`Bass Junkie’ – a GTi-R with serious SPL…

No matter which way you look at it, bass is `in’.

The quest to produce increasingly higher Sound Pressure Levels (SPL) is an obsession to many and Ahim admits to being a certified ‘Bass Junkie’ with four Rockford Punch XLC RFP 2415 15" sub woofers in his Nissan GTi-R.

It was back in his Indonesian homeland that he learned all about serious car audio, but a visit to Perth’s Audioart & Technologies changed his perspective on car audio forever.

He already had a couple of 12" subs in the back of his little Nissan, but Ahim wanted to try a batch of 15s for size, so Audioart’s Paul Chung set about preparing the car for its four big boomers.

With the back of the car gutted, Paul and Audioart’s head man, Yanddy Limadnatta, stood looking into the vacant space and discussed the various options.

That’s `bass’, not `space’
Now remember, the Nissan GTi-R is not a family car and space is certainly at a premium in there, so a bit of thought had to be applied before simply throwing the four 15s in the back of the hatch !

It was ultimately decided to construct two MDF sub boxes of 3.5 cubic feet in volume each, but first, some 20 litres of Rockford Blue sound deadening was applied throughout the vehicle.

Actually, the sound deadener was plastered all over the floorpan, the door skins, the boot lid, the inside of the rear quarter panels and under the hoodlining. After all, if you’re going to create serious sound waves with four 15" subs, the last thing you want is all the panelling in the car resonating like crazy and destroying those thumpin’ bass notes !

With the preparation work performed, Paul set to work on an MDF base plate for mounting the sub boxes.

The base plate is itself mated to numerous MDF blocks which are themselves glued to the metal floorpan. This avoids the old practice of drilling unneccessary holes in the vehicle. and only two ‘non factory’ holes were created for earthing points.

Obviously sensible stuff, the glue used is a special compound which, although exceptionally strong, can be removed with relative ease - thus ensuring that the vehicle can easily be returned to stock trim.

With the base plate in position, the sub boxes were bolted together and slid as one unit into position.

The boxes were then bolted to the base plate and to factory brackets on the GTi-R’s rear strut towers. This, in addition to internal bracing inside each sub box, ensures total rigidity. Finally, the wiring was run up and the Woofers bolted into position.

Sorry, no passengers!
To tell the complete truth though, the construction and fitting of the sub boxes was done in conjunction with making up the MDF display area behind the front seats for all the remaining system hardware.

Not surprisingly, with all of this additional equipment never mind the four 15s, the car’s rear seating arrangement no longer exists!

While the two-channel Rockford Punch 100 amplifier powering the Rockford FNX 1614F front splits is hidden down under the base plate, both Rockford two-channel 250.2 amps used for powering the subs sit on custom pods in the cabin for enhanced air flow and cooling.

Each amp supplies two of the massive subs in bridged mono fashion, pumping a whopping 500 Watts RMS into 4-Ohm loads. Did someone say "Hot"?

Power for those front splits, incidentally, is 100 Watts RMS into 4-Ohm loads each side. (there are no rear splits in the car - why bother, eh !)

Not surprisingly, there’s a fair amount of power cable running through this little Nissan and each of those 250.2 Rockford amps actually runs dual 8 gauge power wire.

The amps are from Rockford’s Power Series and use a low voltage supply for the pre-amp stage and a high voltage supply for the MOSFETs and other power-associated components. The end result is those amazing power figures.

Thankfully, Ahim has one of the renowned Optima yellow top batteries on board and the stock alternator has stood up to the abuse thus far too. And, a couple of Rockford R 87430 1 Farrad stiffening capacitors play a key role too when the bass is pumpin’.

Serious pre-out – and a `black box’, and a Wave Brain and...
Up front and the system in Ahim’s car is headed up by Rockford’s single CD playing RFX 8140 head unit.

This is Rockford’s top of the range competition unit and although only capable of holding a single CD at a time, offers some unique features.

Heading up the stats is a massive 8.5 Volts pre-out, which allows the gains on the amplifiers to be kept as low as possible for minimum distortion. The 8140 can also be connected to the rest of the system via balanced line technology, which effectively reduces the number of earthing points and again ensures that sound quality is maintained.

In this install, Rockford’s balanced line cable connects the 8140 to Rockford’s renowned Symmetry EPX 2 control unit.

While the main control box for the Symmetry is mounted in the rear display area, the interface unit with keypad and LCD display (known as an R-Dat) has been cleverly mounted in the roof.

With the hoodlining removed for the application of the sound deadening, an MDF base plate was measured up and glued to the roof. A custom MDF box containing the interface unit, er, sorry, R-Dat, was then bolted to the base plate, with the wiring running down the driver’s side A-pillar. Some colour matched vaccuum moulded vinyl then completes the look.

In Ahim’s car, there are two outputs from the Symmetry unit to the amplifiers - low pass to the subs at 92 Hz and bandpass from 92 Hz and upwards for the front splits.

And a little device called a Wave Brain has been placed between the EPX2 and the subwoofer amplifiers to boost the signal voltage to the subs even further.

What’s next?
Now, it doesn’t matter whether a vehicle is highly developed for mechanical or audio performance, on-going development is always going to be a part of the game.

So the Audioart crew are now considering replacing the 15s in Ahim’s little Nissan with the very latest Rockford 15s, which are known for even greater tightness and loudness.

Then again, 12s might be considered, which would allow possibly six subs to be used. Or yet again still, they might try and squeeze six 15s in there!