dB/ intensity calculation question (TBR)

[Meredith92]

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TBR on page 9 on physics book 2 says that :
decibel =10 log (I/I0)
Where I0 is a reference sound, which is chosen to be 10^-12W/m^2

But later (on page 11) a question asks
"...In going from a talk to a whisper the intensity level of your voice decreases from 60 to 20 dB. by what factor does your voice correspondingly decrease?"
they solve this by using the equation: change in dB=10 log (If/I0)

they end up getting 10^4=(If/I0)

I'm just confused because now it seems like I0 is the initial intensity, not the reference sound of 10^-12W/m^2

Am I over thinking this?
Thanks for your help!

 

[NuttyEngDude]

TBR on page 9 on physics book 2 says that :
decibel =10 log (I/I0)
Where I0 is a reference sound, which is chosen to be 10^-12W/m^2

But later (on page 11) a question asks
"...In going from a talk to a whisper the intensity level of your voice decreases from 60 to 20 dB. by what factor does your voice correspondingly decrease?"
they solve this by using the equation: change in dB=10 log (If/I0)

they end up getting 10^4=(If/I0)

I'm just confused because now it seems like I0 is the initial intensity, not the reference sound of 10^-12W/m^2

Am I over thinking this?
Thanks for your help!

I always write this down when i read these types of questions:
40 db = 10 log (x)

so log(x) should be 4 or x = 10^4


edit:

I'm just confused because now it seems like I0 is the initial intensity, not the reference sound of 10^-12W/m^2

that number is the lowest or faintest sound a human ear can hear.

I0 is indeed the initial intensity in the equation when you do calculations.

 

[Meredith92]

Okay great thanks for clarifying that!!

 

[sdm33]

If you want to save time,
60-20=40 = 10^4
100-60 = 40 same answer
40-20 = 10^ 2 .....etc
almost any intensity level difference you raise it to 10 power you get the right answer.