PC CPU fan

I read in sci.electronics.design that Terry Pinnell wrote (in ) about 'PC CPU fan', on Mon, 3 Oct 2005:

That's not effective sound insulation. Your wood floor will love to vibrate at 1 Hz, even if it's not tuned to that frequency. You need a THICK pad -- no, thicker than that!

FWIW - Maplin's sound dampening kit (A48AK) works quite well, though not exactly cheap at 18ukp, especially against HD chassis-borne noise.

Get an office that adjoins a machine shop/fab shop. I guarantee, you won't notice the noise from the computer! ;-P

Cheers! Rich

Yup! Can't let them sounds dry out!

I've had things like this happen when the hard drive bracket wasn't screwed down tightly, or the case just poorly designed so it's not as rigid as it should be. Sometimes if the floor is a little uneven and you set it a certain way, some metal part of the case will resonate, sometimes moving it, tightening screws, or sticking a piece of tape between whatever's vibrating and whatever it's attached to will help.

On Mon, 03 Oct 2005 14:05:55 +0100, Terry Pinnell put finger to keyboard and composed:

I would think it unlikely that your two identical drives would spin at a speed that is different enough to produce a 1Hz beat. That's a difference of 1:120, or 1:360 if you consider a possible harmonic effect of the motor's three windings. AFAIK, the speed is crystal locked. Your observation in respect of the 200GB drive sounds more plausible since it could involve different crystal frequencies.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

On Mon, 3 Oct 2005 08:26:38 -0500, "John - kd5yi" put finger to keyboard and composed:

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.

Obviously, the near empty new drive is filled with a minimal amount of data, located on one side of the platter. This causes a considerable unbalance, causing vibration. Just put more stuff on that drive.

And now I will go on with my design of a battery charger that cuts off the charging process based on weight increase of a charged pack.

Take a 12V, 100AH battery. That's 12*100*3600J = 4.32MJ. e=mc^2, so the mass gain from flat to full is e/c^2 = 5e-11N, or about 5e-12Kg. Piece of piss, but works better with bigger batteries.

Paul Burke

Thanks, I'll take a look at it.

But I must say that I'm now into the 2nd day of *relative quiet* ! As described earlier, this significant change has come about simply by not using the 'locking lever' on the back corner of the PC case. In fact, I have to conclude that I must have had it in that unlocked state before installing my new HD.

I can still hear *some* LF noise, but only downstairs in the lounge, not sitting here at the PC!

Thanks, makes sense. Just under 1% is probably acceptable tolerance for an advertised speed of '7200 rpm'. Mind you, given that this new one is Maxtor too, and broadly same 'Diamond' range, I'd have expected the same crystal to be used.

Thanks for all the follow-ups. As per my earlier post, situation is now much improved.

I read in sci.electronics.design that René wrote (in ) about 'PC CPU fan', on Tue, 4 Oct 2005:

Don't forget to correct for the buoyancy of the evolved hydrogen.

I read in sci.electronics.design that Paul Burke wrote (in ) about 'PC CPU fan', on Tue, 4 Oct

In audio(+) sometimes referred to as a difference frequency, and there are also sum frequencies...heterodyning, I think? It's been awhile...

Tom

Once it has evolved, does it turn into Helium? Have to be careful about fusing.

Regards Ian