What is the power output of the speaker?

label Physics
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Oct 20th, 2017

(a) If the dB are sound-intensity dB (dB-SIL), then the reference level is I0 = 10^-12 W/m² 

130 = 10*log(I/I0) = 10*[log(I) + 12] 

13 = log(I) + 12 

log(I) = 1, I = 10 W/m² 

This is covering an area of 4*π*(1.3²), so the total power is 10*4*π*(1.3²) W. 

212.4 W 

(b) 85 dB = 10*[log(I) + 12] 

log(I) = -3.5

I = 10^-3.5 W/m² 

The distance is such that the area covered by 985 W yields 10^-3 W/m²: 

212.4/(4*π*r²) = 10^-3.5

r = √[212.4*10^3.5/(4*π)] 

r = 231.2 m 


Apr 3rd, 2015

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