Metering fan noise

[BSMichel]

First of all (and in fact first post) I wanna congratulate Tom's Hardware staff for all their work. I've been reading you for years and find every piece of data you show us very useful. Next I want to apologize for my english. Excuse any error as it's not my mother language. Said this let's go into the matter.

Nowadays building a computer from scratch or even updating components have some impact on heat dissipating into the case. Most usual solution for this problem pass through designing good airflow and for thus we use fans. Fan specs usually detail the dB of noise this hardware producess but, and here goes the question, how do we theoretically meter the noise in a system with various fans?

For example. Let's suppose a PSU whose little fan produces a 12dB noise. If I use this PSU in a system with a bigger intake fan of 23dB how many total dB will I get? 25 as a result of simply adding dB? Or maybe 23 as the bigger fan "hides" the noise of the little one? Maybe something intermediate?

Thanks for the answers,
BSMichel.

 

[Mr5oh]

No they don't add (well not exactly), it can get rather complicated once you start getting stuff that is different dbs.

For example, if you have one speaker, lets say that speaker is putting out 75 db of sound. If you add another speaker that is identical, you don't get 150 db of sound, you get 78. You only gain 3 db everytime you double the power. (Sort of similar theory with fans)

The db of a louder fan won't hide the quieter one, they will add together, but not directly, it will only add a couple of db. Pretty much any fan or power supply that you can find that is 20 db or so, will be basically silent. Anything that is still 30 or under, will be audible, but won't be obnoxious.

Next, as for your 23 db fan, and 12 db PSU, your noise output should be something like 24 db or so.


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[Crashman]

I'm going to set my fans out-of-phase so they cancel each other out

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[Mr5oh]

Actually I was thinking about trying to do that at one time.

I've read a couple of stories were people have successfully reduced the sound, but obvisuly it is still directional.

It would be awesome if we could successfully cancel out all the noise!

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[Crashman]

the problem is you'll never be able to get one fan to cancel out the noise of the other because the sound they make isn't a perfect sine wave. But if you got enough fans operating at staggered timing you should be able to make white noise...which is less anoying than the normal whine.

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