SVS Subwoofer Isolation feet. Will I lose bass?

Yep @mahgister, the video you provided a link to (I really gotta learn how to do that ;-) is the one to which I was above referring.

I don't believe that demonstrating the reduction of acceleration of a speaker enclosure proves that it will improve the sound.  
First we have no indication of the amplitude of the vibration and acceleration.  It could be inconsequential. 
Second we have no evidence to suggest that the amplitude of the acceleration is audible.  The enclosure may already be sufficiently damped and braced as to make the vibration inaudible.  
Third is that the reduction of audible enclosure panel acceleation (if any) may make the sound quality less pleasing overall, especially if the manufacturer has tuned the resonance to augment the overall frequency response of the speaker.  Reducing that may make the speaker sound thin and less balanced.  
There is a lot more to this than showing a display of zero acceleration.  

I added the SVS isolation feet to my sealed SVS SB4000 subs a few months ago. I did not experience any noticeable change in output.
The reduced db output in the video has nothing to do with the feet or the flooring, it is because the ports are being plugged. Plugging the ports on a ported sub will change the tuning of the cabinet and thusly its output.

@audiorusty  My understanding of the video was it measured much higher plugged without isolation feet.  Then much less with isolation feet.

He talks about why he thinks there was very little difference with/without feet unplugged...  yet a significant difference sealed with/without feet.. So to be clear:

Open ports = almost no difference in stock vs Isolation feet
Sealed = significant drop in db when using isolation feet

do the positives outweigh the negative of less output?.

@dtximages

Aye, there's the rub, for in that sound of boom what sounds may come must give us pause and make cowards of us all.

- When I die Shakespeare will surely have words for me, I'm pretty sure we'll both end up in the same dry, hot place.