Sound Quality - Some Expense Spared

Patches2 · January 22, 2024

Hey all, I wanted to share my build log for my 2023 Sierra SLT. It's still a work in progress, but this information may be useful for anybody thinking of starting an audio project and navigating the mess of (mis)information between model years of the same generation truck.

My goals for this project are

Improve overall sound quality. My truck came with the Bose "premium sound" package with 6+1 channels of below average sound. Stock settings were not great and I was able to get passable sound by bumping bass to around +4, mids -2, and treble +4, but the configurability options are completely disappointing for a modern vehicle. I'm even more disappointed that somebody decided to brand this "premium" instead of simply writing "has speakers and amplification to reproduce sound." No need to lie to us... I think the only worse sound system I've heard in a modern car was from a Mazda MX5, but honestly, who cared about fidelity when the top was down?
Be stingy where possible. I'm a sucker for punishment and doing things the hard way. I've been messing with car audio in some form for about 15 years now and while I learn and move forward, I've retained the "paying for installation is for suckers" mentality. Projects like these help keep me sane.
Use quality components. Saving on the installation lets me spend just a little bit more on good equipment. Not the best, but not throwaway-tier trash. I try to source gear that will perform well and last. Rarely do I splurge for top-of-the-line stuff, especially for a loud pickup truck that's on kid duty for a nonzero amount of time.
Keep some interior storage. I have pets and kids. It's useful to keep stuff under the rear seats for emergencies and I'd prefer to not have to resort to loose gear or worrying about cleanliness and upkeep of things kept in the bed. This means no monster multi-sub setups under the seats.

Next up comes the component list. I'm aiming for SQ without breaking the bank. Full retail price (most of these can be had for less) is around $2k for a complete setup. Factor in another $100 or so for cabling and tools if you're starting from scratch.

Pioneer TS-A709 2.5" speakers in the dash
NVX XSP692 6"x9" speakers in the front doors
Pioneer TS-D65F 6.5" speakers in the rear doors
Alpine PXE-C80-88 DSP/Amp
Fox Acoustics 12" vented sub box (passenger side) with storage cubby (driver side)
NVX VCW122v3 12" 2 ohm DVC subwoofer (while the SI SQL12 is in transit, ETA March?)
Stereo Integrity SQL 12" v2 2 ohm DVC subwoofer
Dynamat Extreme bulk pack (referring to as CLD)

Stage 1

I started out by replacing all of the speakers. Dash speakers are relatively straightforward to swap out. Two bolts behind each grab handle in the A pillars and some tactful pulling gives you access to pry up the entire front portion of the dashboard. Disconnect the blinking red LEDs and all that's left is two screws per speaker. The OEM speakers seemed to have identically sized magnets compared to the replacement Pioneers. I'm not entirely sure that the tweeter is real as I can't see any wires that run up to the center. If these end up disappointing, I've considered splurging for the Audiofrog GS25's as there's not a whole lot available in this size.

Next up I replaced the rear door speakers. Removing two bolts in the middle of the pull handle of each door and an additional one along the bottom edge of the door card lets you tug the entire card up and out. Disconnect the wiring harness and then unclip and guide the little handle pull out and you can safely move the panel to another location. While in each door, I applied some CLD to approximately 25% of the skin of the door and around 50% for the inner portion, taking care to try and seal the cavity as best as I could. I then removed the OEM speakers held on by one bolt and pried the assembly out of the door. I didn't purchase any adapters, so I repurposed what the factory gave me. A large note of caution - do not use powered cutting tools while working on this plastic assembly. It smells absolutely awful and appears to be a fiber reinforced plastic. I first cut the cone and surround for the OEM speaker and tore out the top half of the speaker. I then used an oversized pair of channel locks to systematically break down the plastic support structure until I could remove the bottom portion of the speaker. I then channel-locked away some more until I was left with the shell with a roughly 6.5" speaker sized hole in the middle. It's a smidge too small for the Pioneer speakers I stuffed in with some foam to help the seal, but it worked well enough once motivated with some screws. If you go this route, you may have to modify the backside of the door card in the speaker area. I noticed that the replacement speaker is just large enough that the plastic supports collide with the metal mounting ring. In any case, I spend a little time applying more CLD to approximately 25% of the door plastic just in case. Might not be needed, but I'd rater not keep tearing into the doors.

