Do PWM case fans make sense?

Control: management of fans, temp/rpm monitoring via soft/hardware

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fyleow
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Do PWM case fans make sense?

Post by fyleow » Thu Sep 03, 2015 4:37 pm

I'm currently using an R4 with the 2 stock fans as intake and I bought a Corsair AF 140 (before spcr reviewed them) as an exhaust. I bought a new motherboard with a real PWM chassis header and was thinking if it made sense to swap the exhaust for a PWM fan. Will it help with overall noise levels under load rather than using a constant speed for case fans?

Arbutus
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Re: Do PWM case fans make sense?

Post by Arbutus » Thu Sep 03, 2015 4:42 pm

From a quiet PC perspective it makes more sense for the case fan to be temperature controlled because it is more audible at the case's outside edge than the CPU fan which is inside the case. I have often used a PWM fan splitter cable to operate both the CPU fan and case fan on the CPU fan header.
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fyleow
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Re: Do PWM case fans make sense?

Post by fyleow » Thu Sep 03, 2015 7:08 pm

Arbutus wrote:From a quiet PC perspective it makes more sense for the case fan to be temperature controlled because it is more audible at the case's outside edge than the CPU fan which is inside the case. I have often used a PWM fan splitter cable to operate both the CPU fan and case fan on the CPU fan header.
Well it's the exhaust fan so it has an advantage of being in the rear without a direct path to the user. I usually run the case fans at 5v constantly which makes them practically inaudible but obviously the airflow rate is static regardless of load. I was thinking there would be noise savings under load conditions if the exhaust fan could speed up more under load so the CPU fan doesn't have to as much which results in overall lower noise. For example the case/CPU fan could spin at 700/700 as opposed to a static case fan at 500/1000.

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Re: Do PWM case fans make sense?

Post by CA_Steve » Thu Sep 03, 2015 7:34 pm

I don't think it makes a noticable difference for exhaust. If the motherboard can be set for controlling the three pin fan in voltage mode, it'll effectively be the same. The big benefit for PWM is they generally can run at a lower RPM than voltage controlled fans...so, not your scenario.
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Irrelevant
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Re: Do PWM case fans make sense?

Post by Irrelevant » Thu Sep 03, 2015 8:15 pm

fyleow wrote:Will it help with overall noise levels under load rather than using a constant speed for case fans?
Probably. Computer fans are not nearly as directional in their airflow as one might think, so without enough intake/exhaust to keep air moving, interior fans will waste a lot of work on futile cycling (ie, blowing hot air out only to have it circle around and get sucked back in again), which means more noise for the same cooling. To attain maximum cooling-per-dB, you need to have your case fans match the needs of your CPU/GPU/radiator/whatever fans, and since those needs vary, so should your case fans' speed.

But FYI, you don't need a PWM fan for speed control. Yeah, PWM is better at controlling speeds (RPMs can be lower, startup voltage isn't an issue, and power efficiency is much higher), but most mobos will allow speed-control of 3-pin fans on at least one or two of their fan headers.
Arbutus wrote:I have often used a PWM fan splitter cable to operate both the CPU fan and case fan on the CPU fan header.
IMO, that's the biggest advantage of PWM: allowing control of an effectively unlimited number of fans from a single fan header using a powered splitter.
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fyleow
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Re: Do PWM case fans make sense?

Post by fyleow » Thu Sep 03, 2015 11:35 pm

The R4 gaming guide actually addresses this. Looks like it's not worth it to try increasing the case fans past minimum speed.
We also experimented with the speed of the case fans, but the results frankly weren't worth presenting. Ramping up the case fans resulted in slightly lower temperatures but it also drove the noise level up as well so we were unable to achieve a net positive result. It's almost a shame to have such a versatile fan control system at our disposal when the case fans seem to work optimally at minimum speed all the time.

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