Page "Low-frequency effects" Paragraph 4

The LFE channel originated in Dolby Stereo 70 mm Six Track film prints, as a way of providing louder bass and sub-bass effects, without detracting from the quality of the standard audio channels.

The LFE channel is conventionally played back 10 dB louder than the main channels, giving significantly more recording headroom.

Also, the separate recording allowed a straightforward installation of extra dedicated subwoofers, and removed the need to upgrade the main speakers.