Replacing the front door speakers is largely the same as the rear doors. This time, the stock 6"x9" speaker mount could not be reused because the oval shape was too different. I drilled four small holes and mounted the NVX speakers directly to the door skin with some healthy amount of foam gasket material to keep the seal. One note is that if you apply aggressive sound deadening material to the door cavity, you'll either need to account for a protrusion from the door card or cut it off to allow for everything to come together. Photo of the area I'm describing.

Stage 2

Here I performed a bose-ectomy in an attempt to gain control of the system. There's probably a dozen different ways of skinning this cat, but this worked out for my needs. You'll need to first run power from the battery to the back of the cab. I've taken a few photos of "lessons learned" areas that I'll upload later on. I found that running 4GA cable from the battery to the passenger side fender and through a grommet in front of the passenger front door was a great way to enter the cabin. Here, I ran the cable under and along the plastic trim all the way to the rear wall of the truck. There's some built-in conduit that GM has so kindly provided that works great. Photos of the passthrough for anybody who's curious.

Next I removed the top portion of the rear seats. This entails removing all three headrests, prying the headrest receptacles out, and removing 4 bolts along the underside of the rear seat. You can then use whatever means available to release three latches along the upper portion of the seat to fully release the unit. Gently lift the seatback out and place it somewhere safe, because you may be spending a lot of time at this stage.

There's plenty of space on the back wall for activities, but I wanted to keep the Bose amplifier close to the Alpine amplifier to minimize the amount of wirework I needed to do. I unbolted the black box (an inverter?) and placed it along the driver side of the cab with some toll pass velcro. It has worked well with heat in my experience. I then modified one of the Alpine's brackets by drilling some holes to fit where the inverter once did. This kept the two amplifiers close and cozy, ensuring that cable runs would be kept as short as possible. Next, I did some damage to the wire harnesses coming out of the Bose amplifier. One of the attachments to this post is a wiring diagram that tells us exactly what cables to cut. The X1 connector (top, 8 wires) carries the output for the front doors and the subwoofer. Cut all of those but keep the battery and ground. The X2 connector (middle, bunch of wires) carries the output for everything else. My truck didn't have any center channel speakers, so I cut everything. The X3 connector (bottom, 4 wires) carries the audio data from the factory radio to the Bose amplifier. In previous years it contained some sound canceling wiring, but that's not a thing for at least my truck. Ideally, we'd be able to use the raw unadulterated and unamplified signal sent over the bus, but entire companies exist to decode and sell expensive solutions for this. A DSP will have to do.

I now have two connectors with cut wiring. There's a connector side, which basically takes the Bose output and routs to the input for the Alpine unit, and a harness side, which the Alpine unit outputs back into to reuse stock speaker wiring. This is why I wanted to keep cable lengths short. Nothing is less fun than crimping or soldering 12 individual wires, taking time to verify that you aren't crossing signals, more than two times. It wasn't even fun one time. Of note, the stock subwoofer wiring goes into the Alpine from Bose, but the harness side I taped off and fastened to the wall. We won't be using the stock subwoofer and removing it seems to be a colossal PITA and doesn't recover any useful space from under the center console.

After getting the input/output connectors for the Alpine built, I went about applying some CLD to approximately 30% of the rear wall. I saw some other builds applying some CLD to the little vents and decided that I had nothing to lose, but that got annoying quick. I then finalized my wiring paths and used some adhesive clips to keep things tidy. A lesson learned for this step would be to pay attention to where foam is on the seatback. If you move the inverter, you may want to trim some foam near its new home.

Once everything seemed to be ready, I began inserting connectors back where they belonged, wiring up the amplifier for power and ground, and getting the subwoofer cabling rear. I also made some space for the Alpine control unit running along the driver's side conduit, under the drivers seat, and to the middle console. It's just hanging out until I decide where I want to permanently mount it.

