Bass Response and concrete floors

Herman, they are selling you something, and that something is more bass ("warmth"), but you can't have it for free. You are still going to pay for it in loss of transient response and extra resonance. The fact that they want a slightly different kind of floor only means that they want to shift the resonant frequencies to a different spectrum. There is no magic here: wood floors resonate, concrete pads don't. Yes, some resonances are more euphonic than others, but that doesn't change the fact that they are resonances. Still far better to start with a nonresonant room (note that resonance and reverberation are two entirely different things; a room with good reverberation characteristics does not have to have floor/wall/ceiling resonances at all...) and use subs to create real bass. But I'm not surprised that Avantgarde has this approach; their horns resonate like crazy and I'm sure they are used to tuning their speakers for a (more or less) flat response in spite of the response variations the resonances create. But the time domain isn't fooled by this, and neither is the ear.

Perfectly valid point Herman but i'm not sure were talking about the exact same thing.

This is not rocket science or, if it is, it's not all rocket science. Of course covering cement is going to make a difference. If you have raw cement and go to wood covering you will notice a diff and it usually will be perceived as "warmer". If you have carpet and pad over the cement and then to go to wood the diff will be much less. Especially if the rest of your room surfaces are "warm."

Do you play an instrument? Take an acoustic guitar and and play 18" in front of tile, glass, concrete poured walls, plasterboard, your living room sofa and the sound board of another guitar. What do you like? Surprisingly many people like bright resonant sound. That's why we all sing in the shower - but that's another story. Anyway, it's not a perfect example of a room at higher volume but it will give you the general idea.

There is a difference in trying to add a "shade" to the sound created by your system with room treatment (floors or walls) and trying to extend frequency response of your system using the room. The later is almost always disasterious because it cannot be controlled (the frequency response curve would be anything but straight.) I repeat, if you do not want a speaker that rolls off at 50Hz buy a speaker that does not roll off there! Then treat your room in a manner so that it will effect all bass and treble frequencies somewhat equally and too your liking.

I remain,

Herman, I think the issue being referred to is resonant feedback rather than acoustics. I absolutely agree that if you have a concrete floor then you will get a cooler less involving sound if you do not get the equipment and speaker supports right. For example, I have found with a concrete floor that racks sound much better if they are sand-filled, but sound better if empty on a wooden floor. Better still is to decouple the rack from the concrete floor in a similar way to that you have quoted.

I had a pair of PSB Stratus Gold i's which I used both downstairs (concrete slab w/ carpeting) and upstairs (wood floor with carpeting). Bass downstairs seemed much tighter - punchier even. It was strange, too - downstairs (same room dimensions BTW) I could put them closer to back wall (3 feet or so). Upstairs I needed 6 - 7 feet or else they were your neighbor's kid's aftermarket woofer in the back of his Honda hatchback! Go figure.
As an organist I can tell you that the lowest pedal notes seem to have more punch in concrete floored buildings (yes, obviously different instruments in different buildings, but you get the feel for them after a while, and many are by the same builder).

I have used sub's on concrete floors with spikes. My experience is that the bass is tightened up and sounds very good. The floor gets rid of that flabby mid-bass and I know my sub went below 50hz.