Boring physics question

[that_punk_guy]

I set up my recording PC (a Pentium 3 with nice quiet fans) in the quietest corner of my bedroom but for lack of furniture I had to put it on the floor. As soon as I powered on, I noticed a very deep humming coming from the direction of the machine.

I went over and lifted the machine off the carpet and found that that, without the floor reverberating, the hum was significantly reduced. Of course, you can't just suspend a PC in mid-air (at least, not on my budget) so, not really expecting it to work, I got four plastic bottle caps and placed them under each corner of the base.

How come this worked? Does the increased pressure on each leg actually supress vibrations? Or could it just be that the epicentre of the disturbance is somewhere in the centre of the base?

[that_punk_guy]

{bleep}e, wrong forum. Sorry! :-D

[JaXanim]

The floor was resonating like a sounding board for the case. The case is vibrating at a similar frequency to the fan's hum. It's acting like the diaphragm of a loudspeaker.

Mounting the case on feet reduced the noise cos you made contact with the case well away from its area of maximum vibrational displacement (near the centre I'd expect).

You could try sticking something heavy (like a piece of thin lead sheet) to the bottom of the case to change its resonance frequency and thereby its transmission of fan hum into the floor.

Cheers,

JaX

[Argo]

Get four screw-in eye hooks and some fishing line. Screw hooks in to ceiling. Tie a good lenght of fishing line to two of the hook then tie to other end to the other two hooks. Now give each one a light tug to make sure they are secure. Now place you computer in the loops. One up front and on for the rear. Now you have a budget suspended computer.

[JaXanim]

@Argo

Hmmm...in my experience, ceilings vibrate more than floors. This idea could exacerbate an already serious resonance situation. And what if people live above? Could lead to difficulties.

By all means try some fishing line, but make sure it's low tension/elastic grade. When I tried this with high tension line, the ceiling sounded like the Albert Hall.

So you see, physics needn't be boring! Good luck!

JaX

[KennyR]

Just put some polystyrene squares under your tower.

[that_punk_guy]

:lol:

Cheers!

[Argo]

Ah!, Harmonic Resonance...

[odin]

It's the Crystalline Entity! RUUUUUUN  :shocked:.

[Karlos]

JaXanim wrote:
@Argo

Hmmm...in my experience, ceilings vibrate more than floors. This idea could exacerbate an already serious resonance situation. And what if people live above? Could lead to difficulties.

By all means try some fishing line, but make sure it's low tension/elastic grade. When I tried this with high tension line, the ceiling sounded like the Albert Hall.

So you see, physics needn't be boring! Good luck!

JaX

The perfect revenge on my upstairs neighbours! Just hang my 'puters from the ceiling when they are trying to sleep (like during the day) to make up for all the times they played loud music at 3am :-x

[mikeymike]

odin wrote:
It's the Crystalline Entity! RUUUUUUN  :shocked:.

Cool :-)

KennyR's low-tech solution is probably favourite.  Also making sure that all the drives are screwed in properly may help reduce a bit of the noise.

[that_punk_guy]

That's one problem, it's one of those clever designs where the drives and stuff clip in... Quite impressive, but gives you very little control over how secure the drive is.

[Floid]

that_punk_guy wrote:
That's one problem, it's one of those clever designs where the drives and stuff clip in... Quite impressive, but gives you very little control over how secure the drive is.

Technically, you want the drives uncoupled from the case (by rubber grommets or something), but of course, not rattling.  You might want to look for some thin stick-on foam if you're really neurotic about it... (I found some 'rubber' feet at the local dollar store that are actually the perfect material for this sort of thing, or you can experiment with whether rubber bands wrapped around/wedged-into various places help or hinder, depending on the design...)

The bottle caps are performing roughly the same function as speaker points, so if the bottle caps aren't quite doing it, and you don't mind your floor (or it's carpet, and you want to take advantage of the foam beneath it for dampening), get a few giant cone spikes from the local punk or leather shop, and whatever's appropriate to attach them.

[Framiga]

Hi,

speaker points are the best option IMO

[dmac721]

   Plastic is an insulator and all you did was insulate the harmonics enough to stop reverberation