Photo of the mostly finished setup.

I connected power to verify operation and began reinstalling the rear setback. No nasty surprises or fires here, I still get sound and the Alpine unit connects to my phone over Bluetooth and the little control pad displays some basic information.

Stage 3

I purchased a Fox Acoustics GM-CC-112-V-19-P-STORE subwoofer enclosure for under the rear seats. The driver side contains a large storage cubby while the passenger side is a 1.8 cuft vented 12" subwoofer box tuned to 33hz. I thought this product to be a good compromise between sound quality (low tuned vented, deep-ish subwoofer mount depth at 7.5" and interior storage space. I've moved the jack and tools, along with a first aid kit and small emergency bag in the storage compartment with plenty of room to space. I've made a small modification to the enclosure by adding a pair of terminals to the box to allow for a two-channel wiring solution for each of the sub voice coils. The Alpine amplifier doesn't allow a bridged sub output, so I need to run two sets of signal to the woofer to maximize available output. Once the SQL 12 comes in, I may replace the NVX unit. The NVX sub has a pretty beefy surround with 23mm xmax but I've seen no evidence of contact with the floor. So far so good.

I set up the Alpine Optim8 using both my phone and a computer. The instructions were pretty basic and I'd argue slightly misleading. You will absolutely need a computer to set things up. The phone application will only perform the auto EQ tuning feature. The computer application lets you do everything else you'd expect from a DSP. There's lots of functionality that I didn't end up using, but the gist of my setup was to set the inputs and outputs and adjust crossovers to match the aftermarket speakers. I tested a few songs and noticed an immediate and positive change in sound quality for the better. I may keep tweaking down the line, but I'll probably hold off on anything large until the subwoofer comes in. Again, the sound quality with no subwoofers present (6" Bose sub was disconnected earlier) is already leaps and bounds better than what the truck came with.

TODO: Upload newer photos of the measurements and auto-EQ lines.

The End?

If anybody has any questions, feel free to ask!

Amplifier wiring.pdf

Edited February 7, 2024 by Patches2
Added some links to installation pictures, installation notes for front door speakers, preliminary tuning results

Patches2 · February 7, 2024

Finished a significant portion of this build.

I substituted a NVX VCW233v3 for the SQL12 so I have a subwoofer while the intended speaker is still on a container ship somewhere. They model pretty close to each other, so I'm not anticipating any drastic differences.

One huge point of grief I've found is the Alpine DSP software. It sucks. There's no way to view the measured and applied EQ curves that you take on your phone on a computer. The Anti-EQ section of the application comes with almost zero documentation, has nothing on YouTube or DIYMA, and doesn't seem like something that is meant for human use. The RTA in this section is extremely crude, with level markings every 40db. How are you supposed to make anti-EQ adjustments if you're eyeballing peaks and valleys with 40db of range between hash marks?!

I'm now working on some other mods that I might just lump into this topic as an overall build log. I have a magnetic phone charger mounted to the left of the steering wheel and some footwell lighting installed. I am working on an amber headlight mod at the moment, but working with the molex mx150 connectors is tedious. I'm trying to do something plug and play because these lights are expensive.

Edited February 7, 2024 by Patches2

0ldSoul · February 12, 2024

Hey thanks for documenting this build. That box is neat! I like that it still retains some storage on the opposite side. Any pictures you're willing to upload to show how much it sticks out under the seat? From the manufacturer's website, it seems like it sticks out just a hair, but not by much. Have you sat back there? Can you feel it at all?

romeactual · February 13, 2024

Extremely detailed build! Thanks for putting ideas in my head.

I want to add my experience, but please note I am a bass head (SPL stuff). I currently have a 15" Soundqubed (SQ) HDX3 running on a SQ 2200D at 1ohm, its in a 3.5cft box tuned to 30hz. I haven't metered it, but its loud and respectable in my opinion. Its not making people tap out or anything, but its in your face bass. Surprisingly, stock electrical is holding up good too.

