JBL 6260 - Understanding Loudspeaker Power Ratings

2.7.2
MORE ABOUT
LOUDSPEAKER
POWER
RATINGS
While
there is
no
cut-and-dried
method to
establish an
appropriate
amplifier
power for
a
given
speaker
system, certain
guidelines
do
exist. If
a
loudspeaker
manufacturer
specifies "to
be
used
with
amplifiers rated
at
no more
than
'x'
watts,"
then
neither
speaker nor
amplifier
warranty
is
likely
to
cover damage
if a
larger
amplifier
is used.
If the
amplifier
power
is only
recommended, or
if a
power rating
is given
without
mentioning the
amplifier,
then
the question
as
to whether
the
amplifier
is
"safe"
becomes
more
difficult to answer.
Loudspeakers
usually
fail
due to one
of
two
factors:
thermal
or
mechanical
overload.
Thermal
overload means
overheating,
and
is
almost always
caused
by
applying too
high a
level of
sustained,
average
power;
the
voice coil
insulation
may
burn and
short
circuit,
the
coil may
deform due
to the
heating
and
scrape
in
the
gap,
and, in
some cases,
speaker cones
have been
known to
burst
into flame.
Mechanical
overload is
another
way
of
describ-
ing
excessive
diaphragm/voice
coil
travel. A
single
very
high
power
transient,
especially
at lower
frequencies,
can
literally
tear a
loudspeaker
apart.
Sometimes
mechanical
overload is
more
gradual,
with the
voice
coil "bottoming"
against
the
magnetic
assembly
until
it is
deformed;
a
compression
driver
diaphragm can
strike the
phase plug
and
shatter,
or the
suspension
can be
over-
extended
and
simply
tear apart.
The
frequency
and
waveform
of a
signal
have
a lot to
do
with
the
destructive
potential
of
a
given
power
output.
Band
limited
pink noise
is
somewhat
akin to
"average
program"
power,
although
the
meaning of
such
a
rating
depends
heavily on
crest
factor
(peak
to
average
noise
voltage)
and
specific
frequency
limits.
Unfiltered
or
unweighted
white
noise
stresses
the
tweeters more
than the
woofers.
Swept
sine
waves
may
cause
less
thermal
heat-
ing, but
can
cause
larger
excursions
at
low
frequencies.
With
compression
drivers, the
mechanical
power
handling
capability
is
approximately
quadrupled
simply
by
raising
the
minimum
crossover
frequency by
an
octave. If
any
conclusion
can
be
drawn,
it
is
this:
NO SINGLE
POWER RATING
REALLY
DESCRIBES
THE
POWER
HANDLING
CAPABILITY
OF
ANY
LOUDSPEAKER
OR
LOUDSPEAKER
SYSTEM.
ALSO,
WHEN
A
LOUDSPEAKER
SYSTEM IS
MULTI-AMPLIFIED,
i.e.
A
HIGH
FREQUENCY
DRIVER IS
CONNECTED
DIRECTLY
TO THE
POWER
AMP-
LIFIER
OUTPUT,
A SERIES
PROTECTION
CAPACITOR IS
STRONGLY
RECOMMENDED
TO
REDUCE
THE
POSSIBILITY
OF
ACCIDENTAL
DAMAGE
TO
THE
DRIVER
DIAPHRAGM.
CONSULT
THE
MANUFACTURER
OF
THE
DRIVER
AND HORN FOR
RECOMMENDATIONS
ON
PROTECTION
CAPACITOR
TYPES
AND VALUES.