GT4-12 - JBL Car Audio User Guide / Operation Manual. Page 3

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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.

POS ( + )

NEG ( – )

RED
STRIPE
POS ( + )

BLACK
STRIPE
NEG ( – )

POS ( + )

NEG ( – )

RED
STRIPE
POS ( + )

BLACK
STRIPE
NEG ( – )