The cooling results were, as we suspected, entirely predictable given the small size of the cooler and the fact the fan's RPM is half that of many similarly-sized fans such as SilverStone's AR01. In the LGA1155 test system, dealing with our overclocked Core i7-2600K, the NH-U12S managed a delta T of 47°C, rising to 51°C with the low noise adaptor. This matches many of the other small air coolers although most of the larger models including Noctua's own NH-D14 performed better, as did the majority of the all-in-one liquid coolers on test at their low or default settings too.
Performance in our LGA2011 system was just about okay, with the NH-U12S not quite rising to CPU throttling territory, which many small coolers have. A delta T of 56°C at full speed actually betters the tiny Deepcool GAMMAXX S40 and is only 1°C off the Corsair Hydro H80i on its quiet profile too. However, with the best air-cooled result here being 44°C, it's clear that this isn't a great cooler for an overclocked LGA2011 system.
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So what about noise? Quite simply this is one of the quietest coolers we've tested. It's inaudible outside our test rigs, even at full speed, and with the low noise adaptor, you can't even hear the fan with your ear right next to it above the din of other fans in the case. It's been a long time since we've tested a cooler this quiet and clearly what it lacks in cooling has at least beefed up its low noise credentials as a result.
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Despite the clear appeal of having a super-quiet CPU cooler, they're still rare objects and sub £70 all-in-one liquid coolers and mammoth air coolers are much more popular for the simple reason many offer much better cooling and aren't completely deafening. Some examples of both of these aren't a lot more than the NH-U12S too.
Where the NH-U12S excels is actually being inaudible outside a case - you literally can't make it out amongst other case fans or a graphics card. This is where the extra cash is going - not in cooling but in offering similar performance to other, cheaper air coolers but with a significantly lower noise level. The only way you'd get this level of noise with better cooling is with a custom water cooling system with a double 120mm-fan radiator cooling the CPU alone with two premium fans likely running at 5V or 7V and with the pump tuned down too.
That's going to be an expensive option of course but the real issue for the NH-U12S is that there are much, much cheaper coolers such as SilverStone's AR01 and Deepcool GAMMAXX S40 that offer just as good if not better cooling. It also didn't fare to well in our LGA2011 system. In this light, there are certainly better options if cooling is more important. However, if noise is your primary consideration, then the NH-U12S is almost certainly worth the asking price, with an added bonus that it's compact too. As such, while it loses cooling points, it deserves an award for being brilliantly made as well as being perfect for super quiet, overclocked LGA115X systems.
Intel LGA1155 Score
Intel LGA2011 Score