installation direction determines volume of fan?

[Zumino Zufeilon]

So, finally finishing my new build, and got two new 92mm Panaflows installed up front in my case.

When I first installed them, as required, i installed them backwards so they were exhausing. I do something stupid like this every time I build a computer, never dangerous, just dumb.

Anyways, turned the system on, and these fans were whisper quiet, and I was happy.. . till I reaIized that the fans were in backwards. Flipped them over, so they were blowing air into the case, and suddenly they were loud. Really loud, louder then anything else in the case.

Just to test, I flipped them back over, and quiet again.

Any idea why? I want them to be quiet when blowing air into the case, not when blowing air out of the case, cause their input fans, not exhaust fans.

I've checked, nothings rubbing(besides that would be a very different sound), they're just a lot louder then before.

[mdameron]

Perhaps the motor is on the "back" side of the fan so that when it was exhausting the motor was on the INside of the case?

What kind of noise is it? Like a windy air noise?

[NordicRX8]

I'm no physicist, but here's my theory...

Awww hell.... nevermind... I tried typing it out and it didn't even make sense to me!

simple theory... kinda like mdameron's.... it's louder on one side than the other. LOL.

Anyone out there a physicist or mechanical engineer that can explain this??? :)

[NordicRX8]

LOL.... let me try this again.

I believe it has to do with air pressures.... When you turn the fans around and make them intakes, you're trying to force air INTO the case which is restrictive (not a straight flow of air) and has a higher pressure (temps inside are higher as well). This makes the fans work harder against this pressure and they are louder. When they are set up for exhausting, they are removing air from inside the case (warmer, higher pressure) to outside the case (where there isn't restriction - pressure) and the fans work more efficiently making less noise.

Did that make any sense??? It didn't the first time I typed it out.... but it's worded a lil different.

Someone with a degree in physics needs to chime in. :)

[Arcygenical]

Nordic's explanation is very close to my best guess...