美国专家诺里斯发明了一种超声波扬声器。这种扬声器没有普通扬声器中的振动膜，而是使用了一种晶体薄片，它的振动速度要比传统振动膜块数千倍。振动产生两种人耳听不见的超声波，一种声波恒定，另一种可变，两种声波相互作用产生人耳可听见的第三种声波。该扬声器发出的音响 American expert Norris invented an ultrasonic speaker. Instead of a diaphragm in a normal speaker, this speaker uses a crystal sheet that vibrates thousands of times faster than a conventional diaphragm. Vibrations produce two types of human-ear-audible ultrasound, one of which is constant and the other of which is variable. The two types of sound waves interact to produce the third type of sound that is audible to the human ear. The speaker sounds