If all audible fireballs fulfilled these conditions there would be few problems. But many reports suggest high, swift objects, not as bright as -8 and some considerably fainter and classed as meteors. On numerous occasions it was the sound that caused the observer to look up. An obstacle immediately becomes clear: light from a meteor at an altitude of, say, 80 km (50 miles), would take only 0.0003 second to reach the ground-based observer whereas sound waves would take in excess of four minutes! Simultaneous observations of these two phenomena are not, apparently, possible. The solution to this problem may lie in the "hissing" sound that is often reported.
Havey H. Nininger in his classic book Out of the Sky recalls that in 1934 E.R.Weaver of the US Bureau of Standards suggested that electromagnetic waves - or "ether waves" as Weaver called them - may be produced by meteors and fireballs. These would then be transformed into audible sound by objects such as buildings and cars. Though ignored at the time, the proposal later received much attention, most notably by Colin S.L. Keay of the University of Newcastle in New South Wales, Australia.
Keay has investigated reports of "electrophonic" sound emitted by a number of bright fireballs. In 1980 he showed that the plasma trail of a large fireball could generate Extra Low and Very Low Frequency (ELF/VLF) radio emissions in the range 1 to 10 kHz. His theory was eventually verified in 1988 by three groups of Japanese observers who, working together, managed to obtain simultaneous photographic and radio observations of a bright fireball together with an electrophonic sound report of the event.
While bright fireballs may be capable of producing electrophonic sound there are still problems with the fainter meteors. It seems unlikely that such a small object could produce enough energy to generate ELF/VLF radio emissions, but reports do exist and need to be satisfactorily explained.
The main objection to audible meteors is that humans cannot normally hear electrophonic sound. But various theories have been proposed in which sharp objects - such as aerials, wires and even blades of grass - could convert any ELF/VLF emissions present into audible sound. In effect, the meteor discharges its sound to the ground in the same way that a charged cloud will discharge lightning - a common enough occurrence. Another, though less likely explanation came from A.Paine who speculated that sound may be quite common at certain wavelengths that are outside the normal range of the human ear. He went on to propose "bat-like" sensitivity under certain conditions.
It is interesting to note that the Inuit have a belief that aurorae - which are caused by solar atomic particles interacting with the Earth's magnetic field and atmosphere - can also be heard, despite occurring at altitudes of 100 - 700 km where the air is too thin for the transmission of sound. In Inuit mythology, aurorae are to souls of the dead who, if you listen very carefully, will whisper to you. Clearly, the same processes that make meteors audible may also account for whispering aurorae.
Curved, Kinked, Spiral and Wavy Meteors