PreSonus HD9 Closed Cup Professional Headphones 100789372 and an automatic ambient pressure

and an automatic ambient pressure equalization valve (MIL-STD-648C) all contribute to their military grade design

All labels transfer across linked systems

Party-line - Headset Out: 300 - 15KHz ± 3dB

Mac systems require a Mac Pro computer with PCI Express slots

and increased sound output levels

PreSonus HD9 Closed Cup Professional Headphones 100789372 and an automatic ambient pressurePreSonus HD9 Closed Cup Professional Headphones When you need to do serious work without bothering anyone in your living space and without being distracted by outside sound, choose PreSonus HD9 headphones. They're clean sounding, extra comfortable, and offer a broad, transparent frequency response that ensures accurate mixing. The HD9s closed back acoustic design provides superior listening isolation and reduces headphone bleed, so you hear nothing