Speaker mounting depth

[Kokain]

That's a good question, you are obviously limited on what you can fit inside as the window can catch the magnet on some big 200-300w puppies. I started thinking about it and obviously the space in front of the speaker there is nothing to prevent from using it, question is how. A DIY of some sort, a speaker extension, like a tube...right? I googled the first thing that came to my head in case a product exist already "speaker door card extension", I got nothing. Some non related images etc but then it hit me "speaker door spacers" .
https://i.imgur.com/N710ET3.jpg
http://i.imgur.com/5ftZKOB.jpg
https://i.imgur.com/YYfZnap.png
https://i.imgur.com/dUu1dVz.png
It really won't be hard to get some plywood and make a nice solid piece like in the first picture. But if you don't have the time those plastic spacers can be easily adapted with some longer screws. The plumbing section might have some perfect match stuff that could be worth looking into.
https://i.imgur.com/KRUChYT.jpg
This should give you plenty of ideas to complete your mission. Enjoy