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Ed's AV Handbook
Batting Practice for the AV Professional
and primer for the novice

Chapter 3  Page 1

Sound Reproduction
The Microphone & The Speaker

Sound can be stored and reproduced for our convenience and pleasure.
This technological magic begins and ends with the microphone and the speaker.


The Microphone

A microphone is an acoustical-to-mechanical-to-electrical energy transducer.  There are four popular types of microphones: dynamic, ribbon, condenser, and piezoelectric. 

Dynamic Microphone

A dynamic microphone manages the acoustical-to-mechanical step via a light diaphragm that mechanically shadows and responds to rarefactions and compressions of sound waves.

The mechanical-to-electrical step attaches a light coil of wire to the diaphragm.  The diaphragm mounts over and slides the coiled wire into the gap of a magnet-pole assembly.  The magnet-pole-assembly surrounds the attached-coil. 

Sound waves modulate the diaphragm-coil assembly.  Its modulating magnetic field produces a corresponding modulating voltage. The voltage, an analog of the sound waves, then modulates a speaker or feeds the input of a recording device.

Shure MicrophoneDynamic Mic

Ribbon Microphone

A ribbon microphone replaces the dynamic microphone diaphragm with a thin metal film placed and framed within a magnetic structure.  As the dynamic microphone, the mechanically modulating film within the magnetic field produces a corresponding modulating voltage of the sound waves.

Ribbon MicrophoneRibbon Mic

Condenser Microphone

The acoustical-to-mechanical diaphragm of a condenser microphone is essentially one plate of an electrically charged capacitor.  The mechanical-to-electrical stage places the diaphragm-plate near a battery-charged electro-magnet back-plate.

The modulating distance between the diaphragm and the charged back-plate creates an instantaneous modulating voltage.  That voltage is a corresponding analog of the sound waves.
AKG Condenser MicrophoneCondenser Mic

Piezoelectric Microphone

A piezoelectric microphone replaces the coil-magnet assembly with a piezoelectric crystal.  The microphone's modulating diaphragm applies pressure to the crystal.  The pressure squeezes voltage from the crystal.  The voltage is an analog of the sound waves.

Piezo Microphone illustrationPiezoelectric Mic

JBL L 100 Speaker

The Speaker

The speaker is the inverse of the microphone.  It is an electrical-to-mechanical-to-acoustical transducer.  As the microphone, there are four popular types of speakers: dynamic, ribbon, electrostatic, and piezoelectric. 

Dynamic Loudspeaker

The dynamic loudspeaker is the prevailing loudspeaker technology.  A voice coil (a tight-coil of wire) is connected to an amplifier.  The voice coil, attached to a speaker cone, is placed and aligned into the gap of a fixed magnet.  The modulating output voltage of an amplifier continually reverses its polarity.  Reversing electromagnetic polarity creates a push/pull effect.  The push/pull modulates the speaker cone, which reproduces an analog of the sound waves captured by the microphone.

Dynamic Spk

Ribbon Loudspeaker

A ribbon loudspeaker is the inverse of a ribbon microphone.  Its electrical-to-mechanical mechanism, a thin conductive flat ribbon of metal foil, is sandwiched between fixed-magnets.  The ribbon replaces the voice -coil and speaker-cone of the dynamic speaker.  The amplifiers reversing polarity modulates the ribbon, which reproduces an analog of the original sound waves.

  ribbon based Loudspeaker
Manepan LRSRibbon Spk

Electrostatic Loudspeaker

As the condenser microphone, an electrostatic speaker is essentially a larger flat capacitor.   A thin diaphragm of graphite coated Mylar film sandwiched between two grid-stator-plates.  A power supply applies a constant electrical charge, of fixed polarity, to the coated film.  The stator-plates connect to an amplifier.  The amplifier and stators create an electromagnet field.  Amplifier/stator reversing polarity modulates the film, which reproduces the original sound waves.

Electrostatic Spk DiagramQuad ESL 63 Electrostaic Spk

Piezoelectric Tweeter

The piezoelectric is the inverse of a piezoelectric microphone.  In this case, the amplifier's reversing voltage-polarity is applied to the crystal. 
The voltage-pressure modulates the crystal surface.  The limitations of the surface movement restrict its use to the reproduction of high-frequency sound waves. 
The piezoelectric speaker is a tweeter.
Piezoelectric Circuit         Piezo Tweeter

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Ed's AV Handbook   
Copyright 2007 Txu1-598-288 Revised 2021

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