The center channel speaker is probably the most important speaker in a home theater system. It must reproduce vocals and sound effects clearly and with high fidelity. It must also be timbre matched with the other speaker products in the system. A center speaker is usually placed centered, above or below the visual device.
When choosing front speakers, it is extremely important to use voice matched drivers in order to achieve identical sound characteristics from all speakers. The same type of drivers in all five speakers gives you a seamless experience when the sound is panned across the soundstage. Having timbre matched front speakers guarantees a balanced and natural sound from the front of the room. The fact that the center channel speaker is not equipped with the same bass drivers is not important since the bass information is directed to your left and right front speakers or to the subwoofer.
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.
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.
Dolby Pro Logic and Dolby Digital are registerd trademarks and owned by Dolby Laboratories Licensing Corporation.