Subwoofer & LFE Channel Background Info

THE SUBWOOFER & LFE CHANNEL - BACKGROUND INFO

Checking summing phase cancellation

In a basic 2-channel setup or 5-channel setup (like the ITU-

775)a subwoofer is not specified and is not required. But making audio production to be played back on consumer equipment, one has to ensure that the mix will sound right in this situation. Many consumer setups provide a subwoofer. Hence it is very important to check what the summing of the bass is like. If the program material basically is out of phase, the bass will be cancelled when summed electrically. But this is not the case if the bass signals are reproduced by the main monitors and summed acoustically. A dramatic difference may exist!

Controlling standing waves

It can be very difficult to get two monitors in the right position in order to prevent the excitation of the standing waves. But placing five monitors are even more difficult! Each monitor should play under the same conditions as the others but that is seldom the case.

Three front monitors can normally be placed away from

disturbing boundaries to prohibit the excitation of the standing waves. But in small rooms the rear monitors very often are placed in a corner or on a wall. Having the full frequency range reproduced in a monitor like that, there may occur serious problems which results in a poor low frequency sound distribution in the room.

So this is another reason for using bass management. Simply: Only one monitor - the subwoofer - has to be placed in a safe position. The cross-over frequency can be selected to a value just above the problematic frequency range.

The LFE Channel

LFE is short for Low Frequency Enhancement or Low Frequency Effects, the first being the original name but the second being the most correct with regard to its application.

It is also referred to as the .1-channel, which indicates that the frequency range of this channel is only a fraction of the other channels in a multi channel setup. The actual frequency range is 20 Hz to 120 Hz.

When reproduced the signal is gained by 10 dB compared to the main channels. This provides a possibility of reproducing occasional high-level low frequency contents without affecting the general level setting of the main channels.

Leading signals to the LFE channel should be evaluated carefully in each case as not all transmission or reproduction systems may include this channel. In the music mix there is no special reason for using this channel unless you are recording the 1812 Overture with its canons and all that stuff.