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 Post subject: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 6:39 pm 
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This is just a hypothetical scenario I thought up last night while I was watching TV. Yay for alliteration!

Okay, I hope everyone here is familiar with Helium(He) and what it does when you inhale it. Helium is lighter/less-dense then air, and so it vibrates faster. This causes your voice to increase in pitch when you have Helium in your lungs, as your vocal cords are vibrating much more quickly. The opposite is true with a very dense gas, such as Sulfur Hexaflouride(SF6), which decreases the pitch of your voice.

Now, here's my scenario. Let's take a box, and hook up a speaker and a microphone on the inside(wireless?), and close it off, making it completely 100% air-tight. Inside the box is nothing buy pure Helium (or Sulfur Hexaflouride) instead of regular air.

Finally, we try to record a song played on the speaker with the microphone. Will the recording be slightly higher (or lower) pitched, due to the air inside being much less/more dense? I would assume so, but then again I'm not so sure.

What do you guys think?

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 8:35 pm 
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I think it will not change at all. I'm pretty sure the "pitch" change in your voice is based on how the fluid interacts with your vocal cords, and is not based on the speed of sound in that fluid.

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 9:00 pm 
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um, yes, the pitch would change, sound actually does travel faster through helium, producing the higher pitch.

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 9:08 pm 
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SaiyanKirby is right about the sound traveling through the gases at different speeds. The gases don't interact with your vocal cords at all. Our voices sound the way they do because of how the sound waves pass through the air in our mouths and throat. When you have something that is lighter than air then there is less for the waves to travel through. For heavier gases it acts like a filter for high pitched sounds in our voices.

As for the speaker idea, I'm not sure. I imagine you would have to put the helium filled box on the other side of where the sound is expelled, as in the speaker itself. I see no reason that wouldn't work. That may be what you suggested, but I didn't completely understand your wording. :D

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 9:13 pm 
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I still say no. Lets say we play a middle c on the speaker continuously. This means the speaker vibrates as 261.62 Hz. This means the speaker move back and forth 261.62 times in one second, creating 261.62 pressure waves. For the microphone to hear a higher pitch, it has to receive more than 261.62 pressure waves per second. Changing the density of the gas only affects how fast these waves move, it does not create more waves.

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 9:18 pm 
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I'm pretty sure there will be no change. Here's why. The sound of your voice is caused due to the gas in your larynx resonating. If you reduce the density of the gas it resonates at a higher pitch, hence the helium voice.

But in a speaker sound is not generated via a gas resonating but a cone being driven by an electromagnet. The cone will not suddenly vibrate faster. Yes sound will travel faster in the helium but the pressure waves being driven by the speaker cone will be at the same frequency. The variation in the magnetic field that drives the cone will not change in any way.

I haven't fully thought through what will happen when the waves traveling quickly in the helium interface with a normal air barrier outside of the speaker but I suspect no change.

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Mon Apr 19, 2010 10:01 pm 
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At first, I thought I was just being stupid asking this question, but it seems like there's an actual discussion going on about it! :D
I didn't fully know what the implications of air density would affect, so I'm glad to know more about it.

PS, I typed this on my iPod! Isn't technology amazing?

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Tue Apr 20, 2010 9:57 pm 
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SaiyanKirby wrote:
This is just a hypothetical scenario I thought up last night while I was watching TV. Yay for alliteration!

Okay, I hope everyone here is familiar with Helium(He) and what it does when you inhale it. Helium is lighter/less-dense then air, and so it vibrates faster. This causes your voice to increase in pitch when you have Helium in your lungs, as your vocal cords are vibrating much more quickly. The opposite is true with a very dense gas, such as Sulfur Hexaflouride(SF6), which decreases the pitch of your voice.

Now, here's my scenario. Let's take a box, and hook up a speaker and a microphone on the inside(wireless?), and close it off, making it completely 100% air-tight. Inside the box is nothing buy pure Helium (or Sulfur Hexaflouride) instead of regular air.

Finally, we try to record a song played on the speaker with the microphone. Will the recording be slightly higher (or lower) pitched, due to the air inside being much less/more dense? I would assume so, but then again I'm not so sure.

What do you guys think?


While the sound waves are in helium they travel at a different-from-air speed, and back in air they travel at the usual "speed of sound." A lot will depend on the membrane separating the air and helium. If the frequency think changes going from one substance to another, what is to keep it from changing back when returning to the original substance? Another thing to take into consideration is how hard it is to contain helium. It is a very small atom and it's hard to make membranes that helium cannot pass through.

DJ

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Tue Apr 20, 2010 10:03 pm 
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Your right about containing helium, it is hard. If only we could put it in a reletively light weight membrane then we coul watch it float up and then even hold it by a string, ohh wait those are balloons. I don't think the membrane would be a problem david :wink: .

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 Post subject: Re: Hypothetical Helium Hypothesis
PostPosted: Tue Apr 20, 2010 11:19 pm 
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David J wrote:
If the frequency think changes going from one substance to another, what is to keep it from changing back when returning to the original substance?


If we use light as an example, it changes speed depending on the substance (index of refraction) but the light does not change frequency, only in speed. To compensate for the slower speed, the wavelength contracts to keep the frequency the same. Now, since light always takes the shortest path light bends (is refracted) in substances. I suspect sound pressure waves do the same as refraction is a property of waves and not just light.

That would mean the sound would take a slightly different path in helium and the wavelength would be longer. When the sound crossed the helium boundary and into air, as it slows down the wavelength is contacted and the path it takes is bent (refracted).

Note than in the case of light, the energy is proportional to the frequency. Since we know from thermodynamics that energy is conserved, it makes sense that if lights slows down in a material the wavelength is contacted by just enough to keep the frequency constant. Sound is a bit more complicated because sound is a pressure wave and you have to worry about intensity. I'm pretty sure though by the same reasoning as light, the sound frequency is not changed while traveling through other materials.

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