The stands of my monitors are on concrete slabs, which are on a carpet covering wood floor.
My sub is on an
ASC SubTrap which I can strongly recommend. My notes on the sub trap from 2016, supporting my downward firing REL, read:
"Without subtrap the excellent rhythm & timing that I had gotten used to was diminished to some extent; the bass seemed just a tad slow on rock music. Also, there was a somewhat 'plasticky' and 'thuddy' coloration to the bass. What is more, I could not contain my surprise when, while spinning a piece for six percussionists and choir (Wolfgang Rihm, last part of
Tutuguri), I heard a 'brownish' coloration from large snare drums the sound of which did not even have lots of bass output! (The somewhat thuddy sound upon subsequent entry of the heavy bass drums was the final nail in the coffin for me.) Putting back the subtrap under the subwoofer confirmed that the 'brownish' coloration of the snare drums had been no illusion; the pristine sound that I had been used to returned."
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The SubTrap (available in 18" and 22" format) will accommodate JL Audio subwoofers and smaller RELs, for example. I just ordered dual JL Audio Fathom 112v2 subs, and a second 18" SubTrap to go with them. These subs are front firing, but since without the SubTrap the woofers would be very close to the floor, I expect the same kind of benefits.