noun · an electronic device used to increase the power or volume of an electrical signal

这个扩音机能显著提高音响系统的音质。

noun · a small electronic device worn in or behind the ear to help a person hear better

这款扩音机非常小巧，适合老人佩戴。

noun · a device that converts electrical signals into sound, often used for public addresses

他拿着扩音机向人群喊话。