Quiet SLI Gaming PC Build Guide

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Baseline Noise

Before any stress testing let's take a quick look at the noise produced by each part. The system was kept on but idle, and all the fans were stopped/unplugged (except for the power supply) to isolate individual components. Our ultra-quiet hemi-anechoic chamber has a noise floor of 10~11 [email protected], and the baseline of this system, with just the PSU on, measures barely above that.

2 x GTX 970 + Fortress FT05 System
Component Noise Levels (idle, power supply on)
Noise-producing Components
Avg. Fan Speed
SPL @1m
CPU fan
700 RPM
14~15 dBA
800 RPM
16~17 dBA
1000 RPM
20 dBA
1350 RPM (max)
25 dBA
Case fans
550 RPM
19 dBA
600 RPM
22 dBA
730 RPM (low)
27 dBA
1030 RPM (med)
36~37 dBA
1280 RPM (high)
41~42 dBA
GPU fans
1450 RPM (min)
20 dBA
1680 RPM
24 dBA
1920 RPM
27~28 dBA
2400 RPM (max)
33 dBA
Measuring mic positioned 1m at diagonal angle left/front of case.
Baseline noise level (PSU on only): 11 [email protected]
Ambient noise level: 10~11 [email protected]

The GPU fans are almost always the biggest noise generators in any gaming system, and this machine is no different. What is disappointing is that they limit the idle noise level as well. The GPU fans' minimum speed is 1450 RPM, which effectively produces 20 [email protected] all on their own.

The case fans are even louder if they are controlled by the built-in controller. The low setting causes the fans to spin at 730 RPM, emitting 27 [email protected], well above the noise levels I'm shooting for, even on load, let alone idle. Motherboard fan control can be used to slow them down further, but as mentioned earlier, below 550 RPM, the fan speed can't be detected, and their physical location makes it difficult to measure manually. 550 RPM is still slightly quieter than the GPU fans, so it's a good a starting point as any.

As for the quality of noise, the GPU fans have a benign profile with a mostly smooth sound and little if any tonality. If you put your ear up close to them, a slight rattle is audible but once the side panel is closed, this effect disappears completely.

Similarly, the case fans have a rather clicky nature, something that's afflicted the Air Penetrator series for their entire history but it's difficult to detect at distance during normal operations.

Stress Test Results: CPU-centric

Testing begins with CPU-centric applications to see how it performs with non-gaming tasks. The machine measures 23 [email protected], which is quiet, but quite high for a system with zero/little graphical load being placed on it. The video card fans' minimum speed of 1450 RPM makes it impossible to get the system below 20 [email protected], and while the system fans are spinning at a mere 550 RPM, their large size means they emit much more noise than 120/140 mm models at the same speed.

System Measurements
System State
Idle
x264 Playback
Video Encoding
Prime95x4
CPU Temp
14°C
19°C
31°C
38°C
MB Temp
29°C
28°C
29°C
PCH Temp
34°C
33°C
34°C
SSD Temp
26°C
27°C
GPU1 Temp
26°C
GPU2 Temp
29°C
System Power (AC)
55W
73W
102W
121W
CPU fan at 700 RPM, system fans at 550 RPM, GPU fans at 1450 RPM (minimum/auto).
System noise level: 23 [email protected]
Ambient temperature: 21°C.

When lightly taxed, the system runs quite cool as one would expect, with CPU and GPU temperatures staying slightly below 20°C and 30°C respectively. Video encoding creates much greater demand on the processor, producing a CPU temperature rise of 12°C while running Prime95 brings it up an additional 7°C. Board and GPU temperatures are fairly stable throughout these tests. The extra thermal output from the CPU doesn't really affect the rest of the machine.

Stress Test Results: GPU-centric

For our GPU-intensive states, we use the Resident Evil 6 Benchmark Tool. It doesn't cause a steady load like some synthetic tools but it seems to put the highest peak stress on the GPU. The other test is a more demanding combination of Prime95 and FurMark, an incredibly demanding utility that pins GPUs at their redline. Prime95 is run with only two threads instead of the maximum four, as most games run with less than 50% CPU utilization. The two stress utilities combined still draw more power and creates much more heat than any PC game title. The GPUs' automated fan control is switched off with fan speeds adjusted manually in order to achieve/maintain a target GPU temperature of 85°C or lower.

