Selective hearing headphones

Active noise cancelling is normally used when you want to protect your hearing. Sometimes, this is combined with a radio transceiver. However, there are also many high-noise environments where you actually want to hear the noise, e.g. Concerts, Discos and sports events, but where you might occasionally want to hear your companions over the roar.

For these situations, I propose a set of headphones that normally let ambient noise through* unless someone on your frequency speaks and then it mutes the ambient noise for crystal clear communication.

*There is an optional attenuation dial, in case you are developing a throbbing headache.

This idea was inspired by the "Personal Mute" and "SpeakOver Music" ideas; I'm surprised that it's not been baked or halfbaked (if it is, let me know)