sponge underlay

例句：

1. 1.The underlay was designed to absorb sound and reduce echoes.
   下垫层的设计是为了吸收声音并减少回声。
2. 2.The carpeting was made from a sponge underlay.
   地毯是由海绵底层制成的。
3. 3. The engineer used a sponge underlay to improve the acoustic performance of the room.
   工程师使用了海绵底层来提高房间的声学性能。