What function is served by the upper portion/chamber of the speaker assemblies? They seem to be cut off from the speaker drivers with foam inserts.
"There is a door at the back of the case, you can open it to change ram, no need to open the mac to do so."
That door exists only on the 27" iMac. As the author explained, on the 21.5" iMac, the RAM board is BEHIND the logic board so a door would not give you access, anyway.