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Ampeg SVT

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The Ampeg SVT is a bass guitar amplifier designed by Bill Hughes and Roger Cox for Ampeg and introduced in 1969. The SVT is a stand-alone amplifier or "head" as opposed to a "combo" unit comprising amp and speaker(s) in one cabinet, and was capable of 300 watts output at a time when most amplifiers could not exceed 100 watts output, making the SVT an important amp for bands playing music festivals and other large venues.

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114-482: The SVT has been through many design changes over the years but is still in production today. While the SVT could be used with any 300 watt, 2- or 4-ohm cabinet combination, Ampeg recommended that it be used with a pair of sealed 8x10" speaker enclosures because one cabinet could not handle the power of the SVT. It was not until 1980 that the speakers in the enclosures were updated to a power handling rating of 350 watts, allowing

228-509: A diaphragm that moves back and forth to create pressure waves in the air column in front, and depending on the application, at some angle to the sides. The diaphragm is typically in the shape of a cone for low and mid frequencies or a dome for higher frequencies, or less commonly, a ribbon, and is usually made of coated or uncoated paper or polypropylene plastic. More exotic materials are used on some drivers, such as woven fiberglass , carbon fiber , aluminum , titanium , pure cross carbon and

342-408: A dynamic loudspeaker , uses a lightweight diaphragm , or cone , connected to a rigid basket , or frame , via a flexible suspension, commonly called a spider , that constrains a voice coil to move axially through a cylindrical magnetic gap. A protective dust cap glued in the cone's center prevents dust, most importantly ferromagnetic debris, from entering the gap. When an electrical signal

456-456: A hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18-inch (46 cm) or even 21-inch (53 cm) speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts. The primary role of an enclosure is to prevent sound waves generated by the rearward-facing surface of the diaphragm of an open speaker driver interacting with sound waves generated at

570-460: A Scandinavian driver maker. The design remains uncommon among commercial designs currently available. A reason for this may be that adding damping material is a needlessly inefficient method of increasing damping; the same alignment can be achieved by simply choosing a loudspeaker driver with the appropriate parameters and precisely tuning the enclosure and port for the desired response. A similar technique has been used in aftermarket car audio ; it

684-416: A bass reflex design since such corrections can be as simple as mass adjustments to the drone. The disadvantages are that a passive radiator requires precision construction like a driver, thus increasing costs, and may have excursion limitations. A 4th-order electrical bandpass filter can be simulated by a vented box in which the contribution from the rear face of the driver cone is trapped in a sealed box, and

798-404: A bass reflex, but the bass reflex cabinet will have a lower −3 dB point. The voltage sensitivity above the tuning frequency remains a function of the driver, and not of the cabinet design. The isobaric loudspeaker configuration was first introduced by Harry F. Olson in the early 1950s, and refers to systems in which two or more identical woofers (bass drivers) operate simultaneously, with

912-413: A box size that exploits the almost linear air spring resulting in a −3 dB low-frequency cut-off point of 30–40 Hz from a box of only one to two cubic feet or so. The spring suspension that restores the cone to a neutral position is a combination of an exceptionally compliant (soft) woofer suspension, and the air inside the enclosure. At frequencies below system resonance, the air pressure caused by

1026-460: A broad or narrow frequency range. Small diaphragms are not well suited to moving the large volume of air that is required for good low-frequency response. Conversely, large drivers may have heavy voice coils and cones that limit their ability to move at very high frequencies. Drivers pressed beyond their design limits may have high distortion . In a multi-way loudspeaker system, specialized drivers are provided to produce specific frequency ranges, and

1140-410: A closet or attic. This is often the case with exotic rotary woofer installations, as they are intended to go to frequencies lower than 20 Hz and displace large volumes of air. Infinite baffle ( IB ) is also used as a generic term for sealed enclosures of any size, the name being used because of the ability of a sealed enclosure to prevent any interaction between the forward and rear radiation of

1254-430: A common body of enclosed air adjoining one side of each diaphragm. In practical applications, they are most often used to improve low-end frequency response without increasing cabinet size, though at the expense of cost and weight. Two identical loudspeakers are coupled to work together as one unit: they are mounted one behind the other in a casing to define a chamber of air in between. The volume of this isobaric chamber

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1368-590: A different part of the audible frequency range. In this case the individual speakers are referred to as drivers and the entire unit is called a loudspeaker . Drivers made for reproducing high audio frequencies are called tweeters , those for middle frequencies are called mid-range drivers (much less commonly called squawkers), and those for low frequencies are called woofers , while those for very low bass range are subwoofers . Less common types of drivers are supertweeters and rotary woofers . The electroacoustic mechanism most widely used in speakers to convert

1482-431: A driver at low frequencies. In conceptual terms an infinite baffle is a flat baffle that extends out to infinity – the so-called endless plate . A genuine infinite baffle cannot be constructed but a very large baffle such as the wall of a room can be considered to be a practical equivalent. A genuine infinite-baffle loudspeaker has an infinite volume (a half-space) on each side of the baffle and has no baffle step. However,

1596-426: A driver; each implementation has advantages and disadvantages. Polyester foam, for example, is lightweight and economical, though usually leaks air to some degree and is degraded by time, exposure to ozone, UV light, humidity and elevated temperatures, limiting useful life before failure. The wire in a voice coil is usually made of copper , though aluminum —and, rarely, silver —may be used. The advantage of aluminum

