2pcs 4 Inch DIY Bass Speaker Vibrating Membrane Passive Bass Woofer Diaphragm Plate Working principle: It will vibrating up and down when the speaker working, it will produce airflow, this air flow driven bass diaphragm,to produce low frequency. How to use: the speaker to open a subwoofer hole, the bass film installed, the entire box closed, airtight. Bass vibrating membrane Passive radiator Full-range speakers bass enhancement The hole diameter is 4.65MM Package Including: 2pcs/pcak