When the vocal cords are spread apart ,the air-stream is not blocked at the glottis and it passes freely into the vocal tract（声带系统） without vocal-cord vibration（声带振动） .The sounds produced in this way are called voiceless consonants .　当声带被分开，气流在声门处没有阻碍，并且没有经过声带振动就自由进入到发音系统，以这种方式所发出的音被称为清辅音。