- Bass instrument amplification
Bass instrument amplification for the
bass guitar, double bassand similar instruments is distinct from other types of amplification systems due to the particular challenges associated with low-frequency sound reproduction. This distinction affects the design of the loudspeakers, the cabinet, and the preamplifier and amplifier.
Speaker cabinets for bass instrument amplification usually use larger
loudspeakers(or more loudspeakers) than the cabinets used for other instruments, so that they can move the larger amounts of air needed to reproduce low frequencies. Speakers used for bass instrument amplification tend to be more heavy-duty, because higher sound pressure levels are needed for bass to achieve the same perceived loudnessas other instruments [this is because human hearing is much less sensitive to the lower frequencies] Bass instrument speaker cabinets are typically more rigidly constructed and heavily braced than cabinets for non-bass instrument amplification, and bass cabinets often include bass reflexports or openings.
Bass instrument amplifiers' preamplifier sections have equalization controls that are designed for bass instruments, and extend down to 40 hertz or even below. As well, bass instrument amplifiers are more likely to be designed with cooling fans than regular guitar amplifiers, due to the high power demands of bass instrument amplification, and bass amplifiers are more commonly equipped with
compressoror limitercircuitry to prevent speaker damage.
When the Fender company invented the first widely-produced electric bass guitar in the early 1950s, they also developed a bass amplifier, the
Fender Bassmanamplifier. The Fender Bassman was a 50-watt tube amplifier with four 10" speakers. The Ampeg Bassamp Company, founded in 1949, also produced bass amplifiers that were widely used by electric bass guitarists in the 1950s and 1960s.
The first bass amplifier offered by
Ampegwas an 18 watt model with a single 12" speaker and a rear ventilation port called the Super 800. In 1951, a 20 watt version with a 15" speaker was put on the market. In 1960, they introduced the B-15 Portaflex, a flip-top 25 watt bass amplifier with a single 15" speaker and in the late 1960s, the 300 watt Super Valve Technology (SVT) amplifier head which was intended for large performance venues. The SVT was intended for use with one or two speaker cabinets containing eight 10" speakers.
In the mid-1960s, the bassist for
The Who, John Entwistle, was one of the first major players to make use of Marshall stacks. At a time when most bands used 50-100w amps with single cabinets, Entwistle used twin Stacks with new experimental prototype200w amps. This, in turn, also had a strong influence on the band's contemporaries at the time, with Cream and the Jimi Hendrix Experienceboth following suit. Entwistle also experimented throughout his career with "bi-amping," where the high and low ends of the bass sound are sent through separate signal paths, allowing for more control over the output.
In some cases, the sonic characteristics of bass amplifiers and speaker cabinets appeal to regular electric guitarists. Early Fender Bassman amps, originally designed for bass guitar, have become widely used by guitarists. Their 40-50 watt power rating also made them more suitable for guitar than bass at larger venues & outdoors and as music got louder and more powerful bass amps appeared. Hence, the market for vintage Bassmans became dominated by lead players. Some rock guitarists, such as
Southern rockguitarist Duane Allman, would add a bass cabinet to his Marshall stack.
Conversely, the sonic characteristics and/or built-in effects associated with some lead guitar amplifiers has appealed to some bassists. Along with the extra brightness, reverb, tremolo, etc. of some lead guitar amps, the KT-88/6550 power tubes used in many early Sunn lead & bass guitar amps are the same as those that are used in many top-of-the line tube bass amps. When used with bass guitar speaker cabinets, the low frequency capabilities of some lead guitar amps may approximate that of similar power bass amps. The relatively basic tone controls of some lead amps may make them less tailored to a specific instrument than those with more specialized bands of equalization.
As PA systems have improved, horn-loaded "bass bins" and subwoofers were added and were often well-equipped to amplify directly fed five-string bass guitar and keyboard frequencies. As well, in the 1980s and 1990s, monitor systems were substantially improved, which allowed sound engineers to provide onstage musicians with a loud, clear, and full-range reproduction of their instruments' sound.
