Unfortunately, external noise in many environments prints, distorts, or blocks sound from headphones. If you've tried listening to music on a plane or in a crowded street before, you know the problem well. The roar of engines, the noise of cars, the sounds of people talking, the music makes it hard to hear. Thanks to Modern technology, we can now buy headphones that block out noise and allow us to enjoy nothing but the music we want to hear. These are called Noise-Canceling Headphones. So, how do noise-cancelling headphones work?
Noise cancelling headphones are divided into active type or passive type. Technically, all types of headphones can passively provide noise reduction. This is because the materials on which headphones are made block some sound waves, especially at higher frequencies. So even simply turning off a headset over your ear, as you can imagine, acts as suppressing some external sound, but this basic suppression is far from enough in most cases.
Passive Noise Cancelling Headphones
The best passive noise cancelling headphones are semicircular headphones (Ing: "circum-aural headphones") specially made to maximize noise filtering capabilities. This type of headphones are heavier than regular headphones, as they are filled with high density layers of foam or other sound-absorbing materials. All this extra weight allows for a reduction of about 15 to 20 decibels (dB) in noise. But given that jet engines generate 75 to 80 dB of noise in aircraft cabins, it is clear that passive models have some serious limitations. That's where active noise cancelling headphones come in.
Active Noise Cancelling Headphones
Active noise cancelling headphones can do everything passive types can do. Their structure creates a barrier that blocks high-frequency sound waves. It also adds an extra level of noise reduction by actively erasing lower frequency sound waves. They do this by creating their own sound waves that mimic the noise coming from every angle.
This type of headphones have microphones that receive frequencies of ambient noise. A digital signal processor inside the headset calculates exactly which types of sound waves will cancel out unwanted sounds and generates the necessary sound waves. According to the laws of physics, sound waves with full 180-degree out-of-Phase frequencies with each other cancel each other out, causing silence. To be more precise, it cancels each other when two waves have the same amplitude and frequency, and when their peak and pits are flush. This is called destructive interference. You can see it in more detail in the video below:
Several components are required to achieve the noise reduction effect in headphones:
- Microphone: a microphone placed inside the ear chamber "listens"to external sounds that cannot be passively blocked.
- Noise cancellation circuit: again, the electronic circuit placed in the ear cup detects input from the microphone and creates a "fingerprint" of noise by determining the frequency and amplitude of the incoming wave. It then creates a new wave that is 180 degrees out of phase with noise-related waves.
- Speaker: the "opposite-sound" generated by the noise cancellation circuit is directed to the speakers of the headset along with the normal sound. Opposing-sound erases noise through destructive interference, but does not affect the desired sound waves in normal sound.
- Battery: the term" active " means that energy must be added to the system to create a noise cancellation effect. The source of this energy is a rechargeable battery.
Noise cancelling headphones can provide an additional 20 decibels of noise reduction thanks to these components. This means that about 70 percent of ambient noise is effectively blocked. This reduction rate therefore makes noise cancelling headphones indispensable for airline and train travel, outdoor office environments or other places where background noise is high.