Noise cancelling earbuds/headphones differ from noise isolating earbuds/headphones. Noise isolation just keeps the sound out, whereas noise cancellation actively produces sound in order to "cancel" noise. I understand how this works technologically, however do these sound waves cancel out so that your ears are subjected to reduced decibels? I have tried a friend's pair. When nothing is going on, you hear lots of "static"-like noises. No doubt this is the earbuds trying to cancel ambient sound. Anyhow, i'm wondering if this is good for your hearing, and not just for listening to better music. Can the extra sound waves generated actually increase the ambient volume?