This is the Behringer HA400 4-channel ultra compact microamp.
Using this unit, you can send a signal to 4 different sets of headphones so your musicians can have an in ear monitor. Whether you in the studio making tracks or in a live situation, this headphone microamp is perfect for your monitoring needs. Each channel has its own volume control giving you the ability to change levels on the fly. This headphone unit was conceived and designed by Behringer and therefore was built with high quality components and rugged construction to ensure long life.
Input Channels 1
4.1 x 2.25 x 1.8"