These are not really loads but indicate surfaces that absorb sound . specify the degree of sound absorption as the material property mu ( boundary admittance or absorption coefficient ) 也就是说它的作用是使得边界吸声材料的吸声特性得以发挥。如果是0 ，就是不发生吸声现象。相反，是1 ，就是说明是吸声材料的吸声特性完全发挥。
