News Arctic launches semi-passive Freezer i32 Plus

Fans enabled only over 40% PWM.
https://www.bit-tech.net/news/hardware/2017/01/30/arctic-freezer-i32-plus/1

 

No, they don't - and they can't, either. A PWM controller sends out what is known as a duty cycle, which can be anything from 0 to 100%. At 0%, the connected device will be at its minimum speed; at 100%, its maximum speed. If a fan runs from 800 RPM to 3,000 RPM, then at a 0% PWM duty cycle it's running at 800 RPM; at 100% it's running at 3,000 RPM. There are fans, though, that switch off at 0%; if we take this theoretical 800-3,000 RPM fan, it would be running at 0 RPM at a 0% PWM duty cycle then jump to 800 RPM at a 1% duty cycle.

Arctic's fans as bundled with the Freezer i32/A32 family have a minimum operational speed of 0 RPM. Note that's specifically operational - obviously, any fan can be made to spin at 0 RPM simply by turning it off. Between a PWM duty cycle of 0-40%, the fan will remain at 0 RPM; only at 41% and higher will it begin to spin at all. That's very, very different to the 0%-stopped 1%-go of a typical off-at-0% fan.

As to exactly under what conditions it will and won't spin, that's up to the motherboard manufacturer and how they map temperature to PWM duty cycles. One motherboard might have 50°C as the 50% duty cycle trigger; another might have 35°C as the 50% duty cycle trigger.

This explains how PWM works pretty well (PDF warning).