Noise-cancelling headphones reduce unwanted ambient sounds (i.e.,
acoustic noiseAcoustic noise is any sound in the acoustic domain, either deliberate or unintended. It is important to recognise that the term "noise" is also used to refer to other, non-audible forms, especially in electronics and in the radio/radar spectrum.-Environmental noise:Environmental noise is the...
) by means of
active noise controlActive noise control is a method for reducing unwanted sound.- Explanation :...
(ANC). This involves using one or more microphones placed near the ear, and electronic circuitry which uses the microphone signal to generate an "antinoise" signal. When the antinoise signal is produced by the
speaker driverA speaker driver is an individual transducer that converts electrical energy to sound waves, typically as part of a loudspeaker, television, or other electronics device. Sometimes the transducer is itself referred to as a speaker, particularly when a single one is mounted in an enclosure or as...
in the headphone, destructive interference cancels out the ambient noise as heard within the enclosed volume of the headphone. They should not be confused with Noise Isolating Headphones
Noise cancellation makes it possible to enjoy music without raising the volume excessively. It can also help a passenger sleep in a noisy vehicle such as an airliner.
Retail noise-cancelling headphones typically use ANC to cancel the lower-
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
portions of the noise; they depend on more traditional methods such as
soundproofingSoundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using...
to prevent higher-frequency noise from reaching the ear. This approach is preferred because it reduces the demand for complicated electronic circuitry that would be required for noise cancellation at higher frequencies, where active cancellation is less effective. To truly cancel high frequency components (coming at the ear from all directions), the sensor and emitter for the cancelling waveform would have to be adjacent to the user's eardrum, which is not technically feasible.
History
By the 1950s, systems were created to cancel the noise in helicopter and airplane cockpits. Noise-cancelling in aviation headsets is now commonly available.
Currently, most noise-cancelling headsets use analog technology. This is in contrast to other forms of active noise and vibration control in which digital processing is the standard method.
A number of airlines supply noise-canceling headphones in their business and first class cabins. Noise-cancelling is particularly effective against airplane engine noise. In these cases, the headphones are about the same size as normal headphones. The actual electronics, located in the plane handrest, take the sound from the microphone behind the headphone, invert it, and add it back into the audio signal, which 'cancel out' background noise resulting in a more enjoyable audio experience.
Limitations
Noise-canceling headphones have several limitations (that vary from vendor to vendor):
- They consume power, usually supplied by a USB port or a battery
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
that must occasionally be replaced or rechargedA rechargeable battery or storage battery is a group of one or more electrochemical cells. They are known as secondary cells because their electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything from a button cell to...
. Without power the headsets function like a regular headset or do not function at all. However, some originally developed for military intelligence operations employ a "pass through" system to allow the headphones to continue to operate normally, even if the battery power is expended.
- They may introduce additional noise, usually in the form of high-frequency hiss.
- The noise-cancelling circuitry required for them to operate inherently reduces audio quality.
- Early models were generally bulkier than traditional headphones. However, newer models tend to incorporate the batteries in pre-existing space. While this usually reduces the bulk, it does not reduce the extra weight of noise-cancelling headphones compared to traditional headphones.
See also
- Active vibration control
Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration. With this application, a precision industrial process can be maintained on a platform essentially vibration-free....
- Active noise control
Active noise control is a method for reducing unwanted sound.- Explanation :...
- Noise-canceling microphone
A noise-canceling microphone is a microphone designed to filter out ambient noise from the desired sound, especially useful in noisy environments.-Technical detail:...
- Passive Noise Cancelling Headphones
External links