耳(er)廓外(wai)側面有許多卷(juan)部，形同(tong)(tong)(tong)(tong)一(yi)組凹面鏡，它們可以是外(wai)界傳來的(de)(de)聲音(yin)發生(sheng)反射(she)和折射(she)，從(cong)而(er)使聲音(yin)在麥(mai)克風(feng)位置(zhi)處的(de)(de)聲壓增(zeng)(zeng)大。與耳(er)背式(shi)助(zhu)聽(ting)(ting)(ting)器(qi)相比，耳(er)內式(shi)助(zhu)聽(ting)(ting)(ting)器(qi)的(de)(de)麥(mai)克風(feng)位于耳(er)內，其助(zhu)聽(ting)(ting)(ting)效果(guo)就(jiu)是因(yin)為(wei)(wei)這一(yi)原理而(er)增(zeng)(zeng)強。耳(er)內式(shi)與耳(er)背式(shi)助(zhu)聽(ting)(ting)(ting)器(qi)所占(zhan)耳(er)甲腔/或外(wai)耳(er)道外(wai)耳(er)道的(de)(de)解剖外(wai)置(zhi)不同(tong)(tong)(tong)(tong)，且不同(tong)(tong)(tong)(tong)款(kuan)式(shi)的(de)(de)耳(er)內式(shi)助(zhu)聽(ting)(ting)(ting)器(qi)的(de)(de)麥(mai)克風(feng)位置(zhi)不同(tong)(tong)(tong)(tong)，因(yin)此其聲增(zeng)(zeng)益也有所不同(tong)(tong)(tong)(tong)。高建林的(de)(de)實驗(yan)說明CIC麥(mai)克風(feng)處的(de)(de)聲增(zeng)(zeng)益大，其次為(wei)(wei)ITC，再者ITE。