Where your speakers are located is an important decision that will affect which format you choose, and the quality of sound in your home theater network. For a 5.1 surround system, you will need a subwoofer and 5 speakers located in the front right (R), front left (L), center (C), left side (LS), and right side (RS) of a room. A 7.1 surround system is the same as the 5.1 except with the addition of 2 speakers located at the left back (LB) and right back (RB) location. The subwoofer is designated as the LFE, which stands for Low Frequency Effect. Also, keep in mind that a stand–alone subwoofer is not always necessary especially if they are built into the front speakers. According to Dolby, the figures below describe the ideal location for speakers.
According to the surround sound experts, Dolby.com,
“The shape of your room and how it's furnished will affect the sound you hear. For instance, too many bare surfaces can cause reflections that may add harshness to the sound. Adding carpeting and drapes can help.
If you have a choice of rooms, avoid ones that are perfectly square or have one dimension exactly twice another. These rooms can aggravate resonances that color the sound.
If possible, center your seating area between the surround speakers.
The closer you place a speaker to intersecting room surfaces (corners, wall and ceiling, wall and floor), the stronger the bass output. This can help bass-shy speakers, but it can also add too much bass. Again, just moving a speaker a few inches can often make a big difference in sound.”