I'm probably gonna butcher this, but this is what I think it is; it keeps the impedance constant. When I say that it can either raise or lower the ohm rating that the amp sees. This will allow you to raise or lower the power that the driver receives. For instance: if the driver is rated at 8 ohms but the Lpad is set to 4 ohms than the amp is going to see 4 ohms and send 4 ohms worth of power. This is typically almost double the rated power of 8 ohms. This would raise the driver by 3 dB compared to the other drivers. If you want to lower the volume you would set the Lpad to 16 ohms. This would split the power sent to the driver in half, essentially lowering the volume by 3 dB.