I recently picked up a 2012 Audi A6 3.0T Premium Plus equipped with the factory 10-speaker audio system. Overall, the system was disappointing, with a thin and harsh sound signature paired with weak low-end response. The front doors had previously been upgraded with Hertz HV165L mid-bass drivers, though they were still being powered by the factory amplifier, which delivers roughly 18 watts per channel. The rear doors, tweeters, and factory subwoofer remained completely stock. In addition, the center dash speaker had been replaced with a budget Scosche 4-inch coaxial while the original factory tweeters were left untouched. The end result was a mismatched system with no real consistency in tuning, tonal balance, or overall performance.Rather than starting over completely, the plan is to build the system properly in stages with a structured upgrade path. The entire system will receive new wiring, aftermarket amplification, a dedicated DSP, and a fiber-optic gateway to integrate with the factory MOST network while allowing for a clean digital signal path and full tuning control.




The first phase focused on improving the vehicle’s acoustics. All door panels and speakers were removed, the inner and outer door surfaces were thoroughly cleaned and degreased, and both the inner and outer door skins were treated with sound deadening material to reduce resonance and improve overall speaker performance.With the spare tire and battery removed, the trunk was completely stripped down to expose the rear structure. Sound deadening material was then applied throughout the spare tire well, rear quarter panels, and trunk lid to address common resonance points and significantly reduce rattles and vibration across the rear of the vehicle.
The rear parcel shelf and factory subwoofer assembly were removed to prepare for sound treatment and fabrication work. The parcel shelf was fully treated with sound deadening material, and all factory clips and wire retainers were reinstalled in their original locations to preserve OEM fitment and appearance. The factory subwoofer assembly was then gutted and modified to support the new setup. A bead of polyurethane sealant was applied around the inner circumference of the enclosure, and reticulated polyurethane foam was used to fill the surrounding gaps, creating a dust barrier without restricting airflow to the future enclosure. The entire assembly was then placed under load while curing to ensure proper adhesion and structural integrity between the foam and enclosure.


The build plan consists of a custom subwoofer enclosure in the rear right trunk cubby, reuse of the existing Hertz HV165L mid bass drivers in the front doors, Hertz CK165 component speakers in the rear doors, Morel Virtus IPVWB25.4 speakers in the dash, and a Hertz CX100 center channel, all integrated through a DSP-based system while retaining OEM functionality. The HV165L drivers remain in use despite the previous installation quality, as they are still suitable for the upgraded system. The CK165 components were added to improve rear staging balance, while the Morel tweeters improve high-frequency clarity and the CX100 restores proper center imaging after replacing the previous low-quality aftermarket unit. Once the speaker selection was finalized, the next step was amplification and system control. Since the upgraded speakers exceeded the capabilities of the factory amplifier, I chose the Mobridge K2 8.1.1 DSP amplifier with MOST25 integration. This allows direct integration with the factory fiber optic system while providing amplification, DSP control, and full tuning capability in a single unit. For the subwoofer setup, the plan is to build a custom enclosure in the rear left trunk cubby. I narrowed the subwoofer options down to a Kicker 48CWR84 8 inch subwoofer and a Dayton Audio UMII8-22 Ultimax II 8 inch dual 2 ohm voice coil subwoofer, purchasing both drivers until the final enclosure volume is determined. The Ultimax requires more airspace but offers deeper low frequency extension, while the Kicker requires less volume and would allow for a more flush enclosure design. To power the subwoofer setup, I added a Kicker CXA400.1 mono amplifier, which will support either subwoofer configuration depending on the final enclosure design and impedance setup.
The next phase of the build focused on the fabrication of the subwoofer. For the enclosure location, I chose the right rear trunk cubby to keep the left side accessible for the amplifier and future serviceability. The enclosure was built using a fiberglass mold formed directly against the trunk trim, followed by several reinforcement layers to create a rigid enclosure with approximately 1/2 inch wall thickness. The additional fiberglass strength reduced internal airspace, so the original flush-mount design had to be revised. To achieve the required 0.5 cubic feet of volume for the Dayton Audio UMII8-22 Ultimax II subwoofer, the enclosure extends roughly 3 inches outward from the trunk wall. A Kicker 48CWR84 was also considered, which would have required less airspace and allowed for a fully flush enclosure design.
Right Rear Cubby



The final enclosure uses a 3/4 inch MDF front baffle for strength and proper subwoofer mounting. The goal of the build is clean, controlled low-end response.


