Case fan selection / CFM addition

I've been researching this for a bit, and one thing that im not sure if people realize is that 10dB = 10x pressure. I think it translates to dBA since that is just a realative curve (its probably not linear). Anyways, since many cases have 2 80mm fan slots in the rear, i want to know if you can add or combine CFM? My assumption is yes, with probably a small loss due to interference flow (i just made that term up, but i think you know what i mean). So, im trying to validate:

two 32 CFM fans @ 14 dBA is better than a single 45 CFM fan @ 30 dBA.

Where the criteria is most CFM / dBA.

Here is some reference i found that can help understand my hypothesis.


every 10 db is 10 times louder
For adding several decibel levels
of the same value:
No. of
Equal
Levels Add the Following
Amount to that Level
to Get the Sum
2 3.0 dB
3 4.8 dB
4 6.0 dB
5 7.0 dB
6 7.8 dB
7 8.4 dB
8 9.0 dB
9 9.5 dB
10 10.0 dB
N 10 log N dB
At the final total, round off to the
nearest whole number.

To sum this up, 2 fans @ 32 CFM should produce approx: 64 CFM (minus a few cfm for interefence? this is where i need some help). The dBA from the 2 fans should be 17 according to the chart, which results in the affects of a single 64 CFM @ 17 dBA... more that 10x quieter than the 45 CFM 30dBA counterpart.

I hope to hear some opinions, and please feel free to rip apart my hypothesis.

First off

and 2nd.. HUH?.

i dont get what your trying to prove, i mean, i understand but why spend all this time on CFM and DB ratings for computer fans?

if your computer needs more cooling, add a fan, or upgrade to higher CFMs.. and find the lowest DB you want to deal with, and install them...

i'm not trying to be funny or mean, but this is just way to much thought put into cheap case fans... if this was for some high end water cooling rig with huge amounts of fans, i would not say anything but dang...

In a general sense, you make a very good point which i can agree with. There are 2 reasons why i spent any time thinking about this:

1) Quest for knowledge.
2) the theory extends to other applications, of which i am working on. My project doesn't have the luxury of unlimited cost or size.

Seeing that no one has really responded to my hypothesis, i may have to take this somewhere else.

I personally like larger 12-20cm case fans as they can move the same amount of air as an 8cm, but at lower rpm's and are thus quieter.

Any air moving causes sound.
Its just a matter of what you can tolerate I guess!

yes, two quiet fans at 32 cfm, is better than one loud fan at 45 cfm. and yes, dB is a logarithmic scale and your calculations seem to be good. (i'm persosnally not sure if they are 100% accurate as i have not looked into this as far as you have, but i do know that 2x 15dBa fans does not = 30 dBa - it will be far quieter)

in effect, it is for this same reason that bigger fans are better, they can produce more CFM for less dBa. More fans at lower dBa will end up producing less noise than a single fan at an insane CFM and high dBa.