Archived from groups: alt.internet.wireless (
More info?)
On Sun, 10 Oct 2004 13:08:40 +0200, "MFY" <nospam@no.spam> wrote:
>
>> Looks like routers aren't the only thing that make noises.
>> This is from the Efficient Networks 5360 ADSL modem, which apparently
>> makes a "hissing" sound:
>>
http://kb.efficient.com/display/1n/articleDirect/index.asp?aid=45394&r=0.4748346
>I am still very confused :| Before I go back to the dealer I would like to
>be sure that the sound means that something is not completely right.
>Is the router also retraining some connection as in the case of the modem?
>Is there any real reason for it to make the sound?
No. There is no real or imaginary reason for it to make noise. As
the article:
http://www.practicallynetworked.com/support/hissing.htm
points out, it's not going to explode or start a fire. However, it is
annoying and should not be tolerated. Methinks it's the result of
sloppy component construction (loose inductor windings) and not a
"free running" frequency design issue as the article states. All these
switching power supplies free run as none of them contain anything
resembling a clock oscillator. However, they do change frequency with
different loads and input voltages and may eventually hit the
mechanical resonance of the inductor. That's what you're hearing.
The bad news is that if you exchange it for another unit, there's a
very good chance that it might have the same problem. Since it's a
mechanical issue, it could easily become worse as the inductor loosens
up. The only way to be sure is to try it in the store.
In the case of the Efficient 5360, the noise is also coming from the
switching power supply. However, the article is misleading as
claiming that it's caused by retraining. What's really happening is
that during retraining, the power supply load changes somewhat,
possibly because more LED's are flashing, and that causes power supply
inductor to get noisier.
I have a customer nearby that claimed she could hear the switching
power supply in a desktop computah. It was a custom made P4-2.4GHz in
an ATX box. Nobody else could hear a thing. However, as she was
insistent, I rotated 7 different ATX power supplies through the box,
to see if it helped. I built a rather crude electret microphone,
amplifier, and ultrasonic high pass filter and connected it to my
oscilloscope. As predicted, each power supply belched quite a bit of
ultrasonic acoustic noise, with radical variations in spectrum and
intensity. The power supply she selected was noticeably quieter.
Having declared success, I was then informed that the fan noise was
now a problem. I bit of trial and much error (broken fan blade, cut
finger) showed that the noise was the stock Intel P4 CPU fan. I
ordered an assortment of P4 heatsink and fan assemblies and ran the
same series of tests. I didn't care about audible noise and
concentrated on the ultrasonics. I finally found a huge copper heat
pipe contraption, that had a vertically mounted fan. The conventional
horizontally (parallel to the CPU) mounted fan forces the air to make
a right angle turn where it hits the heat sink. With a little effort,
this can make a fair whistle between the fins. The vertically mounted
fan doesn't have this problem as the air goes in a straight line.
Ultrasonics were way down and I had a satisfied customer (and an
eclectic collection of heat sinks).
I live in the deep dark forest in the Santa Cruz mountains. It's so
quiet that I can have a conversation with the neighbors 100ft away
without shouting. Little noises become a major irritation. My PIII
computah is water cooled but the aquarium pump is still too noisy.
The fridge is on a timer that turns off at night. Buzzing wall warts
have been replaced. Methinks the silence is worth it. (As I write,
the neighbor has elected Sunday morning to be a good time to remove a
large stump with a chain saw. Oh well.)
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
. 
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