JBL 6230 - Page 16

2.7.3
SOMETIMES
A
LARGER
AMPLIFIER
CAN
BE
SAFER
If the
desired
sound level
is high
enough
that
it
requires
a
low
powered
amplifier to
be
operated at a
fairly
high distortion
level (e.g.,
well into
clipping), it
may be
safer to use a
larger
amplifier
that
will be
free
of
distortion.
It is
true
that in
a
small
amp which
is clipping,
peak power
is
restricted by the
size
of the
amplifier's power.
However,
the
average
power
output
rises
due to the
increased
signal
density
caused
by
distortion
components. Not
only does this increase
the
thermal
stress, it
also increases
mechanical stress
because
the
squared
waveforms
place
greater "G"
loads on the
moving parts,
and
abnormally
high
proportions of
high frequency
harmonics are
generated
which can
fry
the
tweeter voice
coils.
A more
powerful
amplifier
which is
able to
generate
the
desired peak
sound
level without
clipping
avoids the
large
increase
in average
power
(thermal) and
the high
acceleration
(mechanical) stresses
caused
by
the
overdriven
small amplifier.
The major
drawback of
the larger
amplifier
is
that it can
produce
higher peak
outputs
that
may
instantly destroy a
loudspeaker.
Therefore,
great care
must be
exercised to
ensure
that
the
ampl-
ifier
will not be
driven at
too
high
a
level,
certainly
never at
a
clip.
This can be
accomplished
either
by knowing
the
program
material (if
recorded)
and
setting levels
accordingly,
or by
using
peak limiters
(with live or
unknown
program
material).
2.7.4
REMEMBER
THE
DIVIDING
NETWORK
(CROSSOVER)
If
the
amplifier
is connected
to a
multi-way
loudspeaker
system
that includes a
passive,
high-level
dividing
network
(crossover),
be sure to
consider
its
presence.
The
network
should be rated to
handle
the
amplifier's
power.
Pre-packaged
speaker
system power
ratings
already take
the
crossover
into
account.
If
you obtain
separate
components
and
assemble a
system,
the
chances are that
the
higher
frequency
drivers will be
rated
at
less
power than the
woofer(s).
This
works out
overall
because
the higher
frequency
drivers tend
to be more
efficient
(more
sound per watt).
In
fact,
higher sensitivity
in the
high
frequency
components
usually
requires some
attenuation to
be
applied in
the dividing
network
(remember,
a
3 dB
more
sensitive
driver must
be driven
with
half the power to
generate
the
same
sound level).
For
example, consider
a typical
two-way system
with
a
200
watt woofer
and 50
watt
high frequency
compression driver.
The
woofer.
1
meter
from its enclosure, generates
100 dB
SPL with
1
watt
at its
input, and
the
compression driver,
1 meter from
its
horn,
generates
106 dB SPL at
1 watt
input. If
both
components
are
driven by a
200 watt
program
signal,
the compression
driver
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