New Delhi, Dec. 29 -- Noise isolation is one of the most misunderstood aspects of over-the-ear headphones. Many people assume that silence comes from electronics or software tricks. In reality, most of the sound blocking happens before any technology is involved. It is physical, mechanical, and deeply tied to how headphones are designed and worn.

Over-the-ear headphones work by covering the entire ear and creating a barrier between your ears and the outside world. When done well, this barrier reduces a surprising amount of everyday noise even before active noise cancellation enters the picture. When done poorly, even expensive headphones struggle to keep distractions out.

Understanding what actually blocks sound helps explain why some h...