What would be louder? 120mm vs (2) 80mm fans....

[caenus]

I'm debating on whether or not to use 2 80mm fans or 1 120mm fan as an exhaust blowhole on the top of my case.

The 120mm fan is panaflo (great fan for anyone interested, very quiet), it moves 69cfm and is only 30dba.

The 80mm fans are Antec, 34.4 cfm and 30dba each. So together they would be roughly 69cfm but 2 30dba each.

I'm assuming 2 sources of 30dba should be louder than a single source of 30dbA. Is this true? Will it be noticeably louder?

Thanks.

 

[dxkj]

call me crazy, but it would probably be twice as loud... now, that doesnt mean 60DB its more along the lines of 45 or 50 I believe... but anyway, why would you want two small instead of one a little bigger? if it fits, that should be pretty neato

 

[caenus]

I know for sure it isn't twice as loud and its not 60dba. The dBA is a curve so something like 40db is twice as loud as 30db. Anyone know the exact curve and numbers. I'm not an audio engineer.

 

[BA]

It's a logarithmic scale. An increase of 10 decibels is 10 times as loud. Multiplying by two is approximately 3db more, so 30db+30db~=33db.

if you want to do the actual math, or add more than two sources:
Divide all the decibel values you want to add together by 10.
(in this case, that gives us 3 and 3)
Then take 10 to those powers
(again, 10^3 gives us 1000, 1000)
Add these together
(so 2000)
and take the log(base 10) of that
(3.301...)
And finally multiply that by 10 again
(viola ~33db)

if you had 3 30db fans, you'd end up with 10*log(3000)~=34.77db

 

[caenus]

Thanks BA, I saved your explanation on my HD for later reference. Very helpful, thanks again.

 

[arod324]

I think you need to note that when when the intensity dB inceases by ten, the intensity "loudness" is increased by ten times. However, human ears only percieve the sound to be twice as loud, not ten times as loud.