1Stereo mixing with in-ear monitoring and able to hear the fullest, most accurate monitoring sound, compared to the traditional mono mode. 2Both mono and stereo operation with a convenient mix function. 3Wireless systems are more complex than wired systems, but more flexible. 4The wireless system has 6 selectable frequencies and can accommodate up to 4 compatible systems for simultaneous use without interference. 5Optional carrier frequency range: 526-535Mhz. Stage monitoring originated in the 1960s, and the rock band that continues to be noisy finds that if each player can hear each other's voice, the performance will be better. Later, people sent a specific mix to the floor-standing speakers on the stage (the "monitor speakers") to fulfill this desire. These wedge-shaped speakers have created the era of monitoring, but they are bulky, noisy, and the sound is limited to one place. Now, the wireless in-ear monitoring system allows you to hear the sound you want to hear without affecting others. These systems are comfortable loudspeakers that replace the wedge floor monitors with "in-ear" headphones. Features: Stereo mixing with in-ear monitoring and able to hear the fullest, most accurate monitoring sound, compared to the traditional mono mode. Both mono and stereo operation with a convenient mix function. Wireless systems are more complex than wired systems, but more flexible. The wireless system has 6 selectable frequencies and can accommodate up to 4 compatible systems for simultaneous use without interference. Optional carrier frequency range: 526-535Mhz. Specification: Type: Wireless Monitoring System Model: S2Product weight: 483g (transmitter), 95g (receiver)(Approx. ) Frequency response: 20Hz-18KHz Antenna: 1/4 wavelength Transmitter power supply: DC9V / 300mA Transmitter built-in o limiter Transmitter RF output power: 10mW Receiver standby time: >12 hours (1.5V 2XAA battery, which is NOT included)Use distance: indoor about 50 meters, outdoor> 100 meters Optional carrier frequency range: 526-535Mhz (Used in US Generally) Package list: 1 * Transmitter 1 * Receiver 1 * Headphone 1 * Power Adapter 1 * Accessory Kit 1 * User Manual Note: 1. Excessive use of this system may result in permanent hearing impairment and use as low volume as possible.2. If you do not use this product for a long time, please remove the battery. 3. Please note that there is NO battery included in the package. 4. Please allow slight error due to manual measurement. 5. Different monitor colors may be different. Thanks for your kind understanding. Transmitter Front Panel: Headphone output port: Can be plugged into 3.5mm headphone plug; VOLUME knob: Adjusts the sound output of the transmitter headphone; Stereo/MONO button: Selects the o connected to the INPUT (L) input and the INPUT (R) input to mix in stereo or mono. In stereo Stereo mode, o connected to INPUT(L) is sent to the left earphone, and o connected to INPUT(R) is sent to the right earphone. In mono MONO mode, o connected to INPUT (L) and (R) is sent to the headphones on both sides.