1

I have a fan on a PC case running at 100% speed making 40dB/A of noise (sound pressure). Then I add a second fan right next to it running at 100% speed making 30dB/A of noise.

  1. What is the combined noise level?

  2. What happens if add and extra 50dB/A fan?

  3. And then 10 more 30dB/A fans?

Forget about space, treat them as sources coming from the same point in 3D space.

EDIT

The total signal level from sources with different strengths can be calculated as:

Lt =  10 log ((S1 + S2 ... + Sn) / Sref)

Where

Lt = total signal level (dB) 

S = signal (signal unit)

Sref = signal reference (signal unit)

Source

I can't directly use this formula because it requires the sound power of fans instead of the sound pressure manufacturers such as Noctua typically provide. How can I convert it? What will I need?

Vulkan
  • 101
  • 2
  • 10

2 Answers2

2

This is a pretty straightforward calculator: https://www.engineeringtoolbox.com/adding-decibel-d_63.html

Basically noise level is dictated by your 2 loudest sources, so 50 dB + 40 dB (assuming they are at or near the same location) would result in about 50.5 dB.

jko
  • 2,357
  • 5
  • 13
1

The standard rule of thumb for adding decibels is that doubling the sound power increases the dB reading by +3dB. Using an on-lone calculator for adding dB's, we find that adding two sound sources that differ in strength by 10dB yields a dB total of 40.25dB.

To the human ear, a difference of 0.25dB is completely inaudible.

niels nielsen
  • 15,513
  • 1
  • 15
  • 33