Taking a Deeper Dive into Performance

So our initial impression upon seeing the results on the previous page was that the SilverStone AR11 cooler had more internal air resistance than the Noctua NH-L9i, which would go a long way to explain both why it was louder and why it ran cooler even when using the same fan. But another test we ran changed our outlook on this entirely. When we removed the top of the case from our test system and re-ran the benchmarks, both heatsinks were completely silent when using the Noctua fan. In other words, the noise had nothing to do with the coolers at all.

The true culprit: resonance created by air being pulled through the case's metal mesh. This phenomenon has reared its ugly head in previous cooler testing using ATX cases, where fans mounted directly behind a front mesh fascia or on the top panel of a case can create a lot of noise, but we just hadn't considered the issue here. As it turns out, there may be a method to Noctua's madness when it comes to offering a cooler smaller than the stock Intel model: if the NH-L9i were the same height as the Intel cooler, as is the SilverStone AR11, it would be louder when pressed into service in cases that actually require such a small cooler. Remember, the Intel cooler has a plastic fan guard about its fan, which effectively makes it shorter than 47mm when it comes to the dynamics of airflow. Noctua probably realized this when it spec'd the NH-L9i to be 10mm shorter, placing its fan at around the same height as the Intel cooler's.

Fans

Now, none of this matters when tested in a huge case, and that's what just about every review on the 'net gets wrong about compact coolers. If you're not testing them in small cases, you aren't testing them right, because to fully understand their behavior, you have to replicate the ecosystem in which they operate. To help provide a bit more data to back up our conclusion here, we dug through our parts box to find a fan that would sit just a bit lower than either the AR11's or NH-L9i's 15mm fans. And we came up with a perfect solution: the TY-100 fan off of a Thermalright AXP-100 cooler we tested in our previous low-profile cooler shootout. There's nothing particularly special about this fan, other than the fact that it's 14mm tall, making it 1mm shorter than the fans on the AR11 and NH-L9i. In the photo shown here, you can see the white Thermalright fan affixed to the AR11 heatsink sitting comfortably below the grille on our case, while the brown Noctua fan, affixed to the same heatsink, it pressed up against it. That 1mm makes all the difference, as you are about to see!

By the way, for the graphs below, we've dropped the Intel cooler, as we've already established what its strenghts and weaknesses are. In its place we've included the AR11 with the TY-100 fan.

Cinebench

In this test, we ran the Cinebench R15 CPU benchmark. As can be seen, the AR11 is better than the Noctua in every configuration, from stock (where it's again too loud), to modified with the Noctua fan, to modified further with the Thermalright fan. But what's key here is that the 14mm-tall Thermalright fan both performs better and runs quieter than the Noctua fan. In fact, it comes close to matching the much louder, much faster SilverStone fan. Just being 1mm further away from the case's top panel mesh meant that air resonance was cut to zero. 

Prime

In this last test, which is the most stressful of all the tests we ran, the out-of-the-box AR11 proves it can't be touched in terms of thermal performance, but of course, it's as loud as always. Interestingly, the AR11 with the TY-100 fan stumbles a bit here, falling behind the AR11/NF-A9x14 combo. No doubt, the Noctua fans is actually better than the Thermalright fan, but what's again key here are the noise levels. Note that the AR11 with the Thermalright fan performs better, at lower noise levels, than the NH-L9i cooler. This establishes without a shadow of a doubt  that the AR11 heatsink is more capable, but that in our test system, its stock fan is doing it a disservice, and in fact any 15mm-tall fan is sub-optimal due to being pressed up against the top of the chassis. Even in bigger cases, we'd recommend users opt for a low-noise adapter like the Noctua NA-SRC7, which ironically comes with the NH-L9i even though it definitely doesn't need it!

Conclusion

Contenders

So, that turned out a little different than we had expected! Indeed, going into our testing, we thought the Noctua NH-L9i would prevail over its brand-new competitor, the SilverStone AR11, simply due to its greater heft and higher-quality fan. In the end, though, we proved three things: the AR11's fan is capable but simply too loud, its lighter, taller heatsink is in fact superior to the Noctua's dense and squat design, and maxing out cooler height limits isn't necessarily a good thing. In the end, this ended up being more of an exploration of the far reaches of the small form factor galaxy than it was a shootout between equals, despite the practically equal price of our contenders.

In fact, we're going to call this shootout a draw. Both the Noctua NH-L9i and the SilverStone AR11 are winning choices in the hands of small form factor PC enthusiasts who understand their particular benefits and drawbacks. Want a stunningly-quiet cooler than can outperform the Intel cooler and is a joy to install? Go with the Noctua. Want a cooler that takes full advantage of the 47mm Intel height specification and can easily cool even an Intel "K" series processor, at the cost of fan noise? You want the SilverStone AR11. And here's another tip: when it comes to downdraft coolers, and fans generally, we recommend you factor in the benefits of leaving an air gap between a fan and the intake grille it's mounted against, as you'll be in for a bad surprise if you try to fill all the space provided. Sometimes, empty space has value too, and in this case it gives these fans a little "room to breathe"!

As of our publication date, the Noctua NH-L9i is available for $39.99 shipped from Amazon, while the new SilverStone AR11 is available for $37.99 shipped from Amazon. As always, your use of the purchase links we provide helps support continued publication of reviews on The Tech Buyer's Guru.

To see all of our top CPU cooler picks, check out our CPU Cooler Buyer's Guide, updated quarterly!

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