Noise canceling headphones reduce ambient noise so the wearer can either enjoy a greater degree of quiet for relaxation, or listen to music at lower volumes than would otherwise be necessary. By removing competing noises from the acoustic envelope, noise canceling headphones create a more pleasurable listening experience. There are two main types of noise canceling: passive and active.
High frequencies in the immediate environment can be blocked to a great degree by using dense materials in the construction of the ear cups. This is referred to as passive noise canceling (PNC) and is especially effective in models with larger ear cups. The drawback is that PNC does not lend itself to lightweight headphones or to in-ear earbuds that sit in the open end of the ear canal. In-canal earbuds, however, slide snugly into the ear and more effectively block high frequency noise.
To block lower frequencies, noise canceling headphones employ on-board electronics that continually sample ambient noise and generate inverse sound waves through the ear cup to exactly cancel the ambient fingerprint. To accomplish this, a small microphone built into the ear cup feeds surrounding noise to the electronics, which generates an opposite wave form, sending it through the ear cups. This is referred to as active noise canceling (ANC) and requires power via a rechargeable battery.
The most effective noise canceling headphones employ both ANC to cancel low frequencies and PNC to cancel high frequencies. Examples of the former might be the hum of a refrigerator motor, A/C unit, subway, or airline's engines. In the latter case, it was on an airliner that Amar Bose, founder of Bose Corporation, first conceived of noise canceling headphones, as the plane's engines drowned out the airline headphones. His idea was soon followed by others, and today there is no shortage of models to choose from.
As with any other technology, ANC and PNC have their limitations. ANC works best on reducing background noises that are consistent, rather than the constantly changing noises of nearby chatter or the cacophony of general hustle and bustle. Also, people who find in-canal earbuds uncomfortable and prefer lightweight ear cups might find that effective noise canceling headphones are a bit pricey. Generally, it is cheaper and easier to build a bulkier, heavier cup.
All things considered, noise canceling headphones can be of great benefit to the user in the right situations. Whether a person wants to block the drone of the neighbor's gardening equipment to take a nap or listen to his or her favorite soft music on an extended coast-to-coast flight, noise canceling headphones could be a good solution to noise problems.