page_title: Subwoofer
section_title: Phase control
hierarchical_section_title: Subwoofer / Construction and features / Phase control
caption_attribution_description: MJA Pro 50 subwoofer
context_page_description: A subwoofer is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be generated by a woofer. 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. Subwoofers are never used alone, as they are intended to augment the low frequency range of loudspeakers that cover the higher frequency bands. While the term "subwoofer" technically only refers to the speaker driver, in common parlance, the term often refers to a subwoofer driver mounted in a speaker enclosure, often with a built-in amplifier.
  Subwoofers are made up of one or more woofers mounted in a loudspeaker enclosure—often made of wood—capable of withstanding air pressure while resisting deformation.
context_section_description: Changing the relative phase of the subwoofer with respect to the woofers in other speakers may or may not help to minimize unwanted destructive acoustic interference in the frequency region covered by both subwoofer and main speakers. It may not help at all frequencies, and may create further problems with frequency response, but is even so generally provided as an adjustment for subwoofer amplifiers. Phase control circuits may be a simple polarity reversal switch or a more complex continuously variable circuits.
  Continuously variable phase control circuits are common in subwoofer amplifiers, and may be found in crossovers and as do-it-yourself electronics projects. Phase controls allow the listener to change the arrival time of the subwoofer sound waves relative to the same frequencies from the main speakers (i.e., at and around the crossover point to the subwoofer). A similar effect can be achieved with the delay control on many home theater receivers. The subwoofer phase control found on many subwoofer amplifiers is actually a polarity inversion switch. It allows users to reverse the polarity of the subwoofer relative to the audio signal it is being given. This type of control allows the subwoofer to either be in phase with the source signal, or 180 degrees out of phase.
  The subwoofer phase can still be changed by moving the subwoofer closer to or further from the listening position, however this may not be always practical.
caption: The rear panel of a down-firing, active subwoofer cabinet
exif: {"Image Make": "Canon", "Image Model": "Canon DIGITAL IXUS 430", "Image Orientation": "Horizontal (normal)", "Image XResolution": "180", "Image YResolution": "180", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2004:12:07 15:06:06", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "196", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "180", "Thumbnail YResolution": "180", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "2548", "Thumbnail JPEGInterchangeFormatLength": "4239", "EXIF ExposureTime": "1/60", "EXIF FNumber": "14/5", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2004:12:07 15:06:06", "EXIF DateTimeDigitized": "2004:12:07 15:06:06", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "5", "EXIF ShutterSpeedValue": "189/32", "EXIF ApertureValue": "95/32", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "95/32", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash fired, auto mode", "EXIF FocalLength": "237/32", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "650", "EXIF ExifImageLength": "754", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "Interoperability RelatedImageWidth": "1704", "Interoperability RelatedImageLength": "2272", "EXIF InteroperabilityOffset": "1860", "EXIF FocalPlaneXResolution": "56800/7", "EXIF FocalPlaneYResolution": "56800/7", "EXIF FocalPlaneResolutionUnit": "2", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF SceneCaptureType": "Standard"}