We measured the noise output of our entire system from a distance of 1m while the CPU cooler's fan(s) operate at 100% (indicating the maximum noise output).
Lower noise levels can be achieved by utilising the Noctua NH-L9i CPU cooler's 4-pin PWM operated fan with a dynamic profile, or by making use of the supplied Low-Noise Adapter (L.N.A.).
With a fan speed of 2500 RPM, the NH-L9i can't compete with Intel's lower-speed cooler. 40.9 dbA isn't a noise level that can be considered as irritating or obtrusive, but when coupled with other quiet components, the NF-A9x14 will be audible to nearby listeners.
Seems like a good deal.
Great products from this company. I want the new NH D14 beater!