Subwoofer 3D Illusion

I have a set of floorstanding speakers, Silverlines, that do a good job at reproducing bass; however, I wondered if a subwoofer would add a more phyiscal presence to bass drums. I bought an economy sub off Audiogon to see if it would do the trick.

I listen in a somewhat of a nearfield arrangment. The mains and my listening chair form an equalateral triangle. I recieved the sub and hooked it up to see if it worked. In the test to see if the sub was mechanically working, I just placed the sub behind my listening chair. Afterwards, I was going to move the sub to a more typical location in the setup, but a strange thing happened.

I have the sub crossing over at the lowest point possible, so it doesn't do much of anything except when percussion kicks in or maybe a piano hits the low registers.

The effect is that mids and highs still come from the mains as before, so does bass, around 40hz, but when something in the lower registers hits, below 40hz, it seems to come from all around, giving a pseudo-larger soundstage. The song Changes, on YES 90125, is a good example. Without the sub, the drums at the start sound great. With the sub it seems to have a more theatrical, dramatic effect.

It is a weird kind of trick. The mains are in front and the sub is right in back of me. The fact that the sub is right next to my listening chair makes me feel the bottom in my gut more than before. I am not sure if I like it or not, but it is a trip for now.

Has anyone else tried this?