Goodbye Helix -> OEM+ Sound System Build Log

[username205]

After selling my previous vehicle, I swore I'd never hack up another car in the name of great sound. This led to me installing the Helix Soundbox to my GTI and it's been great for the minimal labor required to get it running. The issue is that some of my preferred genres have really low bass hits (30Hz) and the Soundbox flat-out omits those, probably to prevent from blowing the dual 6" subwoofers.

I held out as long as I could, but kept finding myself reminiscing about that wonderful, 3-way, fully active + infinite baffle setup from my previous vehicle. I reached a compromise and decided to scratch the itch while keeping a stock appearance.

Gear:
OEM VW MIB2 head unit
Dayton DSC-408 Helix DSP.3S digital signal processor
Pioneer GM-D9705 5-channel amp
Dayton Audio AN25F-4 1" silk dome tweeters (a-pillars)
Dayton Audio Reference RS180-4 7" woofers (front doors)
Peerless SDS-160F25PR01-08 6.5" woofers (rear doors)
Pioneer TS-A3000LS4 shallow-mount 12" subwoofer, fiberglassed over spare tire

The Dayton Audio woofer/tweeter front speakers (custom passive crossover) and Peerless rears (full range) were installed shortly after the Soundbox and will remain when the Helix is removed. I'd love to go 3-way fronts again, but there's no way to get that while utilizing the stock speaker locations. Also, the Helix Soundbox has shown me that, with some clever DSP trickery, it's possible to fill in the 2-way front stage's crossover region (2-4k Hz) with the rear drivers without ruining the soundstage. The Dayton Helix DSP is quite capable and should have no problem replicating this rear-fill trick, it'll just take lots of listening, tweaks, and time.

The subwoofer enclosure will be my first attempt at fiberglassing. Fingers crossed!

 

[username205]

Bench testing the test crossover (ignore the rough workbench, that's been corrected).

MDF baffles and foam tape were used to install the woofers up front. Low-pass filters were hot-glued directly to the door.

The upgraded tweeters and their high-pass filters were installed behind the a-pillars with copious amounts of hot glue.

Sound check before reinstalling the doors and pillars.

 

[username205]

First fiberglass layer down, 4-ish more to go. I now understand why custom fiberglass jobs are so friggin expensive

 

[Cuzoe]

Nice, I did a fiberglass box once, years ago... never again, haha. I'm running an AudioControl D-400.800 AMP/DSP now, after running Helix for several years.

I still have stock tweeters in the pillars and stock speakers in the rear doors. I have some infinity coaxes in the front doors but the surround on one of them is damaged so I'm going to replace both.

Might be copying your setup here for front speakers. I ran wiring (currently unused) to power the front tweeters directly from 2 channels of the amp (which will mean stealing those channels from the rear doors), and the front doors are already fed from the other 2 channels. Subwoofer is using the output from the D-400, feeding a separate sub amp.

 

[username205]

Nice, I did a fiberglass box once, years ago... never again, haha. I'm running an AudioControl D-400.800 AMP/DSP now, after running Helix for several years.

I still have stock tweeters in the pillars and stock speakers in the rear doors. I have some infinity coaxes in the front doors but the surround on one of them is damaged so I'm going to replace both.

Might be copying your setup here for front speakers. I ran wiring (currently unused) to power the front tweeters directly from 2 channels of the amp (which will mean stealing those channels from the rear doors), and the front doors are already fed from the other 2 channels. Subwoofer is using the output from the D-400, feeding a separate sub amp.

I didn't know AudioControl made amps as well. That D-4.800 looks nice, but also costs more than my entire setup plus a steak dinner

Yeah, def replace those shrill tweeters when you get a chance - even a $20 set would be light-years ahead of what was installed from the factory. The AN25F-4 plays low enough to mesh well with the RS180-4's relitively low crossover point (sucks that I had to cross right in the middle of the vocal range, though); I can post a screenshot of my passive schematic when I get back to my laptop.

How is your sub mounted?

 

[Cuzoe]

I would appreciate that schematic, I would much prefer to just leave the wiring as-is. And I like the idea of the rear door speakers as fill. I got the D-4.800 for just under $300 open box on ebay. All the plastic was still on it and the little wire speaker terminals were still in their heat sealed bags. This AudioControl unit is my first ever DSP and it's pretty intuitive, using the computer program, but it's definitely being underutilized with my tuning skill level.

My setup is shown here... with the only change being I now have the D-4.800 in place of the Helix/LC2i I was running before.
Sub is the discontinued Stereo Integrity BM MK V, mounted in an Uber Stealth Box
Sent specs when ordering, requested dual terminal cups for VC flexibility without the need to unmount the sub.

 

[username205]

For anyone interested, here's my front stage passive crossover schematic. The vocals are slightly forward and IMO it's not worth the extra work/parts to flatten that passively when a simple equalizer cut is available. On paper there appears to be a dip around 4kHz, but in-car response sounds much flatter. Crossovers were constructed with Dayton Audio polypropylene capacitors, air core inductors, and wirewound resistors.

combined response

mids

highs

 

[username205]

Made some progress on the enclosure, all that’s left is do the final fiberglass trim and secure the MDF baffle before carpeting.

Black primer on the underside.

Test fit - like a glove!

Level check before marking where to make the final cut. 0.00°.

Subwoofer fit test.

And it all fits under the cover!

 

[username205]

Finally got the baffle mounted. I’ll be adding 1 layer of fiberglass where the MDF meets the enclosure, then one final sanding and carpet.

MDF screwed through the sides, masking tape barrier to contain the resin.

Underside sealed with foil tape.

Resin poured.

 

[username205]

Over a week later and the fiberglass enclosure is finally done. It turned out great, but I could’ve installed four systems on the amount of time it took to build this box

Support dowels screwed & resined in place, carpet glued on.

Terminal & polyfill in place.

Subwoofer mounted.

 

[Cuzoe]

Damn thing looks great!

 

[username205]

Amp “rack” is complete. Things are moving much faster now that I’m done fiberglassing.

Cardboard mockup.

1/8” MDF trimmed and carpeted.

Super snug fit means I won’t even have to screw down the amp shelf. Still need to find a clean way to secure the sub though - maybe L brackets hidden on the sides?

 

[Cuzoe]

My amp rack looks just like that, and never moves without the need for any hardware. It's awesome.

 

[username205]

My amp rack looks just like that, and never moves without the need for any hardware. It's awesome.

How is your sub secured? Does it attach where the spare tire used to?

 

[Cuzoe]

I still have my spare. Sub box sits in it with some rubber on the bottom of the box so it doesn't move to left to right. It can't move front to back because it's "wedged" between the rear trim and the amp rack.

Been running in this way for a few years now including lots of canyon runs with no problem. And it all fits under the floor. The BM MkV requires very little space.