Center Speakers are often underestimated in their importance, they handle the dialogue and much of the front soundstage information. Some say that up to 80% of a movie soundtrack is conveyed through the center channel speaker and therefore the hardest-working speaker in a home theater setup. Ideally, you want your center speaker to share the same tonal qualities as your main right and left speakers. In other words, timbre matched to the left and right speakers. This ensures that your front three speakers all produce balanced, consistent sound.
Surround speakers create that believable audio environment that makes home theater so immersive. They can go beside and/or behind or now with Atmos/DTS:X, above your seated position to provide the ultimate in a three-dimensional audio experience.
Surround speakers can be as simple as a pair bookshelf speakers placed on stands. You can use in-wall speakers for each location. Or you can use specialized bipole/dipole speakers that fire sound in multiple directions.
Upward-firing and in-ceiling speakers are a great choice for overhead surround effects in a Dolby Atmos or DTS:X system.