Physics/Effects of helium on sound
Mikko Levanto wrote at 2009-07-20 07:01:06
Sound is vibration of matter. Each part of matter is moved by adjacent parts, whether similar or different. Therefore each part vibrates with the same frequency. We hear the frequency the source emits. At least as long as there is no other motion.
Whether the frequency of an instrument depends on the quality of air depends on the primary oscillator of the instrument. If that oscillator is air (as in e.g. flutes) the frequency is sensitive to the density of the air. If the oscillator is solid (as in e.g. pianos) the frequency is the same or at most varies only a little as the surrounding air has a very small effect on the string.
Terri Barrett wrote at 2009-10-19 22:09:51
Your observations are duly noted. On Saturday, I thought I would amuse my dogs by inhaling helium from my birthday balloons and doing the 'Donald Duck'. My husband, a Vietnam veteran, described my reaction as a "dead man's fall". I have five stitches in my eye, a monstrous shiner, and a far greater understanding of just how dangerous this seemingly innocuous 'party trick' can be.
kazuhiro nagamitz wrote at 2014-09-08 06:01:13
I am a pipe player. I often play while drinking beer. Hence occasionally I belch whie blowing air into the pipe, and then the sound bends down singnificantly temporarily. From this, I consider the vacal cord has not much to do with bending up or down of the sound in helium or carbon dioxide. As the density of the vibrating air goes up or down, the wavelength of the air lengthens or shortens; this is my theory.