2021 GMC Sierra AT4 - Helix, Audiofrog GB, JL, Resonix

Hello all - this is going to be an abbreviated post from my upload to DIYMA.

https://www.diymobileaudio.com/threa...g-door.444799/

Going to be a long read but hopefully enjoyable to follow along with my rapid descension into the rabbit hole of car audio.

Finally had made arrangements to find a new 2021 6.2L AT4 in Satin Steel Metallic that had a confirmed delivery date to our local GMC dealer. This is a company truck for our family construction business. As most people know, inventory is literally nill nowadays and getting any sort of options on your vehicles (esp. GM trucks) cause major issues with delivery times. We found this truck with production spot but was coming with no options added but the basic AT4 trim is still decent enough. Love the truck and have had 3 of the previous Sierra body types. The 10 speed is fantastic and finally the interior are getting refreshed.

Before I jump into the audio side of this post, I wanted to briefly show what other mods have been done to the truck:

Exterior:

• 20x9 Fuel Vector Wheels
• 275/60/R20 Michelin LTX Defender Tires (Drive 99% on road and the stock Duratracs are noisy af/also have Nokian winter tires)
• Magnum Headache Rack
• OEM Off Road Running Boards
• Illuminated Black Front GMC Emblem
• Black Rear GMC Emblame
• Black CarbonPro AT4 Emblem
• Black OEM Exhaust Tips
• Truxedo Lo Pro Tonneau Cover
• Bed Mat

Interior:

• ProClip Phone Mount
• OEM All Weather Mats

Mechanical:

• S&B Cold Air Intake
• Pulsar LT Programmer
• J&L Oil Separator

Attachment 16966

Attachment 16967

On to the audio side of my journey:

I knew I was going to make some level of audio upgrades because the truck was not coming with Bose system and regardless, the Bose system is a sad system in itself. So I began to research. Hadn't upgraded car audio in anything except high school, had an Infiniti QX4 with Alpine HU, Kicker 700.5, Some Kicker Speakers and CompVR10 Sub. So I started by setting a budget - initially wasn't planning on a sub, just speakers and an amp only and put $1500 as my goal. Long term, boy was I naive on my wants vs price of components.

I am not going to post the other 3 previous audio builds that I did in this truck before I got the system I am posting here. Definitely check out the link above if you want to peak into the progression of the overall build. In short - I certainly underestimated how much time and effort I would sink into this because I find audio and how perceive music fascinating and a piece of advice to my past self. Save for what you want, buy once, install once - I learned a lot in practice but could have saved myself a lot of install hours and returning/selling items had I spent another few weeks researching and talking with experienced installers/DIY'ers.

Ok, on to the build.

My objectives were:

• As stealth as possible (company vehicle)
• Retain ability to return to OEM fit/finish upon trade as well
• Audiophile sound quality
• Accurate, slightly warm but powerful speakers and subwoofers
• Ease of use/straight forward integration with factory head unit
• Reduce/eliminate cabin noise and rattles

Attachment 16968


Parts list with description and reasoning for purchase:

Speakers:

• Front Stage
  
  • Doors - Audiofrog GB60
  • Dash Corners - Audiofrog GB15
  • Long term going to do 3 way - not sure what combination of drivers yet though
  
  
• Rear Stage
  
  • Audiofrog GS62 - 6" Coaxial

​Subwoofers:

• JL Audio Stealthbox with two JL Audio 12" 12TW3-D8 Subwoofers, wired to 2 ohms
  
  • It was between this and a custom box from MTI Acoustics in Texas. I settled on this because of the pocket it provides for the amps, it's sealed fiberglass (extremely well built) and can be installed or removed in under 20 min without any factory modifications. It also ended up cheaper and much faster to ship than the MTI set up. I think I ultimately would have been happy with either.
  • Now that I have them properly tuned and powered with my current Helix P One mono amp (giving them about 900W), they are excellent shallow subs. They play flat down to around 28-29 hz, which I am very happy with considered they are sealed and very thin 12s. I tune towards sound quality with some good low end punch but when I push my sub gain up on the Conductor, they will flex the windows and mirrors on my doors.

