Though I like the idea, I think this is a bit of over engineering. How will the earphone decide what the outside sounds to adjust too? Does it need a microphon

Though I like the idea, I think this is a bit of over engineering. How will the earphone decide what the outside sounds to adjust too? Does it need a microphone? Why not just design the earplug so that it allows outside noise in when appropriate (ignoring the fact that we don't know how to tell which of those noises is appropriate). If you're going to pursue this, and have figured out how to define which noises to let in and which not to, might I suggest that you use the microphone for noise cancelling? Then you ignore the noise cancelling when you want to let in outside sounds and turn off the playing sound. Part of the problem as I see it is that we play our music so loud because we are trying to block out outside sounds. This is the beauty of noise cancelling, everything sounds louder because you aren't trying to overpower the outside sounds.