Does a Subwoofer Make Spiking Redundant?

Always decouple, everything. You cannot be heavy enough or secure enough. The problem is timing. The floor, weather wood concrete or whatever folks use can’t isolate vibration unless it’s thick rubber, THICK rubber like the Kursk 3" thick.... Most people don’t have that type of isolation. 10-12" thick concrete will work. 3.5 or 5.5" is not thick enough unless it’s on friction piers. That is an expensive slab...

It’s better to use air bags, spring or pods. The better isolation you can afford the less the timing issues. Smearing is a PITA until you get rid of it.. Like magic!

Clean up the huge passive bass radiator from the floor walls and ceiling. Treat the standing wave issues in the room, you’re sittin’ in TALL cotton (as my Mom use to say) I use heavy curtains and two pocket doors that slide open on the back wall in one room. My ears don’t like to much pressure. OB servo subs really help. I use to use inner tubes on 2 12cf bass bins and set the feet in a pocket of 4" memory foam, 95% isolation.

On spikes they would have drilled holes in that 41/4" 80 year old concrete floor, close to 300 lb each.

I have a pair right now 250lb (12cf) with no driver holes yet. A pair of 21" Daytons, would act like pile drivers on spikes. Turn up the bass and it would leave concrete dust on the floor.. LOL

Regards

" bolt your speakers to a concrete floor" - this is completely wrong.

The whole purpose in "decoupling" the speakers, and sub, from the floor is to minimize, or eliminate, the vibration from reflecting back into the speaker. This reflecting vibration muddies up the sound of your speakers. Eliminating the reflecting vibrations tightens up your bass, and the speakers’ sound becomes more clearer. Bolting the speakers to the floor will only insure that the vibration passes from the speaker into the floor, and reflecting back into the speaker cabinets.
Spiking the speakers will only minimize this vibration. The best ways are to use springs, as suggested, seismic podiums, or energy dissipating pucks.

My system is on the second floor. I added some of the mentioned Nobsound springs to subwoofers and noticed my kitchen lights (one floor bellow) don't rattle as much. However, I feel as though my subs lost some punch.  

i read a lot of this and find it confusing. certainly contradictory ( what else is new?).
There are many theories, but the most reasonable, to me is that we want speakers to be totally immovable - a solid, stable surface for drivers to push against.  If they resonate, they modulate the drivers - especially the midrange and tweeter where the wavelength is smaller relative to any vibration or rocking motion.

Spikes are often used to cut through a soft, unsupportive material that will allow the speaker to rock, such as a carpet.  The subwoofer OTOH adds lower frequencies and is mostly an orthogonal choice.

Now, a spike on a hard surface is a different animal and I would tend to not use them. Those spikes minimize the surface area (which in the newtonian sense of friction m,akes no difference), but also increase the force per unit area meaning the connection will be more fluid due to material shear. In theory. This is why car tires are non newtonian as well (wider is in fact better).

I prefer mass to stabilize the speaker (big, heavy speakers on a solid 3-points so they don't rock) and maybe as one suggested actually isolating the speaker from floor vibrations especially if its a live floor. I have not experimented with those.

Acoustic Science Corp and Acoustic  Fields have Subwoofer Platform Traps 18” off the floor for more than one reason.