Amps and Controller:

• Helix V8 DSP Amp with HEC HD Bluetooth Card
  
  • 75W x 8 @ 4 ohms or 120W x 8 @ 2 ohms
  • Probably the decision I hesitated with the most until talking with Skizer (Nick). The online community seems to have a perception that midbass or midrange/woofers need to be overpowered to get the output folks need to listen loud. While at the competitor level I'm sure can certainly be true, I don't think it is nearly as important at the common car audiophile level. Most folks run their GB60s at 150 watts+, I run mine at 75 watts with the V8 and they get louder than my ears can handle and I listen to music very, very loud in general. Understanding power to SPL ratios helped me settle my brain a lot. And then just hearing them sold me and then some.
  • There is literally no noise in the system, it's so clean and quiet that I think something is wrong at times. It's also a TINY foot print for an 8 channel amp which was important for me to fit all of my amps under my rear seat. Build quality is S Tier.
  
  
• Helix P One Mono Amp
  
  • 1 x 500W @ 4 ohms, 1 x 880W @ 2 ohms, 1 x 1500W @ 1 ohm
  • My subs are wired @ 2 ohms, rated for 400W, each
  • I scored a great deal from a community member on DIYMA otherwise wasn't actually looking at this amp because of the price tag. I was originally looking at the Helix M One X or the Mosconi Pro 1/10 because of their size.
  • This amp will allow me a ton of flexibility in future builds compared the M One X.
  • When I compare this to 600W I was previously getting from my JL XD1000/5 amp, it is night and day. Output, cleanliness and build quality are much, much better.
  • Also fits extremely well in my under seat location
  
  
• Helix Conductor
  
  • Controls my master volume, subwoofer gain (0.5 db increments), rear fill volume and several different audio presets
  • It's a sexy little piece of engineering

Input Signal:

• Digital (Music) (in order of sequence)
  
  • iPhone 11 Pro Max to
  • Apple CCK3 Camera Kit (powered from a USB-C to Lightning cable plugged into my center console) to
  • Audioquest Pearl USB A-B Cable to
  • Topping D10S DAC (Digital Audio Converter) to
  • Audioquest Pearl Optical plugged into Helix V8 Amp
  • This is what I use to play music directly from phone while completely bypassing the head unit and avoiding any un-needed digital to analog and analog to digital conversions of the signal. It has made a nice difference, especially on Master versions of tracks on Tidal. The Topping D10S is simple and just works.
  
  
• Analog (OEM Bluetooth Sound, Navigation, Phone Calls)
  
  • LLJ Customs out of Arizona who specializes in custom wiring harnesses. They make a full plug and play wiring harness that intercept the 4 high level speaker outputs under the glove box and provides a long harness to mount your amps anywhere in your vehicle. I got the Loopback option which also includes an additional set of speaker wires that use the OEM speaker wiring without splicing, it is a massive time saver. I also had them added an extra set of speaker wires for my tweeters as I was going to go active. Overall a great investment for someone who wants plug and play DIY, just take 5-6 weeks to get.
  • The Helix software auto swaps from Digital to Analog when I get a call and back again seamlessly when the call ends.
  
  
• OEM Controls/Carplay
  
  • If you keep your phone connected to the truck via BT AND use the Apple CCK3 Kit that lets you select which audio output you want, you can have a digital signal out AND retain all OEM controls except master volume. I use the Conductor for the master volume now which actually I prefer over the HU or steering wheel.
  • Carplay - if you have wireless Carplay, same thing. You can retain it via BT but the current iOS software recently screwed up the audio output function and swaps the audio out to Bluetooth every time you swap songs. It is a known issue that supposedly Waze messed up.