1710-818: A few centimetres or inches), those for mid-range frequencies (perhaps 300 Hz to 2 kHz) much larger, perhaps 30 to 60 cm (1 or 2 feet), and for low frequencies (under 300 Hz) very large, a few metres (dozens of feet). In the 1950s, a few high fidelity enthusiasts actually built full-sized horns whose structures were built into a house wall or basement. With the coming of stereo (two speakers) and surround sound (four or more), plain horns became even more impractical. Various speaker manufacturers have produced folded low-frequency horns which are much smaller (e.g., Altec Lansing, JBL, Klipsch, Lowther, Tannoy) and actually fit in practical rooms. These are necessarily compromises, and because they are physically complex, they are expensive. The multiple entry horn (also known under

1824-405: A larger magnet for equivalent performance. Electromagnets were often used in musical instrument amplifiers cabinets well into the 1950s; there were economic savings in those using tube amplifiers as the field coil could, and usually did, do double duty as a power supply choke. Very few manufacturers still produce electrodynamic loudspeakers with electrically powered field coils , as was common in

1938-461: A leaky sealed box or a ported box with large amounts of port damping. By setting up a port, and then blocking it precisely with sufficiently tightly packed fiber filling, it is possible to adjust the damping in the port as desired. The result is control of the resonance behavior of the system which improves low-frequency reproduction, according to some designers. Dynaco was a primary producer of these enclosures for many years, using designs developed by

2052-403: A loss of bass and in comb filtering , i.e., peaks and dips in the response power regardless of the signal that is meant to be reproduced. The resulting response is akin to two loudspeakers playing the same signal but at different distances from the listener, which is like adding a delayed version of the signal to itself, whereby both constructive and destructive interference occurs. Before

2166-462: A lower voltage taps. Other methods are to use voltage regulation. The SVT's pre-amp is notorious for ground loop hum. Re-wiring and separating the audio ground shield from the power return ground lead in the MOLEX connector is one solution. Diodes were later used to by-pass the 22ohm screen resistors. In the event of a tube short failure or simply a transient overload condition the diode will conduct once

2280-406: A metallic or cloth mesh that are used to protect the speaker by forming a protective cover over the speaker's cone while allowing sound to pass through undistorted. Speaker enclosures are used in homes in stereo systems, home cinema systems, televisions , boom boxes and many other audio appliances. Small speaker enclosures are used in car stereo systems. Speaker cabinets are key components of

2394-461: A number of commercial applications, including sound reinforcement systems , movie theatre sound systems and recording studios . Electric musical instruments invented in the 20th century, such as the electric guitar , electric bass and synthesizer , among others, are amplified using instrument amplifiers and speaker cabinets (e.g., guitar amplifier speaker cabinets). Early on, radio loudspeakers consisted of horns , often sold separately from

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2508-420: A number of features to make them easier to transport, such as carrying handles on the top or sides, metal or plastic corner protectors, and metal grilles to protect the speakers. Speaker enclosures designed for use in a home or recording studio typically do not have handles or corner protectors, although they do still usually have a cloth or mesh cover to protect the woofer and tweeter. These speaker grilles are

2622-462: A player to use an SVT head with only one cabinet. SVT originally stood for Super Vacuum Tube , but Ampeg has since revised the meaning of the initialism to Super Valve Technology , with the word "valve" referring to the vacuum tubes (called "valves" in Britain and some other regions) used in the amp. Following Unimusic's acquisition of Ampeg in 1967, the new company management was actively pursuing

2736-471: A polarity switch. In the early 1980s, Ampeg was bought by Music Technologies, Inc. (MTI), which contracted to have SVTs manufactured in Japan. While MTI-era SVTs are mostly identical to the previous versions, they did have differences. Cosmetically, MTI SVTs have black faceplates with white lettering, black grill cloth, "elephant hide" or rougher textured tolex, and rack case-style spring-loaded handles, updated from

2850-553: A role in managing vibration induced by the driver frame and moving airmass within the enclosure, as well as heat generated by driver voice coils and amplifiers (especially where woofers and subwoofers are concerned). Sometimes considered part of the enclosure, the base, may include specially designed feet to decouple the speaker from the floor. Enclosures designed for use in PA systems , sound reinforcement systems and for use by electric musical instrument players (e.g., bass amp cabinets ) have

2964-436: A round hole in the cabinet. It was observed that the enclosure had a strong effect on the bass response of the speaker. Since the rear of the loudspeaker radiates sound out of phase from the front, there can be constructive and destructive interference for loudspeakers without enclosures, and below frequencies related to the baffle dimensions in open-baffled loudspeakers (see §   Background , below) . This results in

3078-440: A sealed enclosure of the same volume, although it actually has less low frequency output at frequencies well below the cut-off frequency, since the rolloff is steeper (24 dB/octave versus 12 dB/octave for a sealed enclosure). Malcolm Hill pioneered the use of these designs in a live event context in the early 1970s. Vented system design using computer modeling has been practiced since about 1985. It made extensive use of

3192-409: A second passive driver, or drone, to produce similar low-frequency extension, or efficiency increase, or enclosure size reduction, similar to ported enclosures. Small and Hurlburt have published the results of research into the analysis and design of passive-radiator loudspeaker systems. The passive-radiator principle was identified as being particularly useful in compact systems where vent realization

