I've finally gotten around to installing the rear speakers I got for Goldie about a year ago. Below is a short description of how I have installed a pair of Infiniti 5002ix 13cm speakers, without cutting or drilling any holes in the chassis. The only element that was modified was the parcel shelf, but in a way that - at least for me - looks great, and as if it were this way all along.
The first problem I've come across was the shape and size of the speakers, which immediately made the OEM chassis openings to small. These are made for 10cm speakers.
The second problem was the mounting hole pattern, which, in true Mercedes-Benz fashion, is entirely different from what everyone else used - three holes in a triangular arrangement, as opposed to four in a cross arrangement.
Since my parcel shelf is already custom made - cut from 3mm MDF and covered with high-pile fine velours carpet - I have decided to modify it in a way that would let me install the 13cm speakers, while using the original 10cm openings. To that end, I've laser cut adapter rings from 3mm plywood, with 158mm/122mm OD/ID, and them made a test fitting to figure out how many I'd need per speaker. The optimal result was five, for 15mm total adapter height. Adding to that 3mm for the MDF and 8mm for sound proofing matt under the parcel rack, the total distance to chassis was 26mm. That raised the speakers enough for the widest parts to clear the chassis opening with room to spare.
Next, I've glued five rings per adapter with PVA glue, and - when dry - cut the carpet around them so that they'd rest against the parcel shelf MDF. I've chamfered the lower edge, so that the ring would fit in a slightly smaller diameter hole, making the carpet fit snug around it when installed. That worked really well, so I've glued the adapter rings to the MDF, then trimmed the 10mm openings pre-cut by my restorer to fit the internal diameter of the adapter ring. Basically, now my parcel shelf has built-in speaker pods
After re-installing everything, the entire setup looks and works really well, albeit I don't fancy removing that at some point (hopefully not in the next 40 years!
, as there's very little space to work with any tools there. I've left the adapter rings unpainted, just sanded them down and waxed with pure bees wax, mixed with turpentine and linseed oil. That gave the plywood a nice, subtle sheen and made the texture pop. Thanks to how the laser beam seared the cut edge, it looks quite close to the original zebrano trim, which is an added bonus.
Here's some pics Raw adapter rings after cuttingParcel shelf carpet pre-cut to original chassis dimensionsAdapter rings glued together and getting finishedFinished adapter ring in-situ, glued into the parcel shelfTest fitting of speaker, to mark where mounting holes need to be pre-drilledFinished look
...and a short video showing the whole thing, before final assembly, in action: https://youtu.be/C6JpbDmlCAg