I listen to rock music and usually in the musical mix, the drum is placed at the center/back of the soundstage, the vocal is at the center/front, and other instruments like guitar, piano are either are the left or right and slightly up front. So this gives a nice weight to the soundstage with the drum and vocal act as a foundation upon which others are built. I notice that in an orchestra, the light instrument such as violin are placed on the left side, whereas the heavier instruments such as the cellos are on the right? Is that the usual convention? Are there any reasons for that? Whenever I listen to a classical piece, I also get this odd feeling like I am listening to the bass part on the right and the light part on the left as if I am listening to two separate events. Can the cellos be places at the center/back of the orchestra? Are there any reason why not?