Up to four bandmates and controlled-producers can collaborate without disturbing family and neighbors using this all-PreSonus monitoring package. You get four comfortable, durable PreSonus HD9 professional studio Headphones, which feature 45 mm dynamic, neodymium drivers in a closed-back acoustic design for superior listening isolation, high power handling, and a tailored frequency response from 10 Hz to 26 kHz. Feed your HD9 headphones using the included PreSonus HP4 headphone amplifier’s four screaming loud, crystal clear headphone preamps with individual level controls and mono summing. Send the stereo signal to studio monitors or daisy-chain another headphone amp using the ¼-inch balanced line outs.