Sound Deadening:

• Outer Door Shell
  
  • Resonix CLD - Performance vs value - it's the best. About 75% coverage on outer shell, beyond this becomes diminishing returns
  • Dynamat Dynaliner CCF 1/4" - Added about 50% coverage of the outer shell with some 1/4" closed cell foam I had left over from my earlier builds.
  
  
• Inner Door Shell
  
  • Soundskins Pro SSK Kits - I bought these as an all-in-one timeaver CLD + CCF deadening solution to seal the inner door shell. The paper is a pain in the ass to peel off during application but they are well made and my doors are literally air tight now.
  
  
• Inner Shell of Plastic Door Panel
  
  • CLD + CCF @ Speaker Pockets
  • Dynamat Dynaliner 1/4" - About 50% coverage to help with rattles
  
  
• Tessa taped all of body clips
• Soundskins Rings @ all speakers

Custom Work:

• Custom ABS speaker mounts - CNC'ed by Delander from DIYMA - a really nice rigid solution to mount to the doors and speakers with
• Custom center console Conductor mount - CNC from Delander, assembled and finished by me and honestly my favorite finish piece of the build.
• Custom ABS amp rack - probably a reach to call this custom but it was a planned and fabbed piece.

Will be posting the entire build process tonight...hope you folks enjoy!

Looking forward to lots of pics... I do mean LOTS... :D

So from the top, here we go. Going to post the build in this order. Sound deadening, speaker install, subwoofer install, input signal, amp rack and wiring, Conductor mount and then some final highlight reel shots.

So first step was getting a full tear down of my doors, A pillars, dash corners and few pieces of my center consoles:

Attachment 16969

Old components: Audiofrog GS60 + GS10 + GS62 (Kept my GS62s for this build but replaced the mounts)
Attachment 16970Attachment 16971

Door condition at beginning of build, existing weather barrier, some limited Dynamat CLD at the speakers and I had Dynaliner CCF on the outer door panels (which was useless and a pain to remove but necessary to properly treat the doors this go around):
Attachment 16972
Attachment 16973

Stripped and ready to treat:
Attachment 16974

All 4 doors have about 75% coverage on the outer door shell with Resonix CLD and Dynaliner 1/4" CCF:
Attachment 16977Attachment 16975
Attachment 16978

Then I moved on to treating the inner shell of the doors with the SoundSkins Pro SSK Door Kit. The paper was a pain to peel but the doors are literally air tight at this point and I am very please with the fit and finish:
Attachment 16979Attachment 16980

All 4 doors treated:
Attachment 16982Attachment 16981

Nice and clean, air tight opening at the OEM speaker locations:
Attachment 16983Attachment 16984

Then I moved on to trimming and cleaning up my inner door plastic panels. I had previously applied some CCF to help with rattles but this time I added from leftover CLD I had to the local surround at each speaker location, trimmed the plastic extrusion to prevent conflicts with my CCF rings and finally tessa taped all my body clips:
Attachment 16985Attachment 16986

Panels with CCF and clips tessa taped:
Attachment 16987Attachment 16988

I can honestly say, I've yet to hear a rattle in my doors. I can barely hear my tires are highway speeds now, can't imagine what it would be like if I fully treated the doors and rear wall of the truck.

Can't wait to see more, great work so far. I covered my Silverado doors like you did. If I had it to do over again I would have sealed up those holes even better with some wood or plastic. That material will still flex under heavy midbass impact. I didn't think I was lacking midbass at the time but now in hindsite I would have deadened even better. Something to think about if you still have the panels off.

From here, I moved on to getting my speakers mounted in the doors. I worked with Delander to create the custom ABS mounts for the GB60s and GS62s and some acrylic rings for GB15s. The fitment was great, only needed some minor trimming on the GB15 mounts.

