Editing Subwoofer (section)

===Equalization===
[[File:Rear panel of a Polk audio sub-woofer.jpg|thumb|The rear panel of a Polk subwoofer cabinet, showing a low-pass filter adjustment knob]]

Equalization can be used to adjust the in-room response of a subwoofer system.<ref name=BCSS /> Designers of active subwoofers sometimes include a degree of corrective equalization to compensate for known performance issues (e.g. a steeper than desired low end [[roll-off]] rate). In addition, many amplifiers include an adjustable low-pass filter, which prevents undesired higher frequencies from reaching the subwoofer driver. For example, if a listener's main speakers are usable down to 100 Hz, then the subwoofer filter can be set so the subwoofer only works below 100 Hz.<ref name="DellaSala" /> Typical filters involve some overlap in frequency ranges; a steep 4th-order 24&nbsp;dB/octave low-pass filter is generally desired for subwoofers in order to minimize the overlap region. The filter section may also include a high-pass "[[Infrasound|infrasonic]]" or "subsonic" filter, which prevents the subwoofer driver from attempting to reproduce frequencies below its safe capabilities. Setting an infrasonic filter is important on bass reflex subwoofer cabinets, as the bass reflex design tends to create the risk of cone overexcursion at pitches below those of the port tuning, which can cause distortion and damage the subwoofer driver. For example, in a ported subwoofer enclosure tuned to 30 Hz, one may wish to filter out pitches below the tuning frequency; that is, frequencies below 30 Hz.

Some systems use parametric equalization in an attempt to correct for room frequency response irregularities.<ref name=Messenger2004 /> Equalization is often unable to achieve flat frequency response at all listening locations, in part because of the resonance (i.e. [[standing wave]]) patterns at low frequencies in nearly all rooms. Careful positioning of the subwoofer within the room can also help flatten the frequency response.<ref name=Plumb2000 /> Multiple subwoofers can manage a flatter general response since they can often be arranged to excite room modes more evenly than a single subwoofer, allowing equalization to be more effective.<ref name=Welti2002 />