Since the floors connect to the walls they re also going to shake.
Downward firing sub carpet.
On surfaces got me thinking at one time also.
The advantages i saw to down firing was getting the woofer away from my ear the cone was about 15 away when it was direct firing.
The higher order harmonics when radiating direct were definitely localizing lower mid bass notes and distorting the sound stage probably due to the.
And even for a down facing subwoofer the amount of sound being absorbed by the carpet is likely going to be negligible.
After that the ceiling comes next.
Most down firing subwoofers are placed on softer surfaces such as carpet.
And since the shaking directly affects the floor the floor starts shaking.
Down firing also tends to mute any higher order issues.
Since the subwoofer is there to push deeper sounds and longer wavelengths the sound waves it s producing simply won t be affected as much as shorter wavelength sounds like those produced at the rest of the speakers in.
A down firing subwoofer box produces a domino effect if placed inside a room.
I have a downword firing 12 inch ksw klipsch sub i now wish i had been smarter and done my homework and bought a better sub for the price anyway on the klipsch forums several posters suggested that if you have carpet like i do to put a large ceramic tile underneath the sub.