How to calculate db?

[Guru]

If I have 2 fans both making 10db noise how much total noise would they make(in theory)? Whats the formula for calculating it?

[Greebe]

double would be 13dB

3dB indicates twice the signal level. But also remember that there will be harmonics cause by the two intereacting with one another (particularly if placed close)

10dB indicates 10x
20dB indicates 100x
30dB indicates 1000x

etc etc

Bels or commonly used in the deci Bel scale is that of a log function.

[Guru]

double would be 13dB

I knew that but what I was looking for is how do you count it? Lets say I have fans 19db, 27db and 23db how much sound would they make?

[Pace]

Mike told you

Take the natural logarithm. You should be able to deduce a formula from that

I would, but I can't be bothered at the moment

P.

[KvHagedorn]

Get a db meter and position it where you are in relation to your rig to measure. I found one at Radio Shack pretty cheaply awhile back, but I don't know if there are Radio Shacks in Finland.

[PeTe]

Just check THIS link, press next couple times and it tells you how to do it in a example... then just calculate it yourself.

PeTe

[PeTe]

.... ok i can run it down here..

First you have to convert the decibels to bels..

19dB = 19/10 bels = 1.9 bels

Then calculate a ratio for it... 10^1.9 = x.xxxx

Do the same thing for all of the dBs .. add them to gether..

you should get ~ 780,14628859658839534339155484243

Then just take a log of that number.. you get 2,8921760467587889626412290491153 bels and then convert it back to decibels by multiplying it by ten..

2,8921760467587889626412290491153 bels*10 = 28,921760467587889626412290491153dB ~ 28.9dB.

19dB+27dB+23dB=28.9dB. MOT.

PeTe

To check you can allways think that 10dB+10dB... 10dB/10=1bels, 1+1bels=2bels, log 2 = 1.30xxxbels, 10*1.30bels =13.0dB

[Pace]

Ah, now I recall why I can't recall it