Sony MDR-HW700 Wireless Digital Surround Headphone for MDR-HW700DS (Japan Import) Driver unit: 50mm Playback frequency: 5Hz-25, 000Hz Impedance: 24 Power supply: Built-in Li-ion rechargeable battery (DC3.7V) Charging time: 3 hours Charging Method: USB charge Battery life time: 12 hours Weight: about 320g Accessories: None