[rescue] Thoughts on system noise...

[Steve Pacenka]

On Sun, 2002-03-24 at 22:14, Innfomail at aol.com wrote:
> I can't remember the title of the story but in the book "Tales from the White 
> Hart" by Arthur C. Clarke an engineer makes a sound canceling machine. IIRC 
> this is the same technology used in the new Noise Canceling headphones.
> 
> It involves generating sound waves with an opposite Polarity? so that the two 
> waves cancel each other out.
> 
> It seems to me that this could be applied to both fan sounds and drive whine, 
> particularly since they are often constant.
> 
> Another opportunity for a creative engineer.

Amazingly enough, the story "Silence Please" is online at the publisher
as a sample:

http://www.randomhouse.com/delrey/sample/talesfromthewhitehart.html

<blockquote>
"Of course, there was rather more to it than that. There had to be an
arrangement to make sure that the cancelling wave was just the right
intensity--otherwise you might be worse off than when you started. But
these are technical details that I won't bore you with. As many of you
will recognise, it's a simple application of negative feed-back."

"Just a moment!" interrupted Eric Maine. Eric, I should mention, is an
electronics expert and edits some television paper or other. He's also
written a radio play about space-flight, but that's another story. "Just
a moment! There's something wrong here. You couldn't get silence that
way. It would be impossible to arrange the phase ..."
</blockquote>

-- SP