Bass instrument amplification

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Bass instrument amplification 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 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 loudness as other instruments ^[1] 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 reflex ports 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 compressor or limiter circuitry to prevent speaker damage.

Contents 1 History 1.1 1950s-1970s 1.2 1980s-Present 2 Types 3 Amplifier technology 3.1 Tube Amplifiers 3.2 Solid State Amplifiers 4 Loudspeakers 4.1 Cabinet Design 4.2 Tweeters 5 Amplifying the double bass 5.1 Natural-sounding amplification 5.2 Feedback Problems 6 Preamplification and effects 7 Manufacturers of upright bass preamplifiers 8 See also 9 References

[edit] History

[edit] 1950s-1970s

When the Fender company invented the first widely-produced electric bass guitar in the early 1950s, they also developed a bass amplifier, the Fender Bassman amplifier. The Fender Bassman is 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 Ampeg was 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.

The large SVT amplifiers and their huge companion speaker cabinets with eight 10" speakers were designed to amplify the electric bass both for the band and for the audience, because few Public Address ("PA") systems from the 1960s could reproduce bass frequencies at high volumes. Moreover, in the 1960s, PA systems typically did not use monitor speaker systems to amplify the music for the onstage musicians. Instead, the musicians were expected to have instrument amplifiers that were powerful enough to provide amplification for the stage and audience.

In some cases, bass amplifiers were also used by regular electric guitarists who wanted to have better low-frequency response from their instruments. The Fender Bassman amplifier, which was originally sold for electric bass players, became widely used as an electric guitar amplifier. In the 1970s, some rock guitarists would use a bass guitar cabinet for this purpose, such as Southern Rock guitarist Duane Allman, who added a bass cabinet to his Marshall stack.

[edit] 1980s-Present

However, over subsequent decades, PA systems were substantially improved, and different approaches such as horn-loaded "bass bins" (in the 1980s) and subwoofers (1990s and 2000s) were used to amplify bass 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. 2000s-era PA systems are well-equipped to amplify bass frequencies, even for extended low-range instruments such as five-string basses.

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; a small combo amplifier patched into the PA will suffice. 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.

[edit] Types

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.

[edit] Amplifier technology

Amplifiers may be based on thermionic ("tube" or "valve") or solid state (transistor) technology.

[edit] Tube Amplifiers

Vacuum tubes were the dominant active electronic components in bass amplifiers from the 1940s and 1950s, and tube amplifers continue to be used for higher-end bass amplifers. 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.

The perception that tube amps produce a "warmer" sound may be due to the "soft clipping" gain non-linearity that tube amps exhibit. 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. ^[2]

[edit] Solid 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 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 heatsinks to radiate away the heat. For high-wattage amplifiers (over 800 watts), a fan is often used to move air across internal heatsinks ^[3].

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. ^[4]

[edit] Loudspeakers

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. ^[5]

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.

[edit] Cabinet Design

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.

[edit] Tweeters

It is also increasingly common for high frequency tweeters, typically horn-loaded, to be included in speaker cabinets. These extended range designs were initially developed in the late 1970s in response to the better quality pickups and electronics being built by Alembic and other high-end manufacturers and to better reproduce the more percussive bass playing styles that were becoming popular at the time.

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-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.

[edit] Amplifying the double bass

[edit] Natural-sounding amplification

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 specialised 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.

[edit] Feedback Problems

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 occuring, 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.

[edit] 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, distortion devices, 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 funk music. 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 distortion unit. 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.

[edit] Manufacturers of upright bass preamplifiers

• Fishman
• L.R. Baggs
• Schertler

[edit] See also

• Bass effects
• List of bass amplifier and loudspeaker manufacturers
• Guitar effects
• Instrument amplifier
• Guitar amplifier
• Distortion (guitar)
• Guitar speaker
• Isolation cabinet (guitar)
• Guitar speaker cabinet

[edit] References