4 Channel Stereo Headphone Amplifiers: 4 channel distribution system allows up to 4 person to listen and play at the same time, with excellent sound quality. Independent Adjusting Knob: Individual volume controls allow each listener to determine their own volume through a dedicated output volume control knob. Low Noise: Enjoy a low noise monitor distribution and music system. The ultra compact stereo headphone amplifier is easy to carry and can be used anytime, anywhere. Widely Used: Ultra compact headphone amplifier system is for studio and stage applications, outdoor performance, mini concert, karaoke, conference speech. Metal Material: Headphone amplifier is made of metal material, strong and durable, with a non slip pad at the bottom for stability.