Subwoofer
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Home Audio, Home Theater Subwoofers
A subwoofer is a loudspeaker device which reproduces sub-bass frequencies below about 60–150 hertz, where the feeling of "punch" and "energy" tends to be located in music and movie soundtracks. It is difficult for small loudspeakers to produce these frequencies, particularly at high output levels, and so it is often advantageous to use a separate speaker dedicated to this task.
The need to reproduce these frequencies has increased since older formats, such as vinyl records, have been displaced by digital formats, such as CD, and particularly 5.1 formats such as Dolby Digital, in which the ".1" channel is dedicated solely to the subwoofer. The .1 channel is usually dedicated to extended bass frequencies, for example, the low frequencies of a gunshot, string bass, or thunder. This track is often used aggressively by mixing artists.
Subwoofers use drivers (woofer) with cones typically coming in 10" or 12" sizes, but can be as large as 34", and as small as 4". Diameter tends to be advantageous because low frequencies involve shifting a great deal of air; a recent trend has been for high excursion, i.e., how far the cone can move from stand still; for example, some can move much as 2.5" in or out, yielding an overall displacement of 5" (this is controlled movement range).
Subwoofers are usually powered by a high power amplifier, and often an electronic crossover ensures that higher frequencies will not be directed to the subwoofer.
It should be noted that a subwoofer does not necessarily provide superior bass performance to large conventional loudspeakers; they are merely subwoofers because they ought to reproduce only the lowest frequencies. A conventional woofer may reproduce frequencies up to 200, 300, or in a two-way speaker a mid-woofer (paired with a tweeter) also handles midrange, up to 3,000 hertz or more.
Rather, the intention may be to use small main ("satellite") speakers (of which there are 2 for stereo, and 5 or more for surround sound) and locate ("hide") the subwoofer elsewhere; to augment an existent speaker to relieve it of reproducing bass and gain output level and/or quality; or because high levels of low bass are required and using a dedicated amplifier and speaker provides the output level and quality required. Thus, subwoofers may be part of a package that includes satellite speakers, purchased separately, or built into the cabinet of a conventional loudspeaker. (e.g., some speakers include a subwoofer in the lower portion of the cabinet.)
Physical separation of subwoofer and "satellite" speakers not only enables placement in an inconspicuous location, but since sub-bass frequencies are particularly sensitive to location (e.g., due to room resonance and 'modes'), the best position of the subwoofer may not be where the "satellite" speakers are located. (e.g., it has been suggested subwoofer(s) be placed in the corner of the room, far from large room openings, and closer to the listener.) This is possible since low bass frequencies have a long wavelength; hence there is little difference between the information reaching our left and right ears, and we are unable to easily locate their direction below 80 Hz. Harmonics at higher frequencies (from the satellites) can then be used, by the auditory system, to calculate the directional information. Note that only one subwoofer need be used, even when using 5 or more satellite speakers—e.g., for surround sound. All low frequency information is sent to the subwoofer. ("Bass management" or "Small" mode for the satellite speakers is common among equipment such as Dolby Digital surround processors/receivers.)
The physically separate subwoofer/satellite arrangement has been popularised by lifestyle systems, such as those manufactured by Bose, and multimedia speakers, examples of which include the Klipsch (http://www.klipsch.com/) ProMedia. Particularly among low cost systems, however, it may be little more than a marketing device: it's not likely that a small woofer in a compact cabinet will have better bass performance than good speakers; as mentioned, the term "subwoofer" is no guarantee of particular bass performance. Most multimedia "subwoofers" should probably have been called "woofers". They are too weak to play any real deep bass. Further, small satellites systems typically cross over the bass above 80 Hz, introducing the subwoofer "localization effect". On the other hand, high end domestic subwoofers are manufactured by companies such as M&K, HSU, Velodyne and REL. These can be purchased separately, to be added to an existent system or when considering a set of speakers; or as part of a high-end speaker package. All of these subwoofers tend to have in-built amplification.
Professional Uses of Subwoofers
Subwoofers are found in professional applications such as live concerts, movie theatres, various other sound reinforcement applications (ranging from nightclubs to theme restaurants) and studios. Some of these applications require subwoofers designed for very high sound levels, such as the JBL (http://www.jbl.com/) 4645 (http://www.jblpro.com/pages/cinema/lfsub.htm) - certified for THX movie theatres - which uses an 18" driver (woofer). Note that movie theatre speakers (situated behind a perforated screen) typically use 15" drivers (woofers), so the use here is only to reproduce the lowest frequencies at high sound pressure levels.
Large concert sound systems always use subwoofers (referred to as "subs" by the engineers and crew). The bulk of the sound system is usually "flown" (suspended from the ceiling by chain hoists) and the subs are usually stacked on the stage or the ground in front of the stage to the left and right of the performance space.
Many times the subs are not part of the entire sound mix but are specifically fed just kick drum, bass guitar and other low-frequency content from a separate output on the main mixing console.