System Measurements
System State
Resident Evil 6, Peak
Resident Evil 6, Peak (106% power)
Prime95x2 + FurMark
Prime95x2 + FurMark (106% power)
GPU1 Fan Speed*
1450 RPM
GPU2 Fan Speed*
1450 RPM
1560 RPM
1920 RPM
GPU1 Clock
1404 MHz
926 MHz
1001 MHz
GPU2 Clock
1404 MHz
1215 MHz
CPU Temp
35°C
36°C
49°C
47°C
MB Temp
46°C
46°C
49°C
49°C
PCH Temp
52°C
53°C
56°C
57°C
SSD Temp
38°C
39°C
42°C
42°C
GPU1 Temp
62°C
63°C
64°C
67°C
GPU2 Temp
78°C
79°C
85°C
85°C
System Power (AC)
404W
422W
429W
443W
23 dBA
23 dBA
23~24 dBA
26 dBA
*set as low as possible to maintain a GPU temperature of ~85°C on load.
CPU fan at 700 RPM, system fans at 550 RPM.
Ambient temperature: 22°C.

The Resident Evil 6 test causes the system to draw more than 400W AC, more than triple the power consumption elicited by a full bout of Prime95. Despite this immense load, the video cards are relatively comfortable, even with their fans set at minimum speed. The card situated closer to the power supply barely breaks a sweat, stabilizing at just 62°C while the warmer card settles at a reasonable 78°C. The motherboard and PCH temperatures increase substantially as one would expect and even the SSD, which is positioned on the opposite of side of the motherboard tray, warms up a great deal. In this state, the GPU uses synchronous clock speeds of 1404 MHz, 34 MHz higher than the designated boost frequency (normal behavior for Nvidia cards). Surprisingly, increasing the cards' power target to maximum (106%) doesn't alter the clock speeds of either card but still causes a small bump in power consumption, though the added load isn't enough to warrant higher fan speeds.

Oddly, our Prime95 + FurMark causes the GPUs to run at asymmetric clock speeds despite being set to sync up in GPU Tweak. This test pushes both GPUs further but as the hotter card runs faster, it's requires a 110 RPM increase in fan speed in order to hold the temperature steady at the desired 85°C, causing the noise level to go up ever so slightly. Weird behavior is encountered once again when the target power is increased. The cooler card experiences a bump in clock speed while the hotter card remains the same, but the later actually heats up further still, requiring drastically higher fan speed to compensate. I'm not sure exactly what's going on here but the end result is a 2~3 dB spike in noise level.

This most demanding state draws about 40W more than than the Resident Evil 6 test at stock settings. This is close to what you can expect with a pair of GTX 980s with similar cooling solutions running Resident Evil 6, though it would probably be quieter as the clock speeds would presumably be in sync.

Our GTX 970 samples do suffer from coil whine, squealing in a waxing and waning manner, particularly during the Resident Evil 6 test, but the effect is mild. With the case sealed up, it isn't noticeable over the sound produced by the other components. Enabling V-Sync dissipates it greatly but the GPUs runs this game with very high framerates and V-Sync caps it at our 60 fps to match our display's 60 Hz refresh rate, reducing the overall stress experienced by the video cards. Overall, the noise generated by the system is fairly inconspicuous, with a nice broadband profile and a lack of distinct tones. The noise level on load is also much lower than any dual GPU system we've ever assembled.

System Measurements (Prime95x2 + FurMark)
CPU Fan Speed
700 RPM
800 RPM
700 RPM
700 RPM
System Fan Speeds
550 RPM
550 RPM
600 RPM
550 RPM
GPU1 Fan
1450 RPM
GPU2 Fan
1560 RPM
1560 RPM
1460 RPM
2070 RPM
CPU Temp
49°C
44°C
43°C
47°C
MB Temp
49°C
48°C
48°C
47°C
PCH Temp
56°C
56°C
55°C
55°C
SSD Temp
42°C
41°C
41°C
40°C
GPU1 Temp
64°C
65°C
64°C
63°C
GPU2 Temp
85°C
85°C
85°C
80°C
System Power (AC)
429W
428W
428W
432W
23~24 dBA
24 dBA
24 dBA
27 dBA
Ambient temperature: 22°C.

Playing with the other fan speeds has some interesting effects. Speeding up the CPU fan by 100 RPM makes the system a tad noisier and cools down the processor by 5°C. Bumping up the intake fans by just 50 RPM is even better for the CPU and also improves temperatures system-wide. This move allows the hotter GPU to return to almost minimum fan speed while maintaining the same temperature. If you prefer an even cooler GPU, in our system, the hotter video card requires a fan speed of more than 2000 RPM to drop the GPU core down to 80°C. The stock cooler is certainly effective but as its fan speed tops out at 2400 RPM, there's not that much upper headroom if you prefer a cooler running card.



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