For fans of the Nokia BH-905i, Järvensivu had this to say about the increase in the cancellation effectiveness:
We went from 99.0% in the BH-905i to 99.8%, which means we quadrupled the total isolation. The BH-905i was the world’s best active noise cancelling Bluetooth headset, and the Essence is even better. It blows everyone else out of the water.
While modern earbuds are good at isolating high and mid-range frequencies, it's the booming bass frequencies that manage to punch through the ear pieces and interfere with one's music listening. Turning up the volume doesn't help either. Therefore, it was explained that the noise cancellation is tuned to this low frequency band to eliminate external noise. Along with this, microphones placed inside the ear buds try to help cancel out the noise caused from the blood flow in your own body.
One very cool side effect that audiophiles would value is that we use feed-back active noise cancellation. It means that the microphone that listens to noise is inside your ear, not on the outside like in more traditional active noise cancelling headphones. This means that it eliminates some other types of noise that can be unexpectedly annoying. For instance, with regular in-ears, if you’re in a quiet room, you can hear your own blood flow inside your head. Our noise cancellation eliminates some of that. Also, when you play a powerful bass note, that note will resonate inside your ear canal and make the bass a bit lazy and booming. We eliminate that resonance as well, resulting in a very tight and accurate bass.
Because earbuds are so much like earplugs, your own voice can sound rather strange too. The engineers behind the Essence have even tried to fix this by letting the frequencies of a normal human voice in through the external microphone and out through the ear buds.
...[R]egular in-ear headphones isolate noise in typical speech frequencies, when you’re on the phone, you can hear your own voice as it echoes inside your head. It’s called occlusion, and it’s very annoying. With the Essence, we use the speech microphone to feed sound from the outside world back into the headphones – but only a very specific frequency band, that’s within your speaking range, 400Hz to 3400Hz. So you have a more natural sound – and that’s what we call “natural speech” in the product. Obviously, the frequencies outside this range are still eliminated, so it’s easier to talk in noisy places, too.
David Gilson for All About Symbian, 7th September 2011.