Here are the mount design and after fabrication (before they were shipped to me):
Attachment 16989
Attachment 16990

Started with getting the GB60s drilled and tapped on to the mounts before I fit the mount to the door:
Attachment 16991Attachment 16992

Attachment 16993Attachment 16994

Didn't take photos of the GS62 prep but same thing. Then I move on to prepping my GB60 wiring. I used the harnesses I got from Crutchfield from my old builds that allow me to plug and play into the OEM harness without splicing:
Attachment 16995Attachment 16996

Then finally through bolted the mounts with stainless hardware and lock washers/nuts, CCF taped the opening and mounted the speakers:
Attachment 16997

Quote:

---

Originally Posted by Stycker

Can't wait to see more, great work so far. I covered my Silverado doors like you did. If I had it to do over again I would have sealed up those holes even better with some wood or plastic. That material will still flex under heavy midbass impact. I didn't think I was lacking midbass at the time but now in hindsite I would have deadened even better. Something to think about if you still have the panels off.

---

Good to note - May ask Nick to cut me some plastic panels for the front doors openings if I swap to an 8" midbass in the future when I go to a 3 way set up. Project is all closed up at this point but I think I have taken these doors off a dozen times so it wouldn't be a huge deal to add those panels.

Then added Soundskins CCF rings to all 4 door speakers:

Attachment 16998Attachment 16999

A before and after of the doors:

Attachment 17000

From here, I jumped to my GB15s. Started by getting some 47 uf, 100V caps installed on a small harness to each tweeter:
Attachment 17001Attachment 17002

Then got the acrylic mounts butyl taped front and back then got the tweeters mounted in the brackets and added some CCF foam rings:
Attachment 17003Attachment 17004

Then dropped the tweeters in the dash and wired them up:
Attachment 17005Attachment 17006

Subwoofer: I had installed the JL Stealthbox as part of my previous builds (aka why you are seeing the JL amp and LCQ-1) but wanted to show a few pics of the fitment and unit itself:

Two 12TW3-D8's wired @ 2 ohms and the amp shelf/pocket.

Attachment 17007Attachment 17008

Installed under rear seat (Again - from my old install):
Attachment 17009Attachment 17010

Seats down:
Attachment 17012Attachment 17011

From here, I moved on to my input signal. I have two items here: My LLJ harness for analog and my Topping D10S for digital.

Here is the LLJ Loopback Harness and where it plugs in under the glove compartment. Has 2 twisted pairs of wires providing high level speaker inputs to my Helix V8 for the factory BT (phone calls and navigation), chimes and FM/AM. Then it also have 6 twisted pairs of speaker outputs - 2 twisted pair each to utilize the OEM wiring of front and rear door speakers and 2 additional pair for the tweeters to bypass the OEM crossovers going to the dash corner locations. It also has a 12V feed and ground for something like a LOC or DSP - I just never used the ground as it caused ground loop noise when I tried it out on my old set up.
Attachment 17014Attachment 17013

Digital Signal: It was probably to aspect of my built that was going to the most design on the fly but very happy with the outcome. Decided I was going to mount the Topping inside my center console after trying out a few locations and was hoping to retain some access to the device visually and wiring wise but still keep it stealth.

Started by drilling holes in the bottom of the console and the console liner. Put some rubber grommets to protect wires:
Attachment 17015Attachment 17016

Nice and clean penetration with grommets:
Attachment 17017

Used some VHB, Dual Lock Velco to mount the Topping:
Attachment 17018Attachment 17019

Mounted and really like the concealed wiring but easy to get to. Audioquest Pearl Optical and USB A-B cables to a Apple CCK Adapter. Easy to open the console check the sampling rate.
Attachment 17020Attachment 17021

The amp rack was probably my most pre-planned aspect of the build. Designed the rack in CAD to give myself some additional shelf space behind the V8 for my distribution blocks (wanted clean fuse access) and this was my final layout:

Attachment 17022
Sourced some 1/4" ABS and got the shape cut out and corners rounded. I ultimately ended up scuffing the surface and putting 2 coats of SEM Trim Black paint as I didn't want the gloss black look. It also helped keep static way down and no more fingerprints :)
Attachment 17023Attachment 17024

