Note: I removed this system from the car in 2022 after six years of enjoyable service. There was nothing wrong with it; I simply decided to downgrade to make room for other electronics. I’ve saved this page as a historical reference for those who may wish to duplicate some of my efforts. Thanks for visiting!
I’ve never been one who’s able to leave “good enough” alone, especially when it comes to electronics. I like deep bass in my music. I outgrew my desire for twin 12-inch subwoofers decades ago, but I still like a deeper sound than what most factory stereo upgrades can give. I’ve been satisfied by various single 10-inch subwoofer systems for over 25 years. So it was a natural pursuit when I decided I wanted to upgrade my GTI. Of course, I “had” to add a ham radio and make the entire installation more complicated than necessary.
I had been mostly pleased with Volkswagen’s MIB II base stereo. It’s no powerhouse, but it’s more than adequate. I had originally planned to simply tap into the rear speaker wires to feed a signal converter, an amplifier, and then a subwoofer. I think I would have been satisfied with such a simple setup. Then VW decided to discontinue its first-gen Helix subwoofer accessory, meaning they slashed the pricing by more than 50% to clear their inventory. I had already purchased supplies for adding a subwoofer, so I already knew I wasn’t going to keep the Helix box after the initial installation and testing. But the super-clean wiring harness and 5-channel amp with DSP were too good to pass up, especially at that price! Helix is a great starting point for a system upgrade.
After installing the Helix system, I routed two pairs of the Helix amp’s subwoofer output into an Audio Control LC2i signal converter. The LC2i accepts up to 400 watts of speaker-level input, restores any bass that may be suppressed by the factory stereo, and then outputs line-level signals to a Rockford Fosgate Power T500X1BR 500-watt mono amplifier. I think Helix’s output is optimized for its six-inch subwoofers. So, adjusting the amplifier’s low-pass crossover frequency to block peaky mid-bass helped to tame what I’ll call “throaty” bass. I also maximized the LC2i’s AccuBASS level so that the system is working with maximum sub-bass signals.
I installed a Rockford Fosgate Power T1S1-10 10-inch high performance shallow-mount subwoofer. My goal was to keep my spare tire and still have room for my other electronics. This subwoofer works in an enclosure as small as 0.4 cubic feet and with a mounting depth of just three inches. A PLC2 Remote Punch Level Control allows me to fine-tune the subwoofer levels from the driver’s seat. It’s mounted just inches from the parking brake handle and is usually set to just 35%, leaving plenty of room to provide much more bass, if desired. In fact, 500 watts through this subwoofer is enough to produce ridiculous amounts of bass in a tiny car. I’ve shared a photo of the remote control in the album at the bottom of this page.
It’s worth noting that I eventually moved the subwoofer from the location shown on this page and into a “truck box” that’s placed behind the driver’s seat. The subwoofer performed quite well in the trunk. However, the expansion of my ham radio project compelled me to move the subwoofer so that I could dedicate the remaining trunk space to my electronics equipment, a Fall 2022 project. Having the subwoofer fire directly into the driver’s seat has changed the way I experience my music! HAHA! I will share updated photos when I have them. But I’m also leaving photos of the original setup here so that you can see it as a working concept.
In short, I replaced the Helix subwoofer with a system that features double the driver size, triple the power, deeper bass response, and retention of the spare tire. Bonus: a 10-inch subwoofer in a hatchback provides even better bass than what I had previously enjoyed in sedans since there’s no “trunk” acting as a sound barrier. Those with the Fender system can duplicate my efforts using the parts and method I shared here. I have shared more photos of my project below. See a YouTube video about this system here.
I have addressed the physical attributes of the electronics panel and a sophisticated 12V power distribution network on separate pages. Both are complex enough to warrant their own pages. Feel free to ask any questions about my rather unusual setup.
Thumpin’ Away,
Scott
The front of the electronics panel is hidden by the folding section of the factory trunk floor…
Top to bottom: Helix 5-channel amplifier with DSP, LC2i signal converter, Rockford Fosgate 500W amplifier, Yaesu FT-857D transceiver…
Clockwise from bottom: VHF/UHF digital transceiver, “Super Booster,” low current fuse box, APO3, 200A relay, high current fuse block, ground block.
Clockwise from the top: ID-5100A transceiver, Super Booster voltage regulator, small fuse block, APO3, quick release data connectors, ground connection, 200A relay, large fuse block.
Remote mounted PLC2 subwoofer control knob.
I chose this part for the remote knob because it’s a cheap part to replace, P/N: 5GM86373982V.
Yes, there is room for a 10-inch subwoofer AND a spare tire…
A “bass port?” HAHA! I replaced the rear trim panel with the trim panel for the Golf with full-sized spare to allow the spare tire to lift straight out.
The same clip that supports the rear deck also holds up the floor when in the raised position.
I usually place the electronics panel on a pair of saw horses to avoid damaging the subwoofer trim ring. I certainly could not do this on the side of the road…
All Rockford Fosgate amplifiers ship with a certificate showing its output parameters.
I thought finding a replacement connector to tap into the Helix subwoofer output would be my greatest challenge. It turns out that this 8-pin 12V extension cable for an ATX motherboard is a great fit. I only used the center four terminals and extended the wires to reach the EQL. I bought my ATX extension at http://www.ebay.com/itm/141678329440.
