No. With Panasonic's 'active shutter' 3D glasses, there's no need to worry about where you sit You can enjoy the full 3D TV experience wherever you sit.
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With some 3D systems, such as those that rely on polarising filters to produce the 3D effect, you have to be pretty picky about where you position yourself, and even the angle at which you hold your head. This is because they rely on controlling the angle at which light from the TV reaches the glasses.
This is particularly true of experimental systems that do away with the need for glasses. They work by aiming the left- and right-hand pictures directly at each eye. Move, and you'll miss it.
Panasonic's 'frame sequential' system sends out one image at a time, and uses the active shutter glasses to close off each eye alternately to ensure that only the correct image goes to each eye. Infra-red transmitters on the TV sync the glasses with the picture on screen, so you can enjoy full 3D from viewing angles of up to 135 degrees.