rar.e.fac.tionn.(名词)A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.稀薄化:介质中密度和压力的下降,例如在空气中,由于声波的穿越而发生The region in which this occurs.稀疏区:发生这种现象的区域【引伸】rar.efac.tiveadj.(形容词)