noise calculation in dB

[cDNA]

I see that many people try to run silent systems and i know that calculating noise level in dB can be tricky, there is quite a little bit of math involved.

But there is an easy way to sum that:

Basicly each time you double the sources of noise you add 3dB;

for example if you have 1 fan that does 20dB, adding a second one will make a total noise level of 23dB.

Then going from 2 of those fan to 4 of those will do 26dB and so on...

So double the sources of noise, add 3dB.

You can also calculate it like this: 10 sources will add 10dB.

This only works if all the sources of noise are identical. Altought, if you have 4 fans at 20dB each and a pump at 26dB the total sound level of your system will be 29dB.

Hope this helps some of you to hestimate the noise level of your cases.

[Guest]

That's actually wrong. An increase of 3dB just means you need to double the power. So if you have a 1000w subwoofer, to get an increase of 3dB you need to add a second 1000w subwoofer. To double in perceived loudness requires 6dB.

[tabuburn]

dB is not everything for silent PC's. You also have to consider the quality of the noise. So a fan at 20dB might be silent but if it has a constant clicking sound, it'll be annoying compare to a fan at 25dB with only moving air as the noise generated.

[cDNA]

That's actually wrong. An increase of 3dB just means you need to double the power. So if you have a 1000w subwoofer, to get an increase of 3dB you need to add a second 1000w subwoofer. To double in perceived loudness requires 6dB.

Well it is not really a question of power. For speaker it is but that is not really my point. The main idea is two identical sources will add 3dB to one source alone.

After that, the way speakers works i cant tell but put two identical speakers next to each other you will have a sound 3dB louder. No matter what power is needed.

[Guest]

The main idea is two identical sources will add 3dB to one source alone.

After that, the way speakers works i cant tell but put two identical speakers next to each other you will have a sound 3dB louder. No matter what power is needed.

That's sort of what I said. If you double the power then you increase by 3dB so if you go from

 

1 source = y dB

1 source -> 2 sources = y +3dB

2 sources -> 4 sources = y +6dB

4 sources -> 8 sources = y +9dB

 

ect

[cDNA]

dB is not everything for silent PC's. You also have to consider the quality of the noise. So a fan at 20dB might be silent but if it has a constant clicking sound, it'll be annoying compare to a fan at 25dB with only moving air as the noise generated.

That is very true, and im not saying i have the ultimate guide for silent pc!

But to a normal distance, human ear cannot perceive 20dB so if you hear a clicking noise it means that the clicking is above 20dB.

Also, you have to add the fact that a case will stop a part of the noise and the distance from you case may vary etc etc, im just giving a general idea on how to calculate noise level

[cDNA]

That's sort of what I said. If you double the power then you increase by 3dB so if you go from

1 source = y dB

1 source -> 2 sources = y +3dB

2 sources -> 4 sources = y +6dB

4 sources -> 8 sources = y +9dB

ect

Well we agree then!

But power is kind of an objective way to talk about noise. And if talking about fans not really relevant...

About speakers i am sure you know more than me!

[tabuburn]

That is very true, and im not saying i have the ultimate guide for silent pc!

But to a normal distance, human ear cannot perceive 20dB so if you hear a clicking noise it means that the clicking is above 20dB.

Also, you have to add the fact that a case will stop a part of the noise and the distance from you case may vary etc etc, im just giving a general idea on how to calculate noise level

Actually, 20dB is still within the range of human hearing:

• Near total silence - 0 dB
• A whisper - 15 dB
• Normal conversation - 60 dB
• A lawnmower - 90 dB
• A car horn - 110 dB
• A rock concert or a jet engine - 120 dB
• A gunshot or firecracker - 140 dB

 

 

 

The average person can hear sounds down to about 0 dB, the level of rustling leaves. Some people with very good hearing can hear sounds down to -15 dB.

Source: http://www.howstuffworks.com/question124.htm

http://www.dangerousdecibels.org/education/information-center/noise-induced-hearing-loss/

http://www.dspguide.com/ch22/1.htm

[cDNA]

Actually, 20dB is still within the range of human hearing:

Source: http://www.howstuffworks.com/question124.htm

http://www.dangerousdecibels.org/education/information-center/noise-induced-hearing-loss/

http://www.dspguide.com/ch22/1.htm

Again you are correct, but as fan manufacturers call it, it's a "virtually inaudible sound" (which doesnt really mean anything^^)

Also, i was taking 20dB as an example, not a true value.

Now i actually wonder what frenquency the sound of a fan usually is... i'll google that for curiosity...

[Brian]

Brain fart.

[cDNA]

Power is not used to measure audio intensity. That is the problem with this entire discussion.

I could go into this further, but it is all very very complex and not really worth discussing as it would likely bore most people here to tears. Understanding audio levels and human perceptions of them is something that takes a bit of time to really understand.

Suffice it to say, doubling the number of fans in a system DOES NOT DOUBLE THE NOISE. If that were true, think how loud a system with 8 fans would be. The math here is: 2 (for the initial doubling) to the power of 7(additional doublings), which is 128. That means my system with 8 fans is 128 times as loud as only having one fan? I don't think so.

Sorry to kinda rain on your parade here, not trying to offend or insult you in any fashion, just thought you should know.

Anyways, check out this website: http://www.sengpielaudio.com/calculator-leveladding.htm It will tell you what the new perceived sound level will be when adding noise sources.

If i remenber well the formula is:

L=10log(I1/I0)

L is the sound in dB

I1 is the intensity of the sound you are measuring

I0 is a reference intensity that is 10^(-12) W/m^(2)

So if you double I1 you end up having +3 dB. So double the amount of noise sources adds 3dB. My point all along.