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Contents 1 Powered speakers 2 Passive speakers 3 History 4 Servo-driven speakers 5 References 6 External links

[edit] Powered speakers

Powered speakers (or active speakers) are speakers that have built-in amplifiers. They can be connected directly to a mixing console or sound source, without the need for an amplifier. Such speakers are available with passive or active crossovers built into them. Powered speakers avoid the necessity of speaker to amplifier matching and limiting is built in. Another advantage of powered speakers is a reduction in the length of cable between amplifier output and speaker driver (some claim this affects maximum slew rate, the rate of change in audio signals) since cable length is very small in powered speakers. Powered speakers ease set-up issues for an audio system, at least to some extent. However since low-level signal cables have to be run to the speakers from a signal source, noise pick-up can be a problem. This can be reduced (even effectively solved) by incorporating "balanced" line inputs into the speakers. When driven by balanced signals (and cables) from the sound source, noise can be greatly reduced. Some powered speaker manufacturers, notably DB Technologies and Phonic, are now incorporating UHF wireless receivers so the speaker requires only a power lead.

[edit] Passive speakers

Alternatively, a passive speaker (or unpowered speaker) is a speaker which does not have its own power source and draws power from somewhere else, as opposed to an active speaker which has a built-in amplifier. Active speakers have a short run of cable between the amplifier and the speaker, which reduces signal and power loss. The amplifier can also be matched to the speaker (chiefly an impedance issue) more exactly. Passive speakers are lighter and cheaper, but require longer lengths of cable to run to a separate amplifier. This can be desirable if you have amplifiers that can run multiple speakers.

[edit] History

Some of the first powered loudspeakers were JBL monitor speakers. With the addition of the SE401 Stereo Energizer, introduced in 1964, any pair of monitor speakers could be converted to a powered and un-powered pair with the second speaker powered by the first.^[1]

The first Studio monitor with active crossover was the OY invented 1967 by Klein + Hummel.^[2]

An early example of a bi-amplified powered Studio monitor speaker 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 for the high frequency compression driver.^[3]

In 1971 while working at McCune Sound Service John Meyer designed the first fully integrated loudspeaker system, the JM3. The system was built for Creedence Clearwater Revival's last tour. It was a fully integrated tri-amped, horn-loaded system with processing electronics.^[4] Three amps were built into in a rack mountable enclosure that would drive two speakers. The enclosure also included preset cross-overs and equalization. The outside of the enclosure was simple: an AC cord, input connectors, and 4-pin connectors that plugged into the loudspeakers. The original model did not have level controls or a power switch.^[5]

[edit] Servo-driven speakers

By including a negative feedback loop in the amplifier-speaker system, distortion can be substantially reduced. If mounted at the speaker cone, the sensor is usually an accelerometer. It's also 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.

[edit] References

[edit] External links

• What is a passive speaker?

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