09 July 2014

Noise Cancelling Headphones

Hello,
 
as it is very interesting task in case of cancelling the noise specially for weakest signals pulling out on lowbands I am looking for best solution for long time. The prices are quite different and the quality may vary. I tested some of them but I did not found succesful efficient solution for reasonable price...
 
Noise cancelling technology

There are two types of ways to achieve noise cancellation, passive noise cancellation and active noise cancellation. Active noise cancellation is to use an extra microphone which emits high pitch frequency to counter the low frequency external sound. Noise cancelling headphones usually use active noise control (ANC), sounds travel through the air or through liquids in the form of waves, and each of those waves has a particular shape. Noise cancelling technologies first rely on small microphones that identify the sounds in a given environment. A digital signal processor determines what sound wave is necessary to cancel the unwanted sound wave and then it generates that sound and amplifies it through speakers or headphones. So basically two different frequency sound waves cancel each other out, thereby bringing the listener closer to silence.


So what’s the point of using ANC?
 
The main aim for ANC is to eliminate sound (noise) from a single source, prevent listeners from turning up the volume to a harmful level just to cover the noise, as cities nowadays are filled with hundreds of different unwanted noise. Headphone users often got interrupted by the noise. In a result of that users cannot fully enjoy their music. So, the purpose of this technology is to cancel or at least keep to the minimal of the unwanted sounds, in order to provide quietness for headphone users who live in busy, noisy area.
 
Fujikon NC-4


In practice, these are good stereo audio headphones like any other. They work fine and are comfortable. They are 32 ohm with maximum power output of 60 mW PMPO (whatever that might mean). They have sensitivity of 116 dB (off) and 122 dB (on). It comes with a long cord (just over five feet) and a 3.5 mm stereo plug; a twin-plug adaptor is also provided. The important bit is that they noise-cancel at 15 dB or greater, at 300 Hz. This means in practice that low-frequency ambient noises are cancelled. Normal audio received down the headphone line is not suppressed. This means that the masking of desired low-frequency audio is removed. The type of ambient noises that are best suppressed are constant engine noises. This includes hum and burble from aircraft noise and from fans, eg amplifiers, computers, airconditioners. These are the most noticeable but even voices (live or TV/radio) are suppressed.

The foldable-version has elbow-joints, just above the two ear-pieces. This allows the head-band to be folded back down between the ear-pieces and to fit nicely into the smart draw-string carrying-bag which is provided. That bag nicely carries the twin-plug adaptor and your spare AAA batteries.

My favourite N-C headphones NC-42
 
More informations You can find in the articles written by Roger Western, G3SXW (Republished from November 2005 CDXC Diges, bi-monthly journal of the Chiltern DX Club.) Published in FOCUS 66 - Spring 2006 (First Class C.W. Operators' Club Magazine) and also on Martin's web pages www.ok1rr.com on Mar 14th 2006...

My related older posts:
N-C headphones part I.
N-C headphones part II.
N-C headphones part III.
N-C headphones part IV.

to be continued...


Petr, OK1RP

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