question: Why does our voices change when we inhale helium?
comment: Helium can pass faster through our voice box, meaning the frequency, and therefore the pitch, increases.
passages: The speed of sound in helium is nearly three times the speed of sound in air. Because the fundamental frequency of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the resonant frequencies of the vocal tract. The fundamental frequency (sometimes called pitch) does not change, since this is produced by direct vibration of the vocal folds, which is unchanged. However, the higher resonant frequencies cause a change in timbre, resulting in a reedy, duck-like vocal quality. The opposite effect, lowering resonant frequencies, can be obtained by inhaling a dense gas such as sulfur hexafluoride or xenon.
   Inhaled helium is occasionally used to drastically change the timbre of the voice. When inhaled, helium changes the resonant properties of the human vocal track resulting in a very high squeaky voice. In Salvatore Martirano’s composition "L’s GA" the singer is required to inhale from a helium mask.
  
  Conversely, an unnaturally low voice may be achieved by asking the singer to inhale sulfur hexafluoride. This technique is less popular than helium inhalation, in part because of the inherent risk of the gas displacing oxygen in the lungs.
  
  Section::::Artificial timbral changes.:Artificial vocal enhancement.
   The process of talking underwater is influenced by the internal geometry of the life support equipment and constraints on the communications systems as well as the physical and physiological influences of the environment on the processes of speaking and vocal sound production. The use of breathing gases under pressure or containing helium causes problems in intelligibility of diver speech due to distortion caused by the different speed of sound in the gas and the different density of the gas compared to air at surface pressure. These parameters induce changes in the vocal tract formants, which affect the timbre, and a slight change of pitch. Several studies indicate that the loss in intelligibility is mainly due to the change in the formants. 
   Helium speech unscramblers are a partial technical solution. They improve intelligibility of transmitted speech to surface personnel.
  
  Section::::Video communications.
   BULLET::::- For entertainment purposes, when breathed, causes the voice to become significantly deeper, due to its density being so much higher than air, as seen in this video, here. This is related to the more well-known effect of breathing low-density helium, which causes someone's voice to become much higher. Both of these effects should only be attempted with caution as these gases displace oxygen that the lungs are attempting to extract from the air. Sulfur hexafluoride is also mildly anesthetic.
   This gives the 9% difference, and would be a typical ratio for speeds of sound at room temperature in helium vs. deuterium, each with a molecular weight of 4. Sound travels faster in helium than deuterium because adiabatic compression heats helium more since the helium molecules can store heat energy from compression only in translation, but not rotation. Thus helium molecules (monatomic molecules) travel faster in a sound wave and transmit sound faster. (Sound travels at about 70% of the mean molecular speed in gases; the figure is 75% in monatomic gases and 68% in diatomic gases).
   The thermal conductivity of nitrogen and oxygen are very similar, and that of helium very different so that the ratio of oxygen and nitrogen in the mix is relatively unimportant, and need not be compensated. This allows a direct reading of helium fraction from these instruments. However, for greater accuracy and compensation to oxygen cross-sensitivity, some instruments include an oxygen cell, and in these cases can generally give a full helium and oxygen analysis of the mixture simultaneously.
  
  Section::::Speed of sound principle.
   Most of the voice change begins around puberty. Adult pitch is reached 2–3 years later but the voice does not stabilize until the early years of adulthood. It usually happens months or years before the development of significant facial hair. Under the influence of androgens, the voice box, or larynx, grows in both sexes. This growth is far more prominent in boys than in girls and is more easily perceived. It causes the voice to drop and deepen. Along with the larynx, the vocal folds (vocal cords) grow significantly longer and thicker.
   Helium at low temperatures is used in cryogenics, and in certain cryogenics applications. As examples of applications, liquid helium is used to cool certain metals to the extremely low temperatures required for superconductivity, such as in superconducting magnets for magnetic resonance imaging. The Large Hadron Collider at CERN uses 96 metric tons of liquid helium to maintain the temperature at 1.9 kelvins.
  
  Section::::As a contaminant.
  
  While chemically inert, helium contamination will impair the operation of microelectromechanical systems such that iPhones may fail.
  
  Section::::Inhalation and safety.
  
  Section::::Inhalation and safety.:Effects.
   BULLET::::- Physics in Speech with audio samples that demonstrate the unchanged voice pitch
  
  BULLET::::- Article about helium and other noble gases
  
  Helium shortage
  
  BULLET::::- America’s Helium Supply: Options for Producing More Helium from Federal Land: Oversight Hearing before the Subcommittee on Energy and Mineral Resources of the Committee on Natural Resources, U.S. House Of Representatives, One Hundred Thirteenth Congress, First Session, Thursday, July 11, 2013
  
  BULLET::::- Helium Program: Urgent Issues Facing BLM's Storage and Sale of Helium Reserves: Testimony before the Committee on Natural Resources, House of Representatives Government Accountability Office
   Voluntary expiration is essential for many types of activities. Phonic respiration (speech generation) is a type of controlled expiration that is used every day. Speech generation is completely dependent on expiration, this can be seen by trying to talk while inhaling. Using airflow from the lungs, one can control the duration, amplitude, and pitch. While the air is expelled it flows through the glottis causing vibrations, which produces sound. Depending on the glottis movement the pitch of the voice changes and the intensity of the air through the glottis change the volume of the sound produced by the glottis.
   Helium and high pressure both cause distortion of speech, which can be partially compensated by electronic unscrambling circuitry.
  