Mock Set Up
The final enclosure uses a 3/4 inch MDF front baffle for strength and proper subwoofer mounting. The goal of the build is clean, controlled low-end response.
With the enclosure work completed, attention shifted to speaker mounting, fitment, and wiring integration throughout the cabin. The front doors utilized custom 1/2-inch MDF baffle rings with a 6.6-inch outer diameter to achieve the required mounting depth, structural rigidity, and window clearance for the mid bass drivers. The rear doors received custom MDF mounting baffles with additional spacer rings to properly position the Hertz CK165 component woofers within the factory locations. All MDF components were pre-drilled, finish-sanded, and sealed with spar urethane to prevent moisture intrusion and long-term deformation within the door cavities. The Hertz CX100 center channel required minor modification to the speaker basket and mounting structure for proper fitment, while the Morel Virtus IP-VWB25.4 tweeters required custom adaptation to integrate into the factory dash mounting locations.
All fabrication and fitment work was performed without permanent modification to the dashboard or interior trim panels, with the exception of the rear door tweeter locations. After removal of the factory tweeters in the rear door panels, the tweeter openings were carefully relieved using a rotary burr to allow the Hertz CK165 tweeters to seat correctly within the OEM housings. The tweeters were then permanently secured using two-part epoxy, and additional sound deadening material was applied behind the assemblies to isolate the front and rear wave paths and minimize acoustic reflections.
Once fitment was finalized, new 16 gauge tinned oxygen-free copper speaker wire was run to each door, the dash speakers, and the subwoofer location. The system is being configured as a fully active setup, with all crossover and tuning functions handled through the DSP rather than passive crossovers.The wiring phase began with the front doors, where the factory Molex connectors were separated and carefully drilled to allow new speaker wire routing without interfering with the factory terminals. Small pilot holes were created in precise locations, and the wiring was fed through the door jambs and connectors before the harnesses were reassembled. Because the system is fully active, the rear doors required three separate wire paths per connector: one dedicated 16 gauge OFC run for the mid bass.driver and separate runs for each tweeter channel to allow independent DSP control. All speaker wiring was routed toward the trunk along factory wire paths. On the left side, the wiring was run through the factory door sill channel, while the right side speaker wires were routed under the carpet and brought across to the left side for centralized integration. Each wire pair was separated and tightly twisted to minimize electrical interference and noise.








At this stage, the subwoofer enclosure has been fully sanded, primed, and painted, and will be upholstered this weekend prior to final installation. I am currently waiting on the arrival of the mObridge interface, which will complete the signal integration portion of the system. Once it arrives, final assembly of the interior panels and remaining hardware will be completed over the weekend. System tuning will then begin in collaboration with a remote mObridge specialist, allowing the DSP and MOST integration to be configured and calibrated properly for the vehicle. The goal is to retain full factory functionality while achieving a significantly higher level of sound quality, staging, and overall system integration than the OEM setup could provide.

 

Cool build, you definitely put a lot of work into it… I find my factory setup sounds pretty good overall. Just the stock Bose system (Prestige). I really only want to upgrade the sub… but not to your extent lol

 

It’s quite a bit of work, but it’s what I love doing.

 

Great project! Especially when you put allot of work and end result is as good or better than expected. Keep up the good work! and thank you for the documentation and pictures.

 

Thank you for appreciating the work.

 

The subwoofer had been upholstered, Polyfill fiber has been added and everything is now installed in the car. The build phase is complete.

 

Any junkyards near you?? grab some truck carpet from a wrecked A6 to factory match the carpet on the box lol.

Looks great man!

 

I actually thought about going that route to get a perfect match 😂