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Question:
I designed an experiment with a "chamber" that I infused with helium gas and then tested various noise producing devices: tuning fork, radio, recorded voice. When exposed to helium none of these sounds changed -- unlike my voice, which changes when I take a small breath of helium gas. I read your response regarding why the human voice changes, but why does not helium change the vibration of these other (non-human) noise makers?



Replies:
The sources that you used all have a the frequency set by something other than the speed of sound in air (or helium). The tuning fork vibrates according to its own mass and stiffness, the radio and recorded voice speaker is driven by its electronics. The physics of the human voice is a bit more like a trumpet, in which the speed and wavelength of the standing waves set up in the vocal tract define the frequency of the sound.

Richard Barrans
Department of Physics and Astronomy
University of Wyoming


Why does it appear our voice changes when inhaled helium is exhaled during vocalization? The high concentration of helium actually moves the now gas mixture faster,....this causing the vocalization to change. In a true confined space with helium blowing, we could, with correct instrumentation measure changes in sound / speed. I would try to measure all gases in this chamber, have the helium gas forced over various sounding devices i.e. speaker, tuning fork, listen and perhaps consider using a triggered sweep oscilloscope.

Prf. Przekop, Physicist



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