a downfiring or sidefiring sub will not be as easy to audibly locate in the room compared to a front firing sub.
Holenneck (Threads | Answers | This Thread)
for a two-channel unit, you'll want to consider a servo controlled sub. Martin Logan has a line of several servo subs that are fast, tight and highly musical. I personally don't think it matters where the woofer fires though.
Jalapenos (Threads | Answers | This Thread)
Down firing will reduce the audibility of harmonic distortion. It generally makes placement easier and will increase the sub efficiency (like a horn - the coupling to the air will be improved at a room boudary). It also means that a huge cone and large voice coil and suspension will not have gravity acting across it from one side...think of a yo-yo - it will remain most balanced and controlled going up and down and is relatively harder to control going straight out in front of you - as gravity has a tendency to make pull it out of alignment and you have to fight this pull to keep the yo-yo going out straight in front of you.
Some people recommend removing front firing subwoofers and rotating them by one screw point each year to stop any gravitational affect eventualy causing cone misalignment.
Shadorne (System | Reviews | Threads | Answers | This Thread)
Down firing subs also cause more vibration to go into the floor instead of the room, which may or may not be a good thing. You can feel the vibrations from the sub in my living room (down-firing) on the other end of the house! Great for special effects, not so great if someone else is trying to sleep.
Ait (Reviews | Threads | Answers | This Thread)
If your going to use the sub below 80hz only, I've found that it really does not matter.
If you need to use the sub, from around 70hz...and on up, stay with front firing,.... if thats how your speakers fire, into the room.
Sogood51 (System | Threads | Answers | This Thread)