1950s–1960s
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 1959 is widely regarded as a classic amplifier design and was copied by many other manufacturers, such as Marshall.
A Kustom 200 bass amplifier from 1971, featuring a separate amp head on top of a 2 x 15" speaker cabinet.
1970s–2000s
Cabinet design
Main article: Loudspeaker enclosure
Bass reflex speaker enclosures, which have a vent or port cut into the cabinet, are widely used for bass cabinets.
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.
[edit] Tweeters
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A 150-watt "combo" bass amp with a horn-loaded tweeter (in the top right of the speaker cabinet)
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.
A bass rack from a professional bass player's touring setup. The bass amplifier is the lowest chassis in the rack; above it are a wireless receiver, several pre-amp devices, and a power conditioner.
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.
In this 2007 photo of The Police's singer-bassist Sting, several 8x10" Ampeg cabinets can be seen on the left side.
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.
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 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.
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 Cream and 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.
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