Bass instrument amplification
Bass instrument amplification, used for the bass guitar, double bass and 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 speaker cabinet and the preamplifier and amplifier. Speaker cabinets for bass instrument amplification usually incorporate larger (or more) loudspeakers than those used for the amplification of other instruments. The loudspeakers themselves must also be sturdier to handle the higher power levels.
Bass instrument speaker cabinets are typically more rigidly constructed and heavily braced than those for non-bass instrument amplification. They usually include tuned bass reflex ports or vents for increased efficiency at low frequencies. Preamplifier sections have equalization controls that are designed for the deeper frequency range of bass instruments, and can extend down to 40 Hz or below. 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. They are also more commonly equipped with limiter circuitry to prevent overloading the power amplifier and to protect the speakers from damage.
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The Ampeg Bassamp Company, founded in 1949 by Everett Hull, produced bass amplifiers that were widely used by electric bass guitarists in the 1950s and 1960s. The first bass amplifier offered by Ampeg was an 18-watt model with a single 12" speaker and a rear ventilation port called the Super 800. In 1951, they introduced a 20-watt version with a 15-inch speaker. In 1960, they introduced the B-15 Portaflex, a flip-top 25-watt bass amplifier with a single 15" speaker. In the late 1960s, the 300-watt Super Vacuum Tube (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.
When the Fender company invented the first widely produced electric bass guitar (the Fender Precision Bass) they also developed a bass amplifier, the Fender Bassman, first produced in 1952. This was a 50-watt tube amplifier with a single 15" speaker. In 1954, the Bassman was redesigned to use four 10" speakers. The circuit design also underwent repeated modifications. The "5F6A" circuit introduced in 1958 is widely regarded as a classic amplifier design and was copied by many other manufacturers, such as Marshall.
In the mid-1960s John Entwistle, the bassist for The Who, was one of the first major players to make use of Marshall stacks. At a time when most bands used 50 to 100-watt amplifiers with single cabinets, Entwistle used twin stacks with new experimental prototype 200-watt amplifiers. This, in turn, also had a strong influence on the band's contemporaries at the time, with Jack Bruce of Cream and Noel Redding of the Jimi Hendrix Experience both following suit. Entwistle also experimented throughout his career with "bi-amplification," where the high and low registers of the bass sound are sent to separate amplifiers and speakers. This allows for more control over the tone, because each register can then be modified (e.g., in terms of tone, added overdrive, etc.) individually. The Versatone Pan-O-Flex amplifier used a different approach to bi-amplification, with separate amplifier sections for bass and treble but a single 12-inch speaker. The Versatone was used by well-known bassists such as Jack Casady and Carol Kaye.
As PA systems improved, horn-loaded "bass bins" and subwoofers were added and were often well-equipped to amplify directly-fed bass guitar and keyboard frequencies. As well, in the 1980s and 1990s, monitor systems were substantially improved, which allowed sound engineers to provide on-stage 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 amplifiers usually have preamp-out jacks that 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 on-stage instrument amplifiers are more likely to be kept at a low volume, because high volume levels on stage makes it harder to control the sound mix and produce a clean sound. As a result, in many large venues much of the on-stage sound reaching the musicians now comes from the monitor speakers, not from the instrument amplifiers. Stacks of huge speaker cabinets and amplifiers are still used in concerts in some genres of music, especially heavy metal, but they tend to be used more for the visual effect than for sound reproduction.
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 sound desired by the bassist. For rehearsals, recording sessions, or small club performances, electric and upright bass players typically use a "combo" amplifier, which combines amplifier and speaker in a single cabinet.
For larger venues such as large clubs and outdoor music festivals, or for music genres that use bass instruments with an extended low range (e.g., metal), bass players often use a more powerful amplifier (300 to 1000 watts) and separate speaker cabinets in various combinations.
Separate bass amplifiers, often called 'heads' or 'amp heads' are usually integrated units, with preamplifier and power amplifier combined in a single unit. Some players use separate preamplifier/power amplifier setups, where one or more preamplifiers drive one or more power amplifiers.
