S4028-6K - 40 x 40 x 28 mm Fan, 250-6000 RPM, PWM-Regulated

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.

I'm using these to cool a CMP 100-210 GPU with a 3D printed attachment. Long story short - at 100%, these fans are still quite quiet - and they move a lot of air. Not nearly as loud as a typical 40mm server fan. I'll probably go with these when I need another 40mm fan. It's good stuff.

Fits well for cooling VRM and ram on mother board

Works great, not too loud

This one is the perfect balance between performance and noise compared to its bigger brother which is insanely loud Keeping my 10Gb network switch perfectly cool!

Man can these things move air. Just be warned, these are not a fan you would put in a switch located in a bedroom or a noise sensitive area.

I got this to cool a 10g network card in my pc as this is the largest fan I could fit in the space I had. In order to move a decent amount of air I have to put it at 45% and the noise is a bit annoying so now I will be trying the noctua 40mm.

If you need a fan of this size, it will do the job. At full speed it can move a lot of air. I will mention that at full speed it is not quiet. This was not a problem for me because it is connected to a header on a motherboard that adjusts fan speed depending on if components are heating up enough to need additional fan RPM's.