Helium

[Hound Dog]

Let's say you have a room to record in that was sealed and you pump it full of Helium gas. You place a guitar amp in the room and a microphone to pick up the sound. What would it sound like? Would it sound like a harmonizor set to a higher frequency?

[Botch.]

Thanks Hound Dog, you just wasted half a morning for four government engineers.

 

We are in pretty tentative agreement here: the sound will not change pitch. The sound will move through the room at a different speed, however, but that will not change the ultimate pitch as each wave produced at the source, will eventually reach the ear at the same rate.

 

The pitch does change in a person's windpipe, though, because the actual wavelength is changed, and the windpipe is actually producing the sound, not merely transmitting it as the helium in the room does.

 

I'm not very good at explaining things in laymen's terms sometimes, hope the preceding makes sense...

[boosh]

My guess is that if the room is filled purely with helium the sound does change.

 

Same as when you're under water.

[not Cereal]

i would guess if you were playing guitar in a sealed room filled only with helium there would be no sound, because you would be dead from suffocation.

 

however if you were not in the room and ran a cord in there i predict the room may lift off the ground and ripp all the wires out of the power sockets thereby once again causing no sound.

 

therefore, sound does not pass through helium.

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there's a reason i never graduated junior high, but i cant remember it.

[Sp3nc3r]

Hmmm. I think that it depends on what percentage that the Helium is lighter than regular air.

 

As we all know, the more dense the medium (generally speaking, of course - there are exceptions) the faster sound will travel through it - and with greater distance, ie.: trains on a track can be heard much earlier by putting your ear to the rail than by traditionally listening through the air. Just make sure you have a buddy looking in both directions for you before you try this experiment

 

Based on that tidbit, in theory, a soundwave's compressions and rarefactions may move slower through the helium, mostly because the molecules are farther apart (less dense), therefore taking longer to transfer the energy from one to the next.

 

Of course, I might be full of shit....

 

Cheers!

Spencer

[boosh]

Originally posted by boosh:

My guess is that if the room is filled purely with helium the sound does change.

 

Same as when you're under water.

Correction: the speed of the sound does change.

 

I forgot speed,..maybe that's because I'm so slow

[Botch.]

Originally posted by boosh:

Originally posted by boosh:

My guess is that if the room is filled purely with helium the sound does change.

 

Same as when you're under water.

Correction: the speed of the sound does change.

 

I forgot speed,..maybe that's because I'm so slow

Can't compare helium and water; helium is a compressible fluid (as are all gases) and water is an incompressible fluid (as are all liquids to my knowledge). Sound transmission laws change completely.

 

The speed of the sound through a gas doesn't change the pitch, the wavelength does change. If your speaker is putting out 60 Hz, 60 beats per second, the listener's ear will receive 60 beats per second, no matter how close or far away he is. The sound will reach him sooner or later, but it will still be 60 beats per second.

[world69]

I thought Kerry King recorded his solo's like this. No?

[boosh]

Isn't that what I said?

 

wherever you put a sound wave through,... no matter what material. The Rho of that material changes the speed of the sound. I didn't mention the pitch.

[Botch.]

You're correct, my bad...

[RG203]

According to this link:

 

http://hypertextbook.com/physics/waves/sound/

 

it will travel about 3x faster.

 

Does that mean you need a faster compressor?

[Hound Dog]

So will the recorded sound be "chipmunk" like? According to what I have read, it should. If the sound travels faster, the pitch is perceived as higher (relative to normal "air") even though the produced pitch doesn't actually change.

[RG203]

Maybe, but for a different reason.

 

Because helium gas is lighter than the usual oxygen/nitrogen blend, it changes the resonant frequency of the human vocal tract, causing a faster vibration and a higher-pitched, cartoon-character sound.

Wouldn't everything (strings, spearkers, etc.) be vibrating faster, and therefore producing a higher pitch?

[Botch.]

