|
The most common type of
loudspeaker is the
MOVING COIL speaker,
where a coil of wire is
suspended in the
magnetic field of a
circular magnet.
When a speech current is
passed through the coil
a varying magnetic field
is generated by the
coil. The two magnetic
fields interact causing
movement of the coil.
The movement of the coil
causes a cone, which is
attached to the coil, to
move back and forth.
This compresses and
decompresses the air
thereby generating sound
waves.
The loudspeaker is a
TRANSDUCER converting
one form of energy to
another.
Loudspeakers have
Impedance, typically 4
or 8 ohms. This must be
matched to the output
impedance of the
amplifier.
Loudspeakers are mounted
in enclosures (boxes).
The design of enclosures
is very complicated.
Large speakers cannot
reproduce high
frequencies and small
ones cannot reproduce
low frequencies.
Therefore two speakers
are used, a large one (a
Woofer) for low
frequencies, and a small
one (a Tweeter) for high
frequencies.
To ensure that the
correct frequencies go
to the desired speaker,
a Crossover Unit is
used.
In the diagram, C1 and
L1 are a low pass
filter.
C2 and L2 are a high
pass filter. (there is a
page on FILTERS).
When using two speakers
together, as in stereo
systems, they must be in
phase.
This means that they
move out and in
together.
This happens if the
speaker leads are
connected correctly.
Speakers can be
connected in series and
parallel but the total
impedance must match the
amplifier impedance.
Using a lower impedance
than the correct one can
blow up the output stage
of your amplifier. |