I have always hated on Bose, but I will say - When you turn bass -10 or -12, the mids and tweets are greatly improved on the stock Bose speakers. Historically, I could never add this much sub to an older vehicle and get away with stock speakers. I always ran amplified mids and tweets prior. These scream and are loud enough to play along with the subs. However, in terms of sound quality, I know many would complain.

I wonder for ease of trying, should I attempt to replace the A pillar speakers and/or door speakers but keep them on the same Bose amp? I know they can be weird impedance speakers. I really don't want to wire a new 2 or 4 channel amp, just seems like a lot of work. I haven't been able to find write ups about this but seems like based on your experience, its pretty easy to swap out those speakers.

Thanks again for detailing your build!

Patches2 · February 13, 2024

22 hours ago, 0ldSoul said:

Hey thanks for documenting this build. That box is neat! I like that it still retains some storage on the opposite side. Any pictures you're willing to upload to show how much it sticks out under the seat? From the manufacturer's website, it seems like it sticks out just a hair, but not by much. Have you sat back there? Can you feel it at all?

Sure, I took a pair of photos with the seat up, exposing the storage cubby, and with the seat down. Ballparking it, the bottom edge seems to approach about where the speaker protrusion begins and the top tapers to about .5" out from the bottom of the seats.

You notice the box when you're getting in the vehicle as you may rub your feet against the corner while stepping up. Adults won't feel anything sitting down because the seats aren't tall enough to tuck your legs back. Children might, but I've heard no complaints.

Adults may notice the sub hump on the passenger side due to how it sticks out. I was okay with this and this is what lets the enclosure accommodate a 7.5" deep sub. As far as I've seen, its the deepest on the market that doesn't require seat height mods.

The storage cubby is much larger than the OEM box and you even have some space behind where you can tuck things like wires, zip ties, etc.

Patches2 · February 13, 2024

4 hours ago, romeactual said:

Extremely detailed build! Thanks for putting ideas in my head.

I want to add my experience, but please note I am a bass head (SPL stuff). I currently have a 15" Soundqubed (SQ) HDX3 running on a SQ 2200D at 1ohm, its in a 3.5cft box tuned to 30hz. I haven't metered it, but its loud and respectable in my opinion. Its not making people tap out or anything, but its in your face bass. Surprisingly, stock electrical is holding up good too.

I have always hated on Bose, but I will say - When you turn bass -10 or -12, the mids and tweets are greatly improved on the stock Bose speakers. Historically, I could never add this much sub to an older vehicle and get away with stock speakers. I always ran amplified mids and tweets prior. These scream and are loud enough to play along with the subs. However, in terms of sound quality, I know many would complain.

I wonder for ease of trying, should I attempt to replace the A pillar speakers and/or door speakers but keep them on the same Bose amp? I know they can be weird impedance speakers. I really don't want to wire a new 2 or 4 channel amp, just seems like a lot of work. I haven't been able to find write ups about this but seems like based on your experience, its pretty easy to swap out those speakers.

Thanks again for detailing your build!

Happy to document. I always found similar guides helpful when I was planning prior builds.

I don't really remember the stock bose sound, but the Alpine PXE whatever does allow me to "un-eq" and run a more or less straight through signal to the speakers. Running unprocessed the sound is very mid-focused.

I've had similar experiences. I've had to dial back highs and tweeters in past builds because the stock speakers were usually okay in that respect. The stock Bose dash speakers are terrible at reproducing higher frequencies.

I've gotten away with adding just subs once in an old first gen Cadillac CTS. I turned the trunk into an IB setup with two Image Dynamics IDQ12s. It was kind of ridiculous, but I learned a lot about sealing compartments.

Edited February 13, 2024 by Patches2

Patches2 · March 25, 2024

Perhaps the last real content update bump.

I finally got a Stereo Integrity SQL 12" D2 in that I preordered a little while ago, so I decided to swap out the subwoofers and redo some EQ work.

First: the SQL 12 is amazing. Despite modeling almost identically to the NVX VCW122V3, it sounds so much tighter, faster, and lower. Sensitivity seems to be about 6db higher, so I turned down the gain going to the subwoofer. Only downsides are that I needed to make the cutout a little larger and that the mounting holes are really close to the spider. If you aren't precise with your cuts, you'll probably need to put some screws in at an angle.

