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Old Jan 24th 2018, 09:58 AM   #1
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Sound Level

Hi guys, I'm back....

So I had this problem:

Jane and Sam alternately pound a railroad spike into a tie with their hammers. The crew chief has a migraine, and notes that Jane's hammer blows cause a sound with intensity 5.0 times greater than the sound that Sam makes when he swings his hammer. What is the difference in sound level between the two sounds?

I'm already having a lot of trouble with getting my head around sound level problems, and my physics book doesn't give any answer for this problem and I can't find anything online about it so I'm not even sure how to approach it. I'm assuming the equation L=(10dB)logI/e-12 is used but I'm pretty stuck. Any help would be greatly appreciated!
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Old Jan 24th 2018, 10:38 PM   #2
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Sound intensity is Logarithmic

That means if you have a music amplifier outputting 1W and you want one twice as loud , you need to trade it for 10W amp.... 100W will be 3 times louder than 1 W ...

A 10,000 W amp will be 5 times louder than 1W ...

So if the chief perceives janes hammer blow as 5 times louder it's 10,000 times different .

Possible , since sam is only "swinging" his hammer , jane is hitting something .
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Old Jan 25th 2018, 10:14 AM   #3
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Oz's answer is perfect. However, to get the actual change in power, you need to be able to estimate the power of the hammer sound for either Jane or Sam and then work out the power of the other sound accordingly.

Here's a link to a set of typical decibel levels for a range of different actions:

http://www.stac-uk.com/downloads/Noise%20Levels.pdf

For "Hammer on nail", the result is 120 dB. Can you calculate the equivalent power of that sound wave? If that sound is generated by Sam, then what would be the power of the sound wave generated by Jane?
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Old Jan 29th 2018, 05:52 AM   #4
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Originally Posted by benit13 View Post
Oz's answer is perfect. However, to get the actual change in power, you need to be able to estimate the power of the hammer sound for either Jane or Sam and then work out the power of the other sound accordingly.

Here's a link to a set of typical decibel levels for a range of different actions:

http://www.stac-uk.com/downloads/Noise%20Levels.pdf

For "Hammer on nail", the result is 120 dB. Can you calculate the equivalent power of that sound wave? If that sound is generated by Sam, then what would be the power of the sound wave generated by Jane?
Thank you!

I got:
120=10log(P/5e-17)
log10(P/5e-17)=12
P/5e-17=10^12
P= 5e-5

So by my calculation Sam's power would be 5e-5 W and Jane's would be 5e-5(10000)= 5e-1W. Is that correct?
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Old Jan 29th 2018, 05:55 AM   #5
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Originally Posted by oz93666 View Post
Sound intensity is Logarithmic

That means if you have a music amplifier outputting 1W and you want one twice as loud , you need to trade it for 10W amp.... 100W will be 3 times louder than 1 W ...

A 10,000 W amp will be 5 times louder than 1W ...

So if the chief perceives janes hammer blow as 5 times louder it's 10,000 times different .

Possible , since sam is only "swinging" his hammer , jane is hitting something .
Thank you!! This makes a lot more sense now
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