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03
Enclosure Calculation and
Building
Recommended box designs
are available from your JBL
Dealer, or at www.jbl.com on the
Internet. You may choose cabinet
dimensions to fit your car, but the
internal volume must not be
changed, since changes in inter-
nal volume will change the tuning
frequency of the enclosure.
Please contact your authorized
JBL dealer if you cannot do
the necessary calculations your-
self. The JBL Speakershop™
dedicated enclosure-design soft-
ware program may also be helpful
for experienced car-audio
enthusiasts.
Your Car And
The BASS Made In It
Depending on the size of the vehi-
cle, bass frequencies below 50Hz
or 80Hz are actually boosted by
nearly 12dB per octave as the
frequency decreases. If you
wanted to purchase that kind of
power, you would need an ampli-
fier that was eight times more
powerful than the one you have.
You can either reduce bass level
to compensate for this, or simply
sit back and enjoy the “free”
bass.
Sealed enclosures exert the most
control over the motion of a sub-
woofer because the air acts like a
spring against the motion of the
woofer cone. Larger boxes allow
for more excursion, thus more
sound output for the amount of
power used. When placed in a
sealed box larger than the rated
compliance (Vas) of the sub-
woofer, it will react as if it were
in an infinite baffle installation.
Vented and bandpass enclosures
have the lowest amount of excur-
sion for the amount of sound out-
put. This is a result of port tuning
reinforcing the sound output.
Vented boxes will not provide
adequate woofer control when
driven below the port tuning
range, meaning proper design is
important. A fourth-order band-
pass box will have the lowest
and the low-frequency response
of a subwoofer. Finally, although
information is available for
Bandpass enclosures from your
JBL Dealer, any variations from
the recommended dimensions
should be made using dedicated
enclosure-design software such as
JBL Speakershop™.
If this type of software is not
available, assistance is available
through JBL‘s Web site at
www.jbl.com or from your autho-
rized JBL dealer.