3306-408: A single piece, called the poleplate or yoke. The size and type of magnet and details of the magnetic circuit differ, depending on design goals. For instance, the shape of the pole piece affects the magnetic interaction between the voice coil and the magnetic field, and is sometimes used to modify a driver's behavior. A shorting ring , or Faraday loop , may be included as a thin copper cap fitted over

3420-438: A sort of open-backed box. A rectangular cross-section is more common than curved ones since it is easier to fabricate in a folded form than a circular one. The baffle dimensions are typically chosen to obtain a particular low-frequency response, with larger dimensions giving a lower frequency before the front and rear waves interfere with each other. A dipole enclosure has a figure-of-eight radiation pattern, which means that there

3534-402: A speaker driver appear out of phase from each other because they are generated through the opposite motion of the diaphragm and because they travel different paths before converging at the listener's position. A speaker driver mounted on a finite baffle will display a physical phenomenon known as interference , which can result in perceivable frequency-dependent sound attenuation. This phenomenon

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3648-487: A thicker 1.6mm two-layer printed circuit board with through-hole plating and increased copper weight. In May, 2018, Yamaha Guitar Group acquired Ampeg from LOUD Audio. Ampeg continues to manufacture and sell Heritage Series and SVT Pro Series models of SVT. The SVT amps with 6146B tubes tend to put out a bit more power as well as have a more pronounced grind in low mids, as opposed to the more round, deeper bass sound provided by SVTs with 6550A tubes. This sound characteristic

3762-458: A very few use PEI, polyimide, PET film plastic film as the cone, dome or radiator. All speaker drivers have a means of electrically inducing back-and-forth motion. Typically there is a tightly wound coil of insulated wire (known as a voice coil ) attached to the neck of the driver's cone. In a ribbon speaker, the voice coil may be printed or bonded onto a sheet of very thin paper, aluminum, fiberglass or plastic. This cone, dome or other radiator

3876-492: A vintage SVT is what is called the "black line" SVT, earning its name from the black (rather than blue) faceplate screen printing. Like the later-revision "blue lines" models, the "black line" SVTs utilize 6550 power vacuum tubes instead of 6146Bs. Later 1970s models have the same features as the "black line" SVTs, except the lines around the tone controls have rounded corners and curve into the tone controls. Additionally, these models included 3-prong power cables, and did not include

3990-491: Is coherent at and around the crossover frequencies in the speaker's normal sound field. The acoustic center of the driver dictates the amount of rearward offset needed to time-align the drivers. Enclosures used for woofers and subwoofers can be adequately modeled in the low-frequency region (approximately 100–200 Hz and below) using acoustics and the lumped component models. Electrical filter theory has been used with considerable success for some enclosure types. For

4104-519: Is a complex sum of the properties of the specific driver, the enclosure and port, because of imperfect understanding of the assorted interactions. These enclosures are sensitive to small variations in driver characteristics and require special quality control concern for uniform performance across a production run. Bass ports are widely used in subwoofers for PA systems and sound reinforcement systems , in bass amp speaker cabinets and in keyboard amp speaker cabinets. A passive radiator speaker uses

4218-435: Is a reduction in sound pressure, or loudness, at the sides as compared to the front and rear. This is useful if it can be used to prevent the sound from being as loud in some places as in others. A horn loudspeaker is a speaker system using a horn to match the driver cone to the air. The horn structure itself does not amplify, but rather improves the coupling between the speaker driver and the air. Properly designed horns have

4332-436: Is an approximation of this, since the driver is mounted on a panel, with dimensions comparable to the longest wavelength to be reproduced. In either case, the driver would need a relatively stiff suspension to provide the restoring force which might have been provided at low frequencies by a smaller sealed or ported enclosure, so few drivers are suitable for this kind of mounting. The forward- and rearward-generated sounds of

4446-406: Is an example of a combination of transmission line and horn effects. It is highly regarded by some speaker designers. The concept is that the sound emitted from the rear of the loudspeaker driver is progressively reflected and absorbed along the length of the tapering tube, almost completely preventing internally reflected sound being retransmitted through the cone of the loudspeaker. The lower part of

4560-416: Is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact in a manner similar to a solenoid , generating a mechanical force that moves the coil (and thus, the attached cone). Application of alternating current moves the cone back and forth, accelerating and reproducing sound under

4674-406: Is based on the time constant of the 150 kΩ mixer resistors and the coupling cap - but by this time it is too late, the bias is pushed too far into the positive and the current gets pushed through the 6146, resulting in blown tubes. Some users have an electronics technician re-wire the 12BH7 feed the same as on the later 6550 heads. By adding a 1K and filter cap feeding from the 220 V screen supply to

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4788-424: Is called aperiodic membrane (AP). A resistive mat is placed in front of or directly behind the loudspeaker driver (usually mounted on the rear deck of the car in order to use the trunk as an enclosure). The loudspeaker driver is sealed to the mat so that all acoustic output in one direction must pass through the mat. This increases mechanical damping, and the resulting decrease in the impedance magnitude at resonance

4902-551: Is designed to be rigid, preventing deformation that could change critical alignments with the magnet gap, perhaps allowing the voice coil to rub against the magnet around the gap. Chassis are typically cast from aluminum alloy, in heavier magnet-structure speakers; or stamped from thin sheet steel in lighter-structure drivers. Other materials such as molded plastic and damped plastic compound baskets are becoming common, especially for inexpensive, low-mass drivers. A metallic chassis can play an important role in conducting heat away from

