Monday

September 22, 2014

September 22, 2014

Posted by **Reed** on Wednesday, February 10, 2010 at 1:20am.

I get 50 m, but the answer is supposed to be 15.8 m. I need to know what I'm doing wrong.

By my (apparently flawed) reasoning:

Point A is 10 dB louder than Point B because +10 db = ~2x louder

+10 dB = *10 Intensity (I), because the dB scale is log 10

Therefore, I(A) = 10*I(B) and I(A)/I(B) = 10

Using the formula I(A)/I(B) = r(B)/r(A), I find that

10 = r(B)/r(A)

Plug in 5 m for the value of r(A), and solve for r(B), which comes out to be 50 m.

So what am I screwing up?

Thanks for your help.

- Physics -
**drwls**, Wednesday, February 10, 2010 at 1:45amIt is not clear to me what they mean by "sounding" half as loud. The sound power per area (intensity) will be down by a factor of 2 if you move sqrt2 times farther away, to a distance of 7.07 meters in this case. The sound level there is 3 dB down from Point A.

At 15.8 m the distance is 3.16 times farther and the sound power is 3.16^2 = 10 times less, which is 10 dB down. Apparently they are saying that 10 dB down "sounds like" half as loud. Other websites I have looked at also make the statement that 10 dB down sounds half as loud, so I guess it is an accepted rule of thumb. i had never heard it before.

**Answer this Question**

**Related Questions**

Physics - A current of 60 mA passes through a loudspeaker of resistance 6 Ω...

physics - Expensive amplifier A is rated at 250 W, while the more modest ...

physics - Expensive amplifier A is rated at 210W , while the more modest ...

LA - For questions 7–11, each sentence is missing one type of punctuation. ...

Physics - Find the distance light travels from its starting point, S to its ...

physics help pleaseee - In the figure below, S is a small loudspeaker driven by ...

Math - If you where to plot the following points for two dimensional X and Y ...

Halp me or i fall - Write the number that makes the statement true. 1. 205.5 m...

Physics - In a resonance-tube containing air, the source of sound is a small ...

physics - a bead on a wire 30m high is released and reaches point A, where is ...