Why is the PS louder while in the case?

IceFire · Post by **IceFire** » Fri Jun 13, 2003 8:18 am

I brought a Fortron FSP300-60PN and test it outside of the case by shorting the green w/ the black wire. It was so quiet that I didn't even think it was on. I have to place my ear about 2 inches (5 cm) from the unit before I can hear it. However, as soon as I put it in the case, it was louder. The noise is more like air flow than fan or vibration. I even have the cover off, but is still sound the same. I know is not a heat issue because it doesn't increase as the case temp increase. MBM report my case temp around 19C. The CPU temp is a bit high (57C) but I think is the motherboard reporting issue because it is using an external probe under the CPU.

Any idea?

dago · Post by **dago** » Fri Jun 13, 2003 12:26 pm

uses (almost) no power while outside the cases -> not plugged to anything

when inside and plugged to the mobo+..., it takes more power, heats more, than, to keep it cool (at the same temp), the fan has to ramp up

no ?

miker · Post by **miker** » Fri Jun 13, 2003 12:29 pm

Dago's explanaation makes sense to me. Also, the fan on the fortron is in the bottom, right by the CPU HSF right? THere could be turbulence from having that device so close to the 120mm fan on the PSU.

Post by **MikeC** » Fri Jun 13, 2003 5:48 pm

It's the combination of added turbulence, a bit of added case resonance and "excitation" of the case air resonance.

Think of the case as something like a poorly sealed ported speaker cabinet. The air in any box that is mostly closed has at least one resonance. When you have holes in it, you have multiple resonance. It is this as much as anything else that causes many noise sources to seem louder inside a PC case than out. With a PSU you have the combination of a pretty direct excape path for the noise, whatever resonance there might be inside the PSU itself, and the case resonance.

So my take on your observation is that even if the PSU fan is running at exactly the same speed, it will seem louder inside the case than out.

Jan Kivar · Post by **Jan Kivar** » Sat Jun 14, 2003 11:50 am

Could the pressure in the case (more accurately the PSU trying to underpressure the case) make a difference in fan noise?

Jan

Post by **MikeC** » Sat Jun 14, 2003 12:48 pm

Pressure -- doubt it; the case is not well sealed enough and the fans in the PSUs we're talking about run too slow to apply much pressure.

IceFire · Post by **IceFire** » Sat Jun 14, 2003 7:04 pm

Mike's explanation make since. Like I said before, I pretty sure is not the heat because it is constant from start to shutdown (after the initial 2 second high speed start).

At first I thought it could be the presure too, but than I left the cover off and it sound the same (a little louder due to the case panel being opened).

So, Mike. Do you have any idea as to how I can solve this? I thinking about getting a new case because of it. Like most of us, I would prefer to work with what I have. I try to put foam in the case but that didn't seem to help. The only fans I have in my case is one NMB low speed fan on the volcano 7 and one on the case exhaust. I have a slk-800a coming but still going to use the same fan.

Anyone else have any idea as to the course or solution if Mike is right?

Thanks!