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DESIGNING A SPEAKER SYSTEM FOR THE GTI AMPLIFIER
NOTE: Although the JBL A6000GTi or
A3000GTi amplifier will drive a system
made up of any subwoofers, we
recommend using JBL GTi subwoofers
with GTi amplifiers.
Both the JBL A6000GTi and A3000GTi
amplifiers provide RMS power that
exceeds the RMS power-handling
rating of nearly every subwoofer
available. To use this amplifier
optimally, you should design a speaker
system made up of several identical
speakers, so that the power delivered
by the amplifier will be shared equally
among the speakers.
The JBL A6000GTi and A3000GTi
amplifiers support a wide range of
impedances, and any speaker system
with a total or equivalent impedance of
1 to 4 ohms will extract full power from
either amplifier. In order to connect
multiple woofers to the A6000GTi or
A3000GTi, you’ll need to connect your
speakers in series, parallel or series-
parallel. We’ve included diagrams for
each connection scheme and a pair of
formulas, which will help you.
SERIES CONNECTIONS
The formula for determining the total
impedance of the two woofers connect-
ed in series is:
Z
total
= Z
1
+ Z
2
+ Z
3
...
Where Z
total
is the total impedance of
all woofers connected in series. Z
1
, Z
2
and Z
3
(and so on) are the nominal
impedance ratings of the individual
speakers. The total impedance of the
voice coils shown in Figure 2 is 8 ohms.
Figure 2. Series connection of two
4-ohm voice coils yields a total
impedance of 8 ohms.
PARALLEL CONNECTIONS
The formula for determining the
equivalent impedance of the voice coils
connected in parallel is:
Z
equivalent
= 1/(1/Z
1
+ 1/Z
2
+ 1/Z
3
…)
Where Z
equivalent
is the equivalent
impedance of the coils connected in
parallel. Z
1
, Z
2
and Z
3
(and so on) are
the nominal impedance ratings of the
individual speakers. The equivalent
impedance of the voice coils shown in
Figure 3 is 2 ohms.
Figure 3. Parallel connection of two
4-ohm voice coils yields a total
impedance of 2 ohms.
DUAL VOICE-COIL
CONNECTIONS
Dual voice-coil subwoofers, such as
JBL’s GTi series, may be connected
in series, as shown in Figure 2;
in parallel, as shown in Figure 3; or in
series-parallel, as shown in Figure 4.
Figure 4. Series-parallel connections
of three W15GTi subwoofers (with a
voice coil impedance of 6 ohms) yields
a total series impedance of 12 ohms
for each subwoofer, and an equivalent
parallel impedance of 4 ohms for all
three subwoofers.
To determine the impedance of a
system of three W15GTi (dual voice-
coil) subwoofers connected in series-
parallel, use the series connection
formula to determine the impedance
of each subwoofer with its voice coils
connected in series. Then insert the
calculated value into the parallel
connection formula to determine the
equivalent impedance for the three sub-
woofers connected in parallel.
NOTE: Each W15GTi voice coil has an
impedance of 6 ohms.
For example, in Figure 4, each woofer
will have an impedance of 12 ohms, by
Z
total
= Z
1
+ Z
2
= 6 + 6 = 12
and the three woofers connected
in parallel will have an equivalent
impedance of 4 ohms, by
Z
equivalent
= 1/(1/Z
1
+ 1/Z
2
+ 1/Z
3
)
= 1/(1/12 + 1/12 + 1/12)
= 1/(3/12)
= 12/3 = 4
NOTE: All subwoofers connected to an
amplifier in a system must be identical
and, if they are dual voice-coil sub-
woofers, their coils must be wired iden-
tically. Do not connect the coils of one
subwoofer together in series and
another in parallel, since doing so will
cause uneven power distribution,
potential damage to the speakers, and
poor overall performance.
ABOUT SPEAKER
POWER HANDLING
The RMS power handling rating of
a speaker indicates the amount of
power it will handle continuously.
Although designing a subwoofer
system by considering the RMS rating
will ultimately provide you with the
most reliable system, your speakers
may be able to handle more power,
depending on what kind of music is
being reproduced.
For music with extended bass notes
(e.g., bass music, hip-hop or techno),
you should design a speaker system
based on the RMS power handling of
your speakers. For music with sharp
transient bass notes (e.g., rock,
country or jazz), the RMS power
handling rating is conservative, and you
can count on your speakers being able
to handle more power than the RMS
rating.
The total power output of your
amplifier will be divided among the
speakers connected to it. For example,
if you are using an A6000GTi and three
W15GTi subwoofers, each subwoofer
will receive 2,000 watts.
It’s important to choose a system of
subwoofers that will handle all of the
power. To determine how much total
power your speaker system will
handle, simply multiply the RMS power
handling rating of one of your speakers
by the total number of speakers that
will be connected.
3
4 ohms 4 ohms
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Terminal Jumper
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Terminal Jumper
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4 ohms 4 ohms