Ashly Electronic Amplifier none User Manual
Page 18
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A CLOSER LOOK AT CROSSOVERS
IMTRODUCTION
The bulk of this instruction manual is concerned with helping a sound system
operator to get his system set up and running, and to answer the questions
"how do I plug it in" and "where should I set the front panel controls." For
those
who
want
more
information
about
the
design
and
application
of
crossovers, this section may be a good starting place, covering such topics as
the
need
for
crossovers,
characteristics
of
filters
used
in
audio,
limitations
of passive crossovers, solutions offered by biamplification, and more detailed
information regarding correct speaker alignment. The information offered here
is only an introduction to the subject, since an in-depth discussion would
certainly fill dozens of books.
As you read this, please try to always keep in mind that your crossover is
only one part of a sound system, and that the electrical performance of a
crossover,
although
predictable
and
well
behaved,
will
almost
never
be
accurately
reflected
in
the
acoustic
performance
of
a
speaker
array.
Also,
there is no "best" approach to reproducing music through loudspeakers; there
are a variety of methods in popular use, and each method has attendant
problems and benefits which make it suitable for a particular application.
WHY USE CROSSOVERS?
The ideal speaker system would use a single small loudspeaker to reproduce the
entire
audible
sound
spectrum
at
any
desired
power
level.
It
would
be
inexpensive, easy to hook up, and have a wel1-controlled coverage pattern that
would
not
vary
significantly
with
frequency.
Unfortunately,
such
a
speaker
does not exist. Perhaps the closest approximation we have is the single
driver headphone,
which can reproduce most of the audio spectrum fairly
accurately.
When
any
larger
amount
of
volume
is
required,
it
becomes
necessary to move greater amounts of air and larger speakers are required.
For a given loudness, reproduction of low frequencies will demand greater
changes in air pressure than high frequencies, and so will require a greater
surface area in contact with the air. A speaker capable of good low-frequency
response,
then,
will
be
relatively
large.
This
characteristic
does
not
favor
good high frequency response, however, since the sheer physical mass of the
large speaker inhibits the rapid back-and-forth movement required to reproduce
high frequencies. A speaker suitable for reproducing high frequencies should
be
light
and
small.
This
disparity
between
low
and
high
frequency
requirements gets worse as the frequency response extremes and power demanded
of a system get larger.
If one speaker cannot satisfy all requirements, then the solution must be to
use
two
speakers,
each
suited
to
a
particular
portion
of
the
frequency
spectrum, and let each do its own job. This neatly solves one problem but
instantly creates several new ones. First of all, if the woofer and tweeter
are both wired in parallel and hooked up to a high power amplifier, there's a
good chance that the tweeter will be destroyed. The tweeter will attempt to
reproduce low frequency information fed to it, but its cone will not allow the
long back and forth excursions necessary for lower frequencies, and so the
excess pov/er being fed to the tweeter will be dissipated in its voice coil as
heat, eventually ruining it. Secondly, if the woofer and tweeter are not well
matched in terms of their sensitivity, then one range of frequencies will be
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