Noctua NH-U14S Slim 140mm Tower Cooler

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Specifications: Noctua NH-U14S Stock Fan
Manufacturer Noctua Power Rating 1.56 W
Model Number NF-A15 PWM Airflow Rating 140.2 m³/h
115.5 m³/h with L.N.A
Bearing Type SSO2 Speed Rating 1500 RPM
1200 RPM with L.N.A
Frame Size 150 x 140 x 25 mm (120 mm holes) Noise Rating 24.6 dBA
19.2 dBA with L.N.A
Hub Size 43 mm Header Type 4-pin PWM
Blade Diameter 133 mm Starting Voltage 4.5 ~ 5.0 V
Cable Length 20 cm Weight 160 g
Corner Type Open Retail Availability No
Additional notes:

The NH-U14S' stock fan carries the model number NF-A15 PWM, which is the same as one we tested during one of our 140 mm fan roundups. However, this is actually a faster variant with a nominal speed of 1500 rather than 1200 RPM. If your motherboard lacks PWM control, a low noise adapter is included that brings down the speed to 1200 RPM (the equivalent of around 9V) but as all modern boards have PWM support, you can most likely toss it to the side or save it for use with a different fan.

This is the screen capture of Fan Xpert 2's auto-analysis of the NH-U14S stock fan on voltage control.

This is the screen capture of Fan Xpert 2's auto-analysis of the NH-U14S stock fan on PWM control.

Hooked up to our fan test system, we were surprised to discover the fan can be dialed down to very low speeds via PWM control. On voltage control, it stopped spinning below 700 RPM (about the equivalent to 5V).

Stock Fan Measurements
1460 RPM
30 dBA
1160 RPM
24 dBA
940 RPM
18~19 dBA
810 RPM
16 dBA
680 RPM
13 dBA
Measuring mic positioned 1m at diagonal angle from the center of the heatsink.
Ambient noise level: 10~11 dBA.

Upping the speed on the NF-A15 PWM may have been an attempt to appeal to overclocking crowd but for the rest of us, it's unnecessary. The fan is very loud at top speed, and the sound output is uncomfortable even with the low noise adapter attached (~1200 RPM). The fan enters the quiet zone (below 20 dBA@1m) at just under 1000 RPM and is barely audible at 5V which is conveniently close to its starting voltage.

While not the same NF-A15 PWM fan you can buy in stores, it does have a similar acoustic character to its slower-spinning brother. At higher speeds it's turbulent and buzzy with a slight rustling sound. At 7V / 940 RPM it's generally quiet and smooth but there is an audible scratchy sound as if some kind of fabric is rubbing up against it slightly. This artifact is fairly soft-sound though and is thus preferable to the typical tonal issues that plague most acoustically-challenged fans. As the speed is decreased further this oddity starts to fade and is replaced with a faint hum.

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