## Sounds of Music C

Flavorflav
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### Re: Sounds of Music C

doctor wrote:b/c alot of ppl make guitars or violins and they want a more variety
making a string instrument is alot easier than making drums
At the competitions I have been at, percussion instruments were most common - chimes, xylophones, and there's always a couples of kids with a tray of glasses or test tubes filled with water to various heights.

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### Re: Sounds of Music C

I would imagine that there would be a lot of those, because they are pretty simple to make.
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blue cobra
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### Re: Sounds of Music C

I'm having some trouble with some equations.
Basic Equations wrote:$I=\frac{P}{A}$

$\beta = 10 log \frac{I}{I_0}$

$A = 4 \pi r^2$
EDIT:
I = intensity
I_0 = threshold of hearing*
Beta = relative intensity
P= power
A = Area

*I think so. I'm reading from a photocopy, and it's cut off.
/EDIT
Practice Problem wrote:A jet plane is found to have a relative intensity upon takeoff of 110 dB. Calculate the intensity of the sound the jet makes. Ans. 0.10 W/m^2
I had a start to this, but looking back it doesn't look correct. It would be greatly appreciated if someone could explain how to solve these types of problems.
Last edited by blue cobra on August 24th, 2010, 5:31 pm, edited 1 time in total.
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paleonaps
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### Re: Sounds of Music C

That post has discouraged me from doing this event. I don't like math.
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ichaelm
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### Re: Sounds of Music C

I don't understand those equations, but in order to find the intensity of anything, including light and sound, you must know how far away you are from the source. So it seems like you don't have enough information to solve it. I may be looking at this the wrong way, because that's the extent of my understanding.

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### Re: Sounds of Music C

does anyone by any chance have a copy of the draft rules for sounds?
i know how the drafts arent posted online or anything but apparently someone has the drafts for towers so just wondering if anyone has it for sounds
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Flavorflav
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### Re: Sounds of Music C

blue cobra wrote:I'm having some trouble with some equations.
Basic Equations wrote:$I=\frac{P}{A}$

$\beta = 10 log \frac{I}{I_0}$

$A = 4 \pi r^2$
EDIT:
I = intensity
I_0 = threshold of hearing*
Beta = relative intensity
P= power
A = Area

*I think so. I'm reading from a photocopy, and it's cut off.
/EDIT
Practice Problem wrote:A jet plane is found to have a relative intensity upon takeoff of 110 dB. Calculate the intensity of the sound the jet makes. Ans. 0.10 W/m^2
I had a start to this, but looking back it doesn't look correct. It would be greatly appreciated if someone could explain how to solve these types of problems.
You just have to know I_0, which is 10^-12 W/M^2. 110 dB = 11 B, so 10^11=I/10^-12, so I = 0.1

ichaelm
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### Re: Sounds of Music C

Oh, that makes much more sense. Good thing I'm probably not doing this event!

blue cobra
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### Re: Sounds of Music C

Flavorflav wrote:<SNIP>
You just have to know I_0, which is 10^-12 W/M^2. 110 dB = 11 B, so 10^11=I/10^-12, so I = 0.1
Thanks, but I'm not clear on what you did to get that answer. How (if at all) is that from $\beta=10log\frac{I}{I_0}$ ?
I honestly have no idea what "log" means here.

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nejanimb
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### Re: Sounds of Music C

You... plug the values into that equation. 110 = 10 * log (I/10^-12). The "log" is just a logarithm, like the mathematical operator.

To solve for I, which is what the problem calls for, just divide the 10 out of both sides, then take the log out of the equation by making both sides the power on 10, so 10^11 = I/10^-12, then multiplying gives you I = 0.1 W/m^2, though that part is all just basic math. Flavor was right - all you needed to know, besides the equations you had, was the numerical value for the threshold for hearing, which is 10^-12 W/m^2.
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