I’m currently driving an old Škoda from the Stone Age — and as charming as it is, its speakers have long since given up. Since I love listening to music while driving, and a Bluetooth box isn’t a long-term solution, my partner and I decided it was finally time to fix the speakers.

When choosing replacements, it quickly became clear that I didn’t just want new speakers — I wanted better sound quality. That meant the car needed some modifications, and custom speaker frames had to be created. 

The frames had to match seamless to the speaker and should fulfill two purposes. 
1.    The new speaker are a slightly larger and therefore can’t be mounted at the original positions.
2.    The added frame height provides enough clearance for the larger speaker depth, ensuring the rear parts don’t interfere with the door components.

To build them, I used two wooden boards — one 21 mm thick and one 24 mm thick — which were later attached together after milling. Why two boards? it was easier to find them at the Baumarkt than a single 45 mm board!
Using CATIA, I designed both frame shapes (for the thinner and thicker boards). With the kind support of Andreas and Cerene, we fine-tuned the design to meet the milling machine’s requirements.
After milling and cutting, the frames were fixed together and painted to protect the wood and to match the color of my inner door parts. During this process, we discovered another challenge: the window rubber seals weren’t as tight as they should be. That means when it rains heavily, water drips inside the door — right where the new speakers sit. Which of course endangers their durability.
 

It seems fixing the window seals is next on the list before the new speakers can finally go in!
 

Thank you again @AG and @CZ for your kind support!