Originally posted by Hound Dog:

So will the recorded sound be "chipmunk" like? According to what I have read, it should. If the sound travels faster, the pitch is perceived as higher (relative to normal "air") even though the produced pitch doesn't actually change.

Nope, it'll still sound the same. Let me try it this way:

 

The speaker does one cycle, "Whoomp". It travels across a room in, say, 30 ms. It hits the eardrum with one cycle, and the listener hears "Whoomp". In the Helium-filled room, the single cycle travels across the room in 10 ms. The listener still hears one "whoomp".

 

Now the speaker does two cycles, 1 ms apart, "whoomp-whoomp". They travel across the room and impinge on the eardrum at 30 and 31 ms, "whoomp-whoomp". The whoomps are 1 ms apart. In the helium room, the whoomps impinge on the eardrum at 10 and 11 ms, "whoomp-whoomp". They are still 1 ms apart, they just arrived at the listener's ear quicker.

 

Now take this one more step: the speaker sends out a "whoomp" every 1/60 of a second, or 60 Hz. "Whoomp-whoomp-whoomp-whoomp". They travel across the room and impinge 30 ms later, but still at the same rate, "Whoomp-whoomp-whoomp-whoomp". The listener hears 60 Hz. In the helium room, they travel across the room in 10 ms, but again still at the same rate, and the listener again hears 60 Hz.

 

Good thing I never became a full-time teacher, huh? Hope that made a little more sense than my first post.

[boosh]

Originally posted by RG203:

Maybe, but for a different reason.

 

Because helium gas is lighter than the usual oxygen/nitrogen blend, it changes the resonant frequency of the human vocal tract, causing a faster vibration and a higher-pitched, cartoon-character sound.

Wouldn't everything (strings, spearkers, etc.) be vibrating faster, and therefore producing a higher pitch?

violins don't have vocal chords or whatever they're called in english,...they vibrate differntly when helium passes them because they're made of human tissue,.. a string is a string and can't adjust,..it still has the same tension,...the thinies in your throat act different.

 

I've asked by brother in law to figure this one out with his collegues at the lab,...they specially in stuff like this.

[theblue1]

Um... isn't the reason for the 'helium voice' that the rapidly expanding He gas chills the tissue of the vocal chords, thereby raising their pitch.

 

This accounts for why the 'helium voice' lasts longer than it takes for the He to dissipate from the voice box.

 

At least that's the way I'm figuring it.

[theblue1]

Well, according to a page from virginia.edu, that's not how it works and (at least some of) you guys are on the right track:

 

Why does breathing helium make our voices sound Mickey Mouse-ish? Is there anything we can drink that will have the same effect for a longer period? - AP

 

The pitch of your voice is largely determined by the dimensions of your larynx. That's why men, with their larger larynxes, generally have lower voices than women. While the sound of your voice originates in the vibrations of your vocal cords, string-shaped objects aren't very good at emitting sound. Just as a violin employs a box to assist its strings in producing sound, you use your larynx to assist your vocal cords in producing sound. Which pitches your larynx produces well depends on its size and on the speed of sound. Both of these factors are important because the air itself vibrates and either decreasing the size of your larynx or allowing sound to move faster from one side of it to the other will raise the pitch of your voice. Because the speed of sound is much higher in helium (965 m/s) than it is in air (331 m/s), the pitch of your voice rises when you breathe in helium gas. However, as soon as the helium has left your lungs and is replaced by air, your voice returns to normal. Apart from breathing gases with high speeds of sound, there isn't anything else that will work. You can't live on pure helium gas, so the only way to sustain this effect would be to breath a helium/oxygen mixture instead of air. Some deep-sea divers do just that and their voices continue to sound "Mickey Mouse-ish" as long as they breathe this mixture.

http://howthingswork.virginia.edu/violins_and_pipe_organs.html

[theblue1]

Originally posted by theblue1:

Well, according to a page from virginia.edu, that's not how it works and (at least some of) you guys are on the right track:

 

Why does breathing helium make our voices sound Mickey Mouse-ish? Is there anything we can drink that will have the same effect for a longer period? - AP

