Sound can be store and reproduced for our
convenience and pleasure.
This technological magic begins and ends with the
microphone and the speaker.
A microphone is an acoustical-to-mechanical-to-electrical
energy transducer. There are four popular types of
microphones: dynamic, ribbon, condenser, and
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
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.
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.
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
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.
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.
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.
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.
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
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.
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.