LFE Crossover

LFE (Low-frequency effect) Crossover, a basic form of bass management, is a technical method in audio equipment to cross-feed a low frequency part of the sound spectrum (the bass) from satellite channels to a low frequency channel, typically feeding a subwoofer.

Lack of LFE Crossover is a common cause of poor bass from home sound equipment.

Why?

Stereo and surround sound signals often contain some or all low frequency (bass) spectral components in the satellite channels, like front, center, side, or rear (surround) channels, because

* there may not be an LFE channel, like in a normal stereo signal (2.0),

* some bass signals may originally not have been mixed into the LFE channel, for various reasons,

* only frequencies below 80 Hz may be in the LFE channel, which is typical for some cinema sound systems, like THX and DTS, but the actually used satellite speakers may, for example, only be able to emit sound from 140 Hz and up, which is typical for small home sound systems.

To achieve a complete bass signal in these cases, it is necessary to take the missing low frequency parts of the sound spectrum from the stereo or surround speaker channels, combine them, cross-feed them to the low frequency channel, usually leading to a subwoofer, and ideally remove them from the surround channels.

How?

A good sound source, like a DVD player or a computer's sound adapter, has an LFE Crossover setting, which either allows to set the size of the satellite speakers or, more precisely, to set an LFE Crossover frequency, typically in the range of 80 to 160 Hz.

The part of the sound spectrum below that frequency is then taken from some or all surround channels, added together, fed to the LFE channel and, in most equipment, removed from the satellite channels.

Since the bass is almost never severely phase-shifted between the satellite channels, simple addition of the signals is sufficient.