POLY CS540 + API-28. Product type: Headset, Wearing style: Ear-hook, Recommended usage: Office/Call center. Connectivity technology: Wireless, Frequency band: 6.8 GHz, Wireless range: 100 m. Ear coupling: Supraaural, Headphone sensitivity: 118 dB. Microphone sensitivity: 85 dB. Talk time: 7 h