As a result of the improvements to PA systems and monitor systems, bass players in the 2000s no longer need to have huge, powerful amplifier systems; instead, contemporary bass amps featuring preamp-out jacks can be patched to the PA. In the 2000s, virtually all of the sound reaching the audience in large venues comes from the
PA system. As well, in the 2000s onstage instrument amplifiers are more likely to be kept at a low volume, because high volume levels onstage makes it harder to control the sound mix and produce a clean sound. As a result, in many large venues much of the onstage sound reaching the musicians now comes from the monitor speakers, not from the instrument amplifiers. While stacks of huge speaker cabinets and amplifiers are still used in concerts, this is often mainly for aesthetics or to create a more authentic tone.
Different types of equipment are used to amplify the electric bass and other bass instruments, depending on the performance setting and style of music, and the type of tone or sound desired by the bassist. For rehearsals, recording sessions, or small club performances, electric and upright bass players will typically use a "combo" amplifier. The "combo" amplifier, which was given this nickname because it combines an amplifier and a speaker in a single cabinet, usually has a modestly-powered amplifier (50 to 200 watts) and a single full-range speaker. While small "combo" amplifiers are easy to transport and set up, this convenience comes at a price; combo amps cannot reproduce the lowest frequencies of the electric or double bass at high volumes.
For larger venues such as large clubs and outdoor music festivals, or for music genres which use bass instruments with an extended low range (e.g., metal) bass players will often use a more powerful amplifier (300 to 1000 watts) and separate speaker cabinets in various combinations. In the largest outdoor venues, such as stadium concerts, bass players may use several powerful amplifiers rated at 1000 or more watts and large, multiple-driver speaker cabinets, such as cabinets containing eight 10" speakers, or large cabinets with 15" or (more rarely) 18" speakers.
Separate bass amplifiers, often called 'heads' or 'amp heads' are usually integrated units, in which the preamplifier and power amplifier are combined in a single unit. More rarely, bass players may use separate preamplifer/power amplifier setups, in which one or more preamplifiers are used to drive one or more power amplifiers. The separate preamplifer/power amplifier setups approach, while more costly, is used by professional bassists who require more flexibility regarding the pairing of different preamplifiers and power amplifiers, to provide a broader "palette" of tones. In some cases, bassists using separate preamplifer/power amplifier setups may use an A-B box or routing device to switch between different pre-amplifier, power amplifier, and speaker cabinet combinations onstage.
It is less common for bass amplifier 'heads' to have the types of effects that are commonly found on electric guitar instrument amplifiers (e.g., distortion, vibrato, delay, chorus, and reverb), because these effects are generally not as effective at low frequencies. Nonetheless, some high-end bass 'heads' include effects such as overdrive,
parametric equalization, compression, or sub-octave generation.
Amplifiers may be based on
thermionic("tube" or "valve") or solid state (transistor) technology.
Vacuum tubes were the dominant active electronic components in bass amplifiers manufactured until the early 1970s, and tubes continue to be used for higher-end units. Tube amplifiers for bass almost always use class AB1 topology for efficiency reasons. Some bass players believe that tube amplifiers produce a "warmer" or more "natural" sound than solid state amps. However, these subjective assessments of the attributes of tube amps'sound qualities are the subject of debate.
Even though tube amplifiers produce more heat than solid state amplifiers, few manufacturers of tube amplifiers include cooling fans in the amplifiers' chassis. While tube amplifers do need to attain a proper operating temperature, if the temperature goes above this operating temperature, it may shorten the tubes' lifespan and lead to tonal inconsistencies. ["Cool it, man"; Michael "Mac" McCulloughhttp://18.104.22.168/search?q=cache:c7BJeOkqVIIJ:www.chitown.com/http/music/Musictips.html+cooling+tube+amplifier&hl=en&gl=ca&ct=clnk&cd=25.]
olid State Amplifiers
By the 1960s and 1970s, semiconductor transistor-based amplifiers began to become more popular because they are less expensive, lighter-weight, and require less maintenance. In some cases, tube and solid state technologies are used together in bass amplifiers. A common setup is the use of a tube preamplifier with a solid state power amplifier. There are also an increasing range of products that use
digital signal processingand digital modeling technology to simulate many different combinations of amp and cabinets.
