Powered speakers
Encyclopedia
Powered speakers, also known as self-powered speakers and active speakers, are loudspeaker
s that have built-in amplifier
s. They can be connected directly to a mixing console
or other low-level audio signal
source without the need for an external amplifier. Active speakers may have greater fidelity
, less intermodulation
distortion (IMD), higher dynamic range
and greater output sound pressure
level (SPL) with fewer blown drivers
. Disadvantages include heavier loudspeaker enclosure
s and more cables.
Powered speakers are available with passive or active crossovers
built into them. Active speakers with internal active crossovers are widely seen in sound reinforcement
applications and in studio monitor
s.
Hybrid active designs exist such as having three drivers powered by two internal amplifiers. In this case, an active 2-way crossover splits the audio signal, usually into low frequencies and mid-high frequencies. The low-frequency driver is driven by its own amplifier channel while the mid- and high-frequency drivers share an amplifier channel the output of which is split by a passive 2-way crossover.
, or they may be built for high-end home use
such as various systems from Naim Audio
and Linn Products
.
monitor speakers. With the addition of the SE401 Stereo Energizer, introduced in 1964, any pair of monitor speakers could be converted to self-powered operation with the second speaker powered by the first. The first studio monitor with an active crossover was the OY invented 1967 by Klein-Hummel.It was a hybrid three-way design with two internal amplfier channels.
An early example of a bi-amplified powered studio monitor is the Altec 9846B, introduced in 1971, which combined the passive 9846-8A speaker with the new 771B Bi-amplifier with 60 watts for the woofer
and 30 watts for the high frequency compression driver
.
In the late 1970s, Paramount Pictures
contracted with AB Systems to design a powered speaker system.
In 1980, Meyer Sound Laboratories
produced an integrated active 2-way system, the passive UPA-1, which incorporated lessons John Meyer
learned on the McCune JM-3. It used active electronics mounted outside of the loudspeaker enclosure, including Meyer's integrated active crossover with feedback comparator circuits determining the level of limiting, often connected to third-party customer-specified amplifiers. In 1990, Meyer produced its first powered speaker: the HD-1, a 2-way studio monitor with all internal electronics. In the early '90s, after years of dealing with the disadvantages of passive systems, especially varying gain settings on third-party amplifiers, John Meyer decided to stop making passive speakers and devote his company to active designs. Meyer said he "hired an ad agency to research how people felt about powered speakers for sound reinforcement, and they came back after a survey and said that nobody wanted them." Sound reinforcement system
operators said they did not want loudspeakers in which they could not see the amplifier meters to determine whether the loudspeakers were working properly during a concert. Nevertheless, Meyer kept to his decision and produced the MSL-4 in 1994, the first powered loudspeaker intended for concert touring. The UPA-1 was converted to a self-powered configuration in 1996 and the rest of Meyer's product line followed suit.
An active speaker often incorporates equalization tailored to each driver's response in the enclosure. This yields a flatter, more neutral sound. Limiting circuits (high-ratio audio compression
circuits) can be incorporated to increase the likelihood of the driver surviving high-SPL use. Such limiters may be carefully matched to driver characteristics, resulting in a more dependable loudspeaker requiring less service. Distortion detection may be designed into the electronics to help determine the onset of protective limiting, reducing output distortion and eliminating clipping
.
Some powered speaker manufacturers are now incorporating UHF wireless receivers so the speaker requires only an AC power cable.
Trucking for a sound system involves transporting all of the various components including amplifier racks, speaker cabling and loudspeaker enclosures. Overall shipping weight for an active loudspeaker system may be less than for a passive system because heavy passive speaker cable bundles are replaced by lighter AC cables and small diameter signal cables. Truck space and weight is reduced by eliminating amplifier racks.
For high-end home use, active speakers usually cost more than passive speakers because of the additional amplifier channels required.
In home audio, the passive speaker is the easiest to install and operate.
loop in the amplifier-speaker system, distortion can be substantially reduced. If mounted at the speaker cone, the sensor is usually an accelerometer. It is possible to monitor the back emf
generated by the driver voice coil as it moves within the magnetic gap. In either case, specialist amplifier designs are needed and so servo speakers are inherently powered speakers.
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s that have built-in amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s. They can be connected directly to a mixing console
Mixing console
In professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...
or other low-level audio signal
Audio signal
An audio signal is an analog representation of sound, typically as an electrical voltage. Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical...
source without the need for an external amplifier. Active speakers may have greater fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
, less intermodulation
Intermodulation
Intermodulation or intermodulation distortion is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities...
distortion (IMD), higher dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
and greater output sound pressure
Sound pressure
Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water...
level (SPL) with fewer blown drivers
Speaker driver
A speaker driver is an individual transducer that converts electrical energy to sound waves, typically as part of a loudspeaker, television, or other electronics device. Sometimes the transducer is itself referred to as a speaker, particularly when a single one is mounted in an enclosure or as...
