Check the listing for details. 2Pcs Passive Radiator 4 Inch Woofer Vibrating. Condition: New. Listed at 15.78 USD. What is this?Subwoofer passive radiator generates mechanical vibration through electromagnetic drive, combined with air pressure conduction to low-frequency energy and optimize acoustic performance.Woofer diaphragm is suitable for various speaker units, such as multimedia entertainment systems, car audio systems, professional audio, etc.What will I get?Material: Rubber, Iron;Mounting Hole Spacing: 82x115mm / 3.23x4.53Inch;Color: Black;2Pcs x Subwoofer Woofer MembraneIs there any advantages of the product?Composite material innovation and structural upgrades enhance low-frequency energy.How to use it?Easy to use, just install it in the corresponding position and you can use it.What should I notice?Please pay attention to whether the selected size is suitable.