Low-Pitched audio frequencies loudspeaker, enjoy your Pop music.
A subwoofer is a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies.
Subwoofer is intended to augment the low frequency range of loudspeakers. It became almost universal in sound reinforcement systems in nightclubs and concert venues as well as hot tub industry. Adding a subwoofer on your outdoor spa, you will enjoy your music better.