Townshend Springs under Speakers

Because allowing the cabinet to move, especially in a low cabinet resonance, pistonic motion, time and phase design smears the signal. On a moving floor this smearing is already happening. RV actually tested the subject product and wrote about the plus / minus achieved by him with his speakers, including measurements and listening. 

As i recall the OP here has 5a.

As always, other speakers or floor combinations may benefit.

Also both the Kento and new 7 extreme use a force cancellation alignment of the unique to Vandersteen Scanspeak bass drivers, reducing already low cabinet movement. 

Fun

Since 1977

if the speaker is on solid ground, 3 spikes is preferred.

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That's the problem there is no such thing, the actual floor becomes a transmission medium and delivers a signal out of time with the actual driver's delivered signal via AIR.. The floor no matter the medium (unless it was 1/2 thick rubber) will deliver a signal at two different times to YOU in the seated position. SPIKES cause it, decoupling stops it.

12" thick concrete is not thick enough, maybe on 4 foot center 12" x 60" friction piers. A 12" thick slab and a 1/2" of rubber.. Drop the speaker on that..

For the best results ALLWAYS decouple, mains and subs, one from the other, and the room surfaces and boundaries.. There is no exception.

Spring, pods, innertubes. There is more than one way to skin a cat..

Regards

i thought the best results were whatever sounds best to you in your listening room.