How loud are two fans?

[Malpine Walis]

Since aggressive air cooling requires a few fans, some consideration needs to be paid to the total output of all the fans in a case. Since dBA is measured on a logarithmic scale, adding the dBA’s together would yield some very wrong numbers.

2 30 dBA fans side by side would not be anywhere near 60dBA. How do I figure how loud this (or some other configuration) will be?

I remember doing logarithms in school and at one time I could figure this out on my own but that was 20 years ago.

[AntmanMike]

around 35 to 40dB. Also, 2 30db fans is not near agressive air flow. I would call that super mild.

[Yodums]

Two fans of the equivilant DBA put together are usually 1.5 the CFM of one.. So Mike said 35-40 and that is supposely correct.

[Malpine Walis]

Granted that 2 relatively small fans would provide minor cooling at best. I used that scenario as an example. Let me try restating where I am going here.

5 25 dBA fans (Globe 80mm standard: 25dBA 29.5 CFM) would not be anywhere near as loud as a single fan that produced 125 dBA (if such a beast even existed). Given the relatively light air flow one would get from the smaller fan , even with 5 of them, cooling would still be minimal.

What I am after is how to calculate the relative sound which I would hear from a complete set of fans whatever fans I end up buying.

[AntmanMike]

125dB would deafen you, sound worry about sound!

[Big_KiD]

my machines has a few fans.....

80mm on the alpha heatsink
2 80mm in the front of my case that are 3 speed ajustable
1 60mm in the back of my case
2 60's in my ps..

believe it or not with the front case fans turned on low and the case under my desk.. i can barely hear it with the tv turned on in the same room...

[Malpine Walis]

But getting back to my original question:

One fan @ xdBA produces a certain amount of sound. Two fans @ xdBA produces twice as much sound.

Since dBA is a logarthmic scale, adding the two number actually results in the square of the sound of a single fan. What I am looking for is the sum of the two numbers...

[smash]

http://forums.overclockers.ws/vb/showthread.php?s=&threadid=49847&highlight=300db