[MudPhud]

Standing on the shoulders of giants...

After reading hundreds of threads on the subject of aftermarket audio upgrades and being inspired by the accomplishment of others and appreciating their willingness to share their knowledge and expertise in this field, I felt compelled to embark on a DIY journey even though I had never before installed any aftermarket audio gear in any car, let alone a brand new and beloved 2011 M3 sedan.

For the project, I purchased Rainbow Audio SLC 210.25 NG (4" midrange + 1" tweeter component) speakers for the front doors, SLC 230.25 NG (5.25" midrange + 1" tweeter component) speakers for the rear deck, two Earthquake SWS-8 (4 ohm) under-the-seat subwoofers, and a JL Audio XD700/5 amp (75W x 4, 300W sub @ 2 ohms).

First of all, credit and kudos to:
1. 6spdcoupe - authorized Rainbow Audio dealer, fantastic service, unbelievable prices (better than W.Etc), very fast shipping
2. Technic - OEM HiFi harness, incredibly well thought-out and executed, perfect fit and even locks down with the OEM harness latch
3. 808MGuy - aluminum alloy custom 4" midrange speaker adapters, beautifully CNC machined, perfect fit for the Rainbow SLC 210.25 NG and the front doors
4. jtsherri - Earthquake SWS-8 spacers for BMW OEM subwoofer enclosures, perfect fit and very sturdy
5. azwillnj - SWS-8 installation guide
6. MendotaMike - aftermarket amp install thread
7. adc - Rainbow SLC NG crossovers fitting in the front doors thread
8. All those posting invaluable info on front door panel removal, rear seat back removal, rear parcel shelf removal, and battery distribution box housings

The installation...
Fig 1: jtsherri's plastic spacer are cut so precisely, that I used them as gaskets and applied 3/8" wide weatherstripping to the undersides of the Earthquake SWS-8 rims to interface with the spacers which in turn contacted the enclosures directly. This way the OEM 'notch' could be covered and sealed fairly well. I also drilled two holes into the spacer at the notch to snugly fit two protruding 14 AWG speaker wires.

Fig 2: Adopting adc's crossover location, I modified it by installing it at an angle to avoid cutting any foam. There are three points of contact between it and the door panel.

Fig 3: At these specific points, Dynamat Extreme was used underneath the crossover to bind it from below. More Dynamat Extreme was applied over it to firmly secure it from above while keeping the ventilation holes open. Decide on your jumper settings before final mounting!

Fig 4: The Rainbow CAL25 tweeter is only ~2 mm wider in diameter than the OEM tweeter, so it will fit directly into the OEM plastic housing albeit with the housing tabs flared out a bit. Thin Dynamat tape helped to secure the tweeter in place while staying hidden from view.

Fig 5: Cardboard template of the 5.25" SLC 230.25 NG to show that it will fit under the OEM rear deck grills.

Fig 6: The smaller circle represents the actual cutout diameter through which the speaker frame fits. The pushpin kept both templates in coaxial alignment to allow tracing two chalk circles, one for the cutout and the other for the speaker frame. Note that two sections of the perimeter ridge also needed to be cut to accomodate the speaker frame.

Fig 7: A 4.75" hole cutter is the perfect size for the Rainbow SLC 230.25 NG as its cutout diameter happens to be 4.72"

Fig 8: Both sides of the rear deck cut out to accomodate a pair of 5.25" midrange drivers.

Fig 9: I used the leftover cutout material to Dremel out crescent shaped fill-ins to block out the remaining gap from the original off-center 4" midrange hole. Note that the tweeter was installed with an angle mount which had already been spray painted matte black.

Fig 10: The 5.25" driver was bolted on the underside to the plastic installation ring that came with the Rainbow component kit. This greatly reinforced the speaker mounting by stiffening the fiberboard and adding structural rigidity to support the extra weight of the 5.25" speakers. Note that the pink OEM insulation material had to be discarded.

Fig 11: Dynamat Extreme, more useful than duct tape!

Fig 12: Two more Rainbow crossovers fit on the rear deck foam and were Dynamat taped in place. Note that the height of the two crossovers when laying on the foam is just barely lower than the rearmost plastic vent piece.

Fig 13: The rear parcel shelf has been reinstalled demonstrating that both crossovers fit with no deformation of the rear deck. OEM foam above and below the crossovers eliminates any noise or vibration. OEM grills fit right back into place without any problems.

Fig 14: 4 AWG +12V power cable routed completely within the trunk and connected to the OEM battery distribution box housing with an OEM connector (teal). 4 AWG ground cable was connected to an OEM ground post.

Fig 15: A wooden plank (13.5" x 8.0" x 0.5" birch) was screwed to two perforated metal straps such that the straps could accommodate OEM 8mm bolts (black) at the correct position. Longer M5-80 bolts (silver) fit through drilled holes and were also in the correct position to fit into two OEM mounting holes.

Fig 16: The amplifier platform was bolted in place with OEM bolts (black) and longer M5-80 bolts (silver) at the exact four positions that the OEM amplifier mounting frame had used. This involved a LOT of test fitting as the mounting positions were NOT in symmetric locations.

Fig 17: JL Audio XD700/5 amp connected to Technic's HiFi harness which is connected to the OEM head unit interface + OEM speaker wires. Tremendous time saver, and NO cutting of OEM wires here! The amplifier screws into the wooden plank. I have since organized the 4 AWG wires more cleanly.

Is there anything unsafe that I need to address? Any glaring deficiencies or omissions? Thus far, I'm extremely happy with the new audio quality and have no regrets with this project.

Observations and critiques welcome.