Sennheiser HD 350BT Black, Over-Ear Bluetooth Headphones, Circumaural, Closed, Bluetooth 5.0 and AA, AptX codec, Compatible with Sennheiser Smart Control App, Up to 30 hours of operation, Maximum SPL: 108 dB (1 kHz / 0 dBFS), Frequency range: 18 - 22000 Hz, THD: