Question on sound intensity and dB

  • Thread starter Krystal111
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  • #1
Krystal111
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Homework Statement:
By what factor is the sound intensity reduced if ear protectors can reduce sound levels by 40dB?
Relevant Equations:
I can't seem to find any
Would we have to use the 3-dB exchange rate? How would we solve this question?
 

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  • #2
haruspex
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Homework Statement:: By what factor is the sound intensity reduced if ear protectors can reduce sound levels by 40dB?
Relevant Equations:: I can't seem to find any

Would we have to use the 3-dB exchange rate? How would we solve this question?
Start with the definition of dB. What is it?
 
  • #3
Krystal111
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A decibel would be a unit of measurement that is equal to one tenth of a bel.
 
  • #4
Arjan82
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And... what is a bel? You need to read also the rest of the wikipedia page.
 
  • #5
Krystal111
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It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 or root-power ratio of 10¹⁄²⁰ - as per what wikipedia states
 
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Moderator's note: Thread title edited.

@Krystal111 first, all caps in a thread title is the Internet equivalent of shouting. Second, the title of your thread should be a brief description of your question, not a statement (irrelevant to anyone responding here in any case) that you need help, let alone need help "ASAP". Please review the rules for posting homework questions.
 
  • #7
Arjan82
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Great, so you can cite Wikipedia. Now what does this all mean? It literally tells you the power ratio for 1 dB, so how would you translate that to 40dB? And what is intensity? How is that related to power?

We're not here to do your homework, but we are here to help you do your homework.
 
  • #8
Arjan82
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And... what in the world does the 3-dB exchange rate have to do with anything? Do you know what that is?
 
  • #9
haruspex
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It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of ##10^{1/10 }## or root-power ratio of 10¹⁄²⁰ - as per what wikipedia states
Right. But can you convert that to an equation that gives the sound intensity ratio in terms of the dB difference?
Or you could cheat and scroll down the Wikipedia entry to find a table expressing 40dB as a power ratio and as an amplitude ratio. Then you just have to pick which of those is the same as sound intensity.
 

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