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Output Transducers

Output Transducers

(Loudspeakers)

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LoudspeakersLoudspeakers

Transducers that convert electrical signals into sound waves

The current flow in the coil causes the diaphragm to move, thus causing changes in sound pressure

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LoudspeakersLoudspeakers

Loudspeakers usually consist of multiple speakers (drivers) to cover the full frequency range

Tweeter

Mid-range

Woofer

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WooferWoofer

Produces Low Frequencies

Cone diaphragmSurround

Basket Spider

Magnet

Voice Coil

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Woofer Frequency ResponseWoofer Frequency Response

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TweeterTweeter

Produces high frequenciesUses only one suspension medium.

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Tweeter Frequency Response

Tweeter Frequency Response

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CrossoverCrossover

Divides and routes the appropriate portions of the signal to each of the speakers in the system

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Crossover High-PassCrossover High-Pass

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Crossover Low-PassCrossover Low-Pass

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Crossover Band-PassCrossover Band-Pass

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Passive CrossoverPassive Crossover

A passive filter is placed after the amplifier

It cannot raise the gain on the signal

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Active FilterActive Filter

An active filter is so called because it requires electric power for its operation and can raise the gain of the signal

enables adjustment of the frequency ranges

In active filtering the signal splitting occurs before it is amplified

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Passive SpeakersPassive Speakers

These do not contain an in-built amplifier and so must be powered by an external ampUsed in most home Hi-Fi systemsDo not require power leadsMay require fairly thick cables to carry the

signal

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Active SpeakersActive Speakers

Have a built in amplifier and so can be used with small output signalsMost PC speakers are active to boost the

weak output (~4W) from most sound cardsRequire only thin signal cablesIncreased weightOverall performance my be restricted by a

poor amplifier

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DistortionDistortion

Distortion is an unwanted change introduced in the original sound when it is reproduced through a loudspeaker system

Intermodulation distortion• the interaction of two or more frequencies

contained in the original sound which produces a third frequency not present in the original sound

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DistortionDistortion

Harmonic distortion• similar to intermodulation distortion, except

it is a reaction involving one frequency Transient distortion

• the inability of a loudspeaker system to properly reproduce transients, short, temporary sounds of less than a second

Loudness distortion• caused by overdriving the loudspeaker

system, producing a loudness level higher than that of the original studio production

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EnclosuresEnclosures

The loudspeaker enclosure serves as a passive processor of the sound, collecting and directing it to the desired location

Without a baffle or enclosure low frequency sound from the front and back of the speaker will cancel each other out

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Infinite BaffleInfinite Baffle

By completely enclosing the back of the speaker we get an infinite degree of blockingStops low frequency

cancellationWastes energy produced by

rear of speaker

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Vented Enclosure (Bass-reflex)

Vented Enclosure (Bass-reflex)

The rear wave from the loudspeaker is delayed so that it emerges from the port in phase with the wave motion from the front

Relies on strict relationship Enclosure sizeSize of opening (port)Resonance of loudspeaker

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FinFin

Fin