There are a lot of factors that will effect the “sweet spot.” If either speaker or the seating is nearer a wall on one side than the other you will likely get slightly higher SPL on that side even if sitting in the middle. Level matching the speaker will help but the wall will still effect the soundstage and tonality coming from the that side. If you can place speakers so that the drivers are at least 3 feet from the side walls it will help minimize this. Sitting close to the back wall will also effect imaging and clarity. Same thing applies with seating, try to keep it more than three feet from any walls.
This is where room correction systems like Audyssey are suppose to help in neutralizing the rooms effects on the sound arriving at your listening position.
Another factor I’ve found has a big effect on the sweet spot is toe-in. By using more toe-in I can create the best possible imaging at the sweet spot but at the cost of poorer imaging farther away. I’ve found that less toe-in generally produced a larger sweet spot at the cost of having the most perfect imaging. Of course the room plays a big role in how toe-in effects the imaging.
Cheers,
Dean