5016-465: Is difficult or impossible, but it can also be applied satisfactorily to larger systems. The passive driver is not wired to an amplifier; instead, it moves in response to changing enclosure pressures. In theory, such designs are variations of the bass reflex type, but with the advantage of avoiding a relatively small port or tube through which air moves, sometimes noisily. Tuning adjustments for a passive radiator are usually accomplished more quickly than with

5130-447: Is due primarily to a reduction in the speed of sound propagation through the filler material as compared to air. The enclosure or driver must have a small leak so that the internal and external pressures can equalise over time, to compensate for changes in barometric pressure or altitude; the porous nature of paper cones, or an imperfectly sealed enclosure, is normally sufficient to provide this slow pressure equalisation. A variation on

5244-406: Is generally provided to cosmetically conceal the drivers and hardware, and to protect the driver from physical damage. In operation, a signal is delivered to the voice coil by means of electrical wires, from the amplifier through speaker cable , then through flexible tinsel wire to the moving coil. The current creates a magnetic field that causes the diaphragm to be alternately forced one way or

5358-399: Is generally the desired effect, though there is no perceived or objective benefit to this. Again, this technique reduces efficiency, and the same result can be achieved through selection of a driver with a lower Q factor , or even via electronic equalization . This is reinforced by the purveyors of AP membranes; they are often sold with an electronic processor which, via equalization, restores

5472-509: Is indeed not much output from the line's port. But it is the inherent resonance (typically at 1/4 wavelength) that can enhance the bass response in this type of enclosure, albeit with less absorbent stuffing. Among the first examples of this enclosure design approach were the projects published in Wireless World by Bailey in the early 1970s, and the commercial designs of the now defunct IMF Electronics which received critical acclaim at about

5586-404: Is its light weight, which reduces the moving mass compared to copper. This raises the resonant frequency of the speaker and increases its efficiency. A disadvantage of aluminum is that it is not easily soldered, and so connections must be robustly crimped together and sealed. Voice-coil wire cross sections can be circular, rectangular, or hexagonal, giving varying amounts of wire volume coverage in

5700-477: Is mostly due to 6146 being much lower in transconductance and less sensitive to drive signal, requiring a higher level from the Pre-amp, which can create more "harmonic growl." The issues with the earliest version of the SVT were in the early design of the driver circuit, not the 6146B tube which is a stable and reliable tube. The earliest SVT driver circuit's design would on occasion result in blown 6146B tubes. Because

5814-438: Is mounted at its outer edge by a flexible surround to a rigid frame which supports a permanent magnet in close proximity to the voice coil. For the sake of efficiency, the relatively lightweight voice coil and cone are the moving parts of the driver, whereas the much heavier magnet remains stationary. Other typical components are a spider or damper, used as the rear suspension element, simple terminals or binding posts to connect

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5928-427: Is of different materials and densities, changing as one gets further from the back of the driver's diaphragm. Consequent to the above, practical transmission line loudspeakers are not true transmission lines, as there is generally output from the vent at the lowest frequencies. They can be thought of as a waveguide in which the structure shifts the phase of the driver's rear output by at least 90° , thereby reinforcing

6042-431: Is particularly noticeable at low frequencies where the wavelengths are large enough that interference will affect the entire listening area. Since infinite baffles are impractical and finite baffles tend to suffer poor response as wavelengths approach the dimensions of the baffle (i.e. at lower frequencies), most loudspeaker cabinets use some sort of structure (usually a box) to contain the out of phase sound energy. The box

6156-408: Is typically made of wood, wood composite, or more recently plastic, for reasons of ease of construction and appearance. Stone, concrete, plaster, and even building structures have also been used. Enclosures can have a significant effect beyond what was intended, with panel resonances , diffraction from cabinet edges and standing wave energy from internal reflection/reinforcement modes being among

6270-767: Is usually chosen to be fairly small for reasons of convenience. The two drivers operating in tandem exhibit exactly the same behavior as one loudspeaker in twice the cabinet. Also known as vented (or ported) systems, these enclosures have a vent or hole cut into the cabinet and a port tube affixed to the hole, to improve low-frequency output, increase efficiency, or reduce the size of an enclosure. Bass reflex designs are used in home stereo speakers (including both low- to mid-priced speaker cabinets and expensive hi-fi cabinets), bass amplifier speaker cabinets, keyboard amplifier cabinets, subwoofer cabinets and PA system speaker cabinets. Vented or ported cabinets use cabinet openings or transform and transmit low-frequency energy from

6384-484: Is well damped to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage. In practice, all three of these criteria cannot be met simultaneously using existing materials; thus, driver design involves trade-offs . For example, paper is light and typically well-damped, but is not stiff; metal may be stiff and light, but it usually has poor damping; plastic can be light, but typically,

6498-464: Is wire the screens in a voltage double arrangement, which will end up at roughly 400 V screen voltage at idle. This will make for a very powerful 400 W SVT. Conversion from a 6550 tube to 6146B tube is a bit trickier, as the 6146B will not tolerate anything over 250 V on the screens or else it will arc over. Some amp technicians prefer to disassemble the PT and tap the windings from the side of the bobbin to create

