Sennheiser HDR 175

System – model: RS 175

Headphones – model: HDR 175

Transmitter – model: TR 175

Transmission frequency 2,406 to 2,474 MHz

Modulation 8-FSK Digital

Signal-to-noise ratio analog input: typ. 85 dBA at 1 V rms

digital input: > 90 dBA

RF output power max. 10 dBm

Range up to 100 m (free line of sight)

Max. number of simultaneously connected headphones - 2

Type circumaural, closed

Transducer principle dynamic, neodymium magnets

Frequency response 17 Hz to 22 kHz

Max. SPL max. 114 dB at 1 kHz, 3 % THD

THD < 0.5 % at 1 kHz, 100 dB SPL

Operating time up to 18 hours

Charging time up to 8.5 hours

2 low self-discharge NiMH

rechargeable batteries,

AAA size, 1.2 V, 820 mAh

Magnetic field strength 2.7 mT

Weight (incl. batteries) approx. 310 g

Connections digital input: optical

analog input: 3.5 mm jack socket

Power supply 9 V , 300 mA

Power consumption operation: typ. 4 W

standby: ≤ 0.3 W (without charging)

https://www.amazon.com/Sennheiser-RS-175-Wireless-Headphone/dp/B00SLUI5SA?th=1