耳廓(kuo)外(wai)(wai)側面(mian)有許多(duo)卷部，形同(tong)(tong)一組凹(ao)面(mian)鏡，它們(men)可以是(shi)外(wai)(wai)界傳來的聲(sheng)音發生反射和折射，從而使聲(sheng)音在麥克風(feng)(feng)位置(zhi)處的聲(sheng)壓(ya)增大(da)。與(yu)耳背式(shi)(shi)助聽(ting)器(qi)相比，耳內(nei)式(shi)(shi)助聽(ting)器(qi)的麥克風(feng)(feng)位于耳內(nei)，其助聽(ting)效果就是(shi)因為這一原理而增強。耳內(nei)式(shi)(shi)與(yu)耳背式(shi)(shi)助聽(ting)器(qi)所(suo)占耳甲腔/或外(wai)(wai)耳道外(wai)(wai)耳道的解剖(pou)外(wai)(wai)置(zhi)不(bu)同(tong)(tong)，且不(bu)同(tong)(tong)款(kuan)式(shi)(shi)的耳內(nei)式(shi)(shi)助聽(ting)器(qi)的麥克風(feng)(feng)位置(zhi)不(bu)同(tong)(tong)，因此其聲(sheng)增益也有所(suo)不(bu)同(tong)(tong)。高(gao)建林(lin)的實驗說明CIC麥克風(feng)(feng)處的聲(sheng)增益大(da)，其次為ITC，再者ITE。