GTO 1204D - JBL Car Audio User Guide / Operation Manual. Page 2

Warning: Playing loud music in
an automobile can permanently dam-
age 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.

Grand Touring Series subwoofers
are optimized to perform best in
small, sealed, vented and prefabri-
cated bandpass enclosures. While
infinite-baffle mounting of GTO subs
is possible, power handling will 
be 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 GTO 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 movement, a woofer
mounted in a sealed enclosure will
handle more power than a woofer
mounted in another enclosure type.
Sealed enclosures provide more
accurate sonic reproduction than
other enclosure types when 
mounted inside a vehicle, so they are
well-suited to all types of music.
Sealed-enclosure construction is

straightforward and there are many
prefabricated sealed enclosures
available. An optimum sealed 
enclosure is always smaller than
other types of enclosures optimized
for a particular speaker, so they
require the smallest amount of space
inside the vehicle.

Vented enclosures provide better 
efficiency 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 at the lowest frequencies. 
If you are using a small amplifier, 
a vented box will provide more 
perceived 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 
characteristics of the woofer, the
enclosure must be built exactly to the
specifications provided. While there
are some prefabricated 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 it or verify that your design is
correct if you wish to build it your-
self. 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 and
the aid of 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 bandpass
enclosure described in the enclosure
design sheet included with this
woofer. Fortunately, there are many
prefabricated bandpass boxes 
available and they are all optimized
to extract the most output possible
from any woofer. Bandpass enclo-
sures can be quite large and may
require a lot of space inside your
vehicle.