What About the Sub-bass?

Specifically, what is the low-frequency effects channel and what is it used for?

The LFE channel can be part of any Dolby Digital (AC-3) bitstream containing more than two main channels. It is intended to carry low-frequency information below 120 Hz to drive a subwoofer, also known as the 0.1 of a 5.1 channel speaker system. The main channels can carry low-frequency effects--such as rumble from explosions, tremors from earthquakes and the like--and the LFE channel can also carry the lowest frequencies.

However, the LFE channel should normally be used in conjunction with one or more of the main channels. This means sending any critical information not just to the LFE channel, since all consumers may not hear it. Two major reasons may prevent the LFE channel from being present. First, if the consumer has only a stereo playback system such as the speaker in a television set, the LFE information is discarded during the downmix. Another reason might be that a consumer has five speakers but no subwoofer. Generally, the LFE information can be rerouted to other speakers such as the front left and front right, but this must be set by the consumer. Yet another reason to be careful of the LFE channel is for the consumer with five speakers and a subwoofer set to reproduce very loudly. The best advice for the LFE channel is to use the power wisely.