### Re: What is the loudest sound in the world?

Date: Mon Aug 7 05:02:58 2000
Posted By: Bruno Putzeys, Staff, Electrpacoustics and Analog Electronics, Philips ITCL
Area of science: Physics
ID: 965007433.Ph
Message:
```
Phew! That's a pretty wide ranging question you put there. I think we'll
have to limit the subject to "sound" in the strictest sense, ie. that it
is in the "audible range" of 20Hz to 20kHz and that it is in air. This
means we're not talking about whale song or earthquakes (which are "sound"
waves travelling through the earth's crust).

I also have to leave explosions out of it, because the formal definition
of a "detonation" is that the flame spreads faster than the speed of
sound. Apart from that, explosions can be made as loud as you want, given
enough explosives...So, our "loudest sound" will quite probably be a roar
or a rumble of some sorts.

The absolute loudest steady-state sound level that can exist anywhere is
given by atmospheric pressure. A sound wave is compression (pressure
increase) and rarefaction (pressure decrease) of air. In the latter case,
it would be impossible to create a pressure of less than zero (vacuum), so
the limit is a peak pressure change of 1Atm (or 100kPa). How sound level
in dB's relates to a sound pressure in Pa can be found in the FAQ linked
below: http://www.point-and-click.com/Campanella_Acoustics/faq/faq.htm
Doing the calculation for ourselves we'll find that 20*log(100kPA/20uPA)
=194dB SPL peak (or 191dB SPL average, which is the more normal measure).

Quite obviously this means that you'll have to be "in the heat of the
event" to find this sound level. For practical reasons, sound levels are
measured at a distance several times larger than the sound source itself.
Usually, we're only interested in the loudness of an event from an
environmental point of view. To determine if a disco is playing too loud,
measurements are made at a few 100 metres from it. For louder sounds, the
measuring distance is even further away.

Now, to get back to the real point: the loudest known sound, for all
intents and purposes, is a space shuttle launch. Some sound levels are
quoted in the link below: http://www.jhu.edu/~cpia/database/820143bb.html
They are speaking of up to 106dB(A) SPL at 6 kilometres. What this means
is that any normal person will automatically cover their ears - at such a
distance!

```

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