Editing Loudspeaker (section)

===Subwoofer===
{{Main|Subwoofer}}

A subwoofer is a woofer driver used only for the lowest-pitched part of the audio spectrum: typically below 200&nbsp;Hz for consumer systems,<ref name="crutchfield.com">[http://www.crutchfield.com/S-5VsEXVgtser/Learn/learningcenter/home/speakers_glossary.html Home Speakers Glossary]. Crutchfield.com (June 21, 2010). Retrieved on October 12, 2010.</ref> below 100&nbsp;Hz for professional live sound,<ref>{{cite web|url=http://www.prosoundweb.com/article/in_depth_the_aux_fed_subwoofer_technique_explained/P2/ |title=In-Depth: The Aux-Fed Subwoofer Technique Explained |last=Young |first=Tom |date=December 1, 2008 |work=Study Hall |publisher=ProSoundWeb |page=2 |access-date=March 3, 2010 |archive-url=https://web.archive.org/web/20100114121638/http://www.prosoundweb.com/article/in_depth_the_aux_fed_subwoofer_technique_explained/P2/ |archive-date=January 14, 2010 }}</ref> and below 80&nbsp;Hz in [[THX]]-approved systems.<ref name="DellaSala">{{cite web|url=http://www.audioholics.com/tweaks/get-good-bass/setting-the-subwoofer-lfe-crossover-for-best-performance|title=Setting the Subwoofer / LFE Crossover for Best Performance |last=DellaSala|first=Gene|date=August 29, 2004|work=Tips & Tricks: Get Good Bass|publisher=Audioholics|access-date=March 3, 2010}}</ref> Because the intended range of frequencies is limited, subwoofer system design is usually simpler in many respects than for conventional loudspeakers, often consisting of a single driver enclosed in a suitable enclosure.  Since sound in this frequency range can easily bend around corners by [[diffraction]], the speaker aperture does not have to face the audience, and subwoofers can be mounted in the bottom of the enclosure, facing the floor.  This is eased by the limitations of human hearing at low frequencies; Such sounds cannot be located in space, due to their large wavelengths compared to higher frequencies which produce differential effects in the ears due to shadowing by the head, and diffraction around it, both of which we rely upon for localization clues.

To accurately reproduce very low bass notes, subwoofer systems must be solidly constructed and properly braced to avoid unwanted sounds from cabinet vibrations. As a result, good subwoofers are typically quite heavy. Many subwoofer systems include integrated [[power amplifier]]s and electronic [[Infrasound|subsonic]]-filters, with additional controls relevant to low-frequency reproduction (e.g. a crossover knob and a phase switch). These variants are known as ''active'' or ''powered'' subwoofers.<ref>{{cite web |url=http://www.home-theater-designers.com/glossary.html |title=Glossary of Terms |work=Home Theater Design |publisher=ETS-eTech |archive-url=https://web.archive.org/web/20120723231911/http://www.home-theater-designers.com/glossary.html |archive-date=July 23, 2012 |page=1 |access-date=March 3, 2010 }}</ref> In contrast, ''passive'' subwoofers require external amplification.

In typical installations, subwoofers are physically separated from the rest of the speaker cabinets.  Because of propagation delay and positioning, their output may be out of phase with the rest of the sound.  Consequently, a subwoofer's power amp often has a phase-delay adjustment which may be used improve performance of the system as a whole. Subwoofers are widely used in large concert and mid-sized venue sound reinforcement systems. Subwoofer cabinets are often built with a [[bass reflex]] port, a design feature which if properly engineered improves bass performance and increases efficiency.