1987 Pontiac Trans Am GTA
One of the neatest features of this GTA's sound system is the subwoofer option integrated into
the sound system. At first sight, this car's C-pillar looks much like the ones found on any
Firebird in the mid 80's with black cloth interior, but underneath it lies a setup quite a bit
different from the way the majority of cars was equipped.
(2000)
The subwoofer option consisted of a pair of C-panel-mounted subwoofers
powered by an amplifier completely separate to the head unit, discussed elsewhere. This setup
replaced the regular 6"x9" speakers in the C-panel with 4"x9" units covering the full audio
frequency range and added 4" subwoofers installed in an ingenious resonant enclosure, to assist
with the reproduction of bass frequencies.
(2000)
The subwoofer enclosure is a molded plastic panel which isolates the space behind the subwoofer
and turns all that unused space between the outer and inner body panels into a resonant box.
To maximize bass performance, the box is a ported design. The port itself is a marvel... it
immediately curves downward deep into the car's rear quarter, allowing it to reach a sufficient
length to properly do its job. The result is a speaker enclosure which makes the best of its
relatively small volume and provides bass response expected from a much larger speaker
box. It's no 'boom box', but the enhanced bass performance is easily noticed. You can spot the
'tube'-like aspect of the port through the hole which normally houses the subwoofer. They even
went so far as to include white sound deadener, to avoid rattly noise byproducts.
(2000)
The subwoofer itself is an odd item, being rather small for this type of speaker. It makes up for
its small size by delivering a rather long speaker-cone excursion, and is equipped with a fairly
meaty and powerful magnet. When playing material above its resonant frequency, it can pack a fairly
solid punch and very rich bass. However, the small size does result in a rather high cutoff
frequency... it definitely does not reproduce the subsonic boom present in most modern dance / house
/ techno / rap music. For most other music style, though, it is a great sounding setup.
(2002)
The amplifier that feeds this pair of subwoofers is located inside the passenger's side of the instrument panel
somewhere not far from the ECM (I've never actually laid eyes on it myself). The amplifier gain is controlled by an
instrument panel mounted slider, which also provides an on/off switch. I'm not sure if this switch is an actual
'on/off' or if it is just a defeat for the amplifier output (effectively the same thing, but an on/off switch will actually
cut power to the amplifier whereas the defeat will keep the amplifier powered up).
(2001)