Most Earthquake subwoofers have dual subwoofer signal input. This serves several purposes.

1. It enables down-mixing of a 2 channel stereo signal into a mono signal that still contains all the original information that was in the stereo signal. This is useful if you have a stereo sub signal, but only one subwoofer.

2. It allows a LFE mono + stereo reproduction. When using two subwoofers, it is possible to use a Y-split LFE signal from the processor sub output. It is also possible to connect the sub placed in the left side to the main-out left from the processor (the output is also used to connect an external effect block to the left front speaker). The same can be done for the right side. The advantage here is that you get to keep both the dedicated LFE signal as well as your left and right stereo bass. This gives a 3D bass rendering many will regard as a significant upgrade.

3. Dual input allows the subwoofer an extra sensitivity adjustment. Normally, it would be enough to use a mono LFE subwoofer signal from its processor. If you have a processor with very low output so you can use a Y-splitter. By using both inputs with the same mono signal doubles the subwoofer sensitivity. This means that there is now only half the signal strength to drive it to full output.