“Quiet” Computer Cases and Airflow

What is better? A computer case with sound dampening features, or a computer case without sound dampening features, with its fans turned down to match the sound produced by the quiet case?  Silent PC cases are damn heavy, and so what I’d like to believe is that the same benefits can be had by giving fans free access to fresh air while running them slower. I was fully prepared to trash my Corsair 550D, but it turns out that answering this question isn’t strait forward.

My case has two panels that can block sound and airflow from the front fans. Following you can see the case with all the front panels on, then only the inner panel, and finally the air filter. I leave the filter on for all my measurements for this article, but you can see the fans are behind it.

My prediction is that airflow will improve when the front panels are off. I can then reduce the speed of the fans to match the noise with the panels on. Airflow will improve enough to compensate for the slower fan speeds.

The computer was off for all measurements. I connected an external, silent power source to the fans. To measure sound levels I placed my generic meter in front of the case. I measured airflow using at Testo 405i with the sensor a few inches behind the fan. I tried to be consistent but I didn’t build a jig.

First, sound levels.

volts doors sound level db(A)
12 closed 41.5
12 open 44.0
8.8 open 41.5

The doors reduce sound levels significantly. What about airflow?

volts doors airflow m^3/h
12 closed 33.3
12 open 28.6
8.8 open 14.8

This is shocking and absurd.  How is it possible that adding obstructions increased airflow? Then it occurred to me that a spinning fan will move air, but it doesn’t mean that the air is moving from outside the computer case to inside. I entirely blocked the flow of air through the fans with cardboard to see how much airflow I would measure.

In spite of the cardboard, I found the airflow was 10 m^3/h. There is no way that the case is getting any more than 29 m^3/h of fresh air with the front panels on.

This experiment turned out to be more interesting than I expected, but I’m sad to not be able to conclude whether quiet computer cases, or at least the Corsair 550D, are worth it or not. On the one hand, my Corsair 550D does reduce the sound level from the front fans. On the other hand, to reach the same sound level when the fan was open to the outside, I had to reduce the airflow by half. But not the entire missing half is fresh air!

It’s entirely possible that merely half of the air moving behind the fan while the doors are closed is from outside the case. If so, then the sound dampening features are are useless. I suspect that the truth is somewhere in the middle: that the front doors do obstruct airflow, but not by half, in which case they have some limited benefit.

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