ARCTIC S4028-6K - 40x40x28 mm Fan, 250-6000 RPM, PWM Regulated, 4-pin Connector, 12 V DC - Black

I picked up one of the 6,000rpm variants of these fans to aim at the 12VHPWR connector on my RTX 5090—you know, just to be safe. I even 3D printed a little right-angle duct adapter to funnel air down over the connector itself. Ultimately, I ended up removing it from the system because I found the noise output unacceptable, even at very low operating speeds. ➤ The Challenge with 40mm Fans 40mm fans can be tricky with noise. Twenty to thirty years ago, 40x10mm was a common size on chipsets and video cards, and I've had quite a few fans in that form factor that were essentially inaudible when installed in a case. I've also had other 40mm fans—like these Arctics—that produce specific tones that pierce through just about anything you mount them to or in. In terms of quantitative noise levels, these are very quiet fans for what they are. I have some 40mm Sanyo Denkis on a 2.5" drive cage that max out at about 13,000rpm and are audible across the house at 8,000rpm; these Arctics are nothing like that. Qualitatively though, the noise these produce is specifically irritating to me. I can sit next to the server with those Sanyo Denkis screaming away and after a few minutes stop noticing them. A cynic might point out that this is because after a few minutes next to that server, I've gone deaf, but this is neither here nor there. By contrast, the single Arctic I had on the 5090, running at ~2,000rpm, was far more irritating in spite of being far quieter. It was *just* audible as a faint ticking buzz over the rest of the system. And unfortunately, at ~2,000rpm, it didn't move enough air to make a difference in my use case, so it was just added irritation with no benefit. It's not that they're loud—it's that the specific tone they make, even in the context of what they are, is particularly grating to me. But this is intrinsically subjective, so your experience may differ. ➤ Use Case Matters For their intended use case (in a 1U server), these are extremely quiet and highly power efficient. For use in a desktop, they become meaningfully audible far before they move a meaningful amount of air. As far as 40mm fans go, these are outstanding. But unless you have a specific need for a 40mm fan, you would generally be better served finding an alternative way to accomplish whatever task you're considering these for. ➤ Bottom Line I can't and won't knock any stars off the fan itself—these earn the full five stars easily. They're power-efficient, quiet for what they are, dual ball bearing, exceptionally well-built, and Arctic provides actual performance data including P/Q curves and PWM curves. Both are generally absent with consumer-grade fans and are hugely useful if you know how to read them, signaling that Arctic is serious about selling these for actual industrial/server use. For the home/enthusiast/desktop user, these are clearly audible below 2,000rpm, and probably outright unacceptable over 3,000rpm. If you have a specific need for them, I'd recommend them very highly. On balance these are likely the best 40mm fans on the market. At the same time, if you can accomplish your goal with a larger fan, you'd probably be happier going that route.

No frills, no marketing bs, just pure performance. I needed good 40mm PWMs to cool my optane rams and these were perfect. I would have gotten the normal AVC used in servers but they're too loud. The 11k RPM version of this would work just as well and is also quiet compared to the AVC but it was not needed for this use case. The rams were hitting 70c prior without proper airflow. They peak at 43c with these fans mounted on top.

Excellent fans!!

This fan offers pretty good cooling for the size, but as other reviewers have mentioned, it is quite noisy when kept at close range

It work fine