History of the car audio subwoofer
Since large drivers require undesirably large cabinets, most subwoofer drivers have large excursions. Unfortunately, high excursion, at high power levels, tends to produce more distortion from inherent mechanical and magnetic effects in electro-dynamic drivers the most common sort. The conflict between assorted goals can never be fully resolved; subwoofer designs necessarily involve tradeoffs and compromises.
Hofmann's Iron Law the efficiency of a woofer system is directly proportional to its cabinet volume as in size and to the cube of its cutoff frequency, that is how low in pitch it will go applies to subwoofers just as to all loudspeakers. The frequency response specification of a speaker describes the range of frequencies or musical tones a speaker can reproduce, measured in hertz Hz. Specifications of frequency response depend wholly for relevance on an accompanying amplitude value—measurements taken with a wider amplitude tolerance will give any loudspeaker a wider frequency response.
Subwoofers also vary in regard to the sound pressure levels achievable and the distortion levels they can produce over their range. Some also include user-adjustable equalization that allows boosted or reduced output at particular frequencies; these vary from a simple "boost" switch, to fully parametric equalizers meant for detailed speaker and room correction.
Some such systems are even supplied with a calibrated microphone to measure the subwoofer's in-room response, so the automatic equalizer can correct the combination of subwoofer, subwoofer location, and room response to minimize effects of room modes and improve low frequency performance. They sometimes incorporate internal passive crossovers, with the filter frequency determined at the factory.
These are generally used with third-party power amplifiers, taking their inputs from active crossovers earlier in the signal chain. Inexpensive Home Theatre in a Box packages often come with a passive subwoofer cabinet that is amplified by the multi-channel amplifier. While few high-end home-theater systems use passive subwoofers, this format is still popular in the professional sound industry. Equalization can be used to adjust the in-room response of a subwoofer system. In addition, many amplifiers include an adjustable low-pass filter, which prevents undesired higher frequencies from reaching the subwoofer driver.
The crossover section may also include a high-pass " infrasonic " or "subsonic" filter which prevents the subwoofer driver from attempting to reproduce frequencies below its safe capabilities. Setting a subsonic 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.
Some systems use parametric equalization in an attempt to correct for room frequency response irregularities. Careful positioning of the subwoofer within the room can also help flatten the frequency response. 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. Continuously variable phase control circuits are common in subwoofer amplifiers, and may be found in crossovers and as do-it-yourself electronics projects. 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.
This type of control allows the subwoofer to either be in phase with the source signal, or 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. Some active subwoofers use a servo feedback mechanism based on cone movement which modifies the signal sent to the voice coil. The servo feedback signal is derived from a comparison of the input signal to the amplifier versus the actual motion of the cone.
The usual source of the feedback signal is a few turns of voice coil attached to the cone or a microchip-based accelerometer placed on the cone itself.
Servo controlled subwoofers are not the same as Tom Danley 's Servodrive subwoofers whose primary mechanism of sound reproduction avoids the normal voice coil and magnet combination in favor of a high-speed belt-driven servomotor. The Servodrive design increases output power, reduces harmonic distortion and virtually eliminates power compression , the loss of loudspeaker output that results from an increase in voice coil impedance due to overheating of the voice coil. This feature allows high power operation for extended periods of time.
The use of a subwoofer augments the bass capability of the main speakers, and allows them to be smaller without sacrificing low frequency capability. A subwoofer does not necessarily provide superior bass performance in comparison to large conventional loudspeakers on ordinary music recordings due to the typical lack of very low frequency content on such sources.
However, there are recordings with substantial low frequency content that most conventional loudspeakers are ill-equipped to handle without the help of a subwoofer, especially at high playback levels, such as music for pipe organs with 32' 9. Frequencies which are sufficiently low are not easily localized by humans, hence many stereo and multichannel audio systems feature only one subwoofer channel and a single subwoofer can be placed off-center without affecting the perceived sound stage, since the sound produced will be difficult to localize. The intention in a system with a subwoofer is often to use small main speakers of which there are two for stereo and five or more for surround sound or movie tracks and to hide the subwoofer elsewhere e.
