All gas samples have the same number of molecules per unit volume at a given pressure and temperature, whether the gas is helium or nitrogen the primary constituent of air. But not all gas molecules have the same mass. Nitrogen and thus air has a mass roughly seven times greater than that of helium. Nitrogen is thus denser than helium and sound waves travel through it more slowly than they do in helium. At 20 degrees Celsius, for example, sound travels at meters a second through helium, but only at meters a second through air.
Like the vibration of a drum or a violin string, the vibration frequency of the vocal cords is independent of the type of gas that surrounds them. Whereas the velocity of the sound waves is faster in helium and the wavelength greater , the frequency remains unchanged because it is determined by the vibrating vocal cords.
Rather the timbre, or quality, of the sound changes in helium: listen closely next time and you will notice that a voice doesnt become squeaky but instead sounds more like Donald Duck. It is the lesser density of the helium--which serves as the medium for the sound waves--flowing through the larynx that produces this differing quality in the voice.
Answer originally posted on June 14, Sign up for our email newsletter. As a postgraduate student, I very ill advisedly tried breathing the heavy, rather inert gas sulphur hexafluoride whose speed of sound is nearly three times slower than in air.
It had the opposite effect, and I become an instant basso profundo; I survived, and a few breaths later my voice returned to normal, but as they say, please don't try this at home! In a sound wave the product of wavelength and frequency is a constant and is equal to the sound speed. I'm afraid this isn't a very rigorous answer but, using this relationship, we know the local sound speed is increased and given that the wavelengths of the noises produced are more or less unchanged presumably since the dominant wavelengths produced in speech depend mainly on the geometry and the dimensions of the throat during a particular articulation the frequency or pitch will therefore rise.
On a tangent to this, natural changes in the composition of air as it is exhaled, due to increased carbon dioxide lower sound speed than oxygen and nitrogen and reduced oxygen, should result in a perceptable downward shift in frequency. This might be noticeable for example when blowing a very long note with a woodwind instrument - that is, if it isn't sub-consciously corrected for. I've never tried it myself. R Telling, Weymouth Dorset Helium is much less dense than air, so our vocal cords encounter far less resistance in this medium, making the vibrations much more frequent.
Lower resistence to vibration will LOWER the frequency of vibration think of loosening a guitar string, or plucking a loose rubberband. The speed of sound travelling through Helium is faster than that in air. For a pressure disturbance to create a pitch, it must vary at a frequency that resonates in our vocal tract. When the speed of sound in increased, the pressure wave reaches the end of our vocal tract before it has completed a full cycle, so it doesn't resonate.
Faster vibrations of our vocal cords produce pressure disturbances which ARE able to resonate in our vocal tract, so it is these higher pitches that we hear.
A related effect is heard by playing a violin in Helium. This is why helium balloons float. This makes your voice sound very high, like Donald Duck. On the other hand, suppose you breathe in a gas that is heavier than air? Sulfur hexafluoride makes your voice sound very low because sound travels slower in heavy gases.
Breathing strange gases in dangerous. People need oxygen to stay alive and some gases are poisonous. U niversity of W isconsin —Madison. What is Heat? What is Light?
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