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Connecting Your Subwoofer to Your Amplifier JBL GT4 Series
JBL GT4 Series subwoofers are
single 4-ohm voice coil. Depending
on the amplifiers you are using, you
may want to use either one or sev-
eral subwoofers in the same enclo-
sure to maximize the power avail-
able from your amplifiers. To achieve
the maximum amplifier output possi-
ble, you should design a speaker
system that provides the lowest
impedance that your amplifier is
rated to drive safely. When designing
a subwoofer system, consider the
following rules:
1. Don’t mix different subwoofer
or enclosure types in the same
system.
2. We recommend that you avoid
connecting separate woofers in
series. The amplifier-damping
factor (the amplifier’s ability to
control the motion of the woofer)
is expressed as a ratio of terminal
impedance (the sum of speaker
impedance, wire resistance and
the D.C. resistance of any
crossover coil connected to the
woofer) to amplifier-output
impedance. Therefore, connecting
separate woofers in series
reduces the damping factor of
the amplifier to a value less
than 1. This will result in poor
transient response.
3. Most amplifiers deliver exactly the
same amount of power bridged
into a 4-ohm load as they do
running a 2-ohm stereo load.
To design a subwoofer system
that maximizes available amplifier
power, keep the following rules
in mind:
1. The total system impedance
of woofers in parallel can be
calculated using the formula:
Impedance =
1
1
+
1
+
1
...
w
1
w
2
w
3
where w is the nominal
impedance of the woofer.
2. The total system impedance
of woofers in series can be calcu-
lated using the formula:
Impedance = w
1
+ w
2
+ w
3
...
The diagrams at right show parallel
and series speaker connections.
Figure 1. Parallel connection
POS ( + )
NEG ( – )
RED
STRIPE
POS ( + )
BLACK
STRIPE
NEG ( – )
Figure 2. Series connection
POS ( + )
NEG ( – )
RED
STRIPE
POS ( + )
BLACK
STRIPE
NEG ( – )