More noise if air in is not equal to air out?

[RDBRUSKI]

I have a theory that the greater the difference there is between the amount of air coming in and going out of a case, then the greater the noise will be over the standard noise the fan makes.

Take for example a car. When you drive down the road at a certain speed and open only the drivers side window, the air noise is at one level. It is usually fairly loud because the motion of the car is causing a sucking effect from the one window. Because there is on other window open, its very loud because nothing is being sucked. Its like turning on a vacuum and holding your hand over the hose.

Now, if you open the window directly behind it just a bit, the noise is greatly reduced. You can even fiddle with that second window to get the noise at its lowest point.

Now, transerring that example to PC cases. If I have 2 big fans in the back of the case sucking 100 cfm of air out, and only 50 or so cfm coming in, that same loud sucking sound could take place on a smaller scale. This would especially be noticeable on cases that are sealed VERY tightley so that air only comes in and out of the fan holes.

Also, if your fans sucking out are sucking more than is coming in, doesn't that cause the motor to strain and make a sound itself? That again is like a running vaccuum cleaner with something stuck in it so only some of the air is being sucked in. It strains the motor and causes more heat and sound.

Wouldn't it make sense to have the same or very close cfm going in as going out to reduce noise considerably?

I don't know, maybe I'm just being anal retentive.

 

[bum_jcrules]

You are looking at air pressures inside and outside the case. You are correct in the assumption that having equalized pressures would be beneficial. Here is the problem. By adding additional fans you are increasing the number of noise making entities and thus increasing the overall noise level. So if you have a partial vacuum or if you have more fans you would still be in a similar noise level situation based on your assumptions.

The real issue of having equalized pressure inside and outside the case in overall airflow and not for noise levels. If you have 50CFM enduced in the front and 100CFM being expulsed out the back, there is a 50CFM deficit and thus the extra 50CFM has to be drawn into the case by the fans in the back. Now if the air is being pulled through the cracks and holes in the case, the fans in the back are under higher strain, thus wearing out those motors, than they would if the pressures were equal. Second, if the extra is being drawn though the opening where the front fan is, that fan is being overworked, the fan speed would be too fast and thus burning it out prematurely also. So my argument isn't sound but air pressures and strain on motors.

The comment about being anal would fit this argument. I have to be also because I am commenting on it.

<b>"Kenny! Give me the whoobie."

"You don't feed a baby chile!" - Mr. Mom</b> :lol:

 

[HonestJhon]

hehe...nice....

-DAvid

-Live, Learn, then build your own computer!-

 

[pr497]

some cases has small holes drilled into the side of it...so air presure woulnt be a problem...

<b><font color=red>ATI</font color=red>'s drivers are like a broken faucet, they both keep on leaking...</b> 😎

 

[bum_jcrules]

He will still create a slight vacuum regardless, holes or no holes. There would be a total negative pressure of around 6 to 7mmH20 with a perfectly sealed case. Even with the hole there would be at least 1/4 to 1/2 of that maximum figure. So it would still strain the motors of the fans in the rear of the case. Think about it. He would be trying to cram 50CF of air into the surrounding airspace from inside the case. The outside air will be forcing back on the blades of the fans and thus straining the motors.

That is like trying to push water into a unopened 2 liter of Dr. Pepper(R). High pressure likes to go to low pressure. The Law of Entropy, a.k.a. the second law of thermodynamics, states that things go to disorder. In layman's terms it means that high-energy state will try to move to a low-energy state.

I don't mean to be so anal but he should at least even the intake and exhaust pressures to provide better flow-through. That in turn will extend the life and efficiency of the fans.

<b>"I put instant coffee in the microwave and almost went back in time" - Steven Wright</b> :lol: