On Tue, 04 Oct 2005 15:20:02 +1000, Franc Zabkar
wrote:

On Mon, 3 Oct 2005 08:26:38 -0500, "John - kd5yi"
put finger to keyboard and composed:


"Terry Pinnell" wrote in message
. ..
Michael Gray wrote:

It is usually the sides of the case behaving like a drum.
Try damping both sides with your hands, and see what happens.

That makes sense, but holding both sides doesn't diminish the beat. I
can now *feel* it as well as hear it (~ 1 Hz). Any other ideas on
stopping it? How about that rpm reduction I mentioned?

--
Terry Pinnell
Hobbyist, West Sussex, UK



You are an exceptional person to be able to hear 1 Hz!

John

The 1Hz is the amplitude modulated envelope (cos b) of a higher
audible frequency (sin a). In other words, you are hearing a higher
frequency signal whose volume fluctuates at 1Hz.

sin (a + b) + sin (a - b) = 2 . sin a . cos b

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

In audio(+) sometimes referred to as a difference frequency, and there
are also sum frequencies...heterodyning, I think? It's been awhile...

Tom