B&W 683 plinth findings

[BWLover]

OK, so you can see my system via my signature below. My system is in a carpeted basement. I've been playing a lot with my speaker placement. I had them on the spikes with no plinth, then with nothing at all, then with the plinth on w/spikes. What i noticed is that going from no spikes and the speakers just resting on the carpet to then having the plinth on (with spikes) the bass dropped a lot. I like the way they look with the plinth on so i think I'm going to leave it on. But my question is why is there more bass with nothing on the bottom of the speaker. Now take into account the floor is carpet/concrete. I think that has a huge impact on the bass because it has nothing to resonate thru. Am I thinking correctly? So three questions remain.

1) what do spikes do for a speaker?
2) why does it seem like there is less bass with the plinth?
3) how does a concrete floor impact the sound?

[emig5m]

I think the spikes just help stabilize the speaker and help with not making marks in the carpet? Can't say I've noticed a difference with spikes on or off. Less bass with the Plinth? Hmmm Bass drivers farther away from the floor? Never even put the Plinths on mine...

[BWLover]

The reason i put the plinths on mine is it makes it a lot harder to tip the speakers over.

[Stoney]

I have often wondered if having the spikes helps the cabinets to be more ridgid. Perhaps with the speakers sitting directly on the carpet the cabinets move slightly in the opposite direction of the drivers when they move. This would effect the bass more due to the larger movements of the LF driver cones. I suppose thats why a solid speaker stand/base is so important.

[sunshdw]

Being as I have a carpet/wood floor I too noticed a bit less bass on the plinths. I'll be curious to your findings........