Calculating combined dB-A...

shaunco · Post by **shaunco** » Sat Nov 13, 2004 3:38 pm

Is it possible to calculate the "Combined dB-A" of six of the same fans?

For example, I have 6 40x40x20mm fans that are each rated at 39.8dB-A (yes they are junk, I have ordered new ones). So, obviously the combined db-A is not "39.8 * 6 = 238.8" (unless I just haven't noticed that all the glass in my house has exploded and my ears are bleeding). I don't have a dB meter, but if I had to guess I would put it around 55-60dBA.

On the same note, my 6 new Sunon fans are listed as 27dB-A each, so it should be ~33% quieter with the new fans, but how many dB is 33% in this case?

Thanks!
-Shaun

BTW: For the sake of simplicity, lets just assume that all fans are free-standing (not in a case), which would mean there is no (or very little) back-pressure and there are no obstructions.

shaunco · Post by **shaunco** » Sat Nov 13, 2004 4:57 pm

After digging around on google, I found this thread:
http://www.abxzone.com/forums/archive/i ... 16943.html

The last five posts try to answer my question...

-Shaun

seangoesbonk · Post by **seangoesbonk** » Sat Nov 13, 2004 5:04 pm

Six of the 39.8dB fans will be ~47.6dB.
Six of the 27dB fans will be ~34.8dB.
A 12.8dB difference.

Post by **Rusty075** » Sat Nov 13, 2004 5:34 pm

The formula:

Total dB = 10* log10[10^(Fan#1/10) + 10^(Fan#2/10) + ...]

So for your example that works out to:

dB= 10*log10[6(10^(39.8/10))]

Which is exactly what seangoesbonk reported, I just wanted to show you how he did it.

shaunco · Post by **shaunco** » Sat Nov 13, 2004 11:35 pm

Thanks

-Shaun

Krispy · Post by **Krispy** » Sun Nov 14, 2004 5:03 am

I'm sure I've seen this mentioned somewhere on SPCR before, however, this freeware Fan Noise Utility by Khaled Ghaben over @ Overclockers will enable you to calculate your combined dbA figure to your hearts content.

This great & informative little application can be downloaded from:

http://www.overclockers.com/tips1129/

Have fun & Respect to Khaled!

Abula · Post by **Abula** » Thu Nov 18, 2004 11:24 am

very nice utility, thanks for the link