Nsgarch is off base here. First, the carpet makes zero differnce in a performance standpoint! Infact, the carpet may benefit, in that it can help hide higher frequency distortion or overlap/crosstalk!. Bass waves in play here are so big, that any carpet depth laying over a hard foundation, is going to affect NOTHING, in terms of intended performance! That is fact.
Second, anchoring a downfiring subwoofer with spikes, as long as the sub is heavy enough, is fine in carpet. Actually, the woofer is moving against the weight that's it's secured to from the box above it! As long as the woofer is pretty stable, and even at that, you're not going to have any downsides on carpet. Placing a down firing woofer on a marble platform is not really going to improve here. Infact, unless the marble platform is exponentially heavy enough, it's probably not as good as spikes into carpet/subflooring.
I've heard many people worry about downfiring sub on carpet, or otherwise. If you wan't to know, just experiment and find out!
Second, anchoring a downfiring subwoofer with spikes, as long as the sub is heavy enough, is fine in carpet. Actually, the woofer is moving against the weight that's it's secured to from the box above it! As long as the woofer is pretty stable, and even at that, you're not going to have any downsides on carpet. Placing a down firing woofer on a marble platform is not really going to improve here. Infact, unless the marble platform is exponentially heavy enough, it's probably not as good as spikes into carpet/subflooring.
I've heard many people worry about downfiring sub on carpet, or otherwise. If you wan't to know, just experiment and find out!