11 September 2014

Noise cancelling headphones - part II.


in preview part I did not mentioned anything about the "second" way of the noise cancellation which I named in my article "the passive noise cancelling" method.

As I realized that it is a bit confusing so I am going to try explain what I mean by these ways of noise cancellation...

Active noise cancellation

As I already mentioned more detailed in the first part - the noise cancellation (more or less known as ANC) takes an active approach to blocking-out an external noise. There are one or more microphones built into the headsets to detect external noise. Using the electronic signal processing an "anti-noise signal" is then generated to cancel-out the external noise.

        Bose QC-15        
In fact it is leaving only the desired outside disturbing noise that is reaching Your ears in the room. With a pair of good ANC headset You should hear your intended radio signals without any background noise.

Passive noise cancellation

The passive noise cancellation does not make use of any electronics to blocking-out surrounding noise. In fact it is using the different of construction materials and an ergonomic design to blocking-out as much background noise as possible coming to the ear canal. With respect to this fact it is better to talk about "noise isolation" instead of cancellation job...
For big headsets (mostly known as over-ear) it is commonly done by soft and thick memory foam earcups padding that fits snuggly over your ears. The fact that it fit "airtight" inside your ears keeps the noise out.
For in-ear earphones which are probably not used for ham radio applications so often the eartips are ergonomically customized to fit securely in the ear canal which effectively forms a sealing chamber within the ear canal and blocks out external noise significantly.
So in summary...
Noise isolation or passive noise cancellation or noise reduction

is provided when headphones totally cover the outside of the ear or ear buds can be used that fit snugly into the ear canal thereby preventing external background noise, buzzing or sound reaching the listener in the first place. Passive noise reduction (better we should call it noise isolation whenever) is mostly used to cancel-out unwanted high frequency sound which is difficult to effectively removing using an Active Noise Cancelling (ANC) system. This is the reason why better headsets are using both - good noise isolation as same as the ANC gadget inside...

 Goldring NS-1000

For example in my small radio room I measured over 78dB of background noise when all power amplifiers, power sources, computers and other fan's equiped stuffs running and it really make sense for weak signals pulling out. Just to compare > when all is down the ambient noise is measured around 30dB in the room. So this is my personal reason of looking for good quality and effective ANC headset.

Another headphones test by Mark, PA5MW can be found here.
Hope it helps a bit.
73 - Petr, OK1RP

No comments:

Post a Comment