On Mon, 9 Jun 2008, Bob McConnell wrote:
On Behalf Of cpghost
On Sun, 8 Jun 2008 21:40:17 -0600
James <[EMAIL PROTECTED]> wrote:
I have a high pitched whine coming from my motherboard when the EHCI
USB 2.0 controller is enabled in the BIOS. The whine only starts
once
FreeBSD 7.0-RELEASE is halfway through booting.
The whine also goes away when I plugin a USB drive in with EHCI
controller enabled (usb keyboard and mouse being already plugged in).
Is this a hardware problem, or could it possibly be software
related???
Hard to tell. I've had whining EPIA-boards when run at 1000 Hz,
and after switching kern.hz to 100 Hz in /boot/loader.conf, the
high-pitched whine stopped entirely. It also stopped when I
slightly deviated from the 1000 Hz (to, say, 900 Hz or 1100 Hz),
so there was obviously some hardware component on the boards
oscillating like mad at this very frequency.
I'm no specialist and it may be an urban legend, but from
what I gathered, some coils could exhibit the behavior of
generating those high-pitched whines when exposed to certain
frequencies.
-cpghost.
No legends here. The horizontal sweep frequency for televisions in the
US is 17,500 Hz.
It was 15,750 for original NTSC (black and white RS170), and changed to
15,734 when color (RS170A) came in in the 1950s. The vertical scan
(field) rate also changed from 60 Hz to 59.94. These numbers were chosen
because they are relatively easily derived from the newfangled color
subcarrier of 3.579545 MHz, yet close enough to the old values that old
pre-color TV sets could still lock to the new color signals.
Many people could hear that whistle from cheap flyback transformers.
Other devices would buzz, hum or rattle when they resonated with EM
fields. Occasionally they can be heard by humans, more frequently they
can be heard by their pets. As I have gotten older, I don't notice it
as much.
The joke used to go, "Why did they pick that frequency?" "Well, the
crusty old engineers just cranked it up until they couldn't hear the
flyback anymore". I can still hear it, but then I'm still [just] on the
candy-coated side of 50.
I guess this is getting a little OT here... but by way of a half-assed
response to the OP's question, I think Bob is on the right track - seems
like an electromechanical resonance of some sort.
--
Chris Hill [EMAIL PROTECTED]
** [ Busy Expunging <|> ]
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