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Noise Cancelling Headphones - part I.

5. října 2007 v 10:12 | Petr, OK1RP |  Technical topics
THE NEW WEAPON: N-C HEADPHONES

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...

Maybe I am the last person on the planet to experience this new piece of technology. If so, my apologies - please ignore what is to follow. But I get the impression that few DXers have tried noise-cancelling (N-C) headphones on the air. Here is my story so far. I was impressed when my friend Ian, G3WVG, let me listen to his £60 headphones, a while ago, on an aeroplane. The effect was dramatic. It killed a large proportion of the in-flight noise. But, ahem, that seemed rather a large sum to pay for this pleasure. However, I could see that this might help to reduce fatigue and to increase listening-pleasure on long-haul flights. Then I saw an advertisement in RadCom for the Fujikon noisecancelling stereo headphones at less than £20. Now you're talking! So I bought them. See RadCom, October 2005, page 98, bottomleft, Waters & Stanton. You can buy the Fujikon NC-2 for £18.95 or the folding design NC-4 for £19.95. I splashed out the extra one pound.

Physical
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.
In-Flight
The effect is quite dramatic. Suddenly you can hear the movie sound-track clearly. It is like chalk and cheese. You know that feeling of frustration when you are trying to listen to a movie or your favourite jazz soundtrack and you have to struggle. Those days are gone.

I have suffered for some while with tinnitus (the hissing type), so I perhaps pay attention to hearing issues more than most people. I am convinced that the world is becoming a noisier place and that we are all conditioned to accept this as the norm. A result is degradation of pleasure but when flying, for example, I wonder the extent to which it also adds to fatigue. You get home from a long flight feeling exhausted, yet you have just been sat there doing nothing all day. I can honestly say that getting home recently from two back-to-back eleven-hour flights while using these N-C headphones I actually felt human.
On-Air
Anyone who has operated the bands with the benefit of a beverage receiving-antenna will know the magic that they can perform. Suddenly you can copy a signal which was previously below the noise. This only works when the signal to noise ratio is marginal - you can just about hear the signal but cannot copy it. Switch in the beverage and the S-N ratio improves by just a few dB, enough to copy the signal. At 5U5Z last November our transmit signal was greatly enhanced by use of the tall Titanex vertical, but without the beverage we would have made hardly any contacts because almost all signals were below the noise.

Forget installing beverages - use N-C headphones. I am exaggerating of course. It would be best to use both, but the affect is similar. Those marginal signals are so frustrating; you can hear them calling but they're not quite loud enough to copy. Switch on the N-C headphones and suddenly those low-frequency ambient noises are killed and you can copy him. This occurs rather infrequently.

Most signals can be copied or else cannot be heard at all, but for those few signals which are right on the margin it's like a piece of wonderful magic. Beyond making signals copyable, there is also a perceived increase in audio-quality. It actually feels more complete and enjoyable and even your CW sidetone sounds more crisp (and louder) when it is not being masked by those low-frequency ambient-noises.
Convinced
I am convinced. This is the new secret weapon for any DXer or contester. Go buy them (no, I am not on commission). It is the best new operating-aid since they invented the iambic-keyer or the computer-logger. Downside? Well, only one, these N-C headphones work with one AAA battery that only last about 24 hours. So, firstly, just get into the habit when slipping them off the head of flicking the 'off' switch. For one-off longhaul flights (rather infrequent for most people) this is not a problem- just load a new battery before travelling. For a contester, not a problem, maybe you need to put in one new battery to get you through a weekend. For regular use at home, maybe you leave them switched off until you hear that marginal signal which needs the N-C help. When the battery starts to fade you notice that the 'On' red LED fades. Then when the battery has died the LED does not light at all, the NC effect stops, but normal audio continues as usual. Finally, at the complete death of the battery you hear popping-noises whenever they are switched to 'on' position.

As you might begin to surmise, I am rather impressed. The cost/benefit ratio could seldom be better.
From Bruce, AA4Z (from the FCG Reflector)
Noise Cancelling Stereo headphones were easy to find in the Clearwater, Florida, USA area. The local CVS store had them displayed along side personal DVD players. They were priced at $14.95 but were on special offer for $9.95!

First of all, they are a reasonable set of headphones for $9.95. In series with the cord there is a control with a volume control, a mute switch, and an on/off switch for the noise cancelling feature. They require one AAA battery, not included. The specification states 15 dB of background noise reduction at 300 Hz and 5 dB at 1200 Hz. I do not have a calibrated ear, but they did a good job of dropping down the TV (and the XYL). They are padded and reasonably comfortable. Even without the noise cancelling feature, they are as good or better than any cheap set I have found from Radio Shack.
From Chris, G4BUE
Just after reading Roger's article in the CDXC Digest, I saw a pair of the Fujikon folding noise-cancelling stereo headphones on eBay. After successfully bidding for them, I found them to be exactly as Roger has described.

One of my pleasures is trying to work weak DX signals on the LF bands and the NC headphones have proved to be the best aid since I put up my first four-square on 40 metres! They are very bit as Roger described. Like all new things, I am now wondering how I managed so long without them!

I forgot to take them with me when we went to Florida in January, but soon after we arrived there I walked into the local OfficeMax store in Sebring with N4TO and what did we see? N-C headphones on special offer for $25 reduced from $50. We both bought a pair. They are Phillips SBC HN050 and hang around the back of your neck (as opposed to going over your head) which I find very comfortable. They have an impedance of 45 ohms, a frequency response of 40-20000 Hz and a sensitivity of 102 dB/mW, but the noise cancelling figures are not given. They come with a five feet cord which includes an in-line 'on+off' switch designed to clip on your lapel for easy access, and the same two-way adapter for using with aircraft audio systems.

They work well but are not as good as the Fujikon headphones. They are as good at what we primarily want them to do, to help us to hear weak signals buried in the noise better, but they are not nearly as good at cutting out background noises, which would be very important if you intend using them in a noisy environment, such as an aircraft to listen to the in-flight audio.

Thanks Roger for bringing the advantage of using N-C headphones to our attention.
As its very interesting task in case of cancelling the noise specialy on Topband I am looking for solution also for myself. As the prices are quite different and the quality may vary I will try to put over there more informations step by step as I will getting them...
73, Petr OK1RP
 

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