Higher upper limits for the subwoofer e. Home theatre systems typically use one subwoofer cabinet the "1" in 5. However, to "improve bass distribution in a room that has multiple seating locations, and prevent "node" or "null points" with weakened bass response, some home cinema enthusiasts use "5. Some users add a subwoofer because high levels of low bass are desired, even beyond what is in the original recording, as in the case of house music enthusiasts. Thus, subwoofers may be part of a package that includes satellite speakers, may be purchased separately, or may be built into the same cabinet as a conventional speaker system.
For instance, some floor standing tower speakers include a subwoofer driver in the lower portion of the same cabinet. Physical separation of subwoofer and "satellite" speakers not only allows placement in an inconspicuous location, but since sub-bass frequencies are particularly sensitive to room location due to room resonances and reverberation 'modes' , the best position for the subwoofer is not likely to be where the "satellite" speakers are located.
For greatest efficiency and best coupling to the room's air volume, subwoofers can be placed in a 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 a listener's left and right ears, and so they cannot be readily localized. All low frequency information is sent to the subwoofer.
The Beginning: Car Audio Systems from the 1930s
However, unless the sound tracks have been carefully mixed for a single subwoofer channel, it is possible to have some cancellation of low frequencies if bass information in one channel's speaker is out of phase with another. Particularly among lower cost " Home Theater in a Box " systems and with "boom boxes", however, inclusion of a subwoofer may be little more than a marketing device. It is unlikely that a small woofer in an inexpensively-built compact plastic cabinet will have better bass performance than well-designed conventional and typically larger speakers in a plywood or MDF cabinet.
Mere use of the term "subwoofer" is no guarantee of good or extended bass performance. This is usually due to poor crossover designs or choices too high crossover point or insufficient crossover slope used in many computer and home theater systems; localization also comes from port noise and from typically large amounts of harmonic distortion in the subwoofer design. Automobiles are not well suited for the "hidden" subwoofer approach due to space limitations in the passenger compartments.
It is not possible, in most circumstances, to fit such large drivers and enclosures into doors or dashboards, so subwoofers are installed in the trunk or back seat space. Some car audio enthusiasts compete to produce very high sound pressure levels in the confines of their vehicle's cabin; sometimes dangerously high. The "SPL wars" have drawn much attention to subwoofers in general, but subjective competitions in sound quality "SQ" have not gained equivalent popularity.
Top SPL cars are not able to play normal music, or perhaps even to drive normally as they are designed solely for competition. Many non-competition subwoofers are also capable of generating high levels in cars due to the small volume of a typical car interior. High sound levels can cause hearing loss and tinnitus if one is exposed to them for an extended period of time.
PARTAGER NOTRE PASSION
In the s, several car audio manufacturers produced subwoofers using non-circular shapes, including Boston Acoustic, Kicker, Sony, Bazooka, and X-Tant. Other major car audio manufacturers like Rockford Fosgate did not follow suit since non-circular subwoofer shapes typically carry some sort of distortion penalties. An important factor in the "square sub vs round sub" argument is the effects of the enclosure used. In a sealed enclosure, the maximum displacement is determined by.
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After the introduction of Sensurround, movie theater owners began installing permanent subwoofer systems. Dolby Stereo 70 mm Six Track was a six channel film sound format introduced in that used two subwoofer channels for stereo reproduction of low frequencies. Starting in , THX certification of the cinema sound experience quantified the parameters of good audio for watching films, including requirements for subwoofer performance levels and enough isolation from outside sounds so that noise did not interfere with the listening experience.
In , Dolby Digital 's six-channel film sound format incorporated a single LFE channel, the "point one" in 5. Tom Horral, a Boston-based acoustician, blames complaints about modern movies being too loud on subwoofers.
He says that before subwoofers made it possible to have loud, relatively undistorted bass, movie sound levels were limited by the distortion in less capable systems at low frequency and high levels. Professional audio subwoofers used in rock concerts in stadiums, DJ performances at dance music venues e. This is reflected in the design attention given in the s to the subwoofer applications for sound reinforcement, public address systems , dance club systems and concert systems.
