An old thread back up, but it's relevant.

What's the consensus of on the value of active noise cancellation on in-ear phones? I use a pair of Etymotic 6i which are excellent passive noise reduction. But I'm considering augmenting them with in-ear phones with active noise cancellation. But will I hear much of an improvement?

My budget is modest and my guess is that active in-ear phones will be somewhat poorer as passive blocking, but the active technology might make up for this.