Re: PC speaker

From: Clemens Koller
Date: Tue Jun 12 2007 - 17:15:33 EST

R.F. Burns schrieb:
On 6/12/07, Lee Revell <rlrevell@xxxxxxxxxxx> wrote:
On 6/12/07, R.F. Burns <burnsrf@xxxxxxxxx> wrote:
> Is it possible to write a kernel module which, when loaded, will blow the PC
> speaker?

LOL. May I ask what your use case is?

I am helping a small school system with a number of Linux
workstations. Previously, the students (middle and high schools)
abused the sound cards in the systems. This was remedied by changing
the permissions on sound devices so that non-root users would be
denied access (something easily done remotely, and on an automated
> [...]

What about denying students permissions to change all unwanted
<foo> on the system? They propably don't need to be root.

At that point, the students started finding creative ways to abuse the
PC speaker, which became rather distracting. We unloaded and disabled
the PC speaker kernel module, which remedied the situation for a

Disable kernel modules at all. Compile in what you need, and kick
out all unwanted stuff. Disable booting from anything else than
harddisk or network...

[OT on]

So, the idea was raised about seeing if there was a way to blow the PC
speaker by loading a kernel module. If so, a mass-deployment of a
kernel module overnight would take care of the PC speaker problem once
and for all.

A speaker is basically an inductor. Together with the driving circuit,
it may form a resonant circuit. If you drive it exactly with the resonant
frequency[1], you might be able to overheat it. But take care, not to
burn your CPU too, when you reach microwave frequencies and get electromagnetic
waves reflected in the computer's case. Cross-check with Maxwell's
equations! ;-)

OTOH the students propably learn more in hacking a linux system than in any
other lesson. Tell them that the first one gets an A who can get real speech
output working on the PC speaker.


[OT off]

Good luck,
Clemens Koller
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Straße 45/1
Linhof Werksgelände
D-81379 München
Fax 089-741518-19
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