6612-426: The open baffle approach is to mount the loudspeaker driver in a very large sealed enclosure, providing minimal air spring restoring force to the cone. This minimizes the change in the driver's resonance frequency caused by the enclosure. The low-frequency response of infinite baffle loudspeaker systems has been extensively analysed by Benson. Some infinite baffle enclosures have used an adjoining room, basement, or

6726-528: The spider , which connects the diaphragm or voice coil to the lower frame and provides the majority of the restoring force, and the surround , which helps center the coil/cone assembly and allows free pistonic motion aligned with the magnetic gap. The spider is usually made of a corrugated fabric disk, impregnated with a stiffening resin. The name comes from the shape of early suspensions, which were two concentric rings of Bakelite material, joined by six or eight curved legs . Variations of this topology included

6840-423: The 1950s many manufacturers did not fully enclose their loudspeaker cabinets; the back of the cabinet was typically left open. This was done for several reasons, not least because electronics (at that time tube equipment) could be placed inside and cooled by convection in the open enclosure. Most of the enclosure types discussed in this article were invented either to wall off the out of phase sound from one side of

6954-914: The 2 Ω tap. Fun fact: Paul Gilbert (known for being part of "Mr. Big") on his 2005 album "Space Ship One" pays tribute to the SVT, on a track simply called "SVT". Speaker enclosure A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., loudspeakers and tweeters ) and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers , are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4-inch (10 cm) woofers and small tweeters designed for listening to music with

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7068-555: The 22 Ω resistor, however the peak over-current in the diode can only sustain for a short duration. The 6550A version usually idles with roughly 700 V DC on the plate and 350 V DC on the Screens (though during full clean sine wave 300 W power output, operating voltages will dip to roughly 650 V DC on the Plate and 325 V on the Screens). The output transformer plate load is 1.6 K at 4 Ω tap and 1.75 K at

7182-905: The SVT-CL (Classic). In 2005, LOUD Technologies (now LOUD Audio, LLC) acquired St. Louis Music, including Ampeg. Under LOUD's management, production of Ampeg and versions of SVTs and cabinets was moved to Asia. In 2010, Ampeg introduced the Heritage Series line, manufactured in LOUD Technologies' facility in Woodinville, Washington, including the Heritage SVT-CL head and SVT-810E and SVT-410HLF cabinets. The updated head featured JJ-branded preamp and driver tubes and "Winged C" 6550 power amp tubes, all tested and matched by Ruby Tubes in California, along with

7296-411: The addition of a felt disc to provide a barrier to particles that might otherwise cause the voice coil to rub. The cone surround can be rubber or polyester foam , treated paper or a ring of corrugated, resin-coated fabric; it is attached to both the outer cone circumference and to the upper frame. These diverse surround materials, their shape and treatment can dramatically affect the acoustic output of

7410-476: The audio signal, and possibly a compliant gasket to seal the joint between the chassis and enclosure. Drivers are almost universally mounted into a rigid enclosure of wood, plastic, or occasionally metal. This loudspeaker enclosure or speaker box isolates the acoustic energy from the front of the cone from that of the back of the cone. A horn may be employed to increase efficiency and directionality. A grille , fabric mesh , or other acoustically neutral screen

7524-405: The balanced position established when the driver was assembled at the factory. In addition, each contributes to centering the voice coil and cone, both concentrically within the magnet assembly, and front-to-back, restoring the voice coil to a critical position within the magnetic gap, neither toward one end nor the other. The voice coil and magnet essentially form a linear motor working against

7638-402: The band to use five prototype high-output amplifier heads of a new model being developed by Bill Hughes and Roger Cox. These new amps employed a 14-tube design to generate 300 watts of power in an era when most tube amps generated less than 100. The Rolling Stones took these prototype Ampeg amps on tour along with Rich Mandella, playing all guitars and basses through them for the entire tour. After

7752-530: The bass output lost through the mechanical damping. The effect of the equalization is opposite to that of the AP membrane, resulting in a loss of damping and an effective response similar to that of the loudspeaker without the aperiodic membrane and electronic processor. A dipole enclosure in its simplest form is a driver located on a flat baffle panel, similar to older open back cabinet designs. The baffle's edges are sometimes folded back to reduce its apparent size, creating

7866-507: The bass output. Such designs tend to be less dominant in certain bass frequencies than the more common bass reflex designs and followers of such designs claim an advantage in clarity of the bass with a better congruency of the fundamental frequencies to the overtones. Some loudspeaker designers like Martin J. King and Bjørn Johannessen consider the term quarter wave enclosure as a more fitting term for most transmission lines and since acoustically, quarter wavelengths produce standing waves inside

7980-425: The centering "spring tension" of the spider and surround. If there were no restriction on travel distance imposed by the spider and surround, the voice coil could be ejected from the magnet assembly at high power levels, or travel inward deep enough to collide with the back of the magnet assembly. The majority of speaker drivers work only against the centering forces of the spider and surround and do not actively monitor

8094-431: The cone motion is the dominant force. Developed by Edgar Villchur in 1954, this technique was used in the very successful Acoustic Research line of bookshelf speakers in the 1960s–70s. The acoustic suspension principle takes advantage of this relatively linear spring. The enhanced suspension linearity of this type of system is an advantage. For a specific driver, an optimal acoustic suspension cabinet will be smaller than

