A passive subwoofer is a type of speaker designed to reproduce low-frequency sounds, such as bass. Unlike active subwoofers, passive subwoofers do not have a built-in amplifier. Instead, they require an external amplifier to power them, which can be connected to a home theater system or audio setup. These subwoofers are often used in conjunction with other speakers to enhance the overall sound experience. They are popular in both home audio systems and professional sound setups, providing deep bass that adds richness to music and movie soundtracks. Properly pairing a passive subwoofer with an amplifier is essential for optimal performance.