A subwoofer (or "sub") is a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies known as bass. The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below 80 Hz in THX-approved systems.

Subwoofer
Subwoofer speaker system
How Many Subwoofers are Enough?
Impedance analysis of subwoofer systems
The rotary subwoofer: A controllable infrasound source
Low-Frequency Optimization Using Multiple Subwoofers
Evaluation of a method for the measurement of subwoofers in usual rooms
Passive voice coil feedback control of closed-box subwoofer systems
Comments on "Low-frequency optimization using multiple subwoofers"- Authors' reply
The Impact of Decorrelated Low-Frequency Reproduction on Auditory Spatial Imagery: Are Two Subwoofers Better Than One?