Fan noise question

[brtspears2]

If I have the following combonation of fans...

1x 60mm Delta 38cfm at 46.0dB
2x 80mm Sunon 32cfm at 32.0db
2x 80mm Antec 34cfm at 30.0dB

What is total average noise in dB?

 

[Elledan]

You'll hear the loudest fan the most, thus total noise would be 46 dB. The other fans simply make less noise than the 46dB one.

 

[brtspears2]

Hmm, I swear there is a nice increase in noise when I have ALL these fans running at once.

Though Mr. Delta is the big screamer...

 

[Elledan]

Well, the noise level is 46 dB, but since not all fans are vibrating with the same frequency, you'll hear more noise (on different frequencies) than with just one type of fan.

 

[sanaka]

there's an excellent link (i forget to where exactly) through 7volts.com that explains this exactly - it's something i always wondered myself. If I remember right, the total db level of a bunch of various noise sources going on at the same time cannot exceed the loudest single source by more than 3db. If they are in phase or harmonically related it can be up to 6db louder. It's a "logarithmic sum," whatever that is.

edit: BTW, a 3db increase sounds twice as loud.

 

[Yo Ma Ma]

Here is a similar link with that information.

 

[highwire]

Total noise power, 46db + 32db + 30db expressed as a percentage of the 46db unit would be 100% + ~4% + ~2.5% = ~106.5% noise power.

This small increase in noise would only be perceptible because different noise frequencies are likely present. (previouly suggested)

My oldie but goody calculator gives a total noise level of 46.27db for all 3 fans.

sanka - 3db IS a ratio of 2 to 1 - twice the power. But the logarithmic ear generally perceives 6db (or a little less) as twice as loud.

The link by yo-ma-ma seems to be a good one on the subject.