The Mackie HM-4 is a 4-way headphone amplifier designed to provide simple and effective headphone amplification for artists, musicians, and engineers monitoring through headphones in home, project, commercial, and mobile-recording studios. Its single 1/4″ TRS stereo input and four 1/4″ TRS stereo outputs allow you to distribute a stereo source to up to four pairs of headphones.

https://www.youtube.com/watch?v=3_aDLiBAfb8