 

The pitch of your voice is largely determined by the dimensions of your larynx. That's why men, with their larger larynxes, generally have lower voices than women. While the sound of your voice originates in the vibrations of your vocal cords, string-shaped objects aren't very good at emitting sound. Just as a violin employs a box to assist its strings in producing sound, you use your larynx to assist your vocal cords in producing sound. Which pitches your larynx produces well depends on its size and on the speed of sound. Both of these factors are important because the air itself vibrates and either decreasing the size of your larynx or allowing sound to move faster from one side of it to the other will raise the pitch of your voice. Because the speed of sound is much higher in helium (965 m/s) than it is in air (331 m/s), the pitch of your voice rises when you breathe in helium gas. However, as soon as the helium has left your lungs and is replaced by air, your voice returns to normal. Apart from breathing gases with high speeds of sound, there isn't anything else that will work. You can't live on pure helium gas, so the only way to sustain this effect would be to breath a helium/oxygen mixture instead of air. Some deep-sea divers do just that and their voices continue to sound "Mickey Mouse-ish" as long as they breathe this mixture.

http://howthingswork.virginia.edu/violins_and_pipe_organs.html

Mind you, I'm not entirely happy with that explanation, since the first sentences is, at the very least, misleading. The way I read it, it's just plain wrong: "The pitch of your voice is largely determined by the dimensions of your larynx."

 

But as they go further in their explanation, it become clear they are talking about the resonant cavity's tendancy to emphasize certain frequencies -- which to my way of thinking is not synonymous with 'largely determining the pitch of your voice.'

 

I had a few college instructors who couldn't express themselves in English, either, but it's still annoying when an educational institution promotes such shoddy work.

[theblue1]

Get enough hard science academics in a room and you're sure to produce some kind of cognitive dissonance. Here are two more conflicting explanations for 'helium voice' -- also from academics.

 

What is the physics behind the voice change which occurs when one inhales Helium?

 

Asked by: Forster Ruhl

 

Answer

 

Sound is created when something compresses the air and the region of compression moves away from the source to soneone's ears.

 

An analogy can be made with a huge crowd of people packed closely together. If the people in the back of the crowd all decide to push foward rapidly and then back off, the region of compression will move out into the crowd. Each layer of people will be pushed from behind and in response they will move foward and push the people in front of them. When the push from behind stops, they will move back again. Everyone ends up in roughly the same place they started, but the compression wave moves. If the crowd is composed of big heavy people, the wave will move slowly, because big people are hard to move. If the crowd were instead made of balloons the wave would move much more rapidly.

 

It turns out that the number of molecules in a fixed volume of gas at a given temperature and pressure is the same, regardless of the gas used (provided the pressures are reasonably low). Helium atoms have a molecular weight of about 4 grams per mole (a mole is 602200000000000000000000 molecules). Air is about 80% Nitrogen which has a molecular weight of about 28 grams per mole; it is seven times havier than helium. This means that a compression wave will propagate faster through helium than it will through air.

When a series compression waves (your voice) leave the helium in your lungs and hit the denser air, the wave train is suddenly slowed down. The wave in front is slowed first while the wave behind it is still moving fast. Then the second wave is slowed while the third is still moving fast, and so on. It's like fast moving traffic on an open freeway suddenly coming to a slow point in the road, all the cars bunch up close to each other.

Your ear interprets closely bunched sound waves as a higher pitch than widely spaced waves. So when your voice originates in helium and then travels through the air to someone's ear, it sounds higher. If both you and the listener were in a room filled with helium, your voice would get to their ears faster than normal, but there would be no pitch change.

Another interesting experiment which is too dangerous to play with is to breath a gas that is heavier than air. When you do this, your voice sounds almost demonic.

In this case the sound waves spread out when they go from the dense gas to air and your voice sounds lower than normal.

This is dangerous because heavy gases settle in the bottom of your lungs and you can easily suffocate if you don't hang upside down immediatly after the experiment.

