"Terry Pinnell" bravely wrote to "All" (03 Oct 05 08:50:32)
--- on the heady topic of "PC CPU fan"

Terry,

I had a similar annoying problem with a freezer fan. It would knock
like your computer at about 1 beat per second. What was happening was
that the fridge was slightly tilted backwards and fan rotor was
travelling up the bearing and then sliding back in one shot sharply
against the backstop. Who would have thought!?

Your solution may be as simple as leveling your computer's case the
other way. As for the freezer fan I added a small spring on the shaft.

A*s*i*m*o*v


TP From: Terry Pinnell
TP sci.electronics.design:511555

TP I'm getting a sort of 'beat' effect from my PC. It seems to have been
TP triggered (or maybe just increased to a level at which I've become
TP aware of it) by adding a new (third) HD.

TP I'm at my desk, and the PC is on the carpet 3 feet away, at the side
TP of the desk. I can just hear this beat from here, behind the familiar
TP high frequency fan and HD spinning sound. Kneeling on the floor with
TP my ear by the PC case, I can hear the beat distinctly, at about 1
TP cycle per second. But my real gripe is that directly below, downstairs
TP in the lounge, it's surprisingly distinct. By no means deafening, but
TP it is intrusive. I'm aware of it even while watching TV. This is
TP through carpet, underlay and 2 layers of plasterboard.

TP I did also have mechanical noise from the fan (which itself may have
TP been due to multiple causes, such as bearings, dust and one loose
TP screw). But I've fixed that, and am left with this pesky beat. It
TP doesn't appear to be anything I can stop by touching any PC panels, or
TP even holding the fan itself. So I assume it's some sort of beat in the
TP air itself, caused by the rpm speeds of various components being very
TP close together? Rather like 'heterodyning' in radio terms?

TP I'm not sure what the best approach is. Presumably I can take the beat
TP frequency out of this apparently sensitive LF region by lowering the
TP CPU fan speed rpm a bit? I could wire a couple of series diodes in the
TP supply. Maybe as an initial step I should buy a new 60mm CPU fan,
TP which is surely unlikely to be similar in rpm speed to the present
TP one.

TP Any advice would be appreciated please. Anyone else had similar
TP behaviour?

TP --
TP Terry Pinnell
TP Hobbyist, West Sussex, UK

.... Modulation in all things...