. Disadvantages include heavier loudspeaker enclosure
Loudspeaker enclosure
A loudspeaker enclosure is a purpose-engineered cabinet in which speaker drivers and associated electronic hardware, such as crossover circuits and amplifiers, are mounted...
s and more cables.
Powered speakers are available with passive or active crossovers
Audio crossover
Audio crossovers are a class of electronic filter used in audio applications. Most individual loudspeaker drivers are incapable of covering the entire audio spectrum from low frequencies to high frequencies with acceptable relative volume and lack of distortion so most hi-fi speaker systems use a...
built into them. Active speakers with internal active crossovers are widely seen in sound reinforcement
Sound reinforcement system
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
applications and in studio monitor
Studio monitor
Studio monitors, also called reference monitors, are loudspeakers specifically designed for audio production applications such as recording studios, filmmaking, television studios and radio studios where accurate audio reproduction is crucial....
s.
Differences between passive, powered and active speakers
The terms "powered" and "active" have been used interchangeably in regard to loudspeaker designs, however, a differentiation may be made between the terms:- In a passive loudspeaker system the low-level audio signal is first amplified by an external power amplifier before being sent to the loudspeaker where the signal is split by a passive crossover into the appropriate frequency ranges before being sent to the individual drivers. This design is common in home audioHome audioHome audio, essentially, refers to any audio electronics intended for home use, such as shelf stereos and surround sound receivers, which are becoming the most popular piece of home audio equipment...
as well as profession concert audio. - A powered loudspeaker works the same way as a passive speaker but the power amplifier is built into the loudspeaker enclosure. This design is common in compact personal speakers such as those used to amplify portable digital music devices.
- In a fully active loudspeaker system each driver has its own dedicated power amplifier. The low-level audio signal is first sent through an active crossover to split the audio signal into the appropriate frequency ranges before being sent to the power amplifiers and then on to the drivers. This design is commonly seen in studio monitors and professional concert audio.
Hybrid active designs exist such as having three drivers powered by two internal amplifiers. In this case, an active 2-way crossover splits the audio signal, usually into low frequencies and mid-high frequencies. The low-frequency driver is driven by its own amplifier channel while the mid- and high-frequency drivers share an amplifier channel the output of which is split by a passive 2-way crossover.
Integrated active systems
A few observers use the term "active speakers" to refer to an integrated "active system" in which passive loudspeakers are mated to an external system of multiple amplifiers fed by an active crossover. These active loudspeaker systems may be built for professional concert touring such as the pioneering JM-3 system designed in 1971 by Harry McCune Sound ServiceMcCune Audio/Video/Lighting
McCune Audio Video Lighting is an American company based in South San Francisco, California, with offices in Monterey and Anaheim. It is one of the oldest and largest rental and sound services in the U.S...
, or they may be built for high-end home use
High-end audio
High-end audio is a term used to describe a class of consumer home audio equipment marketed to audio enthusiasts on the basis of high price or quality, and esoteric or novel sound reproduction technologies. High-end audio can refer simply to the price, to the build quality of the components, or to...
such as various systems from Naim Audio
Naim Audio
Naim Audio is a British manufacturer of high fidelity audio products for domestic use, based in Salisbury, Wiltshire, United Kingdom.-History:...
and Linn Products
Linn Products
Linn Products is a Scottish company, based in Glasgow, that manufactures hi-fi audio equipment, home theatre, and multi-room integrated audio systems...
.
History
Some of the first powered loudspeakers were JBLJBL
JBL is an American audio electronics company currently owned by Harman International. It was founded in 1946 by James Bullough Lansing. Their primary products are loudspeakers and associated electronics. There are two independent divisions within the company — JBL Consumer and JBL Professional...
monitor speakers. With the addition of the SE401 Stereo Energizer, introduced in 1964, any pair of monitor speakers could be converted to self-powered operation with the second speaker powered by the first. The first studio monitor with an active crossover was the OY invented 1967 by Klein-Hummel.It was a hybrid three-way design with two internal amplfier channels.
An early example of a bi-amplified powered studio monitor is the Altec 9846B, introduced in 1971, which combined the passive 9846-8A speaker with the new 771B Bi-amplifier with 60 watts for the woofer
Woofer
Woofer is the term commonly used for a loudspeaker driver designed to produce low frequency sounds, typically from around 40 hertz up to about a kilohertz or higher. The name is from the onomatopoeic English word for a dog's bark, "woof"...
and 30 watts for the high frequency compression driver
Compression driver
A compression driver is a type of loudspeaker driver which uses the technique of "compression" to achieve high efficiencies. In this context compression refers to the fact that the area of the loudspeaker diaphragm is significantly larger than the aperture through which the sound is radiated....
.
In the late 1970s, Paramount Pictures
Paramount Pictures
Paramount Pictures Corporation is an American film production and distribution company, located at 5555 Melrose Avenue in Hollywood. Founded in 1912 and currently owned by media conglomerate Viacom, it is America's oldest existing film studio; it is also the last major film studio still...
contracted with AB Systems to design a powered speaker system.
