Dual channel headphones are an important feature if you wish to watch two DVD's at the same time in the back seat.  Please note all headphones from OnFair are dual channel headphones. 

Dual channel headphones are equipped to receive the IR (infrared) signal on two frequencies.  Typically they are simplified to channel A and channel B.  We always recommend setting up one headrest to channel A and the other headrest to channel B.  Then setup your headphones to channel A and B accordingly. 

The IR signal from the headrests to the headphones is a "Line of sight" singal meaning you need to be sitting directly behind or within less than a 30 degree position to receive the IR signal. 

We have many large families who wish to install 4 headrests into one vehicle.  We always recommend alternating the A/B audio signals from left to right.  Meaning that in the middle seat have channel A on the left and channel B on the right side.  Then in the back seat, alternate it so channel B is on the left side and channel a is on the right side.  We're told this works well at reducing any overlap and signal interference.