How Do Noise Cancelling Headphones Work?
Noise cancellation was first patented by Paul Lueg in the early 1930’s. Lueg had recognized that the technical merits of sound cancellation would require creating an identical but opposite sound wave to cancel out ambient noise. By the 1980’s electronic noise cancellation technology was being implemented in aircraft headphones to protect pilots from hearing damage. The most common type of noise cancellation is “Passive” while “Active” noise cancellation technology is now preferred. Below is a brief description of the two types of cancellation technologies.
Passive Noise Cancelling:
All headphones have some form of passive noise cancellation (also referred to as noise isolation) due to the materials used in their construction. Over-ear headphones enclose the wearer’s ear completely and provide passive noise cancelling due to their design. Passive noise cancelling headphones take it a step further and are packed with super dense foam or sound-absorbing material and are made with thick plastics or metal alloys to block high-frequency ambient noise. The downside of this thick material is added weight which can induce strain and fatigue on the wearer over long periods of time. In-ear headphones are small and have little room for added noise dampening material so their tips are designed to block ambient noise. Earbuds can work like earplugs and sometimes rival the noise cancelling capabilities of active noise cancelling systems.
Active Noise Cancelling:
Advancements in sound electronics technology have lead to active noise cancelling which utilizes a 4-step system to erase lower frequency ambient noise. These headphones create their own sound waves that are identical to the incoming sound waves with one exception: they produce waves that are 180 degrees out of phase or reversed from the incoming sound. This is known as destructive interference and causes the two waves to cancel out resulting in silence, if we lived in a perfect world of course.
To accomplish this destructive interference, microphones placed in the ear cups “listen” to external sounds that cannot be blocked passively and send that information to noise-canceling circuitry. The electronics, usually placed in the ear cup or in line with the signal cable, duplicates the frequency and amplitude of the incoming wave and inverts it 180 degrees. Then the speaker produces this new frequency along with normal sound waves to effectively erase noise. A downfall of active noise cancelling circuitry is that they require a battery to energize the system which can decrease convenience.
This active cancelling technology works well for continuous sounds such as the humming of a jet engine, train or a refrigerator. This technology is still in the early stages so it does not completely omit all sounds. On average, active noise cancelling headphones provide an additional reduction in noise of about 20 decibels, which is 70 percent of ambient noise. Because these systems are battery powered they often induce noise into the headphones in the form of a high-frequency hum. This noise is often unheard when actually listening to music but might become annoying to some who use active noise cancelling headphones just to get some peace and quiet. Regardless of any drawbacks, most people will never steer away from noise cancelling headphones back to normal headphones again.
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