In 1980, Meyer Sound Laboratories
Meyer Sound Laboratories
Meyer Sound Laboratories is an American company based in Berkeley, California that manufactures self-powered loudspeakers, multichannel audio show control systems, electroacoustic architecture, and audio analysis tools for the professional sound reinforcement, fixed installation, and sound...
produced an integrated active 2-way system, the passive UPA-1, which incorporated lessons John Meyer
John Meyer (audio engineer)
John Meyer is a pioneer in the sound reinforcement industry. In 1979 he founded founded Meyer Sound Laboratories with his wife, Helen Meyer.John Meyer grew up in Berkeley, California. His earliest involvement with audio was in the late 50s hanging out at the local radio station KPFA...
learned on the McCune JM-3. It used active electronics mounted outside of the loudspeaker enclosure, including Meyer's integrated active crossover with feedback comparator circuits determining the level of limiting, often connected to third-party customer-specified amplifiers. In 1990, Meyer produced its first powered speaker: the HD-1, a 2-way studio monitor with all internal electronics. In the early '90s, after years of dealing with the disadvantages of passive systems, especially varying gain settings on third-party amplifiers, John Meyer decided to stop making passive speakers and devote his company to active designs. Meyer said he "hired an ad agency to research how people felt about powered speakers for sound reinforcement, and they came back after a survey and said that nobody wanted them." Sound reinforcement system
Sound reinforcement system
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
operators said they did not want loudspeakers in which they could not see the amplifier meters to determine whether the loudspeakers were working properly during a concert. Nevertheless, Meyer kept to his decision and produced the MSL-4 in 1994, the first powered loudspeaker intended for concert touring. The UPA-1 was converted to a self-powered configuration in 1996 and the rest of Meyer's product line followed suit.
Fidelity
The main benefit of active versus passive speakers is in the higher fidelity associated with active crossovers and multiple amplifiers, including less IMD, higher dynamic range and greater output power. The amplifiers within the loudspeaker enclosure may be ideally matched to the individual drivers, eliminating the need for each amplifier channel to operate in the entire audio bandpass. Driver characteristics such as power handling and impedance may be matched to amplifier capabilities. More specifically, active speakers have very short speaker cables inside the enclosure, so very little current and control is lost in long speaker cables with higher resistance.An active speaker often incorporates equalization tailored to each driver's response in the enclosure. This yields a flatter, more neutral sound. Limiting circuits (high-ratio audio compression
Audio compression
Audio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...
circuits) can be incorporated to increase the likelihood of the driver surviving high-SPL use. Such limiters may be carefully matched to driver characteristics, resulting in a more dependable loudspeaker requiring less service. Distortion detection may be designed into the electronics to help determine the onset of protective limiting, reducing output distortion and eliminating clipping
Clipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
.
Cabling
Passive speakers need only one speaker cable but active speakers need two cables: an audio signal cable and an AC power cable. For multiple-enclosure high-power concert systems, the AC cabling is often smaller in diameter than the equivalent speaker cable bundles, so less copper is used.Some powered speaker manufacturers are now incorporating UHF wireless receivers so the speaker requires only an AC power cable.
Weight
A powered speaker usually weighs more than an equivalent passive speaker because the internal amplifier circuitry usually outweighs a speaker-level passive crossover. A loudspeaker associated with an integrated active system is even lighter because it has no internal crossover. A lightweight loudspeaker can be more easily carried and it is less of a load in rigging (flying). However, active speakers using lightweight Class-D amplifiers have narrowed the difference.Trucking for a sound system involves transporting all of the various components including amplifier racks, speaker cabling and loudspeaker enclosures. Overall shipping weight for an active loudspeaker system may be less than for a passive system because heavy passive speaker cable bundles are replaced by lighter AC cables and small diameter signal cables. Truck space and weight is reduced by eliminating amplifier racks.
Cost
The expense of a large concert active speaker system is less than the expense of an equivalent passive system. The passive system, or integrated active system with external electronics, requires separate components such as crossovers, equalizers, limiters and amplifiers, all mounted in rolling racks. Cabling for passive concert systems is heavy, large-diameter speaker cable, more expensive than smaller diameter AC power cables and much smaller audio signal cables.For high-end home use, active speakers usually cost more than passive speakers because of the additional amplifier channels required.
Ease of use
In professional audio, the active speaker is easier to use because it eliminates the complexity of properly setting crossover frequencies, equalizer curves and limiter thresholds. Cabling is not as simple, however, because active speakers require two cables instead of one.In home audio, the passive speaker is the easiest to install and operate.
Servo-driven speakers
By including a negative feedbackNegative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
loop in the amplifier-speaker system, distortion can be substantially reduced. If mounted at the speaker cone, the sensor is usually an accelerometer. It is possible to monitor the back emf
Electromotive force
In physics, electromotive force, emf , or electromotance refers to voltage generated by a battery or by the magnetic force according to Faraday's Law, which states that a time varying magnetic field will induce an electric current.It is important to note that the electromotive "force" is not a...
generated by the driver voice coil as it moves within the magnetic gap. In either case, specialist amplifier designs are needed and so servo speakers are inherently powered speakers.