Surround speakers
The surround speakers in a Dolby Pro Logic system are used to create an atmosphere and a sense of space. The sound has limited bandwidth and is produced in mono. Therefore the speakers can be small and do not have to be voice matched. They should be aimed away from the listener and reflect the sound off the wall boundaries. Digital systems, like Dolby Digital and DTS, need more attention. The surround speakers in a 5.1 system, reproduce sound in stereo with full bandwith. Therefore, using speakers that are voice matched with the front set-up and directing the speakers directly towards the listener is recommended.

Subwoofer
A separate subwoofer is designed to accurately and dynamically reproduce low bass frequencies. It creates a better sound experience in the entire system whether listening to movie soundtracks or musical recordings. By adding a subwoofer, the low frequency information is directed to the subwoofer and the satellites are relieved from the stress of reproducing low bass resulting in a more dynamic sound system. In systems using Dolby Digital or DTS technology, the use of a separate subwoofer is mandatory since a large part of the lower frequencies are mixed to the discrete subwoofer channel for added impact.