Subwoofer Footing - Connect or Isolate?

I agree...put a sub on springs is ridiculous at best.Maybe good if your trying to bounce around like a pogo stick.

Somewhere Richard Vandersteen posted an excellent article on speaker isolation and he makes a very good point I've made before:

You want to prevent the speaker's ability from moving back and forth.  The forces of the drivers push against the cabinet and can cause it to move, which is audible even when there's very little of it.

So, I would stick to IsoAcoustic style of pucks for a subwoofer and nothing more springy.

Wow a lot of bad info here.  Isolating things that move is important when you don't want to excite other elements of the listening room that add to and change the total sound you perceive.  This is an issue of mass vs frequency.

The total sound you perceive is the speaker direct sound + speaker indirect [reflected] sound + room dimensional sound + all vibrating materials in the room [tables, floors, walls etc]. 

Wooden speaker stands vs heavy Sound Anchor stands is clear evidence of this idea as the wooden stands will vibrate at an audible frequency (knock on them with your knuckles to hear an example) vs hi mass Sound Anchors which vibrate differently due to high mass.

For the spring idea to work, it must be tuned for the weight of thing moving.  Random springs set for an unknown weight will not solve your problem.  Look at a car or truck, springs are set very specifically depending on weight and the many factors of behavior once excited.   

Decoupling sources of LF is important to not waste unwanted mechanical energy vs the energy you want: acoustic energy.  Giant generators are isolated from the concrete pad they sit to control vibration that turns into LF hum that can penetrate an entire building and make it impossible to work. 

See  Noisia Studio Tour | Razer Music - Bing video
this shows the springs used under some fairly heavy (150+ lbs) ATC monitors.  Very specific spring rates.
Brad

The last thing you want to do is put a subwoofer on springs. At some low frequency it will start shaking.

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WRONG... Just wrong..

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Giant generators are isolated from the concrete pad they sit to control vibration that turns into LF hum that can penetrate an entire building and make it impossible to work.

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I don’t know what constitutes "Giant" I’ve worked on Cats 1250kW mobile and stationary gen sets.

That same "Isolation Tech" Springs, Gummy Puffers and point of contact accumulators, keeps just about anything isolated, One from the Other.

12 to 15 tons of Generator can really put out LF harmonics. You couldn’t keep concrete UNDER it.
It would crumble it.. The engine perches would break, nothing would hold up. It has to be isolated.
They have used cancellation tech in machinery for a long time.. Joe Blow, human hearing application not so long.
30 years or so..

Regards

A REL engineer told me that the only thing I might want to try is some BlueTak under each foot. But with or without the ’Tak, he said the sub will perform properly on my hardwood floors over a crawl space using the T5 as REL designed it. I tried the BluTak, and in my room, but while I could discern no dramatic differences, I left it on the sub feet because, well, it’s just sooo sticky. :)

I suspect that REL knows how to build subwoofers a heckuva lot better than I do.