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. Weight 6 oz.1. Four 3.5mm listening positions for most listening groups2. Rugged ABS plastic casing for durability and school safety3. Silver-plated contacts prevent " crackling" sound heard when connecting with other jackboxes4. Customized preferences with individual volume control5. Skid-resistant pads at each corner won't mar or scrape surface6. 3.5mm stereo plug with detachable 6' patch cord (not shown) connects with media playersIdeal for Itinerant Teachers and situations requiring portable equipment with quality sound. Can be used for Listening Centers, ELD / ELL / Title 3 / Special Education applications as well as Language Labs and call center training.