Exhaust struggling against CPU Fan?

[Speakerator]

Hey there

 

I'd like some comments on the following situation:

 

I have a Dark Rock 3 in my case, a T9 Value with 2 intakes in the front and one exhaust in the back. The CPU cooler fits quite snug in the case, there's only a few millimeters between the top and the side panel. Since I had to raise the fan a bit in nearly touches the side. Right below in the topmost PCI slot is a Strix 970, sitting right between the two front intakes. Their airflow is separated by a hard disk/ SSD sitting just between them, which means the lower fans blows air below the GPU and the top one blows directly at the CPU, effectively creating two separate compartments. So far so good.

 

A while ago my rear fan broke and I quickly replaced it with a cheapo replacement fan (Arctic Cooling F12) to have at least some exhaust and it works reasonably quiet. That was before I got the DR3.

 

My problem is, that I get noticeable airflow noise when the sidepanel is closed. My best bet is that the F12 is struggling to suck air out since the noticeably slower-running DR3 restricts airflow to the rear in the "upper compartment" above the GPU. When I open the side, everything is quiet.

 

I thought about completely removing the exhaust fan and leave it to the DR3 to push air out the rear. How bad of an idea is it regarding the Non-rear-exhaust GPU and the probable difference in GPU /CPU load resulting in possibly slower CPU/exhaust combination fan speed?

 

Any different recommendations? Possible fans to match air volume moved by CPU to exhaust fan?

 

Best regards

Chris

 

Edit: added the picture for better explanation.

 

Might as well be something completely different, feel free to point it out

[MrBucket101]

As long as the fan orientation is the same, I don't see an issue with the fans running at different RPMs

[Speakerator]

As long as the fan orientation is the same, I don't see an issue with the fans running at different RPMs

Yeah, sure, they are not really working 'against' each other. My thought was that the restricted space and airflow through the 'slow' CPU fan forced the exhaust to pull air elsewhere, hence creating the noice. First question was if that logic makes sense and second, whether that could be solved by a.) removing the fan  or b.) getting a fan that moves a similar amount of air. (leading to the question what kind of specification that one'd need.

[MrBucket101]

can't say it makes much sense to me

 

The air will still be there for the fan to move, whether or not it is already headed in that direction

I think you're over analyzing this, one of your fans is probably just louder than the other

[Speakerator]

Yeah, might be. Should be doing stuff for my grad studies so I guess it's kinda tempting to search for different stuff to do 

Though it'd be interesting to know why it gets louder when the panel is closed.

[MrBucket101]

Though it'd be interesting to know why it gets louder when the panel is closed.

the sound echoes? 

The temp goes up, so the fan spins faster?

[Speakerator]

p

 

the sound echoes? 

The temp goes up, so the fan spins faster?

Temps would'nt go up the second you close the case. And as I said, it's more like airflow noise, but I guess I'll stick with it now and probably get a lower rpm fan someday...^^

[ThomasD]

A computer chassis is a ridgid container, so you can have varying amounts of pressure at different locations.  Areas of high flow tend to have negative (or less positive) pressure.  But noise is usually indicative of turbulent flow.  That would be my guess - there is a mismatch  between what the rear fan wants to move, and what it is being forced to move by the other fans in the upper part of the system - which are effectively working in tandem.

 

The simplest thing to try is removing that exhaust fan.  If noise is better, and temps don't rise significantly call it good.  If noise drops but temps go too high then you will need to find a fan that offers a better match to the overall flow rate of the upper portion of that chassis. 

 

A third option is the try using that exhaust fan on the CPU cooler in a push/pull, with passive rear chassis exhaust.

[Speakerator]

A computer chassis is a ridgid container, so you can have varying amounts of pressure at different locations.  Areas of high flow tend to have negative (or less positive) pressure.  But noise is usually indicative of turbulent flow.  That would be my guess - there is a mismatch  between what the rear fan wants to move, and what it is being forced to move by the other fans in the upper part of the system - which are effectively working in tandem.

 

The simplest thing to try is removing that exhaust fan.  If noise is better, and temps don't rise significantly call it good.  If noise drops but temps go too high then you will need to find a fan that offers a better match to the overall flow rate of the upper portion of that chassis. 

 

A third option is the try using that exhaust fan on the CPU cooler in a push/pull, with passive rear chassis exhaust.

Thank you very much, that was kind of what I was looking for. I already tried removing the rear fan, noise is great. Few ours of internet research and office also went fine. However, after an hour of gaming or so, Grafic and CPU temps were noticeably higher than before. And it took the system ages to cool down again, air temp in the case was way hotter than usual. So I guess no exhaust fan is no option.

Since I am running quite low on controlled fan headers wanted to disconnect the exhaust from the CPU load anyway (GPU use may be higher most of the time), I was thinking of using one of the "Power fan" connectors, setting it to a constant vaslue and put quiet 800rpm fan in, maybe with a low-noise adapter.

 

Anyone know 120mm fans that are 800rpm max and come with a LNA? I heard the new Fractal ones do come with LNA, but I think they are > 1200rpm

[ThomasD]

Thank you very much, that was kind of what I was looking for. I already tried removing the rear fan, noise is great. Few ours of internet research and office also went fine. However, after an hour of gaming or so, Grafic and CPU temps were noticeably higher than before. And it took the system ages to cool down again, air temp in the case was way hotter than usual. So I guess no exhaust fan is no option.

Since I am running quite low on controlled fan headers wanted to disconnect the exhaust from the CPU load anyway (GPU use may be higher most of the time), I was thinking of using one of the "Power fan" connectors, setting it to a constant vaslue and put quiet 800rpm fan in, maybe with a low-noise adapter.

 

Anyone know 120mm fans that are 800rpm max and come with a LNA? I heard the new Fractal ones do come with LNA, but I think they are > 1200rpm

LNAs are just a fixed voltage divider, they reduce noise by slowing fan speed.

[Speakerator]

LNAs are just a fixed voltage divider, they reduce noise by slowing fan speed.

Yes, I know. That's why I intend to use them^^ Just thought I may get them bundled as a bargain, though they shouldn't be that expensive. In the end it's a sleeved resistor and two connectors.