passive radiator, also known as a bass diaphragm or vibration membrane, typically used in speaker systems. 

• It is a speaker component that resembles a traditional driver but lacks an active voice coil or magnet. 

• Its primary function is to enhance the low-frequency output (bass) of a speaker without requiring additional power or amplification. 

• The passive radiator is moved by the air pressure changes within the speaker enclosure, which are created by the active speaker cone. 

• It is often used in compact speaker designs to achieve deeper, more powerful bass where space is limited.