong)(tong)(tong)。高建(jian)林(lin)的(de)(de)實驗(yan)說明CIC麥克風處(chu)的(de)(de)聲(sheng)(sheng)增益大(da)，其(qi)次(ci)為ITC，再者ITE。