passive radiator speaker diaphragm, also known as a bass vibration speaker auxiliary membrane. This component is used in speaker systems to enhance bass response. 

• Function: Passive radiators work by using the air pressure generated by the active driver to resonate and produce deeper bass frequencies without needing an additional voice coil or magnet.

• Material: The outer part is typically made of rubber or silicone for flexibility, and the central diaphragm can be metal (as pictured), plastic, or paper composite.

• Shape: They come in various shapes, including the oval design shown, to fit different speaker enclosures.

• Shopping Information: These parts are widely available online from electronics retailers and marketplaces, often listed under "passive radiator," "speaker diaphragm," or "bass auxiliary membrane".

• Compatibility: When purchasing, ensure the dimensions and weight are compatible with the specific active speaker driver and enclosure volume for optimal performance.