Specifications: FM system carrier frequency: R-ch 2.8 MHz / L-ch 2.3 MHz Speaker: 40mm mylar cone Impedance: 32 Ohms?0% Effective distance: 10 meters(max.) Power source: DC 3V (2x1.5V AAA batteries) Features: Light weight design for wearing comfort Auto muting on headphone Auto power off when no signal Volume control and on/off switch on headphone Mono/stereo switch on headphone