Let's start off with the i7-3960X running at the default Turbo speed of 3900MHz. Our ASUS X79 Rampage IV board is pumping 1.25Vcore on the AUTO Bios setting. Notice that at idle, the CPU is not dropping back to a lower multiplier. After 15 minutes of idling we got the following results with the Noctua NH-D15 cooler in a single and dual fan configuration (PNP). Both fans were running at the 1200rpm setting all the time ( PWM setting was disabled in the BIOS)

Without any real surprise this gigantic cooling monster has the best idle value of our current tested air coolers. The Dual fan setup is only slightly better as the cooler isn't really pushed by the heat output of the hexacore 3960X CPU. Time to crank it up and let Prime95 run its custom stress test on the available cores. Again no surprises here, the NH-D15 makes mince meat out of the air coolers in the lineup, this even in a single fan configuration. Nestling itself in between the two AIO coolers we added to the stock test bed chart, the Fractal Design Kelvin T12 and the Cooler Master Eisberg 120L. Take note that the two listed AIOs are equipped with two fans in a push and pull configuration.

After we OC the i7-3960X to 4500MHz at 1.35VCore the idle temps increase by 6-7°C, take note again that the ASUS Rampage IV BE board doesn't down clock to 1600MHz (unless we force the C-states) Thus our idle test results might vary from yours, this in case your mainboard throttles down the OC'ed CPU in idle state. Nevertheless again no surprise that the bulky Noctua D15 Twin tower Air cooler is a brilliant performer. It can even easily play along with several 120 All In One coolers out there, which is just awesome.

Once the six OC'ed cores start crunching the Mersenne Prime numbers the NH-D15 doesn't even break a sweat. Adding a 2nd Fan, even when not in an optimum airflow position it still nibbles off a few precious degrees from the single Fan configuration. Again we spot the NH-D15 cooling down the Intel Hexacore i7-3960X at the same level as many 120 AIOs. Noctua has got another brilliant performer in their lineup, topping the cooling performance of the widely sold All In One coolers from Corsair and co. But best of all this is done at a far lower noise level, as most of the 120 AIOs need a fast spinning fan to push a decent amount of airflow through their radiators; the gap between the 240 radiator is also decreasing. Take note that this i7-3960X pumps out some serious heat, easily besting the heat output of our i7-5960X when running at similar clock speeds.

Since the introduction of the 140mm Fans once gets easily accustomed to the good airflow they provide at a far more enjoyable noise level then their little 120 counterparts. Since the Noctua NF-A15PWMs fan are only spinning around the 1200rpm mark we measured them around 28dBa. Adding a second fan also increases the noise output though once the case is closed even when both fans are spinning at full blast this Noctua NH-D15 remains very enjoyable to the ears. One of the trademarks of this Austrian company, near silent operation warranted!

We did not test the Low Noise Adaptor (LNA) as the fans are as good as they get, providing great airflow at a very acceptable noise level. Using the LNA has a bigger impact on the cooling capacity than on the noise level as the NF-A15 are hardly noticeable in a closed case when being operated in a normal living room environment.