D Peter Maus wrote:
Telamon wrote:

I keep reading these posts about using headphones or speakers that limit
the frequency response. I think that is a poor strategy. Get a high
fidelity speakers and headphones and use the radio tone controls and
filters to limit the response when conditions create noisy signal
reception. When reception is good you get the fullest bandwidth possible
for the best sound. That's what I do to enjoy program listening, which
comprises most of my listening.



For the most part, you're correct: shaping the audio at the receiver
is the more versatile solution. But consider that the audio stages of
most comm receivers tend to have a higher noise floor, and higher
distortion than a hi-fi music listening system for which the wideband
headphones were created. Wideband headphones will exacerbate not only
the distortion components of the audio, but the noise as well. And it's
the noise, more than the distortion, that will just flat wear you out
with long term use. To the degree that, as the mind adapts to the
listening conditions, you'll actually experience subtle, but important,
shifts to your natural hearing sensitivities. Eventually, with
sufficient exposure, you could begin to lose some sensitivity at
specific frequency ranges. This noise is generally not variable with
volume, but, being a component level product of the electronics, is more
or less a constant. Shaped headphone response reduces it's apparent
presence, and reduces tendencies to fatigue.

Consider also, that SW audio, itself, is frequency shaped, but
atmospheric and electronic noises are not. Even entertainment
programming is bandwidth limited. So, at best, wideband headphones or
speakers will accurately reproduce the noise, while but the program
audio will still be bandwidth limited. Often no more than 5khz bandwidth
is transmitted. And comm audio, itself, is of higher distortion than
wideband entertainment audio, and that distortion, with higher end
headphones will be far more irritating than with shaped response. ICOM
R71 audio is legendary for being horrid, despite the fact that the audio
stage amp is actually quite low in distortion. The bulk of the
distortions are generated in the mixer and detector stages, with
distortion components approaching 20%. Believe me when I tell you,
headphones don't make it any easier to listen to. JRC audio isn't much
better. And when listening to SW, also bear in mind that the audio is
distorted at the transmitter.

Frequency shaping at the receiver, in such cases can reduce, but not
eliminate, the offending distortion products, and highly detailed
headphones can permit these products to be heard anyway. And the
offending thermal noise is still there, which can now be easily
distinguished and work it's fatigue over the electronically shaped audio.

It's in cases like these that users often prefer to use a pair of
Trimm's or Brush Clevites for long term listening. As bad as they sound,
they eliminate the offending noises and distortions from the audio
reaching the ear canal. Granted, they do introduce distortions of their
own, but often these distortions are far less offensive than the noises
and distortions accurately reproduced through wideband headphones and
speakers.

Some broadcasters I know still prefer to use Trimms or Clevites when
working on the air. First, they match damn near anything, and you can
listen to phono cartridge output with them, so loading is less of an
issue. But the main idea is that the audio is less detailed, so they
don't hear the artifacts in the air monitor, but rather simply use the
phones as a reference to detect that they are, in fact, on the air, and
rely on their instincts and experience to fill in the details. They can
then concentrate on what they're doing, instead of listening to themselves.

What it comes down to, in the final analysis, is personal
preference. And in that, if what you're doing is working for you, then
there is no need to change. But if you notice ear fatigue after a period
of extended listening, it may be time to consider an alternative strategy.

I have spent a lot of time listening to and trying to quantify some of
the
variables in a HF-SW audio chain. I have found that while distortion is
a very
important issue, it not the "do all and end all". As you point out the
noise
bandwidth and program audio bandwidth are very different.I have found
that
there are apparantly conflicting effects. The "best" audio systems are
flat in repsonse. However, "best" is not the best when real world
effects
of weak signals and atomspheric noise are considered. In most real
world
situations some sort of bandwidth limiting is needed. Having good and
effective
IF fitlers is a must, but not the end fo the banwidth issue. Speakers
or
earphones will often need some sort of frequency shaping. For earphones
I think that the bandwidth response limiting is accomplished with AF
fitlers.
For speakers I think it is much better to have a limited frequency
response
as a natural charactoristics of the transducer set.

For example, I use a pair of Radio Shack Minimus-7 speakers and a pair
of JBL
5.1 surround speakers. The JBLs start rolling off right at 5KHz and by
7KHz they
are essentially mute. I have three speaker options, the Minimus-7
stock, Minmus-7
with the tweeter switched off, which leaves the woofer/midrange that
has very little
response above ~4KHz, and the JBLs. I have found that for good clean
signals the
stock Minimus are great. For bad conditions, say 99% of the time, the
JBLs are
better and for very bad conditions, the Minimus-7's with the tweaters
switched off are
the best choice.

I love my Sennheiser HD-424's but they have flat response out to at
least 15KHz.
For SWl there is nothing out there. I found that by adding a 1K series
resistor
and having several switchable capacitors I can limit the HF response
and improve
intelligibility.

%ALCONS (Percentage Articulation Loss of Consonants) is a little used
measure
of one of the factors that effect intelligibility. In a band limited
voice setting one can't
hear the difference betweenthe words "failing" and "sailing". While we
can't often do
that much to improve the bandwidth limited nature of the singals we
listen to, we
can take steps no to mangle the audio any more then we have too.

My chief complaint about the Trimm's or Clevites is they "ring" Not
completly accurate,
but that is the best discription I can come up for for the effect.

I suspect that each and every SWL will find that the best choice for
them may
not be what anyone found best. Try every earphone set you can get your
hands on
under every signal condition you can. Try to keep notes. Over time you
will arrive
at a comprimise that works for you. What I found best is very unlilkey
to be the bet
for you. As I mentioned once before it is very usefull to have a
hearing test to find
what oddities your hearing has. I have Tinnitus and some serious HF
loss. My wife
has perfect hearing. Our choices for speakers and earphones is very
different.

Terry

Terry