First if your subwoofer is ported on the rear of the cabinet you can stuff the port with tennis balls rubber balls or even rolled up socks to seal the cabinet and cut down its interaction with.
Downward firing subwoofer on carpet.
In a down firing design the driver points down through a hole in the subwoofer cabinet toward the floor.
My rel sub is on carpet and fires down.
The subwoofer can sit right on the carpet and the sound should be propagated from the subwoofer and mixed with the.
Is it worth the time to cut out a small 13 x 13 piece of plywood to sit the subwoofer on to increase bass rather than just have it sitting directly on the carpet.
Although carpet will absorb some of the sound it is better to place the down fire on carpet than it is on hard smooth surfaces as these will reflect sound directly and cause a boomy listening experience that can be fairly unpleasant.
Imho most all sub s are placed on carpeted floors and most are downward firing.
If your home theater room is carpeted you ll probably have an easier go of figuring out the speaker system that you otherwise might in a hard floor room.
My family room is fairly small 15 x 12 and carpeted.
Most down firing subwoofers are placed on softer surfaces such as carpet.
You don t lose low frequencies reflecting off carpet only high frequencies so there should be no problem at all.