3.27 Why do I need a center channel in my car, and how do I do it? [HK, JSC]
If a proper center image isn't achievable via a two channel configuration, installation of a center channel can help. Since the majority of recordings are done in two channel, a two channel system designed correctly should be able to reproduce a center image which was captured during recording. A center channel is not simply a summation of the left and right channels, like bridging an amplifier; rather, it is an extraction of common signals from the left and right channels. This usually means the lead vocals, and perhaps one or two instruments. These signals will then be localized to the center of the stage, instead of perhaps drifting between the left center and right center of the stage. A signal processor is usually required in order to properly create a center channel image. The image should then be sent to a driver in the physical center of the front of the car, at an amplification level somewhat lower than the rest of the speakers. The correct frequency range and power levels will depend on the particular installation, though a good starting point is perhaps a pass band of 250-3000Hz at an amplification level of half the power of the main speakers (3dB down).
CAF comment: With the arrival of Video systems, true surround sound is now a reality for car, with that in mind, many surround sound processors make use of a center channel.