Sennheiser RS 175 RF Wireless Headphone System Compact, ergonomic over-ear headphones. Connectivity Technology: Wireless Bass boost & surround sound listening modes. Maximum sound pressure level : 114 dB at 1kHz, 3 percentage THD. THD, total harmonic distortion : &lt;0.5 percentage at 1 kHz, 100 dB SPL Digital wireless technology ensures that signal transmission remains clear & accurate Easy to set up & enjoy MAIN controls located on headphones