 

Answered by: Joe Larsen, Ph.D. Chemistry, Rockwell Science Center, Los Angeles, CA

 

Indeed, the majority of components in air are more massive than helium atoms. The end result is that across a helium/air interface, the wavelength of a sound wave will be changed. The frequency of this wave, however, will not be changed. The ear uses the frequency of a sound wave in order to determine pitch. Thus, the pitch generated by the voice box will be the pitch heard by the ear regardless of the fact that the sound wave has traveled through a helium/air interface.

 

A more likely explanation for the increased pitch caused by inhaling helium is due to the sound producing mechanism itself. Consider the voice box modeled as a simple vibrating membrane (or perhaps a speaker cone) whose vibration acts on the ambient gas around it causing the formation of sound waves. By controlling different characteristics of the membrane (tension, shape, etc.), qualities of the created sound waves (i.e. pitch) can be controlled. In this model, the ambient gas acts as a resistance to the motion of the membrane since energy from the vibrating membrane is imparted to the gas. When the molecules composing the gas are heavy, the resistance is greater than when the molecules in the gas are light: The heavier molecules have a greater inertia for the membrane to overcome. When humans breathe helium and speak, their vocal chords, which are 'tuned' for normal atmosphere conditions, do the same things that they always do with substantially less resistance from the lighter gas. The result is that the chords will vibrate at a higher frequency.

 

Notice that this model predicts an elevated pitch received by a listener even if the entire atmosphere were helium. This would be a good comparison of our respective models if we could figure out how to keep the experimental subjects from keeling over.

My model is a simplification of the real process and should not be taken as gospel. However, I believe it does hint at the underlying priciples involved.

 

Answered by: Matthew Kirsch

 

Hell, I might just stick with my original explanation, after all, since the multi-degreed experts can't agree.

 

[Botch.]

When theories collide, scientists set up experiments!

Press a helium balloon against your ear, then put a digital tuner set to an audible pitch against the far side of the balloon. Does the pitch change?

Where can I get a helium-filled balloon at 5 pm?

[Lee Flier]

Originally posted by Botch.:

Thanks Hound Dog, you just wasted half a morning for four government engineers.

Well hey, it's a better use of our tax dollars than a lot of other things they spend it on...

[Super 8]

Originally posted by Botch.:

Thanks Hound Dog, you just wasted half a morning for four government engineers.

 

We are in pretty tentative agreement here: the sound will not change pitch.

Did you guys use math to figure this out?

[Prague]

A string tuned at a certain tension will be able to vibrate faster in helium as opposed to oxygen. So the strings pitch will be diffrent in heluim as opposed to oxygen.

 

As to the tone/timbre, I don't know.

[Prague]

I lost my connection.

 

A speaker in the helium room, though, is a controlled device. If it is fed a 1kHz signal, it won't go faster or slower than 1 kHz. But, I do believe the timbre would change since harmonics resulting from the mechanical action of the speaker would be affected by the thinner helium. Any porting of the cab, since it is tuned in air, would be affected.

 

I'm not sure of the resilincy of, say, a dynamic mic in helium. I would have to guess that it's response in a medum other than air would be altered, but it would still be being fed a 1kHz wave from the speaker.

 

But, play a 1kHz sine wave and remember the pitch. Now play a 1kHz square wave. The pitch changes upward. The odd harmonics algebraeically add at your ear differently than the odd and even harmonics of the sine wave.

 

So, if the harmonic content is changed, it may be that the mic would pick up an altered pitch. Since it and the speaker are both in the same environment, the helium factor may "cancel".

 

Great question!

[Philip OKeefe]

3,294 FPS is the approximate speed of sound in He. In air, it is 1,130 FPS.

 

Now the speaker does two cycles, 1 ms apart, "whoomp-whoomp". They travel across the room and impinge on the eardrum at 30 and 31 ms, "whoomp-whoomp". The whoomps are 1 ms apart. In the helium room, the whoomps impinge on the eardrum at 10 and 11 ms, "whoomp-whoomp". They are still 1 ms apart, they just arrived at the listener's ear quicker.

