The loudness of a sound we hear is determined by the amplitude of the pressure waves and is limited by the fact that eventually, the low pressure point hits zero pressure ---> at 194dB.
We often measure loudness using a unit called the decibel (named after Alexander Graham Bell).
Louder sounds have a larger oscillation between the low and high pressure sections of the wave (loud sounds have higher high-pressure and lower low-pressure parts than quiet sounds).
For sounds through the air on Earth’s surface, the average of the high-pressure and low-pressure parts of the wave is our normal atmospheric pressure (what we call 1 “atmosphere” of pressure). So a sound wave might have a high pressure component of 1.0001 atmospheres and a low pressure component of .9999 atmospheres, and a louder sound might be 1.01/.99 instead—but in both cases, the average of the two is 1 atmosphere.
Depending on where you are, sound has a hard maximum. The reason is that sound isn’t a thing in itself (it’s a pressure wave moving through a medium). And since the average of the high and low pressure points of a sound wave has to be the normal pressure of the medium,
loudness is limited by the fact that eventually, the low pressure point hits zero pressure.
The wave alternates between double the normal atmospheric pressure and no air at all, a vacuum, not something you want to be present for ). Since the low pressure can’t go any lower, that’s the max amplitude of a sound wave on the Earth’s surface and the loudest a sound can be here.
One thing to keep in mind is that with decibels, each increase of 10 dB multiplies the sound intensity, or the power, of the wave by ten.
But a 10x increase in power only sounds about 2x as loud to our ears, so for our purposes, the 2x increase is more relevant.
So 20 dB is twice as loud as 10 dB, 30 dB is four times as loud as 10 dB, and 80 dB is 128 times louder than 10 dB.
