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Decibel Question

  1. Oct 28, 2008 #1
    Preface

    This question proves my ignorance. You have been warned.

    Background

    - I am building a new "near silent" computer and I am looking at different types of fans.
    - The case requires 3 fans.
    - I am looking to purchase and install 3 Identical fans that have a rating of 10 dB.

    Question

    - One fan will obviously produce 10 dB of "noise"
    - How many dB of "noise" will all three fans produce?

    - The answer I assume is only 10 dB, however I could be wrong if dB can "accumulate" (meaning 3 fans would produce 30 dB). Furthermore, I may be completely off base and it is neither 10 dB or 30 dB.

    I have been thinking about this too much and it is driving me crazy. Please enlighten me!

    Thanks
     
  2. jcsd
  3. Oct 28, 2008 #2

    atyy

    User Avatar
    Science Advisor

    Let's suppose 10 dB corresponds to a pressure amplitude P, and you want to find Y dB corresponding to 3P.
    Po is the reference pressure in both cases.

    10 = 20log10(P/Po)

    Y= 20log10(3P/Po)

    Y-10
    =20log10(3P/Po)-20log10(P/Po)
    =20log10(3P/P)=20log10(3)=20(0.5)=10 dB

    So if 1 fan produced 10 dB, 3 fans would produce (10+10)=20 dB, and 10 fans would produce 30 dB.

    http://trace.wisc.edu/docs/2004-About-dB/
     
  4. Oct 28, 2008 #3
    Genius.

    Thanks so much! It makes perfect sense.
     
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