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. Many bass players believe that tube amplifiers produce a "warmer" or more "natural" sound than solid state amplifiers when lightly or moderately driven, and more pleasing distortion characteristics when overdriven. Some also believe that they have a greater level of perceived loudness for a given amount of amplifier power. Even though tube amplifiers produce more heat than solid state amplifiers, few manufacturers of tube amplifiers include cooling fans in the amplifiers' chassis. Usually adequate cooling is provided by passive convection. Adequate airflow is needed to prevent excessive heat from shortening the tubes' lifespan or producing tonal inconsistencies.
Solid state amplification
By the 1960s and 1970s, semiconductor transistor-based amplifiers began to become popular. This was in large part because solid state amplifiers are less expensive, lighter weight, and require less maintenance than tube amplifiers. In some cases, tube and solid state technologies are used together, usually with a tube preamplifier driving a solid state power amplifier. There are also an increasing range of products that use digital signal processing and 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 heat sinks to radiate away the heat. For high-wattage amplifiers, a fan is often used to move air across internal heatsinks. 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 use class AB or so-called "push-pull" topology. These need heavy transformers and require 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 kilograms (about 4 pounds). Class-D amplifiers use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) rather than 'ordinary' (bipolar) transistors, and generate a pulse-width modulated signal that is filtered before it reaches the speaker.
The lowest note on the double bass or four-stringed electric bass is E1, two octaves below middle C (approximately 41 Hz), and on a five-string it is B0 (approximately 31 Hz). 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. The choice of speaker represents a compromise: while some speakers more effectively reproduce low frequencies, they may have poorer midrange and transient response.
Bassists who want powerful low end may use a subwoofer cabinet designed for a PA system. Subwoofers can only produce frequencies up to about 150 or 200 Hz, so a subwoofer cabinet must be paired with a full range speaker to obtain the full tonal range of an electric bass or upright bass. Bass guitar players who may use subwoofer cabinets include performers who play with extended range basses with include notes between B0 (about 31 Hz); and C#0 (17Hz); bassists who play in styles where a very powerful sub-bass response is an important part of the sound (e.g., funk, Latin, gospel, R & B, etc.).
Keyboard players who use subwoofers for on-stage monitoring include electric organ players who use bass pedal keyboards (which go down to a low "C" which is about 33 Hz) and synth bass players who play rumbling sub-bass parts that go as low as 18 Hz. Of all of the keyboard instruments that are amplified onstage, synthesizers can produce some of the lowest pitches, because unlike a traditional electric piano or electric organ, which have as their lowest notes a low "A" and a low "C", respectively, a synth does not have a fixed lowest octave. A synth player can add lower octaves to a patch by pressing an "octave down" button, which can produce pitches that are at the limits of human hearing.
Several concert sound subwoofer manufacturers suggest that their subs can be used for bass instrument amplification. Meyer Sound suggests that its 650-R2 Concert Series Subwoofer, a 14-square-foot (1.3 m2) enclosure with two 18-inch drivers, can be used for bass instrument amplification. While performers who use concert sound subwoofers for onstage monitoring may like the powerful sub-bass sound that they get onstage, sound engineers may find the use of large subwoofers (e.g., two 18" drivers) for onstage instrument monitoring to be problematic, because it may interfere with the "Front of House" sub-bass sound.
Most bass speaker cabinets employ a vented bass-reflex design, which use a port or vent. Others use acoustic suspension designs with sealed cabinets; these are relatively uncommon because they tend to be less efficient. Some cabinets use a transmission-line design similar to bass-reflex, and some large cabinets use horn-loading of the woofers.
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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 (1.5 m) 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.
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 amplifiers 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, since overdriving the amplifier adds a great deal of high frequency information to the signal. 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-Krueger and Carvin allow 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
Double bass players performing in genres where the bass is slapped, either by pulling the string until it snaps back onto the fingerboard or striking the strings, such as traditional blues, rockabilly, psychobilly 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. The two sound signals are blended using a simple mixer and then routed to the amplifier.
