Fan noise, does orientation/direction make a difference?

chickadee · 1 Dec 2016 at 06:20

So I was messing about with fan direction to make my top fan an exhaust instead of intake, I was sick of the dust...

So I swapped a few fan directions around and now I have an annoying whine going on.

Its rather high pitched and driving me crazy trying to figure out why...

All I did was swap the rear fan and make it an intake and the top fan and make it an exhaust. I also swapped the fan in the middle of my Noctua D14.

I don't get why this would make any extra noise, any ideas would be great.

Bantu · 1 Dec 2016 at 11:38

There was a post on this recently in the cooling sections. The gist is that by swapping fans you are moving the blades closer to the mounting surface, possibly causing resonance:

doyll said:
pull tends to be louder, mostly due to how close fan blades are to mounting surface. The structural frame on exhaust side of fan that fan motor is mounted on means fan is spaced cc 5 mm from face of housing .. on intake side the fan is almost flush with face of housing. That few mm often cause harmonic noise to be generated byfan blade moving closer to mounting surface. Almost all fans are quieter with 10-15mm space between fan and mounting surface.

There are a few fans that the blade design does make a performance difference, but very few.

That suggests that your new rear intake fan could be the culprit.

chickadee · 1 Dec 2016 at 11:51

Bantu said:
There was a post on this recently in the cooling sections. The gist is that by swapping fans you are moving the blades closer to the mounting surface, possibly causing resonance:

That suggests that your new rear intake fan could be the culprit.

Ok so I wonder if maybe I could make a small shim out of rubber/plastic to make the fan stick out a little extra while also reducing vibration.

I will remove fans one by one to see if its one fan in particular thats making this noise and then try making a homemade shim.

I find it hard to understand as all I have done is flip a fan around to the same direction as the intake fan on every case, its not like its different in any way from 50% of all fans out there.

Bantu · 1 Dec 2016 at 12:08

Most cases are made to have the rear fan as an exhaust don't they?

pigeonguyuk · 1 Dec 2016 at 12:55

Bantu said:
Most cases are made to have the rear fan as an exhaust don't they?

Correct. Some companies put a lot of money into R&D for cases to give the best airflow to reduce the overall temperatures.

Hot air rises, so logically speaking Tops and Rear (which in 95% of cases is again at the top of the case) are exhaust as this is the natural air flow. Front and bottom would be considered as Intake

those with side fans can be either in or out mainly used to aid GPU cooling or GPU heat removal.

chickadee · 1 Dec 2016 at 13:02

Bantu said:
Most cases are made to have the rear fan as an exhaust don't they?

Yeh it is designed like that but when you have a 200mm top fan as an intake with a really bad dust filter its basically a nightmare so i swapped the rear exhaust and top intake around.

Im not worried about temps as my CPU even on 100% load never goes past 40c and my GPU never past 60c. At idle my CPU is about 5c hotter than ambient an my GPU 12c above. My system runs so cold so I would prefer a cleaner machine even if temps rise a few C (which they haven't at all btw).

I think its much more important in cases that are smaller and have hotter components, for me i could turn all my case fans off and still be perfectly fine.

Bantu · 1 Dec 2016 at 13:12

Fair enough. If it works for you then that's what matters, but i would argue that you should have the top AND rear as exhaust fans, instead moving your intakes to the front and bottom of the case.

chickadee · 1 Dec 2016 at 13:46

Bantu said:
Fair enough. If it works for you then that's what matters, but i would argue that you should have the top AND rear as exhaust fans, instead moving your intakes to the front and bottom of the case.

I only have 3 fans- front, back and top, if I do 2 exhaust then my case will have a negative pressure meaning dust will be sucked in.....

Need to keep a positive pressure for a clean case.

Bantu · 1 Dec 2016 at 13:57

ah i see. Is that you physically only have 3 fans or there are only 3 places on your case you could mount your fans?

If the former you could look into getting a few more fans or moving yours around (e.g. 2 at the front as intakes, 1 at the rear as exhaust).
If the latter then, yes, you'll want positive pressure, but you can also achieve that by running fans at different speeds, having different sizes of fans, etc.

chickadee · 1 Dec 2016 at 14:22

Bantu said:
ah i see. Is that you physically only have 3 fans or there are only 3 places on your case you could mount your fans?

If the former you could look into getting a few more fans or moving yours around (e.g. 2 at the front as intakes, 1 at the rear as exhaust).
If the latter then, yes, you'll want positive pressure, but you can also achieve that by running fans at different speeds, having different sizes of fans, etc.

Na its only got 3 fan mounting spots, 2 are 200mm so its got plenty of airflow. I could change some 5 1/4 bays into a 120mm fan area but when my temperatures are basically ambient temperature anyway then whats the point. When I had my old GTX280 in the case it was a lot more of a problem but the X5660 and GTX780 are both mega cool cards. My motherboard never gets above 30c either......

Its this case: http://silverstonetek.com/product.php?pid=200&area=en

Bantu · 1 Dec 2016 at 14:24

cool. as long as it works that's all that matters really. maybe play around with the fans speeds of your rear intake to try and reduce the noise. Good luck