retransmission of unacknowledged message -- attempt #2:
Forwarded message:
Posted: Fri, Feb 25, 1994 11:02 PM GMT Msg: CGJE-5979-2045
From: E.SCACE
To: ("RFC-822": <CQ-Contest-Relay(a)TGV.COM>, SITE:INTERNET)
Subj: RE: results of AGC survey
RE: AGC on/off thread.........
A number of commenters expressed concern about the potential
for hearing damage if AGC was run off all of the time. There are
steps which can be taken to keep good ears.
I am not a medical doctor, but have always felt that maintaining
good hearing requires constant vigilance, both on and OFF the air.
This means:
- wearing ear protectors when running the generator
- wearing ear protectors when mowing the lawn
- wearing ear protectors when drilling metal plates for antennas, etc
- wearing ear protectors when snowblowing the driveway
- wearing ear plugs (the squeezable foam cushions) when driving -- always!
This is NOT dangerous; the foam cushions reduce the signal level
for everything by about 20-24 dB. You can still hear the traffic
around you quite normally ... just all of the "signals" are set
down at a quieter level.
This is especially important when listening to car stereo!!!!
- wearing ear plugs while flying
- ALWAYS wear ear plugs at rock concerts and at the disco, and bring them
to a jazz club just in case. (Bring them for your date, too; it's a
nice courtesy.) Even a solo trumpet can really blast you if your
table is up close...
If you are stuck in a loud environment without ear protection (e.g., someone
hammering), you can get some measure of hearing protection by humming. This
seems odd at first, but actually, whenever you start to vocalize (speak, sing,
hum), a nerve signal goes to your middle ear a few milliseconds before your
vocal cords start to vibrate. This nerve signal causes a muscle in the
middle ear to tighten, loosening the connection between the bones of the
middle ear that conduct sound from the ear drum to the cochlea. It is a
kind of automatic attenuator that the body has to prevent the local transmitter
(your voice) from overwhelming the ears! This is especially helpful for
sudden sharp sounds, like a hammer blow, because the ear can not anticipate
their arrival. During continuous loud sounds, this muscle will also engage...
but only after the initial onslaught of sound hits the inner ear!
Lastly, in my station, I wear two levels of hearing protection:
a) my headphones are Heil headphone elements, mounted inside standard
industrial ear protectors. The industrial ear protectors knock down
external noise (amplifier fans, other ops talking) by about 20-25 dB,
depending on frequency and design. There are many different styles of
industrial ear protectors available, so you can find one that fits comforta-
ably for a long period of time easily. Most have a plastic shell which
completely covers the ear; the wire to the headphone element can be routed
through a small hole and the headphone element usually can just sit loosely
under the foam cushioning that is stuffed inside. A microphone boom can be
easily mounted to the outside of the shell.
b) I wear the foam ear plugs in addition, and just turn up the receiver volume
slightly to compensate.
This means that distracting outside sounds (fan noise especially) are
knocked down 40-50 dB before entering my ears. I only need a LOW level of
receiver volume in order to hear the receiver or band noise floor. Usually
I have to crack the receiver volume control a bit in order to bring the
receiver/band noise floor above the blood noise level (yes, your ear's
internal noise floor is the sound of blood zooming around nearby). This means
that, with AGC off and setting the noise floor just above blood-noise level,
my ears have LOTS of dynamic range to play around with. Most receiver audio
amplifiers can not deliver enough dynamic range to hurt anything in this
configuration.
As additional protection, one can mount a couple of diodes across the
headphone lines to clip signals above a certain voltage level, just in case
the volume control gets set too high. I have not found this necessary when
the above precautions are taken.
Sorry for the long note, but you CAN maximize the possibility of keeping
good hearing AND enjoy AGC=OFF when appropriate. As a final indication of
results: I can finish an entire 48 hour contest single op, put the headphones
down, and go upstairs without my ears ringing after the contest like what
used to happen in earlier years before adopting this system.
Use HEARING PROTECTION ALWAYS. The major contests represent only a
few percent of the days of the year... but your ears can be damaged by
regular exposure to ANY loud sounds. While I would be happy to win
over the competition, I would prefer to do so on the basis of operating
skill, not because my friends' hearing has gone down the drain over the
years.
Take care of your ears ALL OF THE TIME; it's not much of a hobby without
them!
-- Eric K3NA
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