The Jan/feb issue of the National Contest Journal has a great article on
the subject of fighting local audible noise and QRM.
The article describes:
- experiences with some isolation headphones
- how to make your own (extreme isolation headphone with small drivers
build in D.I.Y. kit)
- commercial noise canceling headphones
- David Clark professional passive and active isolation headphones
There is a graph showing the isolation of various tested products vs
frequency.
It also shows the human body limitation because at some level your bone
structure is acting as a transmission channel and beyond that value there
is no further attenuation possible.
My current QRL does offers some 40-100 new models for the consumer
electronics market each year. I do a lot of consumer testing with some
models, especially on the wireless versions and those having noise
cancelling. I have not found a decent one yet which truly allows me to dig
deeper into the noise and copy that cw signal in noisy environments. The
noise cancellation types do offer 'some' relief which becomes avid after
many hours of use during contests and dx-pedition etc....
Earlier this week I received my ordered "chopper-headphone" from
http://www.davidclark.com/StereoHeadset.html.
This device has great passive noise isolation with specs from -15dB at 125
Hz to quickly into -25db in the midranges to -38dB at 4 - 8Khz.
I wanted this special model, since it incorporates full range drivers
(10Hz--20000Hz). From my former QRL (Dali Hi-Fi loudspeakers, Rogers
Hi-Fi loudspeakers) I learned that some drivers with restricted ranges can
be too stiff. They simply needed a lot of energy before they start moving
following/replicating the swing of the input signal. Typical "burn-in"
time solved this to some (minor) extent, but the especially designed high
quality drivers were much better capable of setting up a detailed
soundstage at an already much lower input volume. That is why I initially
skipped the D/C 200Hz -5500 Hz versions which even has some 4dB better
spec. i terms of passive noise cancellation. I cannot tell if my former
experience with stiff cone material is also valid for current mylar
headphone drivers as well and might affect copying weak signals in
received HF audio, I simply did not want to take that risk.
Anyway how does that green chopper headphone perform?
It does great !
Both at audio quality and especially at how it almost totally kills your
noisy environment, almost scary to say the least.
I compared it to a professional passive isolation headphone as is required
on construction sites etc., the green chopper does soo much better.
It does however allow you to focus on what you do want to hear.
Price? exactly the same as a Heil pro set, but without the mic-boom which
an be ordered as a seperate kit.
I have no application for any mics at HF at my home :)
Will use this green chopper during ARRL dx at PI4TUE , which shack is
stacked with zillions of pc servers and other loud noise producing stuff
(loud students, noisy YL-operators etc..)
73 Mark, PA5MW
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