Ashly Electronic Amplifier none User Manual
Page 20
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with the frequency spectrum thus divided, it becomes possible to discard some
of the signal being sent to the tweeter, making level-matching with the woofer
a simple matter.
PASSIVE CROSSOVERS AND FULL RA^IGE SYSTEMS
The simplest type of crossover feeds the full-range amplifier output to a
crossover network with two passive filters, a low-pass and a high-pass. The
appropriate filter outputs are then connected to the woofer and tweeter, as
shown in figure 20.
■ To tweeter
To woofer
Figure 20 Passive Crossover
The advantages of the simple passive crossover are that they are simple to
hook up, they accomplish their primary job of speaker protection, and they are
cost-effective
for
low
power
applications.
When
built
by
a
loudspeaker
manufacturer for inclusion in a specific speaker system, the characteristics
of the individual
can be
to
requiremencs or tne system.
However, the list of problems created by the use of passive crossovers is
fairly lengthy, particularly when used in modern high-power PA systems. First
of
all,
they
offer
no
flexibility
to
the
sound
system
operator.
Passive
crossovers have fixed operating parameters; you can't change their crossover
frequency or filter shape. If your speaker system requirements change, you're
stuck.
Other
problems
have
to
do
with
the
components
of
the
passive
filters
themselves,
notably
the
inductors.
Inductors
are
physically
quite
bulky,
the
more so for low frequency and high power applications, making them difficult
and
expensive
to
manufacture.
Electrically,
they
are
non-linear
and
subject
to saturation and ringing, and are very sensitive to external magnetic fields.
Passive crossovers are difficult to design because they are always terminated
by speakers, which present varying loads to the network. As the impedance of
a speaker varies with frequency, so will the behavior of the filter to which
it is connected. This interaction between speaker and crossover is of no help
when you're trying to achieve a certain response from your system.
Using one amplifier for the entire audio spectrum is also found to be less
than
ideal.
For
one
thing,
it
doesn't
adequately
answer
the
problem
of
mismatched
sensitivities
of
the
woofer
and
tweeter.
If
a
horn
loaded
compression driver is much louder than the woofer in a passive system, the
only answer is to "throw away" some of the high frequency signal by use of an
attenuator on the crossover's high frequency output. This is certainly not
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