JBL GT150D - Manual (Page 3)

03
Connecting Your Subwoofer to Your Amplifier JBL GT Series
JBL GT Series subwoofers
are available in two different
configurations: as a single 4-ohm
voice coil or as dual 4-ohm voice
coils. Depending on the amplifiers
you are using, you may use either
single-voice coil or dual-voice coil
subwoofers in singles or multiples
to maximize the power available
from your amplifiers. To achieve
the maximum amplifier output
possible, 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 (use all single-coil
woofers or all dual-coil woofers).
2. You may connect the coils of a
dual-voice coil woofer in series,
but 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. You must use both coils of a
dual-voice coil woofer connected
either in series or in parallel.
4. 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 voice coils (or woofers) in
series can be calculated 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 ( – )