8208-486: The control of the applied electrical signal coming from the amplifier. The following is a description of the individual components of this type of loudspeaker. The diaphragm is usually manufactured with a cone- or dome-shaped profile. A variety of different materials may be used, but the most common are paper, plastic, and metal. The ideal material is rigid, to prevent uncontrolled cone motions, has low mass to minimize starting force requirements and energy storage issues and

8322-466: The current in the 22ohm screen resistor reaches 30mA and beyond, preventing further burning of the PCBA. The diode will clamp the current in the 22ohm screen resistor to 30mA, so preferably the plate resistor will blow, since the plate resistor is acting as a "fuse". Plate resistors should be kept off the circuit board by approx 1/2" min to prevent PCBA burning. The diode is taking on the current surge to protect

8436-425: The driver, or to modify it so that it could be used to enhance the sound produced from the other side. In some respects, the ideal mounting for a low-frequency loudspeaker driver would be a rigid flat panel of infinite size with infinite space behind it. This would entirely prevent the rear sound waves from interfering (i.e., comb filter cancellations) with the sound waves from the front. An open baffle loudspeaker

8550-459: The earliest designs. Alnico , an alloy of aluminum, nickel, and cobalt became popular after WWII, since it dispensed with the problems of field-coil drivers. Alnico was commonly used until the 1960s, despite the problem of alnico magnets being partially demagnetized . In the 1960s, most driver manufacturers switched from alnico to ferrite magnets , which are made from a mix of ceramic clay and fine particles of barium or strontium ferrite. Although

8664-491: The effect of making the speaker cone transfer more of the electrical energy in the voice coil into the air; in effect the driver appears to have higher efficiency. Horns can help control dispersion at higher frequencies which is useful in some applications such as sound reinforcement. The mathematical theory of horn coupling is well developed and understood, though implementation is sometimes difficult. Properly designed horns for high frequencies are small (above say 3 kHz or so,

8778-507: The electric current to sound waves is the dynamic or electrodynamic driver, invented in 1925 by Edward W. Kellogg and Chester W. Rice , which creates sound with a coil of wire called a voice coil suspended between the poles of a magnet . There are others that are far less widely used: electrostatic drivers , piezoelectric drivers , planar magnetic drivers , Heil air motion drivers , and ionic drivers , among other speaker designs . The most common type of driver, commonly called

8892-477: The enclosure that are used to produce the bass response emanating from the port. These designs can be considered a mass-loaded transmission line design or a bass reflex design, as well as a quarter wave enclosure. Quarter wave resonators have seen a revival as commercial applications with the onset of neodymium drivers that enable this design to produce relatively low bass extensions within a relatively small speaker enclosure. The tapered quarter-wave pipe (TQWP)

9006-442: The energy per kilogram of these ceramic magnets is lower than alnico, it is substantially less expensive, allowing designers to use larger yet more economical magnets to achieve a given performance. Due to increases in transportation costs and a desire for smaller, lighter devices, there is a trend toward the use of more compact rare-earth magnets made from materials such as neodymium and samarium cobalt . Speaker drivers include

9120-410: The frequencies near the driver's free-air resonance frequency f s . Transmission lines tend to be larger than ported enclosures of approximately comparable performance, due to the size and length of the guide that is required (typically 1/4 the longest wavelength of interest). The design is often described as non-resonant, and some designs are sufficiently stuffed with absorbent material that there

9234-422: The frequency of peak impedance. In a closed-box loudspeaker, the air inside the box acts as a spring, returning the cone to the zero position in the absence of a signal. A significant increase in the effective volume of a closed-box loudspeaker can be achieved by a filling of fibrous material, typically fiberglass, bonded acetate fiber (BAF) or long-fiber wool. The effective volume increase can be as much as 40% and

9348-615: The frequency range is also possible. A uniform pattern is handy for smoothly arraying multiple enclosures. Both sides of a long-excursion high-power driver in a tapped horn enclosure are ported into the horn itself, with one path length long and the other short. These two paths combine in phase at the horn's mouth within the frequency range of interest. This design is especially effective at subwoofer frequencies and offers reductions in enclosure size along with more output. A perfect transmission line loudspeaker enclosure has an infinitely long line, stuffed with absorbent material such that all

9462-476: The front end 12BH7 voltage amplifier is fed from the 430 V node, during loud transients and overloads this will produce an AC signal that far exceeds the 12BH7 follower that has 220 V on the plates. So when the follower grid is driven well over its own plate voltage, it saturates on the positive half of the signal and thus takes over the BIAS voltage, forcing it very positive. The time for this voltage to come back to normal

9576-455: The front of the speaker driver. Because the forward- and rearward-generated sounds are out of phase with each other, any interaction between the two in the listening space creates a distortion of the original signal as it was intended to be reproduced. As such, a loudspeaker cannot be used without installing it in a baffle of some type, such as a closed box, vented box, open baffle, or a wall or ceiling (infinite baffle). An enclosure also plays

9690-445: The front voltage amp of the 12BH7, a 6146B tube runs reliably with far fewer issues. However, conversion of 6146B to 6550 tubes also has a dramatic impact on the output power. The amp will produce roughly 225 watts, due to the screen voltage being too low. As such, the power transformer of a 6146B SVT will be about 220 V DC on the screen supply at idle instead of the typical 350 V idle screen voltage normally seen on 6550 amps. One solution

