question: I know that the amount of time it takes to hear thunder after seeing lightning determines how far away it is, but what does the loudness mean?
comment: How strong the discharge is. The higher the voltage and current of the discharge, the more energy is released. Louder thunder means more electricity.
passages: For its multi-week March 2016 event, the Houston Livestock Show & Rodeo had an LRAD mass notification system on the grounds in case attendees needed to be warned of emergencies or extreme weather events.
  
  San Jose, CA city officials ordered three long range acoustic hailing devices after complaints that the city did not adequately notify neighborhood residents of rapidly rising floodwaters in February 2017.
  
  San Jose, CA city officials tested its LRAD emergency alert system in October 2017, 8 months after the February 2017 Coyote Creek floods.
   The National Lightning Safety Institute recommends using the F-B (flash to boom) method to gauge distance to a lightning strike. The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels 300,000 kilometers in a second, almost a million times the speed of sound. Sound travels at the slower speed of 344 m/s, so the flash of lightning is seen before thunder is heard. A method to determine the distance between lightning strike and viewer, involves counting the seconds between the lightning flash and thunder. Then, dividing by three to determine the distance in kilometers, or by five for miles. Immediate precautions against lightning should be taken if the F-B time is 25 seconds or less, that is, if the lightning is closer than .
   BULLET::::- All clear: A 30 second steady tone that marks testing of the sirens every first Saturday each month at noon and the end of an emergency for which the immediate danger signal was sounded.
   Lightning at a sufficient distance may be seen and not heard; there is data that a lightning storm can be seen at over 100 miles whereas the thunder travels about 20 miles. Anecdotally, there are many examples of people saying 'the storm was directly overhead or all-around and yet there was no thunder'. There is no coherent data available.
  
  Section::::Effects.:High-energy radiation.
   The Loudest Sound Ever Heard
  
  The Loudest Sound Ever Heard is the 13th studio album by Christian alternative rock band The Choir, released on May 15, 2012, although prior to that date, a rough mix of "The Forest" was made available to those who pre-ordered the album via the band's official website.
  
  An additional track, "Shadow of the Cross," was recorded after the main studio sessions on July 22, 2012 and later released on August 9, 2012 as a digital single. It features a portion of the "Loudest Sound" cover art as its artwork.
  
  Section::::Musicians.
   Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. It is mainly caused by cloud-to-ground flashes as the current is much stronger than that of cloud-to-cloud flashes. On a worldwide scale, 3.5 million lightning flashes occur daily. This is about 40 lightning flashes per second.
  
  The sum of all these lightning flashes results in atmospheric noise. It can be observed, with a radio receiver, in the form of a combination of white noise (coming from distant thunderstorms) and impulse noise (coming from a near thunderstorm). The power-sum varies with seasons and nearness of thunderstorm centers.
   Section::::LiDAR.
   In the case of a sound source located in free field positioned over a reflecting plane (i.e. the ground), in air at ambient temperature, the sound power level at distance "r" from the sound source is approximately related to sound pressure level (SPL) by
  
  where
  
  BULLET::::- "L" is the sound pressure level;
  
  BULLET::::- "A" = 1 m;
  
  BULLET::::- formula_11 defines the surface area of a hemisphere; and
  
  BULLET::::- "r" must be sufficient that the hemisphere fully encloses the source.
  
  Derivation of this equation:
  
  For a "progressive" spherical wave,
  
  where "z" is the characteristic specific acoustic impedance.
  
  Consequently,
   Wind shear can have a pronounced effect upon sound propagation in the lower atmosphere, where waves can be "bent" by refraction phenomenon. The audibility of sounds from distant sources, such as thunder or gunshots, is very dependent on the amount of shear. The result of these differing sound levels is key in noise pollution considerations, for example from roadway noise and aircraft noise, and must be considered in the design of noise barriers. This phenomenon was first applied to the field of noise pollution study in the 1960s, contributing to the design of urban highways as well as noise barriers.
   Atmospheric noise
  
  Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, there are about 40 lightning flashes per second – ≈3.5 million lightning discharges per day.
  
  Section::::History.
  
