Sennheiser’s HMD 46-II Series of very lightweight, extremely comfortable headsets are designed specifically for all air traffic control communication and C3 (Command, Control & Communications) operators requiring excellent sound and long-term wearing comfort. A noise-cancelling microphone delivers optimum speech clarity for reduced “call-back/read-back” events. The headset can be operated in two channel mode. Soft acoustic foam ear pads and patented two-piece automatic headband deliver first class comfort with a perfect, secure fit. A flip away headphone allows for single-sided listening and a reinforced flexible microphone boom allows for left or right sided use. The headsets feature a single sided cable which is easy to exchange. Sennheiser ActiveGard technology protects users hearing against acoustic injury caused by a sudden sound burst on the line, without interrupting communications - an added safety feature that differs from traditional acoustic shock clipping circuitry. The headset features a dynamic microphone and the series consists of two variants: HMD 46-3-II (double-sided including ActiveGard) and HMD 46-31-II (double-sided without ActiveGard )