I then mocked up the V8 (covered in packing tape to protect during the install/fab process) and made some final layout adjustments for the holes needed for the connections to the V8:
Attachment 17025Attachment 17026

From here - I began to pre-drill all of the holes I was going to need for power and speaker wiring. Loaded up my drill press and went to town and then mocked up with the distro blocks mounted
Attachment 17027Attachment 17028

Got my new P One amp the next day and then added that the amp rack and confirmed layout. Picked up a couple 90 deg Audioquest RCA adapters that gained me some critical clearances on the input side of the P One.
Attachment 17029Attachment 17030

Then finally, dropped the rack in for a quick test fit, can't lie, this part got me so excited that I ended up working most of the night on the truck:
Attachment 17031

Then came wiring and tidying up the amp rack.

Mounted the amps on some small rubber washers and through bolted them. Trying to isolate them from as much vibration as I can as they are mounted on my sub enclosure:
Attachment 17032Attachment 17033

From there, I wired up the amp rack (to the extent I could outside of the truck) and added a couple layers of 1/4" CCF to the bottom of the rack to conceal the nuts and provide some additional vibration isolation:
Attachment 17034Attachment 17035

Then finally I dropped the amp rack in and wired it all up. Sat for a good half hour after I finished this phase and just enjoyed the view, stoked how well it came out for an amateur install:
Attachment 17036

Clean and tidy, easily accessible for service.
Attachment 17037Attachment 17038

Getting interrupted from uploading for a few hours but still have the Conductor mount fabrication, "finish product" photos and some tuning to cover.

Great work... and nice "big" drill press! What brand of distro blocks are those, don't think I've seen them before?

Thanks man! - Those are T-Spec Distro blocks - T-Spec v12 Series VDB2 - Ground Block

T-Spec v12 Series VFDB2 - Fused Power Block

The Conductor and its mount - this one piece drove a ton a major decisions in my system - swapping to digital input with my vehicle (no NavTV currently offered) meant an alternate control for master volume and I wanted to retain subwoofer gain control up front as well. The Director is nearly impossible to fit without major cosmetic modifications and I didn't care for the look or mounting options of the URC.3 - so the Conductor was my go to piece. I worked through several mounting locations and settled on making a mount in my center console cup holder. Again, another easy piece to remove and place a small plug to cover the small hole I drilled when I trade the vehicle.

This is from concept drawing, paper mock up to final implementation:
Attachment 17039

Now how we got there. I worked with Delander from DIYMA to take my CAD design and have him make some pieces from polycarbonate that I would then assemble and finish. The design:
Attachment 17040Attachment 17041

Then cut with his CNC:
Attachment 17042Attachment 17043

Then I glued, sanded, testfit, sanded some more and then finally painted (primed with Krylon then used 4 coats of SEM Trim Black:
Attachment 17044Attachment 17045

And the money shot, almost looks OEM:
Attachment 17046

And finally my favorite shots of the final build:

Attachment 17049

Attachment 17047

Attachment 17048

From here - we tuned :happy:

I started initially using the AutoEQ feature in the Helix Suite with a UMIK-1 and honestly got some decent results. A little boomy in the 500 - 2k hz area but honestly for a 5 min tune, it was very passable.

Parameters for AutoEQ were:
All crossovers were LR 24db/octave
Subs were 20hz HP and 80hz LP
GB60s were 80hz HP and 1800hz LP
GB15s were 1800hz HP only
GS62 in rear were 80hz HP only

Attachment 17050

I played a bit with it but eventually got a remote tune. I hooked up with Shannon Price this Saturday to knock out a a basic remote tune of the system. He was very competitively priced and figured it would at least be a small crash course in witnessing how he tunes, measures, adjusts, etc. as I have never seen the process done live. He spent a couple hours with me and got me pretty much 90% there and I tweaked the rest of the way to finalize the center of the stage, integrate my rears and global EQ.

