反相 = phase revers
no matter audio signal running in audio cable or
sound wave by air particle,they all have "sin wave" properties.
when 2 identicle 同相 "sound" addup, the sound level increase.
ehwn 2 identicle 反相 "sound" addup, the sound level decrease due
to phase cancallation.
反相 is a very interesting topic and useful technique in ProAudio,
like phantom image placement, flanger effect, surround sound,
bi-aura sound .............