Popular sub systems in use currently are made by companies such as EAW (http://www.eaw.com) but usually the subs will be made by the manufacturer of the rest of the PA system such as L-Acoustics (http://www.l-acoustics-us.com/) and their V-Dosc Line Array with its matching dual 18-inch sub cabinets. Similar popular PA systems are made by JBL, Electro-Voice, EAW and Meyer Sound (http://www.meyersound.com).
The 18-inch woofer driver is the primary majority device for pro audio applications. They are usually direct radiating in a ported enclosure built of 13-ply birch. For a pop music concert with about 10,000 audience members there could be as many as 8 double-18-inch cabinets on either side of the stage. 12-inch drivers in very large folded horns are also becoming popular now. One of the most powerful subs manufactured can play as low as 25 Hz and can cover thousands of feet and uses 12-inch woofers on a 13-foot (4 m) long folded horn.
A now-discontinued but popular Electro-Voice (http://www.electrovoice.com/) subwoofer employed "Manifold Technology" configuration to fit four 18-inch drivers into a relatively compact enclosure. Intended for applications such as night club installations and concert sound reinforcement this cabinet is still popular with PA system equipment rental companies.
Another extreme pro audio device is the ServoDrive (http://www.servodrive.com/) ContraBass (http://www.servodrive.com/contrabass.html), where the driver's cone is moved using a belt-drive coupled servo motor! A large horn-loaded version called the BassTech-7 can be found in venues such as theme park rides.
Pro Audio subs have to be capable of very high output levels - after all, concert venues may seat 10,000s of individuals outdoors - a lot of air to shift! On average, music applications generally require less capability than movie soundtracks in the very lowest octave, but modern popular music is changing this preconception and this is reflected in the design attention given to the subwoofer section of the PA system nowadays compared to a couple decades ago. People used to bass in home audio systems and car audio many times think that the subs in a concert PA system aren't putting out that much. Considering they work outdoors and the average listener is hundreds if not thousands of feet away from the devices it's quite amazing.
Car Audio Subwoofers
The automobile is ideal for the "hidden" subwoofer approach, due to space limitations of locations such as doors (ignoring the acoustic problems of a car interior). Typically, subwoofers are installed in the trunk. Curiously, some car stereo enthusiasts seem intent on producing ultra-high sound pressure levels in the confines of their vehicle's cabin. In international car stereo competitions, up to 64 subwoofers driven by some 100,000 watts have been used to generate up to 175 decibels. Naturally, these sound levels are not safe for humans. Such "SPL wars" have drawn much attention to subwoofers in general, but subjective competitions of sound quality ("SQ") has not gained similar popularity.
Indeed, hearing loss is one concern, alongside space considerations and neighbour relations. Since much bass is felt, sub-bass can be augmented using tactile transducers. These have recently emerged as a device that attaches to furniture, such as one's seat, via which vibrations are transmitted to the body; they can be connected to an amplifier as per a normal loudspeaker. However, some feel that the vibrations are a little disembodied from the rest of the auditory experience.
Non-Round Subwoofers in Car Audio
Within the last few years, the car audio field has seen a variety of subwoofers utilizing non-round shapes. Stillwater Designs, nicknamed Kicker, released a square subwoofer several years ago, the Solo-Baric series and recently, the Solo X. Bazooka has introduced a triangular subwoofer. Xtant has introduced a hexagonal subwoofer. Other companies, such as Sony, have jumped on the bandwagon, producing non-round subwoofers of their own. There is no known auditory advantage to these shapes.
The intent of a square subwoofer is to increase the surface area of the woofer's cone. In enclosures of the same size, it is possible to achieve more subwoofer cone surface area with a square design than a circular design. The increased surface area translates into moving more air and higher sound pressure levels. However, a triangular design decreases the surface area of the woofer cone relative to a circular or square design in an enclosure of the same size.
See also
External Links
- Kicker (http://www.kicker.com)
- HSU Research (http://www.hsuresearch.com.com) - subwoofer designs by Dr. Poh Ser Hsu
- TC Sounds (http://www.tcsounds.com/) - subwoofer manufacturer for a number of car audio brands.
- SAS Bazooka (http://www.bazooka.com/)
- Bazooka's triangular subwoofers (http://www.bazooka.com/productAutoRawWoofersRX.asp)
- Xtant (http://www.xtant.com)
- Xtant's hexagonal subwoofers (http://www.xtant.com/html/products/XSubwoofers.cfm)
- Sony (http://www.sony.com)
- Sony's Car Audio (http://www.sonystyle.com/is-bin/INTERSHOP.enfinity/eCS/Store/en/-/USD/SY_ViewStatic-Start;sid=4PCt-XLpkwit7jK5LIyn8j3nDM1r2SkMteU=?page=static%2fcar_audio%2fsy_car_audio%2eisml)
- Crutchfield (http://www.crutchfield.com)
- CarDomain (http://www.cardomain.com/shop/subwoofers)de:Subwoofer