Stereo imaging

[drgopu]

Dear friends.
since saturday I am facing a strange problem. I am not getting the perfect stereo image. vocals are shifted to the left. this happened after I interchanged my speakers position. when I restored them back, it's ok. but I am perplexed by the strange phenomenon. kindly throw some light on it..

 

[Sumanta]

I think one of your speaker is closer to its side wall than the other at the same time speakers are different to each other in terms of net sound output (or may be just one driver related to mid frequencies).
When you interchanged your speakers the weak one not getting help from the side wall is now producing less output.