Mackie HM-4 4-Way Headphones AmplifierThe Mackie HM 4 is a 4 way headphones amplifier designed to provide simple and effective headphones 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. Each output is controlled via a dedicated level knob, allowing varied