Cerwin Vega states that when a subwoofer cabinet is added to an existing full-range speaker system, this is advantageous, as it moves the " As a result, your main [full-range] cabinets will run more efficiently and at higher volumes.
"subwoofer" in Audio & GPS in Ontario
Consumer applications as in home use are considerably less demanding due to much smaller listening space and lower playback levels. Subwoofers are now almost universal in professional sound applications such as live concert sound, churches, nightclubs, and theme parks. Movie theatres certified to the THX standard for playback always include high capability subwoofers. The number of subwoofer enclosures used in a concert depends on a number of factors, including the size of the venue, whether it is indoors or outdoors, the amount of low-frequency content in the band's sound, the desired volume of the concert, and the design and construction of the enclosures e.
A tiny coffeehouse may only need a single inch subwoofer cabinet to augment the bass provided by the full-range speakers. In the largest stadium venues, there may be a very large number of subwoofer enclosures. The main speakers may be 'flown' from the ceiling of a venue on chain hoists, and 'flying points' i. Subwoofers can be flown or stacked on the ground near the stage. One of the reasons subwoofers may be installed on the ground is that on the ground installation can increase the bass performance, particularly if the sub is placed in the corner of a room conversely, if a sub cabinet is perceived as too loud, alternatives to on the ground or in-corner installation may be considered.
Just as consumer subwoofer enclosures can be made of Medium-density fibreboard MDF , Oriented strand board OSB , plywood , plastic or other dense material, professional subwoofer enclosures can be built from the same materials. Touring subwoofer cabinets are typically designed with features that facilitate moving the enclosure e.
In the s, many small-to mid-size subwoofers designed for bands' live sound use and DJ applications are "powered subs"; that is, they have an integrated power amplifier.
The History of Car Audio
These models typically have a built-in crossover. Some models have a metal-reinforced hole in which a speaker pole can be mounted for elevating full-frequency range cabinets. In professional concert sound system design, subwoofers can be incorporated seamlessly with the main speakers into a stereo or mono full-range system by using an active crossover.
The audio engineer typically adjusts the frequency point at which lower frequency sounds are routed to the subwoofer speaker s , and mid- and higher frequency sounds are sent to the full-range speakers. Such a system receives its signal from the main mono or stereo mixing console mix bus and amplifies all frequencies together in the desired balance.
If the main sound system is stereo, the subwoofers can also be in stereo. Otherwise, a mono subwoofer channel can be derived within the crossover from a stereo mix, depending on the crossover make and model. While era subwoofer cabinet manufacturers suggest placing subwoofers on either side of a stage as implied by the inclusion of pole cups for the full-range PA cabinets, Dave Purton argues that for club gigs, having two subwoofer cabinets on either side of a stage will lead to gaps in bass coverage in the venue; he states that putting the two subwoofer cabinets together will create a more even, omnidirectional sub-bass tone.
Instead of being incorporated into a full-range system, concert subwoofers can be supplied with their own signal from a separate mix bus on the mixing console; often one of the auxiliary sends "aux" or "auxes" is used. This configuration is called "aux-fed subwoofers", and has been observed to significantly reduce low frequency "muddiness" that can build up in a concert sound system which has on stage a number of microphones each picking up low frequencies and each having different phase relationships of those low frequencies.
This simplifies the signal sent to the subwoofers and makes for greater clarity and low punch. To keep low frequency sound focused on the audience area and not on the stage, and to keep low frequencies from bothering people outside of the event space, a variety of techniques have been developed in concert sound to turn the naturally omnidirectional radiation of subwoofers into a more directional pattern. Several examples of sound reinforcement system applications where sound engineers seek to provide more directional bass sound are music festivals , which often have several bands performing at the same time on different stages; large raves or EDM events, where there are multiple DJs performing at the same time in different rooms or stages; and multiplex movie theatres , in which there are many films being shown simultaneously in auditoriums that share common walls.
These techniques include setting up subwoofers in a vertical array; using combinations of delay and polarity inversion; and setting up a delay-shaded system.