Output Transducers

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Output Transducers

• (Loudspeakers)

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Loudspeakers

• 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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Loudspeakers

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

Tweeter
Mid-range
Woofer
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Woofer

• Produces Low Frequencies

Cone diaphragm
Surround
Magnet
Basket
Spider
Voice Coil
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Woofer Frequency Response
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Tweeter

• Produces high frequencies
• Uses only one suspension medium.

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Tweeter Frequency Response
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Crossover

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

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Crossover High-Pass
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Crossover Low-Pass
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Crossover Band-Pass
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Passive Crossover

• A passive filter is placed after the amplifier
• It cannot raise the gain on the signal

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Active Filter

• In active filtering the signal splitting occurs
  before it is amplified

• 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

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Passive Speakers

• These do not contain an in-built amplifier and so
  must be powered by an external amp
  
• Used in most home Hi-Fi systems
• Do not require power leads
• May require fairly thick cables to carry the
  signal

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Active Speakers

• Have a built in amplifier and so can be used with
  small output signals
  
• Most PC speakers are active to boost the weak
  output (4W) from most sound cards
  
• Require only thin signal cables
• Increased weight
• Overall performance my be restricted by a poor
  amplifier

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Distortion

• 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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Distortion

• 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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Enclosures

• 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 Baffle

• By completely enclosing the back of the speaker
  we get an infinite degree of blocking
  
• Stops low frequency cancellation
• Wastes energy produced by rear of speaker

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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 size
• Size of opening (port)
• Resonance of loudspeaker

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Fin

• Fin