Down firing subwoofers are popularly used with surround sound systems to increase the vibrations and rumbles heard and felt during film viewing.
Front firing subwoofer on carpet.
Scott wilkinson and chris boylan have an answer.
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Also subs have dedicated power on board lessening the strain on your a v.
I just ordered a pswi 225 down firing wireless sub.
Subwoofers are less obtrusive than the sort of floor standing speakers with drivers big enough to pull off the same task.
The same rule of heaviness applies here.
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.
The default position most subwoofers end up in is at the front of the room near the entertainment system.
A word of caution for placing subwoofers on tables cabinets or shelves.
My family room is fairly small 15 x 12 and carpeted.
For decoupling vibration pads can be placed beneath the shelf or cabinet so that minimum sound vibrations are transferred to the floor.
If the subwoofer is front firing it can be placed on a shelf or in a cabinet.