The Junction Boxes are available in several versions, with either six or eight headphone jacks, and with or without volume controls for each jack. Each junction box also has two expansion jacks for connection of additional junction boxes. The only limit on the number of headphones that can be connected is the output capacity of the audio source. Junction Boxes Cat. Each listening center contains a junction box and a complete set of six or eight headphones in a high-impact plastic carrying case.
All audio sources have an output load capacity, called output impedance.
Headphones are also rated in ohms, and when connecting a headphone to an amplifier, it is important that the ohms rating of the headphone should be equal to or greater than the ohms rating of the amplifier. For example, if the amplifier is rated for eight ohms, the headphones should be at least eight ohms. Headphone impedance is dramatically reduced when connecting multiple headphones. The audio source must have an impedance of 37.5 ohms or less. This formula only works when all headphones are of the same impedance.