Moving on, I've come to the conclusion that the Alpine Optim8 PXE-C80-88 isn't the autotuning wonder it is seemingly hailed to be. The automatic EQ feature only really affects how the speakers sound if given a perfectly flat signal. Anyone with BOSE knows that this clearly isn't happening. The anti EQ is manual and crude. The small RTA is measured in increments of like 20dB, meaning that it's functionally impossible to undo signal modifications with just the built-in software.

I caved and used REW to measure the frequency response and generate a fairly flat Harmon curve. I've applied the 17 corrections and gave a quick listen. I might perform a second measurement in the future to see how close the suggested EQ points got to a linear response.

Edited March 25, 2024 by Patches2

Sherly Gavell · March 25, 2024

interesting

Badbird2000 · March 25, 2024

Thanks for the write-up! I placed an order for a 2024 RST Crew cab with Bose back in December, my order hasn't even been accepted yet, but here i am looking to add to the system before i receive it.

Well done... and, well played.

Patches2 · March 25, 2024

1 hour ago, Badbird2000 said:

Thanks for the write-up! I placed an order for a 2024 RST Crew cab with Bose back in December, my order hasn't even been accepted yet, but here i am looking to add to the system before i receive it.

Well done... and, well played.

You will have plenty of options to change things up. Whatever you decide on, consider using some sort of DSP. Simply swapping speakers and using the OEM amplifier doesn't sound that great. I wish we had access to clean signal that we could easily use without relying on Bose interpreting what's sent over the bus.

hoitzed · March 25, 2024

Any chance you have an RTA graph for the original Bose setup? Curious to how that looked before your mods.

wblackburn86 · March 27, 2024

Love the builds and ideas here! I went down the rabbit hole and started to gut my 22 LTZ Z71. The BOSE amp is the devil, and there is really only one solution out there to get a clean signal and that's the Axxess AXDSPX-ETH1. It is a DSP giving 31 bands of EQ and will give a flat signal after removing the BOSE amplifier. I went with a complete active setup, ordering the Audio Control ACX600.6 for the doors and ACX600.1 for the sub. I wanted to keep a small footprint and these amps are tiny! I am replacing all the speakers with Audio Control PNW-69 in the doors, PNW-275 in the dash and PNW-65 in the rears along with a single 10" SPK-10S2 Sub under the rear passenger seat. I was able to find a custom enclosure color matched to the interior from a shop in Florida. Super excited to get this project under way!!

mattwag · November 2, 2024

I'm confused on exactly how you tapped the Ethernet signal before the Bose amp. Did you completely bypass the Bose? On the X3 connector (exact pin out I have for my 2024 AT4 HD) pins 1, 2 says Ethernet bus 6+ and 6- respectively and pins 11, 12 say AUTOSAR CAN Bus Serial Data+ and Serial Data-. Exactly how did you utilize these 4 connections to go directly into a DSP amp? And, did all factory chimes, warnings, phone and OnStar still function properly. I assume the volume control for the chimes/warnings and turn signals are probably very loud. Can you please elaborate? Thank you.

Peterbiltg · February 1, 2025

So yea guys the factory highs suck in theses trucks... im replacing all dash n doors speakers... i have 2 8inch skar zvx with a skar RP 2000.1M class D under back seats facing towards the back of the truck... i custom built box myself but it does stick out past the seat a little... ( cause skar recommend 1.25 cf per woofer) and most boxes you see out there for under the seat never have more than 1.5 total for both subs 8, 10, 12's.... and the box is still not 2.5 but adding polyester inside box makes huge difference as well....but i swear u would think this was a suv or i have a blow thru... never in my life have i ever heard or felt 2 8" woofers move so much air.... and i was skeptic about buying some skars just cause the price... but im tell you im very impressed... ive been in spl for almost 30yrs ..i have had everything every brand every amp every size speaker.. if ur looking for some rumble check out the skar zvx 8's...and they are cheap.. no more than 200.00 a sub...