Split Audio Source When Plugged

[1nth3m1x]

This is for a special project. I have a long audio cable coming from a PC. I want to split into two 3.5mm connectors (one for headphones and one for speakers). What do I need for when I plug in the headphone, the sound from the speaker stops?

 

[Alabalcho]

You can build one with parts costing like $10, or you can get 3.5mm stereo selector.