In full disclosure, I ran out of time to save my final measurements properly (new REW user) after I integrated my rear speakers and did some final global eq adjusting. The small hole you see @ 50-60 hz is filled and I took a touch off of the hump at 80-100hz to create a much more linear rise from 200 hz up to ~35 hz. I have rears crossed at 155 hz, 24 and 5000, 24 - this helped keeping them from distracting from my front stage at all, just a compliment.

Overall, this was a drastic step up from the AutoEQ but still think the AutoEQ has a ton of value vs time invested tuning.

I had Shannon measure my the autoEQ in red and it is shown here against his final tune (before my rears were added and my Global EQ adjustments) and you can see the big improvement. I had suspected my 200 - 1000hz was off after realizing things sounded a little boomy, esp with lower male vocals, lower end guitar/piano notes and that certainly seemed consistent with the measurements we saw.
Attachment 17051

We started on the left side - GB60s crossed at 80 hz, 24db and 1800 hz, 24db. This shows left mid, left tweet and both measured together. Had a little hole @ 800hz that we boosted gently to ease the curse but mostly disappeared once we got the whole front stage tied together.
Attachment 17053

Right side of the front stage. Had a nasty hole at 200 hz that again blended mostly away after we got the whole front stage together.
Attachment 17054
Left Front Stage, Right Front Stage and Overall Front Stage. Ended up quite balanced.
Attachment 17052
From there, we added the subs. Ended up inverting the polarity of my subs and crossing them at 64hz, 24 db to deal with some issues we were having at the 80-150 hz area. I have to say the the blending of my bass to midbass and location of where bass is coming from is superior with this tune. Feels like the bass rises universally from the floor of the vehicle.
Attachment 17055

Overall, the system just gets better with time and break in. I will continue to tweak some really minor things and hopefully can make some time to hook up with Nick for an in person tune later this spring. I think that will be another big step forward but right now, with the tools at my disposal, I am stoked. The ability to hear a bass drum getting hit by the pedal AND feeling it in your chest is hard to explain to the average listener. Or hearing the breath and tongue clicks between words, the strings of an upright bass vibrating off the fingerboard in Lake Street Dive recordings just makes me want to sit and listen to everything again. I also now notice a distinct difference between well mixed music and poor recordings, it's amazing how much more detail you pick up on.

I am currently playing around with adding the bass augmentation because I find at lower volumes (when I have passengers), the low end is lacking without a major adjustment to the my sub gain on my Conductor. I will probably experiment with differential real fill and the stage expander as well to see what it does.

Lastly, this is what my Helix EQ looks like.

Attachment 17056

Now to begin designing and dreaming about 3 way front stage combinations that fit in these pods:

https://www.instagram.com/p/CBtiKFfp...e-fb3421979177

That looks awesome! I love the attention to detail.
One of my bosses has an AT4 with the same Fuel Offroad wheels that I have on my Z71

Cool, I appreciate the info!

Awesome choice on placement of the Conductor... very clever use of space!

Welp 2 way lasted 2 weeks.

Just pulled the trigger on a juicy 3 way from BLAM.

WS8.100 - 2 ohm, 8” mid bass
Multix MS3 - 3” midrange
TSM 25Mg 45HR - 1” Tweeter

Will have the GB60/15 for sale in a few weeks. Looking for $1150 for the combo, will have only a month or so of use.

damn excited to see what this 3 way is capable of, esp with a tune from Nick.

Great write up....very interesting to me as I am in the early planning stages of a 2-way active in my F150. My question the whole time reading was....why didnt you use a Helix P6?...then I read your last post about going 3-way. Did the 2-way...just not do it for ya? My initial plans are to do a 2-way..using the P6 to power frts and re fill. With thoughts going of leaving 3-way down the road a year or so later and eliminate the rear fill.

Any thoughts/suggestions on my plans after going thru it yourself?