Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio

Chapter Three
Sound Reproduction

Page 1

Batting practice for the audio/video pro and a primer for the novice

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The Microphone and 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.

Handbook Note: This chapter assumes you read chapter two page 2.

The Microphone

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

Dynamic Mic

          A dynamic microphone manages the acoustical-to-mechanical step via a light diaphragm that mechanically shadows-and-responds to the rarefactions and compressions of sound.
          The mechanical-to-electrical step attaches a coil of wire surrounded by a magnet
to a light diaphragm.  Sound waves modulate the diaphram-coil in the magnetic field which produces a small voltage.  This voltage is an analog of the original sound that can be amplified or recorded.

Ribbon Mic
         A ribbon mic places a 
thin aluminum film/metal element between magnetic poles rather than a dynamic mic diaphragm.  As the dynamic mic, the modulating film and its magnetic field produces a small voltage.  As the dynamic mic, that voltage is an analog of the original sound.

Condenser Mic
acoustic-to-mechanical diaphragm of a condenser mic is essentially one plate
of an electric-static-charged capacitor.  The mechanical-to-electrical stage places this diaphragm plate
near a battery supplied electro-magnet backplate.  Changes in the modulating distance between the diaphragm and the charged backplate creates an instantaneous voltage.  That voltage is an analog of the original sound.

Piezoelectric Mic
          A piezoelectric mic uses
an allmost all-in-one acoustic-to-mechanical-to-electrical transducer.  This transducer uses a natural crystal that produces voltage when sound pressure is applied by a modulating diaphram.  Piezoelectric microphones literally squeeze voltage from the crystal.   Its voltage is an analog of the original sound.

The Speaker

         A speaker is an inverted microphone.  It's an electrical-to-mechanical-to-acoustic transducer.  As the microphone there are four popular types of speakers: dynamic, ribbon, electrostatic, and piezoelectric.

Dynamic Loudspeaker
          The dynamic loudspeaker is the most prominent type of loudspeaker.  The output
from an amplifier is connected to a coiled wire (creating an electromagnet) surrounded by a fixed magnet.  Continuous modulating changing electromagnetic polarity of the amplifier creates a push/pull effect.  The electro-magnet-coil is attached to a speaker cone.  The modulating voltage from the amplifier modulates the coiled-cone-assembly which in turn reproduces the original
sound from a microphone or a recording.

Ribbon Loudspeaker
          A ribbon loudspeaker is the reversal of a ribbon mic.  The electrical-to-mechanical mechanism is comprised of thin conductive wires attached to a thin ribbon of Mylar
film placed between vertical arrays of magnet strips.
 An amplifier modulates the Mylar
sheet which reproduces an analog of the original sound.

Electrostatic Loudspeaker
          As the condenser mic an electrostatic speaker is essentially a large flat capacitor.
Similar to the condenser mic, a power supply creates 
an electro-static charged field.  The electric-to-mechanical diaphragm is a graphite coated mylar film placed between charged corrugated grid stators.  An amplifiers modulates the diaphragm  which in turn reproduces the original sound.

Piezoelectric Speaker
          I did not refer to this speaker as a loudspeaker.  This type of speaker is limited to the reproduction of high frequency sound in a high fidelity system --- it's a tweeter.  This 'tweeter' is the reverse of a piezoelectric microphone element.  In this case an amplifier's voltage is applied to the crystal.  The modulating pressure/voltage squeezes the piezoelectric crystal, which modulates its surface and reproduces the original high frequency sound.

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Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288   Revised 2018