  In 1925, AT&T Bell Laboratories started investigating the sources of noise in its transatlantic radio telephone service.
   Light travels at about 300,000,000 m/s, and sound travels through air at about 343 m/s. An observer can approximate the distance to the strike by timing the interval between the visible lightning and the audible thunder it generates. A lightning flash preceding its thunder by one second would be approximately in distance; a delay of three seconds would indicate a distance of about (3×343 m). A flash preceding thunder by five seconds would indicate a distance of approximately (5×343 m). Consequently, a lightning strike observed at a very close distance will be accompanied by a sudden clap of thunder, with almost no perceptible time lapse, possibly accompanied by the smell of ozone (O).
   Section::::Reception.
   In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as ITU-R BS.1770 refer to relative loudness of different segments of electronically reproduced sounds, such as for broadcasting and cinema. Others, such as ISO 532A (Stevens loudness, measured in sones), ISO 532B (Zwicker loudness), DIN 45631 and ASA/ANSI S3.4, have a more general scope and are often used to characterize loudness of environmental noise.
   The reference sound power "P" is defined as the sound power with the reference sound intensity passing through a surface of area :
  
  hence the reference value .
  
  Section::::Sound power level definition.:Relationship with sound pressure level.
  
  The generic calculation of sound power from sound pressure is as follows:
  
  where:
  
  formula_9 defines the area of a surface that wholly encompasses the source. This surface may be any shape, but it must fully enclose the source. 
   The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound. The relationship between SPL and loudness of a single tone can be approximated by Stevens's power law in which SPL has an exponent of 0.67. More precise measurements, a model known as the "Inflected Exponential" function, indicate that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.
   The phon unit is not an SI unit in metrology. It is used as a unit of loudness level by the American National Standards Institute (ANSI).
   Section::::Sound power level "L".
   As shown above, the approximate value 1000/3 = 333.33... m/s is exact a little below 5 °C and is a good approximation for all "usual" outside temperatures (in temperate climates, at least), hence the usual rule of thumb to determine how far lightning has struck: count the seconds from the start of the lightning flash to the start of the corresponding roll of thunder and divide by 3: the result is the distance in kilometers to the nearest point of the lightning bolt.
  
  Section::::Mach number.
   Historically, loudness was measured using an "ear-balance" audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Contemporary standards for measurement of loudness are based on summation of energy in critical bands.
  
  Section::::Hearing loss.
   BULLET::::- No all-clear signal is defined by either document.
   When there is a civil emergency such as a ballistic missile heading towards Japan, a special air raid siren sounds across loudspeakers and on TV and radio. When the siren starts, if it ends when the square waves hit at 329 kHz and 203 kHz, that means that a civil emergency is in effect. If the square waves reach 261 kHz and 283 kHz, that means the missile has passed.
  
  Section::::Information transmission capabilities.
  
  BULLET::::- Earthquake
  
  BULLET::::- Earthquake Early Warning
  
  BULLET::::- Quick updates on hypocenter, magnitude, and precautions of possible tsunami
  
  BULLET::::- Information of hypocenter, magnitude, intensities of various areas, and the presence of tsunami
   Manowar registered an SPL of 139 dB during the sound check (not the actual performance) at the Magic Circle Fest in 2008.
  
  Section::::Decibel records.:2009.
  
  On July 15 of 2009, at a Canadian concert in Ottawa, the band Kiss recorded an SPL of 136 dB measured during their live performance. Noise complaints from residents in the area eventually forced the band to turn the volume down.
  
  Section::::Deafening sound.
  
  Loud sounds have long been known to cause damage to ears. In Norway, this fact was proved for coppersmiths as far back as 1731.
   The cord is a unit of measure of dry volume used in Canada and the United States to measure firewood and pulpwood. A cord is the amount of wood that, when "ranked and well stowed" (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of . This corresponds to a well-stacked woodpile, 4 feet deep by 4 feet high by 8 feet wide , or any other arrangement of linear measurements that yields the same volume. A more unusual measurement for firewood is the "rick" or face cord. It is stacked deep with the other measurements kept the same as a cord, making it of a cord; however, regional variations mean that its precise definition is nonstandardized.
   The Menlo Park Fire District demonstrated its Long Range Acoustic Device (LRAD) community notification system on April 18, 2019. The fire district also showed how the ShakeAlert system could eventually be tied together with its LRAD to provide area wide audible alerts for earthquake, flood, fire and other emergencies. “ShakeAlert will notify and protect our Station firefighters, but we also believe coupled with the LRAD public address system, it can help to bridge the ‘notification gap’ as another important public safety tool and option for community early warning messaging for earthquakes as well as for fire and flooding information and evacuation signaling," said Fire Chief Harold Schapelhouman.
   The Columbus, OH Police Department (CPD) demonstrated a Long Range Acoustic Device to the local media on November 21, 2016. CPD expects to use the device for crowd control, barricaded suspect operations, and to communicate to residents during emergencies and natural disasters.
  
  The Washington D.C. Metropolitan Police Department used a LRAD at the January 21, 2017 Women's March.
  