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.
|