SVS Subwoofer Isolation feet. Will I lose bass?

There's a YouTube vid I watched from a guy last night who did some measurements but I wasn't quite convinced I understood what he was saying.. He has a PB4000 (ported)..  Ran REW both ported and sealed with the SVS feet.  According to the chart, it appeared (again I'm not sure what I saw because it was like 2am) that they made almost no measureable difference while ported, but significant decline in output when sealed.

When he explained it, it made sense given theres much less cabinet pressure to move when ported.

Just wondering yall's opinions.

The primary reason to isolate the subwoofer is to eliminate mechanical feedback to the system via the floor. The secondary reason is to reduce subwoofer cabinet resonance. It’s two, two mints in one! 🤗

geoffkait, I understand that.  But if you have a sealed sub on a slab, wouldn't the "wobblyness" be counteractive to the woofer?  Lessening its effectiveness?  Lowering its output?

According that dudes youtube vid, that's exactly what happened I think!  But I have not heard others say this is an issue.  

I figured, surely, someone has first hand knowledge of the effectiveness of these feet, or Auralic Subdude on their sealed slab-sitting sub.

No. The (appropriate) springs have very high lateral stability for subwoofers, as we say in the trade. Stiffness to any civilians out there. No wobbling.