[vox-tech] powersupply + capacitor whine when CPU is idle

[Chanoch (Ken) Bloom]

On Mon, 2009-02-16 at 13:52 -0800, jim wrote:
> 
>    i've never heard capacitors make noise and am 
> interested to know if that happens. my guess is 
> the noise is coming from a fan, either in the 
> power supply itself, or in the case, or on the 
> heatsink of the CPU, or.... 


Capacitor whine is real. Look at
http://en.wikipedia.org/wiki/Capacitor#Instability_of_capacitance

"Capacitors, especially older components, can absorb sound waves
resulting in a microphonic effect. Vibration moves the plates, causing
the capacitance to vary, in turn inducing AC current. Some dielectrics
also generate piezoelectricity. The resulting interference is especially
problematic in audio applications, potentially causing feedback or
unintended recording. In the reverse microphonic effect, the varying
electric field between the capacitor plates exerts a physical force,
moving them as a speaker. This can generate audible sound, but drains
energy and stresses the dielectric and the electrolyte, if any."

-- 
Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/

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