The output transistors of solid state amplifiers can be passively cooled by using metal fins called heatsinks to radiate away the heat. For high-wattage amplifiers (over 800 watts), a fan is often used to move air across internal heatsinks [http://Power Amplifiers - General Information: Yorkville Sound: www.yorkville.com/default.asp?p1=6&p2=17&p_id=25.] .
Since transistor bass amplifiers used for large venues need to produce a high output, this usually means that bass amplifiers are very heavy. Most powerful transistorized bass amplifiers are
Class AB amplifiers, which need heavy transformers of copper wiring and large metal heat sinks for cooling. However, Class D amplifiers (also called "switching amplifiers") are more efficient than conventional Class-AB amplifiers, and so are lighter in weight and smaller. The Acoustic Image "Focus" head, for example, produces 800 watts of power and weighs 2.2 kilos. Class-D amplifiers use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) rather than 'ordinary' (bipolar) transistors and they generate a pulse-width modulated signal which is filtered before it reaches the speaker. [David Mellor What is Class-D amplification? The benefits explainedhttp://www.soundonsound.com/sos/jun06/articles/loudandlight.htm]
The requirement to reproduce low frequencies at high
sound pressure levels means that most loudspeakers used for bass guitar amplification are designed around large diameter, heavy-duty drivers, with 10", 12" and 15" being most common. As a rule of thumb, performers desiring a deeper bass tone (e.g., punk, metal, or hard rock bassists) prefer the larger speakers, while performers wanting a more articulate tone (e.g. jazz or fusion bassists) tend to prefer the smaller speakers with better extended mid-range response. However, a trend towards to cabinets with smaller, multiple drivers (e.g. 8 x 10) has been developing. [Bassists in the "heavier" genres are using these cabinets. The manufacturers claim that the multiple drivers enable a tighter, more focused response of the smaller driver allows better projection and clarity, allowing the bass to "cut through the mix." While this is debatable, it can be credibly argued that having multiple drivers allows for greater power handling]
Speaker cabinets are largely designed around a single type of driver (common examples are 1X10" ,1x12", 1x15" and 2x10" or 4x10"). Bass players sometimes stack two or more cabinets containing different-sized drivers to obtain a particular sound. Players with five- or six-string basses or those who perform in louder, heavier styles of music sometimes add a 1X18" cabinet to reproduce the lowest notes.
Bass cabinet companies make many advertising claims about their products, such as that certain speaker sizes "respond more quickly", create a "more focused sound" or "move more air."
Ampeg, for example, claims that their 8x10 cabinet enclosures are capable of moving an amount of air equivalent to that of five 18" speakers, or six 15" speakers, making them much more efficient than larger speakers. Some of these advertising claims have been debated by sound engineers and audio experts.
The speakers are built into speaker cabinets, which contain one or more drivers. The sound of these cabinets is influenced not only by the choice of driver but also the size and construction of the cabinets. In general, larger speaker cabinets (in relation to the diameter of the speaker) are able to produce a deeper bass output. Bass instrument speakers are typically mounted in more rigidly-constructed and heavily-braced cabinets than speakers for non-bass instrument amplification, because speaker cabinets for bass produce much more vibration. Most bass speaker cabinets employ a vented bass-reflex design, which use a port or vent, while others have sealed cabinets. Some cabinets use a transmission-line design which is similar to bass-reflex, and some very large cabinets use horn-loading of the woofers.
When a vented bass-reflex design is used, an opening is cut into the cabinet and a tubular or rectangular conduit is typically mounted in the opening. These tuned openings increase the speaker cabinet's efficiency and output, and reduce the movement of the cone near the port tuning frequency, which lowers distortion. One disadvantage of using a vented design is that there is no air pressure difference to help limit the driver cone excursion at frequencies below port resonance. As a result, infrasonic (very low-frequency) signals such as those caused by fingers hitting strings may cause very large and potentially damaging movements of the speaker cones. Ported systems can suffer from port noise or "chuffing" due to turbulence in the port, and poorly designed ported systems may ring excessively at the resonance frequency they are tuned to, which may give a boomy or "one-note" sound.
Another option is to use a passive radiator (PR) or drone. A PR looks like a speaker driver, except that it does not have an electrically activated voice coil. Passive radiator speakers are used instead of a bass reflex port, to tune small volumes to low frequencies, where a port would need to be very long.
