How Noise Cancelling Headphones Work To Improve Sound Quality



One of the determining factors in the final sound quality we perceive through our hi-fi headphones is ambient noise , especially if we live in neighborhood noises and we do not have an acoustically isolated room, or we are in public places or just traveling In any means of transport.

There are several formulas to avoid annoying environmental noise, or at least to minimize it to the point that it is no longer perceptible to a large majority of users, which we can classify in active and passive technologies .

Passive techniques are commonly known as acoustic insulation systems and their mission is to prevent the external sound from entering our auditory system, which is why it is usual to interpose insulating material between the casing or outside of the earphone and the part that will go Stuck to our ear or ear.

Noise-Cancelling Headphones Work

It is the simplest, cheapest technology that is usually used in all headphones with more or less fortune. However, it has the disadvantage that it does not cancel the external noise, it only attenuates it (in values ​​that can go from 8 to 20 dB depending on the materials used, whether they surround all or part of the ear or if they are intrauricular) and depending on the insulation May not work well at low frequencies (below 100 Hz).

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Active Noise Canceling: What it is and how it works

If we want to go a step further and eliminate outside noise as much as possible, we must opt ​​for those known as Active Noise Control ( ANC ) systems. What does it consist on? For they base their operation on the theory of waves interference.

Sound is a low-frequency wave (the human perception limit is below 20 or 22 kHz) which complies with the principle of superposition of wave theory, which could be summarized as that when two or more waves Find in the same point, the resulting total wave is the vector sum of the incident waves.

Thanks to this feature it is theoretically possible to create an artificial sound wave that added to the original wave results in the total or partial cancellation of a part of it, is what is known as destructive interference of waves.

Acoustic waves

Moved to the world of headphones, the original signal is the sum of the signal we want to hear, i.e the music, plus background ambient noise surrounding us. The artificial signal will be a sound wave created by an electronic circuit that will cancel this ambient noise.

As it does? First, through one or more microphones located in the body of the headset or the cable picks up the noise that comes to him and by processing it generates an equal but opposite phase signal that when reproduced next to the original signal will give as Resulting in destructive interference and a sound free of external noises. Or that at least says the theory, since active noise cancellation is not 100% perfect (although it usually manages to reduce noise by more than 25 or 30 dB) and its operation is limited by the main frequencies that conform The noise signal.

Active noise canceling headphones

So, for example, the usual thing is that it works very well if we have a low frequency noise and constant type like the one produced by the engine of an airplane, a car, even the hum of the fans of a computer equipment ( here you have a Example of this technique applied to actively reduce the noise of the typical fans of the computer). In fact, headphones incorporate preset listening modes for each of these situations, such as the ATH-ANC9 QuietPoint .

However, its effectiveness decreases with high frequency sounds, although fortunately this is where the efficiency of the aforementioned acoustic insulation improves, so that the total resulting insulation factor is usually very good.

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Active Noise Canceling: Main Drawbacks

The first and most immediate disadvantage of active cancellation versus only passive systems is that they need external power to operate the noise detection system and wave generation in phase shift. This power is usually provided either by the USB connector of the headset (if using this system), or by small batteries (usually AAA type) or rechargeable batteries, a factor to consider if we think of taking the headset travel.

Another disadvantage is that the active cancellation system itself introduces modifications to the final signal , which in some cases degrades it due to the imperfections of the noise detection system, which can introduce annoying background hisses , which are generally more noticeable the more Cheap is the technology used.

The cost is its third main drawback, since incorporating the system into a headset causes its price to increase appreciably . Also, it should be noted that in some models (especially in the older ones), the fact of carrying an ANC system implied an increase in the volume and weight of the equipment, something that has fortunately been minimized with the passage of the weather.

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