New 92mm-fan Tower Coolers from Noctua

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STOCK FAN MEASUREMENTS

Specifications: Noctua NF-A9 PWM Fan
Manufacturer Noctua Power Rating 1.2 W
Model Number NF-A9 PWM Airflow Rating 78.9 m³/h;
62.6 m³/h with L.N.A.
Bearing Type SSO2 Speed Rating 2000 RPM
1550 RPM with L.N.A
Frame Size 92 x 92 x 25 mm Noise Rating 22.8 dB(A)
16.3 dB(A) with L.N.A.
Hub Size 34 mm Header Type 4-pin PWM
Blade Diameter 85 mm Starting Voltage 4.2~4.4 V
Cable Length 20 cm Weight 100 g
Corner Type Open Retail Availability Yes
Additional notes:

The same NF-A9 PWM fan is used in both of these new heatsinks: A 7-blade 92mm fan with 4 struts, good geometry for low tonality and rubber vibration-damping corner covers. The low noise adapter (L.N.A) brings the fan speed down to about 1550 RPM, but if you plan on using PWM motherboard headers, the LNA can be better utilized elsewhere in your system. The Noctua NF-A9 PWM fan is available as a retail fan, packaged with a rich set of accessories: 30cm extension cable, 4-pin Y cable (for use with another fan on the same header), LNA, 4x fan screws and 4x anti-vibration plug mounts.


Noctua NF-A9 PWM retail fan package.



The stock fan's range according to Fan Xpert2: PWM control on the top top, DC control on the bottom.

According to ASUS Fan Xpert2, the stock fan can effectively operate at less than 200 RPM under PWM control. Fan Xpert2 states that the startup threshold for voltage control is >800 RPM and we confirmed manually that our samples could reliably start with 4.2~4.4V at ~800 RPM. Since these are PWM fans meant to be connected to the CPU fan header on the motherboard, they were checked for speed/noise only on PWM control. All motherboards have PWM control on the CPU fan header these days. The % value and RPM shown in the table below were the same whether controlled via the ASUS FanXpert 2 or SpeedFan. There's little point going below about 800 RPM; the fan is so quiet at this point that it's almost inaudible even in our anechoic chamber.

Stock Fan Measurements
PWM %
RPM
off cooler
on cooler
2 fans on cooler
100
2000
29.0
30.0
32.7
72
1500
21.2
21.5
24.5
60
1280
18.2
17.3
20.0
50
1080
15.0
14.0
16.2
40
870
12.0
12.2
13.5
35
780
11.7
11.8
12.7
Measuring mic positioned 1m at diagonal angle from the center of the heatsink.
Ambient noise level: 10~11 dBA.

Measuring 29 [email protected] off the heatsink(s) in our custom frame, the stock fan is fairly loud at their top speed of ~2,000 RPM. The smaller diameter blades, compared to 120mm and larger fans, sound higher pitched, but it's a fairly smooth sounding fan. The low noise adapter reduces speed to ~1,550 RPM, which makes the fan fairly quiet at 21~22 [email protected] It needs to get under ~1350 RPM to fall below 20 dBA. By about 1100 RPM, it is close to the ambient noise level of a very quiet room. Anything below 1000 RPM makes it near silent.

Mounted on either cooler, the fan makes more noise due to the turbulence effects of the heatsink fins being so close. When two fans are used, the +3 dB rule of a second identical noise source holds only in the upper half of the measured points. As SPL gets closer to the ambient noise floor of the chamber (10~11 dBA), the measured difference gets smaller. This is a measurement error; below about 15 dBA, our readings become higher than they should be. For example, if our chamber had a noise floor of 0 dBA, the single fan would probably measure lower than 11.8 dBA and we'd see closer to a 3 dBA difference between one fan and two fans. In terms of perceived noise, the difference between two fans and one on the heatsink is hard to tell at speeds below 1,000 RPM. One has to get quite close to the cooler to differentiate. Undoubtedly, our subjective perception is influenced by the ambient noise floor, not just our measurement gear.





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