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Thank you for purchasing a new
JBL GT Series subwoofer. Subwoofer
installation often requires woodworking
skills and some experience disassem-
bling and reassembling automotive inte-
riors. If you lack the tools or necessary
skills, have your subwoofer installed by
an authorized JBL dealer.
Warning: Playing loud music in an auto-
mobile can permanently damage your
hearing as well as hinder your ability to
hear traffic. We recommend listening at
low levels while driving. JBL accepts no
liability for hearing loss, bodily injury or
property damage resulting from use or
misuse of this product.
construction is straightforward and there
are many prefabricated sealed enclo-
sures available. An optimum sealed
enclosure is always smaller than other
types of enclosures optimized for a par-
ticular speaker, so they require the small-
est amount of space inside the vehicle.
Vented enclosures provide better effi-
ciency in the 40Hz – 50Hz range, but this
efficiency comes at the expense of sound
in the lowest octave (below 40Hz), and at
the expense of some control and power
handling. If you are using a small
amplifier, a vented box will provide more
bass output from less power. Vented
enclosures are also well suited to a
variety of music types. Because vented
enclosures require the volume of the
enclosure and the size of the port to have
a specific relationship with the character-
istics of the woofer, the enclosure must
be built exactly to the specifications
provided. While there are some prefabri-
cated vented boxes available, matching a
prefabricated box to a particular woofer
is difficult. If you wish to use a vented
enclosure, we strongly recommend
having your authorized JBL dealer build
02
Choosing an Enclosure
GT Series subwoofers are optimized to
perform best in small sealed, vented
and prefabricated bandpass enclosures.
While infinite-baffle mounting of
GT Series subs is possible, power
handling is greatly compromised
because there’s no enclosed volume of
air to prevent the speaker’s cone from
moving past its limit. For this reason,
we do not recommend infinite-baffle
mounting for GT Series subwoofers.
You should choose the enclosure you
will use based on the type of music you
listen to, how much amplifier power you
will use for the subwoofer and how
much space inside the vehicle you can
devote to a subwoofer enclosure.
Because a sealed enclosure provides the
most control over the woofer’s move-
ment, a woofer mounted in a sealed
enclosure can handle more power than a
woofer mounted in another enclosure
type. Sealed enclosures provide more
accurate sonic reproduction than other
enclosure types, so they are well suited
to all types of music. Sealed-enclosure
it, or verify that your design is correct
if you wish to build it yourself. An
optimum vented enclosure is always
larger than the optimum sealed box for
the same woofer, and will require more
space inside the vehicle.
Bandpass enclosures often provide
the most output available from any
amplifier-and-subwoofer combination at
the expense of sonic accuracy. If sheer
SPL (sound-pressure level) is what you
desire most, choose a bandpass
enclosure. Bandpass-enclosure design
is very tricky; using a computer and
enclosure-design software is necessary.
If you are an experienced installer or
have some woodworking experience,
you may wish to build the enclosure
described in the
Specifications
chart in
this manual. Fortunately, there are many
prefabricated bandpass boxes available,
and they are all optimized to extract the
most output possible from any woofer.
Bandpass enclosures can be quite large
and may require a lot of space inside
your vehicle.
GT Series Owners Manual 5/14/99 9:49 AM Page 2