The key to listening centers and group sound fields is the jackbox, the distribution point to the headphones. Califone gives more attention to this mini four-position stereo unit with silver-plated contact points for a solid connection and moisture resistance, individual volume controls, 3.5mm plugs and rugged ABS plastic housing for durability.-World's smallest 4-person jackbox for classroom portability and versatility -3.5mm input with individual volume control and stereo sound