is a kind of sound control element. Sound is generated by vibration. Sound waves propagate in the air. If it encounters a solid, it will transmit the vibration to the solid.

the sound control element is such a material that is sensitive to vibration. When there is sound, it is turned on (the resistance becomes smaller), and when there is no sound, it is turned off (the resistance becomes very large). By delaying the circuit and the chip, the circuit can be turned on for a period of time when there is sound. Whether it's a voice control light or something, it's all the same principle, but the final load is different.