9804-505: The lower frequencies, can be alleviated by the shape of the enclosure, such as by avoiding sharp corners on the front of the enclosure. A comprehensive study of the effect of cabinet configuration on the sound distribution pattern and overall response-frequency characteristics of loudspeakers was undertaken by Harry F. Olson . It involved a very wide number of different enclosure shapes, and it showed that curved loudspeaker baffles reduce some response deviations due to sound wave diffraction. It

9918-426: The lowest output frequency. It is important to distinguish between genuine infinite-baffle topology and so-called infinite-baffle or IB enclosures which may not meet genuine infinite-baffle criteria. The distinction becomes important when interpreting textbook usage of the term (see Beranek (1954, p. 118) and Watkinson (2004) ). Acoustic suspension or air suspension is a variation of the closed-box enclosure, using

10032-420: The magnetic gap space. The coil is oriented co-axially inside the gap; it moves back and forth within a small circular volume (a hole, slot, or groove) in the magnetic structure. The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside ring of the gap is one pole, and the center post (called the pole piece) is the other. The pole piece and backplate are often made as

10146-424: The other, by the magnetic field produced by current flowing in the voice coil, against the field established in the magnetic gap by the fixed magnet structure as the electrical signal varies. The resulting back-and-forth motion drives the air in front of the diaphragm, resulting in pressure differentials that travel away as sound waves . The spider and surround act as a spring-restoring mechanism for motion away from

10260-422: The pipe acts as a horn while the top can be visualised as an extended compression chamber. The entire pipe can also be seen as a tapered transmission line in inverted form. (A traditional tapered transmission line, confusingly also sometimes referred to as a TQWP, has a smaller mouth area than throat area.) Its relatively low adoption in commercial speakers can mostly be attributed to the large resulting dimensions of

10374-453: The pole tip or as a heavy ring situated within the magnet-pole cavity. The benefits of this complication is reduced impedance at high frequencies, providing extended treble output, reduced harmonic distortion, and a reduction in the inductance modulation that typically accompanies large voice coil excursions. On the other hand, the copper cap requires a wider voice-coil gap, with increased magnetic reluctance; this reduces available flux, requiring

10488-514: The ports may generally be replaced by passive radiators if desired. An eighth-order bandpass box is another variation which also has a narrow frequency range. They are often used to achieve sound pressure levels in which case a bass tone of a specific frequency would be used versus anything musical. They are complicated to build and must be done quite precisely in order to perform nearly as intended. This design falls between acoustic suspension and bass reflex enclosures. It can be thought of as either

10602-518: The position of the driver element or attempt to precisely position it. Some speaker driver designs have provisions to do so (typically termed servomechanisms ); these are generally used only in woofers and especially subwoofers, due to the greatly increased cone excursions required at those frequencies in a driver whose cone size is well under the wavelength of some of the sounds it is made to reproduce (ie, bass frequencies below perhaps 100 Hz or so). Speaker drivers may be designed to operate within

10716-565: The possible problems. Bothersome resonances can be reduced by increasing enclosure mass or rigidity, by increasing the damping of enclosure walls or wall/surface treatment combinations, by adding stiff cross bracing, or by adding internal absorption. Wharfedale , in some designs, reduced panel resonance by using two wooden cabinets (one inside the other) with the space between filled with sand . Home experimenters have even designed speakers built from concrete , granite and other exotic materials for similar reasons. Many diffraction problems, above

10830-413: The previous (and painful) rubber-covered metal strap handles. These SVTs also include a back panel selector toggle for 2 or 4 ohm speaker impedance loads and a longer and thicker gauge 3-prong power cable. Additionally, some components, such as the transformers, on MTI-era SVTs are of Japanese origin as opposed to the original SVT transformers made by Chicago-based ETC. In 1986, St. Louis Music acquired

10944-550: The purposes of this type of analysis, each enclosure must be classified according to a specific topology. The designer must balance low bass extension, linear frequency response, efficiency, distortion, loudness and enclosure size, while simultaneously addressing issues higher in the audible frequency range such as diffraction from enclosure edges, the baffle step effect when wavelengths approach enclosure dimensions, crossovers, and driver blending. The loudspeaker driver's moving mass and compliance (slackness or reciprocal stiffness of

11058-530: The radiation from the front surface of the cone is directed into a ported chamber. This modifies the resonance of the driver. In its simplest form a compound enclosure has two chambers. The dividing wall between the chambers holds the driver; typically only one chamber is ported. If the enclosure on each side of the woofer has a port in it then the enclosure yields a 6th-order band-pass response. These are considerably harder to design and tend to be very sensitive to driver characteristics. As in other reflex enclosures,

11172-407: The radio itself (typically a small wooden box containing the radio's electronic circuits, so they were not usually housed in an enclosure. When paper cone loudspeaker drivers were introduced in the mid 1920s, radio cabinets began to be made larger to enclose both the electronics and the loudspeaker. These cabinets were made largely for the sake of appearance, with the loudspeaker simply mounted behind

11286-408: The rear of the speaker to the listener. They deliberately and successfully exploit Helmholtz resonance . As with sealed enclosures, they may be empty, lined, filled or (rarely) stuffed with damping materials. Port tuning frequency is a function of the cross-sectional area of the port and its length. This enclosure type is very common, and provides more sound pressure level near the tuning frequency than

