Why do passive isolation headphones work so well?

Direct Sound Headphones are Noise Cancelling by Passive Isolation. This means you don’t need batteries.

Specially Designed cushions act as a barrier between your ears and the outside world. While other headphones may measure their noise reduction capabilities at one specific frequency these offer true passive isolation over a wide frequency range. The Headphones include the latest in TruSound® delivering a full range of frequency response to make the listening experience full and enjoyable.