When a bass speaker is built into a completely sealed cabinet, the cabinets use the trapped volume of air to act as a 'spring' or cushion for the bass speaker. These designs require more amplifier power to produce low-frequency sounds, because the speaker has to overcome the force of the air pressure in the cabinet and there is no reinforcement of the output of the speaker cones. This design is less common due to the need for very high output in live music venues. The advantage of using sealed cabinets is that they do not produce noise of rushing, pressurized air. As well, some cabinet manufacturers claim that sealed bass cabinets can exhibit faster transient response and produce a more precise sound.
In the 2000s, high frequency
tweeters, typically horn-loaded, are included in some bass instrument speaker cabinets. Vox's 1960s-era "Super Beatle" amplifier was an early enclosure that used horn tweeters. During the late 1960s Acoustic's 260 Series guitar amp used a treble horn in the dual 15" 261 guitar enclosure, and Kustom's nearly 5 foot tall 2J + 1H guitar enclosure used two 15" speakers and a 15" diameter treble horn. Horn-equipped cabinets were not available for bass players until much later.
The use of dual throat "W" style folded horns was used in some bass guitar amps in the late 1960s and early 1970, such as Acoustic's 360 & 370 Series. This further advanced the tradeoff of treble for higher bass efficiency, as the already limited treble range and dispersion of the large 18" drivers used in these cabinets was diminished further in negotiating the bends in the folded horn. Some folded horn PA enclosures of the same period contained mid and treble horns, such as the "W"-style Electro-Voice (EV) Eliminator. These PA cabinets were used by some bass players seeking high output and full range sound which was unavailable from many traditional bass amps and bass cabinets.
Folded horn bass guitar cabinets (nicknamed "bass bins") were used by some bassists in the early 1970s. They were similar to the design of the Sunn 118RH & 115RH. By the late 1970's Sunn introduced the Beta Series guitar and bass amplifiers; the Beta 105H used a 100 watt, 47 pound bass reflex enclosure containing a 15" woofer and an exponential horn tweeter. The higher powered Sunn Concert Series and the Coliseum Series Musical Instrument (M.I.) amps continued to be offered with folded horn and direct-radiating horn-loaded enclosures that lacked tweeters.
In the early 1980s, some performers began using two-way or three-way cabinets that used 15" woofers, a vented midrange driver and a horn/driver, with a crossover directing the signal to the appropriate driver. Folded horn bass guitar rigs have remained more the exception than the rule due to their size and weight. As well, since the 1990s, most clubs have PA systems with subwoofers that can handle the low range of the bass guitar. Extended range designs with tweeters were more the exception than the rule until the 1990s. The more common use of tweeters in traditional bass guitar amps in the 1990s helped bassists to use effects and perform more soloistic playing styles, which emphasize the higher range of the instrument.
One problem with adding a tweeter to a bass speaker cabinet is that the driver may be damaged by the overdriven amplifier tone that is popular in some musical genres, such as hard rock and heavy metal. Horns and speakers in the same cabinet are sometimes wired separately, so that they can be driven by separate amplifiers. Biamplified systems and separately-wired cabinets produced by manufacturers such as
Gallien-Kruegerand Carvinallow bassists to send an overdriven sound to the speaker, and a crisp high sound to the horn, which prevents this problem.
Amplifying the double bass
Natural-sounding amplification of the double bass requires three elements: a piezoelectric transducer to pick up the attack of the bass tone and the lower fundamentals; a condenser microphone to pick up the resonance coming from the body and the sounds of the strings being plucked, bowed, or slapped, and; a high-quality amplifier that produces a clean, undistorted bass tone. Piezoelectric transducers are often used on upright bass to pick up the vibrations in the bridge or top of the instrument. However, to provide a full-sounding tone, piezoelectric pickups need a specialized preamplifier because of their very high impedance (a partial list of manufacturers is provided at the end of the article).
Double bass players performing in traditional blues, rockabilly, jazz, folk, and bluegrass often blend the sounds picked up by a piezoelectric transducer with the sounds picked up by a small condenser microphone mounted on the bridge. The microphone picks up the resonance coming from the body and the sounds of the strings being plucked, bowed, or slapped against. The two sound signals are blended using a simple mixer and then routed to the amplifier.