  The communications system may have 4 component systems.
  
  BULLET::::- The ubiquitous hardwired intercom system, an amplified voice system with speech unscrambler to reduce the pitch of the speech of the occupants of the pressurized system. This system will provide communications between the main control console and the bell and accommodation chambers. This two-way system is the primary communications mode.
   During speech, the respiratory cycle is modified to accommodate both linguistic and biological needs. Exhalation, usually about 60 percent of the respiratory cycle at rest, is increased to about 90 percent of the respiratory cycle. Because metabolic needs are relatively stable, the total volume of air moved in most cases of speech remains about the same as quiet tidal breathing. Increases in speech intensity of 18 dB (a loud conversation) has relatively little impact on the volume of air moved. Because their respiratory systems are not as developed as adults, children tend to use a larger proportion of their vital capacity compared to adults, with more deep inhales.
   The vocal was also released for the iOS app Mobile Vocaloid Editor, and the "Lite" version was supplied with the app as the first vocal. The full vocal could be downloaded among the vocals offered by the app.
   Throughout the film, Frank Booth uses a medical mask and tube to inhale some kind of stimulant from an aerosol canister. The identity of this gas is a subject of controversy. Lynch's script specified helium, to raise Frank's voice and have it resemble that of an infant. However, during filming, Hopper, an experienced drug user, claimed to have insight into Frank's choice of drug, and said that helium was inappropriate. Lynch later explained the change:
   Helium is found in significant amounts only in natural gas, from which it is extracted at low temperatures by fractional distillation.
  
  Section::::For diving and other hyperbaric use.:Individual component gases.:Neon.
  
  Neon (Ne) is an inert gas sometimes used in deep commercial diving but is very expensive. Like helium, it is less narcotic than nitrogen, but unlike helium, it does not distort the diver's voice. Compared to helium, neon has superior thermal insulating properties.
  
  Section::::For diving and other hyperbaric use.:Individual component gases.:Hydrogen.
   This can occur as divers switch from a nitrogen mixture to a helium mixture (diffusivity of helium is 2.65 times faster than nitrogen), or when saturation divers breathing hydreliox switch to a heliox mixture.
  
  There is another effect which can manifest as a result of the disparity in solubility between inert breathing gas diluents, which occurs in isobaric gas switches near the decompression ceiling between a low solubility gas (typically helium, and a higher solubility gas, typically nitrogen)
   In low molecular weight gases such as helium, sound propagates faster as compared to heavier gases such as xenon. For monatomic gases, the speed of sound is about 75% of the mean speed that the atoms move in that gas.
   Section::::Mechanism.:Inert gases.
  
  The main inert gas in air is nitrogen, but nitrogen is not the only gas that can cause DCS. Breathing gas mixtures such as trimix and heliox include helium, which can also cause decompression sickness. Helium both enters and leaves the body faster than nitrogen, so different decompression schedules are required, but, since helium does not cause narcosis, it is preferred over nitrogen in gas mixtures for deep diving.
   Generally speaking, the mechanism for generating the human voice can be subdivided into three parts; the lungs, the vocal folds within the larynx (voice box), and the articulators. The lung, the "pump" must produce adequate airflow and air pressure to vibrate vocal folds. The vocal folds (vocal cords) then vibrate to use airflow from the lungs to create audible pulses that form the laryngeal sound source. The muscles of the larynx adjust the length and tension of the vocal folds to ‘fine-tune’ pitch and tone. The articulators (the parts of the vocal tract above the larynx consisting of tongue, palate, cheek, lips, etc.) articulate and filter the sound emanating from the larynx and to some degree can interact with the laryngeal airflow to strengthen it or weaken it as a sound source.
   Voiced speech is produced by air streaming from the lungs through the vocal cords, setting them into an oscillating movement. In every oscillation, the vocal folds are closed for a short period of time. When the folds reopen the pressure under the folds is released. These changes in pressure form the waves called (voiced) speech.
  
  Section::::Loading on tissue in vocal folds.
   Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced. A well-known but minor use is as a lifting gas in balloons and airships. As with any gas whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice. In scientific research, the behavior of the two fluid phases of helium-4 (helium I and helium II) is important to researchers studying quantum mechanics (in particular the property of superfluidity) and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero.
   Section::::Known solid phases.:Perovskites.
  
  Helium can be inserted into the A sites of negative thermal expansion perovskites that otherwise have defects at the A site. At room temperature and 350 Mpa helium is included into CaZrF to expand its unit cell yielding HeCaZrF. About half of the A sites are filled by helium atoms. This substance loses helium over several minutes on depressurisation at ambient temperature, but below 130K it retains helium when depressurised.
  
  Section::::Known solid phases.:Formates.
   Testosterone, an androgen secreted by the testes, will cause changes in the cartilages and musculature of the larynx for males during puberty. In women, androgens are secreted principally by the adrenal cortex and the ovaries and can have irreversible masculinizing effects if present in high enough concentration. In men, they are essential to male sexuality. In muscles, they cause a hypertrophy of striated muscles with a reduction in the fat cells in skeletal muscles, and a reduction in the whole body fatty mass. Androgens are the most important hormones responsible for the passage of the boy-child voice to man voice, and the change is irreversible. The thyroid prominence appears, the vocal folds lengthen and become rounded, and the epithelium thickens with the formation of three distinct layers in the lamina propria.
   Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood.
  