 

If a sound hits the ears 30 ms after it is generated (in normal air), and the second sound arrives at 31 ms, we can assume the source was about 26.5 feet away. If we take that same distance, fill the room with a pure helium atmosphere (where sound travels at about 3,294 FPS), the sound will arrive in approximately one third the time. If the first "whump" takes 30 ms in air to arrive, and the second "whump" which was generated 1 ms later arrives at 31 ms when traveling through air, the two whumps will arrive at 10 ms and 10.33 ms IF you were of the opinion that helium has a effect on the pitch of a sound traveling through it... that's 1/3rd the time, right? But that's not correct because the sound itself can't start traveling through ANY medium before it is generated - and you have a stable figure on that in both environments - the two pulses are generated exactly 1 ms apart at the source. The fact that the sound travels faster through the helium makes no difference in terms of when it was generated.

 

I am in agreement with Botch and the US Government engineers. As far as to the exact reasons why pitch is effected when someone breathes helium gas and speaks, I'd want to give some thought to that - but I do not believe it will have anything to do with the fact that sound travels faster in helium than in air. And assuming you can tune the vibrating source to the frequency you want (pitch - and helium may very well have an effect on that in some cases - not certain about that), I see no reason why the sound's frequency would behave any differently, beyond traveling from source to listener faster.

 

Botch, you could try an experiment if you can get ahold of some divers in a SeaLab type environment where they are living in a helium / oxygen gas mixture. Have a guy bring a small electric travel guitar, tune it with a cable and electronic tuner, and have him play it into the com system and see if the guys on the surface detect any difference in the pitch. Would take some doing to get ahold of the right people to set it up. But it would give a definitive answer to the question. And I wouldn't be surprised if someone already did such an experiment.

 

I've got to get back to work, but I'll try to give this one some more thought later when I have a bit more time.

[Sp3nc3r]

Originally posted by RG203:

According to this link:

 

http://hypertextbook.com/physics/waves/sound/

 

it will travel about 3x faster.

That means I was wrong....again.

 

Dammit, how did I graduate high school with Honours?!!

 

Cheers!

Spencer

[Hound Dog]

Most of the stuff I read (and I also found some contradictory info on how helium affects the voice) indicates that it is not really the actual pitch that is affected, but the percieved harmonics of a given pitch. In other words, when you hear the speach of someone who has inhaled helium, you are hearing the higher order harmonics of the same pitch.

 

I think most agree that the sound would move faster in a helium atmosphere. Does the speed of sound affect its timbre, i.e. the way we hear it?

[Botch.]

A string tuned at a certain tension will be able to vibrate faster in helium as opposed to oxygen. So the strings pitch will be diffrent in heluim as opposed to oxygen.

Nope. String vibration depends only on string mass, string tension, and string length; the surrounding medium won't have any effect other than slowing the vibration down over time via drag (a string should vibrate longer in helium). Dig up an old thread about "piano capos" where Wewus and I got into it for some funny discussion on this.

 

Thanks for the support Phil, you explained it a little better than I did.

 

I called an old boss of mine last night who has a PhD in Physics and posted this question to him. He agreed the pitch would not change on music coming out of a speaker or a vibrating string. What was interesting, though, is he said the pitch of a wind instrument, say a sax or trumpet, will change!!! This is because the horn bore is filled with helium, just as the human throat is in our example, and that will change the properties of the sound generator, and not the transmission medium.

 

I still want to find a helium balloon and try this out, though.

[Hound Dog]

I found this:

 

This

 

It sounds convincing and is supported by other things I have read. Seemingly the writer would conclude that the pitch of the guitar in the Helium room would be higher.

[Jeff Klopmeyer]

Well, something around here is higher.

 

Could it be... ALL OF YOU, for having this discussion in the first place?

 

 

- Jeff