Found the answer myself!
There’s a russian YouTube video that shows the insides the of the speaker. It seems like there’s stuffing originally.
I should have listened to my mom whenever she said: ‚Think before you speak‘.
so what I’ve found out by removing every driver an the top plate:
There’s stuffing in every driver‘s chamber. Even though the woofer’s chamber is only stuffed at the very bottom. Other chambers are fully stuffed.
For people owning the HP530s like I do:
Removing the top is fairly easy by removing the glass plate with something like a suction cup. After that there’s 7 screws holding the the top.
Then you’ll see the woofer(s).
For the woofers I have to say that I’m not really sure what this concept‘s advantages are.
The drivers are mounted to together with what seems like a tube (I didn’t tear them apart). If someone with some kind of expertise would try and elaborate on this, I‘d be more than happy.
If you’d like I could even upload some pictures of the disassembly and insides.