耳(er)(er)廓(kuo)外(wai)側面(mian)有許多卷部(bu)，形同(tong)(tong)一組凹面(mian)鏡(jing)，它們可以是外(wai)界傳來的聲(sheng)音發生反射和折射，從(cong)而使(shi)聲(sheng)音在麥克(ke)風(feng)位(wei)置(zhi)處的聲(sheng)壓增大。與耳(er)(er)背式(shi)(shi)(shi)助聽器相比，耳(er)(er)內式(shi)(shi)(shi)助聽器的麥克(ke)風(feng)位(wei)于耳(er)(er)內，其助聽效果就是因為(wei)這一原理而增強(qiang)。耳(er)(er)內式(shi)(shi)(shi)與耳(er)(er)背式(shi)(shi)(shi)助聽器所(suo)占耳(er)(er)甲腔/或外(wai)耳(er)(er)道(dao)外(wai)耳(er)(er)道(dao)的解剖外(wai)置(zhi)不(bu)(bu)同(tong)(tong)，且不(bu)(bu)同(tong)(tong)款式(shi)(shi)(shi)的耳(er)(er)內式(shi)(shi)(shi)助聽器的麥克(ke)風(feng)位(wei)置(zhi)不(bu)(bu)同(tong)(tong)，因此(ci)其聲(sheng)增益(yi)也有所(suo)不(bu)(bu)同(tong)(tong)。高建林的實驗說(shuo)明(ming)CIC麥克(ke)風(feng)處的聲(sheng)增益(yi)大，其次為(wei)ITC，再者ITE。