First of all, the metal fan protection is removed, secondly - it somehow works. I mean temperature drops by ~ 2 degrees and noise drops ~6 dB.
I actually bought it on ebay for another Antminer.
Nice man, that's sweet.
Check out this setup I did. I wouldn't say this is the best by any means though. All for testing and fun.
https://imgur.com/a/E2D3cVDI got these from home depot and just cut one side off and took the flap off and they fit the holes for the miners perfectly:
https://www.homedepot.com/p/Everbilt-4-in-Inline-Vent-Draft-Blocker-BD04HD/205046954