11400-401: The rear radiation of the driver is fully absorbed, down to the lowest frequencies. Theoretically, the vent at the far end could be closed or open with no difference in performance. The density of and material used for the stuffing is critical, as too much stuffing will cause reflections due to back-pressure, whilst insufficient stuffing will allow sound to pass through to the vent. Stuffing often

11514-509: The rights to the Ampeg name and took possession of all remaining MTI inventory, which contained enough original components to build 500 amps. These 1987 Limited Edition SVTs were built in the U.S. by SLM's own Skunk Works crew, and each included an engraved panel indicating the unit's number within the production of 500 total units. In 1990, Ampeg introduced the SVT-II and SVT-II Pro, and in 1994, introduced

11628-511: The rock market, opening offices in Chicago, Nashville, and Hollywood, and developing products designed to address the needs of rock musicians. When The Rolling Stones began rehearsing for their 1969 U.S. Tour in Hollywood, a power conversion failure blew up all of their UK Fender amplifiers. Their road manager, Ian Stewart contacted Rich Mandella at the Ampeg office in Hollywood, and Rich arranged for

11742-476: The same time. A variation on the transmission line enclosure uses a tapered tube, with the terminus (opening/port) having a smaller area than the throat. The tapering tube can be coiled for lower frequency driver enclosures to reduce the dimensions of the speaker system, resulting in a seashell like appearance. Bose uses similar patented technology on their Wave and Acoustic Waveguide music systems. Numerical simulations by Augspurger and King have helped refine

11856-431: The speaker produced and the expense of manufacturing a rigid tapering tube. The TQWP is also known as a Voigt pipe , and was introduced in 1934 by Paul G. A. H. Voigt, Lowther's original driver designer. Speaker driver An electrodynamic speaker driver , often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves . While

11970-435: The stiffer it is made, the poorer the damping. As a result, many cones are made of some sort of composite material. For example, a cone might be made of cellulose paper, into which some carbon fiber , Kevlar , glass , hemp or bamboo fibers have been added; or it might use a honeycomb sandwich construction; or a coating might be applied to it so as to provide additional stiffening or damping. The chassis, frame, or basket,

12084-436: The suspension) determines the driver's resonance frequency ( F s ). In combination with the damping properties of the system (both mechanical and electrical) all these factors affect the low-frequency response of sealed-box systems. The response of closed-box loudspeaker systems has been extensively studied by Small and Benson, amongst many others. Output falls below the system's resonance frequency ( F c ), defined as

12198-519: The term infinite-baffle loudspeaker can fairly be applied to any loudspeaker that behaves (or closely approximates) in all respects as if the drive unit is mounted in a genuine infinite baffle. The term is often and erroneously used of sealed enclosures which cannot exhibit infinite-baffle behavior unless their internal volume is much greater than the Vas Thiele/Small of the drive unit AND the front baffle dimensions are ideally several wavelengths of

12312-406: The term is sometimes used interchangeably with the term speaker ( loudspeaker ), it is usually applied to specialized transducers that reproduce only a portion of the audible frequency range, or to the one or more drivers within a loudspeaker cabinet (or simply "speaker".). For high fidelity reproduction of sound, multiple loudspeakers are often mounted in the same enclosure , each reproducing

12426-429: The theory and practical design of these systems. A quarter wave resonator is a transmission line tuned to form a standing quarter wave at a frequency somewhat below the driver's resonance frequency F s . When properly designed, a port that is of much smaller diameter than the main pipe located at the end of the pipe then produces the driver's backward radiation in phase with the speaker driver itself; greatly adding to

12540-408: The theory developed by researchers such as Thiele, Benson, Small and Keele, who had systematically applied electrical filter theory to the acoustic behavior of loudspeakers in enclosures. In particular Thiele and Small became very well known for their work. While ported loudspeakers had been produced for many years before computer modeling, achieving optimum performance was challenging, as it

12654-522: The tour, Ampeg put the SVT into production, introducing it at the NAMM Show in 1969. There are three types of original SVT amps. The first are the "blue line" SVTs, so named after the blue screen printing that surrounds the tone controls. Early 1969-70 "blue lines" used 6146B beam power vacuum tubes in the output stage, which proved unstable and was switched to the more robust, reliable and commonly-used 6550 tube around mid-1970. The second version of

12768-430: The trademarks CoEntrant, Unity or Synergy horn) is a manifold speaker design; it uses several different drivers mounted on the horn at stepped distances from the horn's apex, where the high frequency driver is placed. Depending on implementation, this design offers an improvement in transient response as each of the drivers is aligned in phase and time and exits the same horn mouth. A more uniform radiation pattern throughout

12882-405: The voice coil; heating during operation changes resistance, causes physical dimensional changes, and if extreme, broils the varnish on the voice coil; it may even demagnetize permanent magnets. The suspension system keeps the coil centered in the gap and provides a restoring (centering) force that returns the cone to a neutral position after moving. A typical suspension system consists of two parts:

12996-399: Was discovered later that careful placement of a speaker on a sharp-edged baffle can reduce diffraction-caused response problems. Sometimes the differences in phase response at frequencies shared by different drivers can be addressed by adjusting the vertical location of the smaller drivers (usually backwards), or by leaning or stepping the front baffle, so that the wavefront from all drivers

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