JBL 6260 - Grounding Procedures and Safety

laws,
it
generates
a
current
opposite
to
that
of
the
original
driving
signal.
This
current
induces a
voltage
or
"back
EMF"
at
the
amplifier's
output
terminals.
The
back
EMF
travels
through the
amplifier's
output
source
impedance
to
ground.
The lower
that
impedance,
the
better
the
"braking"
action
on the
voice
coil; a
direct
short
across
the
coil
(zero
ohms)
would allow
minimal
overshoot.
Low
impedance
equals
high
damping
factor, so
the
benefits
of
high
damping
factor
become
obvious
—
tighter
control
of
the
loudspeaker.
The
theoretical
damping
factor
of an
amplifier
may
not
be
realized
at
the
speaker
because
cables
always
have a
finite
resistance
or
impedance;
the
back
EMF
must
also
travel
through
the
cable,
so
the
damping
becomes
less.
Hence,
larger
gauge
cables
not only
reduce
signal
losses,
they
improve
performance
by
affecting
damping
factor
less
than
smaller
gauge
cables.
2.8.3
CALCULATING
LOSSES
IN
SPEAKER
CABLE
WIRE
DIAM.
(mm)
SOLID
A.W.G.
WIRE
GAUGE
DC
RESISTANCE
PER
30
m
(100
ft)
OF
TWO-CONDUCTOR
CABLE
(OHMS)
CABLE
LENGTH
PRODUCE A
ONE
WHICH
WILL
dB
POWER
LOSS
0
POUR
meters
ohms
feet
0
EIGHT
meters
ohms
feet
4.115
6
0.08
366
1200
740
2425
3.264
8
0.13
244
800
488
1600
2.588
10
0.20
145
475
290
950
2.05
12
0.32
91
300
183
600
1.63
14
0.52
58
190
114
375
1 .29
16
0.82
37
120
73
240
1.02
18
1.32
23
75
46
150
0.813
20
2.08
15
50
30
100
0.643
22
3.30
9
30
18
60
POWER
LOSSES
IN
SPEAKER
CABLES
This
chart
may be
consulted
to
establish
the
approximate
power
loss
(and
damping
factor
degradation)
for
various
wire
gauges.
2 . 9
GROUNDING
For
safe
operation
the
amplifier
must be
connected
to a
good
mechanical
ground.
This
provides
for a
current
path
for
any
voltage
which
should
appear on
the
chassis due
to a
fault
in
the
amplifier.
This
current
path
will
result
in
blowing
the
main
power
supply
fuse.
Without
this
current
path,
the
amplifier
-
14
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