Look, I'm too old to argue with people on the internet, lets just assume I want to ruin my car and burn down the world. But like you, I can't leave well enough alone. If you believe that a frequency which is literally just a wave form with a time period changes based on the speaker size, then you have it. Different speaker sizes produce different frequencies, they don't change them.
I'm not sure what you are confused about with the box vs the driver. I already have the box with a pretty closely known size. I am matching the speaker to the box. Not the other way around. Your point makes no sense. The whole reason I made the post was so I can look for a driver that fits and matches the box. (0.7sqft approx). I am not buying a free air speaker, you are just being silly now.
And yes you have some stickers, and I have engineering degree with 15 years of experience in industrial vibrational control and damping. So I know things too, weeeee we all know things and have cool shit to put on our walls/windows. Hooray Science, or whatever I just wanted to say science too cause it makes me sound cool, or nerdy, I can't tell any more, nerds seem to be cooler these days. Whatever, this is fun.
Let me type slower…like I usually have to do with engineers to get them to understand things.
Remove the oem enclosure.
Measure for depth and opening size.
Fill it with water.
Yes water.
Measure the volume of water.
Now you know the actual enclosure size.
Now measure the port length and diameter.
Calculate the port volume.
Set the enclosure aside to dry.
Start comparing subs that require that size enclosure, with the same port requirements.
Maybe you get lucky and find something that will actually work.
Also consider sealing the port, measuring the entire volume and hunt down a sub that works with those particular specs.
Then realize the oem enclosure is a cheap, thin POS and not worth the effort.
Then do some research on running different size subs and how they can cancel each other out giving you LESS bass than you started with.
Now spend the same amount of money buying a matching 12 and having a new enclosure built so you’ll actually be happy in the end….because an 8 will not be able to match the output of your 12 and you’re going to wind up with multiple issues that I already covered earlier And FYI if you think say a 3” driver will produce the same frequencies as a 12 with any discernible output…well I can’t help ya.
What you are asking to do it a recipe for failure. Period. You can’t reinvent the wheel no matter how much you think you can.