The final element to producing "natural-sounding" amplified double bass tone is the use of a high-quality amplifier and speaker system that produces a clean, undistorted bass tone. In many rock and blues genres, electric bass players purposely use amplifiers such as tube amplifiers that produce a mildly overdriven signal. However, to produce a natural-sounding amplified double bass tone, bass players often use high-wattage amplifiers with a high degree of "overhead," so that the amplifier will be able to produce a clean, undistorted sound. In addition, bass players may use a speaker cabinet that contains a horn or high-frequency driver, for a clearer articulation of the instrument's higher harmonics and the sounds of the fingers on the fingerboard.
Double bass players playing in genres where a louder amplified tone (emphasizing the fundamental frequencies) is desired for the bass may be more likely to face the problem of feedback. Feedback for double bass generally manifests itself as a sharp, sudden high-volume "howling" sound which can damage the loudspeakers. Instruments with laminated (plywood) tops are less prone to feedback problems than those with solid wood tops. When acoustic instruments with resonant bodies are amplified with microphones and piezoelectric transducer pickups, the common approach used for amplified double basses, they are prone to have feedback problems. In addition, musical performances where there is a loud onstage volume from other amplifiers (e.g., guitar, organ, harmonica) and low-pitched drums (e.g., floor toms) increase the likelihood for double bass feedback.
There are several ways of reducing the likelihood of feedback. The bass player can lower the volume of their onstage amplifier, position themselves further away from their onstage amplifier, or experiment with different placements of their microphone. Since feedback in the double bass is generated from resonances in the open strings and the instrument body, another solution is to "damp" the vibrations of instrument by inserting foam under the tailpiece, under the non-sounding parts of the strings (between the tailpiece and the bridge), and/or in the "F" holes. The disadvantage of this approach is that it also changes the sound and responsiveness of the instrument, especially for held notes and bowed playing.
Another approach is to electronically lessen the responsiveness of the frequencies that are feeding back. This can be done in several ways. The least precise way to lessen the responsiveness of the frequencies that are feeding back is to use the tone controls on the bass amplifier. Since most bass amplifiers only have three or four knobs for controlling the frequencies, by lowering the range in which the feedback is occurring, many of the desirable frequencies that are part of the instrument's tone will also be affected. By using a graphic equalizer or a parametric equalizer, the frequencies that are feeding back can be reduced more precisely, with less impact on the desired frequencies. In the 2000s, several automatic feedback eliminator devices went on to the market, which detect the onset of feedback and notch out that frequency before the feedback occurs.
Preamplification and effects
The basic sound of the amplified electric bass or double bass can be modified by electronic
bass effects. In the 1990s and 2000s, signal processors such as equalizers, distortiondevices, and compressors or limiters became increasingly popular. Because the electric bass plays the low-register foundation for the band, the so-called "modulation" bass effects, such as chorus, flanger, and phaser, are used much less frequently than with the electric guitar. Although there has been a much smaller variety of bass-specific effects available throughout much of the history of the instrument, since the late 1990s, many bass-specific effects have become available. Of these, preamplifiers, "compression", limiting, and equalization are the most widely-used effects for bass.
Nonetheless, a range of other effects are used in various genres. "
Wah-wah" and "synth" bass effects are associated with funkmusic. As well, since the 1960s and 1970's, bands have experimented with "fuzz bass" where the bass is distorted either by overdriving the amp or by using a distortionunit. Since the 1990s a heavier type of distortion with a "grinding" tone is used by some metal and punk bass players. Octave-generating effects, which generate an octave below the pitch being played are also used by bass players. Bass players from alternative and experimental bands use bass effects to create unique timbres and tones.
In the 1990s and 2000s, digital signal processing units were developed that provide multiple effects (distortion, compression, etc.) and modeled simulations of the tone of different bass amp models, speaker cabinets and microphone placements. Although many of these effects sound similar to guitar effects, players often use specialized bass effects units, which are adapted to work with the lower frequency range of the bass.
Manufacturers of upright bass preamplifiers
* L.R. Baggs
List of bass amplifier and loudspeaker manufacturers
Isolation cabinet (guitar)
Guitar speaker cabinet
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