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 that can damage loudspeakers. 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. For acoustic bass guitars, soft plastic discs are available to block the sound hole, thus reducing feedback. Upright bass players sometimes use homemade foam or styrofoam inserts to fill in the "f" holes of the double bass, which can reduce feedback.
Other ways to reduce feedback include: playing with the speakers in front of, rather than behind, the instrument; reducing the onstage volume; signal phase reversing; using a "notch filter" EQ to turn down the frequency that is feeding back; or using "feedback eliminators", which are basically automatic notch filters that find and turn down the frequency that is "howling."
Preamplification and effects
The basic sound of the amplified electric bass or double bass can be modified by electronic bass effects. Since the bass typically plays an "anchoring" role in many styles of music, preamplifiers, compression, limiting, and equalization are the most widely used effects for bass. The types of pedals used for electric guitar (phaser, flanger, etc.) are uncommonly used for bass.
A range of other effects are used in various genres. "Wah-wah" and "synth" bass effects are associated with funk music. As well, since the 1960s and 1970s, bands have experimented with "fuzz bass" where the bass is distorted either by overdriving the amp or by using a distortion unit. Octave-generating effects, which generate an octave below the pitch being played are also used by bass players. Many bassists in modern-day hard rock and heavy metal bands use overdrive pedals made for bass guitar. Since the late 1980s, bass-specific overdrive pedals have been available; these pedals maintain the low fundamental pitch. Using a regular guitar distortion pedal for bass would result in the lower frequencies being greatly lessened. Well-known overdrive effects for bass include the BOSS ODB-3 Bass Overdrive, Electro-Harmonix Bass Blogger, Tech21 Sansamp Bass Driver, the DigiTech|DigiTech XBD Bass Driver , and the Electro-Harmonix Big Muff.
Overdrive built into amplifiers
Some bass amplifiers have an "overdrive" or distortion effect built into the unit. The Peavey Century 200 has an onboard "distortion" effect on the second channel. The Peavey VB-2 also has built-in overdrive. Aguilar Amplification's AG 500 bass head is a two-channel amplifier, one of which offers a "saturation" control for overdrive. A variety of BOSS combo amplifiers have a built-in "drive" effect. Gallien-Krueger's bass amp heads have a "boost" control which provides a simulated tube overdrive effect. The Behringer Ultrabass BVT5500H Bass Amplifier Head has a built-in limiter and overdrive. The LowDown LD 150 bass amp has a range of overdrive sounds, from a slight hint to heavy distortion. The CUBE-20XL BASS amp includes built-in overdrive.
The 75 Watt Fender Rumble 75 Bass Combo Amp and its 150 Watt and 300 Watt counterparts can produce an overdrive effect by using the gain and blend controls, giving overdrive sounds ranging from "mellow warmth [to] heavy distorted tones". The Fender SuperBassman is a 300-watt tube head which has a built-in overdrive channel. The Fender Bronco 40 includes a range of effects including modern bass overdrive, vintage overdrive and fuzz.
The MESA Bigblock 750 has a built-in overdrive channel. The Mesa M2000 has a high gain switch which can be engaged with a footswitch. The Marshall MB450 head and combo bass amplifiers have a tube pre-amp on the "Classic" channel which can be overdriven. The Ashdown ABM 500 EVO III 575W Bass amp head has a built-in overdrive effect. Overdrive is also available on many Crate bass amplifiers. The Yamaha BBT500H has three types of built-in drive effects: overdrive, distortion and fuzz. The Ampeg B5R Bass Amplifier has two channels: clean and overdrive, with the ability to combine the two.
Verellen, a boutique amp company, produces a bass amplifier with a built in overdrive channel.
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- Bass effects
- Guitar effects
- Instrument amplifier
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- Isolation cabinet (guitar)
- List of bass amplifier and loudspeaker manufacturers
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