Conventional refrigerators chill items by compressing and expanding chemicals called refrigerants. This transfers heat from inside the fridge to the outside, cooling the inside. Sound waves can do the same job: very powerful sound waves can also conduct heat. In an acoustic refrigerator, helium is compressed in a small steel cylinder to a pressure 10 times that of the Earth's atmosphere. Then a speaker blasts a long unchanging note, sending sound waves vibrating through the helium-filled cylinder.
The pressure changes caused by the sound waves bouncing around in the sealed space alternately heat and cool the enclosed gas.
The sound waves force the helium through a fine-meshed stainless steel screen, and heat is transferred from the gas to the steel. As the sound passes through the screens, it causes the sound wave to drop in pressure. This causes the helium to expand and cool even more before it reaches a reservoir of ethyl alcohol.
The now-cold helium draws heat from the alcohol. The cold alcohol is then pumped through the walls of the refrigerator to cool the inside, and pumped back to the reservoir, where the helium chills it again.
Your ear works much like the acoustic refrigerator. Sound waves inside your ear vibrate the eardrum. As the eardrum swings back and forth, a fluid inside picks up those waves, just like the refrigerator's helium cylinder. Instead of turning the energy from the waves into heat, as the refrigerator does, the waves' energy vibrates tiny hairs that are tuned to the different pitches of the sound. The sound you hear consists of different frequencies or wavelengths, which determine their pitch.
Loud sounds can cause pain at 120 dB -- what you would hear near the stage at a heavy metal concern. At 165 dB, your hair would catch fire from the heat caused by the friction from the sound vibrations. Acoustic refrigerators have sound levels of 173-196 dB -- similar to the sound of a space shuttle launch at ground zero -- safely contained in a pressurized tube. Even if the tube shattered, the sound would instantly spread out through the atmosphere and return to harmless levels.