... for classroom,meeting room,public security organs, procuratorial organs... E.TRADIO: Clear Speech Microphone,Omni Directional, Monitor Range 10- ... -directional Dynamic Range 104dB(1KHz at Max dB SPL)Maximum Level Input 120dB SPL (1KHz,THD 1%)Impedance 600ohm (imbalance ... , Jail, Classroom, Army's department.*According with CE standard. E.TRADIO High-Fidelity,clear speech audio surveillance microphone