Mk7 Golf R Helix Subwoofer Upgrade: More Punch Without Wrecking Your Wallet

If you own a Mk7 Golf with the Volkswagen Helix Subwoofer, you already know it's a surprisingly capable system for an optional dealer accessory. The Helix DSP amplifier and spare-tire-mounted subwoofer enclosure with dual 5.25" drivers do a decent job of waking up the factory speakers, but you have probably felt the same thing I did. There is very little punch or clarity from the subwoofer and the bass runs out of steam when raising the volume.

I've been thinking about how to improve this for a while, and I finally accomplished it. Here's what I changed, how it works, and what you should know before attempting it yourself.

The Goal

I track my 2016 Golf R regularly, and when I am doing my track prep, I want to be able to easily pull the subwoofer enclosure out entirely. It's heavy, it's in the spare-tire well, and it's not doing anything useful for me at the track. That means any audio upgrade I do has to be fully reversible with no permanent wiring modifications and easy disconnects.

My objectives for these mods were:

• More bass output and low-end extension from the subwoofer.
• Maintain the factory head unit and Helix DSP integration.
• Keep the install easily reversible.
• Ability to remove everything quickly for my track days.

What I Changed

Driver Swap: Tang Band W5-1138SMF

The factory Helix enclosure uses two small dual voice coil (DVC) drivers. They are fine for what they are and easy to drive, but they're not built for serious output. I replaced them with two Tang Band W5-1138SMF 5-1/4" paper cone subwoofer drivers.

The Tang Bands are single voice coil at 4Ω each. They feature a vented pole piece for better thermal management, a large roll rubber surround for high excursion, and a paper cone that balances stiffness and weight well for bass applications. In a compact enclosure where the drivers are working hard, the improved excursion capability makes a real difference.

The mounting holes on the Tang Bands do not line up exactly with the threads on the enclosure, so you will either need to use wood screws like I did or modify the Tang Band mounting holes to get them installed in the sub.

Dedicated Subwoofer Amplifier: AudioControl ACX-300.1

The factory Helix amplifier powers both the door speakers and the subwoofer and does all that behind a 20A fuse. Pulling subwoofer duty away from the Helix amp and giving the new drivers a dedicated amp was the other half of the upgrade.

I chose the AudioControl ACX-300.1 which is a mono-amplifier rated at 300W @ 2Ω. It's a small but mighty subwoofer amplifier and has a number of features which make it a great fit:

• It accepts high-level inputs directly so there is no need for a separate line output converter (LOC).
• It has "AccuBASS" which is AudioControl's bass management circuit that compensates for the factory head unit's tendency to roll off bass at higher volumes.
• It has "GTO Signal Sense" which will automatically turn the amp on when it detects signal, so no remote wire is needed.

How It's Wired

Rewiring the Enclosure

I rewired the enclosure to pass four oxygen-free copper (OFC) 16 AWG wire to the new drivers as opposed to reusing the stock eight 18 AWG wires. With 300 watts RMS available from the amp, the stock wires are no longer adequate and should be replaced.

The Helix uses Molex connectors which makes it easy to disconnect things. I decided to do the same. The new wires get pinned into an 8-pin Molex connector so each driver gets independent runs. These are oriented in the same way so that I could theoretically still use the Helix amp to drive the sub.

AMP +  →  Pin 1 (Driver 1 +)
       →  Pin 3 (Driver 2 +)

AMP -  →  Pin 2 (Driver 1 -)
       →  Pin 4 (Driver 2 -)

Signal: Using the Helix Sub Output

Rather than tapping a door speaker or running a new signal source, I pull signal directly from the Helix amp's subwoofer output. The Helix outputs a filtered and DSP-tuned sub signal. Using it means the ACX-300.1 sees a clean, low-pass-filtered input with the Helix's Golf model specific room correction applied.

This is done using an 8-pin Molex connector that normally carries the signal from the Helix amp to the subwoofer drivers. I pull one channel pair from that connector and convert it to RCA which can be plugged directly into the ACX-300.1 input with the high input mode set on the amp.

Output: Parallel Wiring at 2Ω

With the two 4Ω SVC drivers, wiring matters a lot:

Wiring the drivers in parallel at 2Ω is the only configuration that makes sense here and allows for the full RMS capabilities of the ACX-300.1.

To do this, I created a jumper harness which connects the positive and negative output of the ACX-300.1 and splits into two separate wire pairs pinned into an 8-pin Molex that can plug into the sub.

AudioControl makes wiring the amp easy by providing pre-terminated pigtail leads for the speaker outputs. Each one has a weatherproof connector that plugs into the amp and bare wire-ends that you splice to your own runs, so the outputs unplug cleanly.

Power: Clean Run from the Battery

The ACX-300.1 gets a dedicated 8 AWG power run from the battery. I mounted a 30A resettable circuit breaker to the aluminum ECS Tuning battery tray. The button kills power to the amp or resets the breaker in one press.

The positive wire routes through the firewall grommet on the driver side, down the door sill, and back to the hatch. Ground is a short 8 AWG run to a stud near the rear seat, which I wire-wheeled to expose the chassis metal for a solid connection.

This video gives an excellent overview of running the 12V and ground wires:

The power and ground use the same AudioControl-supplied pigtail system, so the amp unplugs from power as easily as it does from speaker output.

Completed Install

Here's the full setup sitting in the spare tire well:

Everything tucks cleanly into the well and hides under the cargo mat. The ACX-300.1 sits in the lower cargo area, the Helix DSP is secured in the upper corner, and all connections are removable in minutes.

Results

The difference is immediately obvious. The Tang Band drivers have noticeably more excursion than the factory units, and the ACX-300.1 is delivering substantially more power for those low notes. Bass is deeper, louder, and better controlled even with the gain on the amp set low.

The bass no longer runs out of steam, nothing got cut, and the whole system unplugs in minutes. Exactly what a daily-driven track car needs.

Parts List