Strategies to Hear for a Lifetime: 1. Turn it down
People using noise-cancellation earphones listen about 4 dB lower than those without noise-cancellation technology. This is especially useful when listening in noisy environments such as an airplane or school bus.
Remember phase? When 2 sounds are 180 degrees out of phase, they can cancel each other out.
Phase is the fraction of a complete wave cycle elapsed as measured from a specified reference point and often expressed as an angle. Sound is cancelled (eliminated) when two sounds are presented at 180 degrees out of phase.