Whats a more effective top exhaust blowhole?

[Emericana]

If I place 3 80mm fans, all 33cfm on the top for a blowhole, in a triangle position, or one 120mm 80cfm fan at the top. The 80mm fans are all around 30dba so it would be quieter than a 35dba 120mm.

 

[deadhead]

just my opinion, but wouldnt
30+30+30 dba=90dba and that would be louder than the 35 dba

 

[JigPu]

just my opinion, but wouldnt
30+30+30 dba=90dba and that would be louder than the 35 dba

No, sound level is logarithmic so it would add up to a little over 35dBa. The 80mm would be quiter but not by much. So, you can get a little quiter or an extra 19cfm.

JigPu

 

[Iron Hawk]

does any one know of a simple formula for adding dB? or is it quite complex and requries things like placement of the sound emitting objects etc.?

 

[takiwa]

when acoustical sound doubles, it increases 3.01dB...I could give you the formula, but just add 3.01dB and you'll be fine

30dB = 1 fan
33.01dB = 2 fans
36.02dB = 3 fans

The 1dB difference would be non-audible to the human ear, so I would go with the 3 fans for more CFM...IMHO