Why is the upper limit of sound 194 decibels?

What is the loudest sound in everyone's mind? Some people may say it is the sound of a ship's whistle, or the sound of a dance hall's speakers, or the sound of firecrackers during the Chinese New Year.

"I'm afraid the firecrackers on New Year's Eve will be too noisy..."

This is indeed a louder sound that we can hear in our daily lives, but it is still far from the limit of sound.

So why is the maximum value of sound 194 decibels? What will happen to sound if it exceeds the energy limit? Next, let's take a look at the generation and propagation of "sound" and its power.

Do you really understand "sound"?

The generation and propagation of sound

Sound is produced by the vibration of an object. Some vibrations are obvious, such as a plucked string, but some vibrations are so weak that they are difficult to observe. But in any case, once the vibration of an object stops, the sound stops.

Of course, human hearing is not that strong in nature. We can only hear sounds with frequencies between 20 and 20,000 Hz, which refers to the number of times an object vibrates in one second. However, even if an object vibrates faster, sound still needs a medium to propagate, and the propagation speed is different in different media.

Sound propagation is also affected by the medium

Generally speaking, the speed of restless waves in solids is greater than that in liquids and greater than that in gases. However, when it comes to the vacuum environment of the universe, sound cannot propagate.

Therefore, the signals people receive in the universe are definitely not sounds. In other words, the entire universe is actually silent. Even the explosion of the death of a star is a silent "fireworks show."

The vast and quiet universe

Fortunately, there is air everywhere on the earth, which can be used as a medium for sound transmission, allowing humans to hear sounds. Otherwise, imagine living in a silent environment, which must be very frustrating. In addition, sound is also very important for communication.

In addition, sound has many characteristics such as loudness, pitch, timbre, etc. What we are talking about today is that the maximum sound is 194 decibels, which actually refers to the loudness of the sound.

Loudness is a measure of how loud a sound is.

The loudness is often determined by the amplitude and the distance from the sound source. For example, the sound of an eruption heard by you standing next to a crater is obviously different from the sound heard dozens of kilometers away.

So why does sound have an upper limit of 194 decibels? What will happen if the sound exceeds this limit?

The sound becomes weaker as it propagates.

The upper limit of sound is 194 decibels

As we mentioned above, sound must rely on a medium to propagate, which leads to an extreme value. The stronger the vibration of particles in the air, the higher the decibel value of the sound. However, when it reaches the limit of 194 decibels, the energy will explode and form a "vacuum state".

As we all know, sound cannot propagate in a vacuum, so this is the upper limit of sound.

It seems that there is indeed an upper limit to the sound.

If you still can't understand, you might as well consider it from the perspective of air compression. Since air cannot be compressed infinitely, there is an upper limit to decibels.

However, it should be noted that the 194 decibels mentioned here refers to the maximum sound under standard atmospheric pressure. In other environments, the sound can reach higher decibels.

Standard atmospheric pressure is approximately 101.325 kPa

Many people may say that no matter what the upper limit is, we have never heard such a loud sound. In fact, it is normal for us to be curious about the sound of 194 decibels under the standard atmospheric pressure of the earth, but our ears cannot bear such a sound, because when the decibel value of the sound is greater than 150, it will cause damage to human hearing.

So if you want to hear a sound of 194 decibels, you should be deaf before you hear it.

Sound decibel diagram

So, what terrible things will happen when the sound exceeds the limit of 194 decibels?

You can recall the classic clip in "Kung Fu" first. When the landlady performed the Lion Roar Kung Fu, we saw the horror of sound. When the sound in the air exceeds the energy limit, it will change from sound to shock wave.

This shock wave is mainly because the energy pushes the air outwards, and in the process of pushing away, a vacuum is formed in the center. Once the sound limit exceeds 194 decibels, this shock wave will appear, and there is gas compressed to the limit at the edge of the shock wave.

Imagine that when the gas is squeezed from a loose state into a dense "solid" existence, the sound wave becomes a weapon, and everything in its path will be impacted. It is worth mentioning that the shock wave is not only as powerful as a freshly sharpened knife, but also because the air is compressed to a certain extent, the friction between the molecules getting closer and closer is more intense, which increases the temperature of the shock wave.

Concept art of shockwave

Therefore, it is still very easy to kill someone with a shock wave that exceeds the limit. Moreover, killing someone with a sound shock wave also depends on the distance. If the person is far away, it is fine. If the person is close, he may be "cut" and shattered directly.

For example, the atomic bomb dropped by the United States on Japan previously produced a huge shock wave after the explosion, which directly razed the area within several kilometers to the ground.

Nagasaki, Japan, in ruins

When a volcano erupted in Indonesia in the 19th century, it produced the loudest sound ever detected by humans. Not only did it directly blow up a nearby island, but the sound was also heard more than 160 kilometers away, with a volume of more than 170 decibels. You can imagine how terrifying it was.

It is reported that many residents living nearby were injured by the powerful sound waves. The injuries were not limited to the eardrums, but even the internal organs in the body were damaged to varying degrees.

Conceptual image of the eruption of Mount Tambora in Indonesia

In addition, volcanic eruptions also produce infrasound waves. Although this infrasound wave with a frequency less than 20 Hz cannot be heard by humans, it is not easily attenuated and absorbed, so it can circle the earth several times, just like an excellent "marathon runner."

Some people may say that it is a good thing that we cannot hear infrasound, otherwise we would be annoyed to death by the "looping" infrasound.

Although infrasound cannot be heard, infrasound waves of certain frequencies can resonate with human organs and can still cause death in severe cases.

Infrasound of a certain intensity will stimulate the human nervous system

Therefore, never underestimate the power of a volcanic eruption. In addition to the visible volcanic ash, there are sound waves that can only be felt when you are close, and infrasound waves that surround you from multiple angles. These are all "invisible killers."

For example, the Tonga volcano erupted in early 2022. Eight and a half hours after the eruption, the Kunming Infrasound Array, 10,151 kilometers away from the volcanic eruption site, recorded extremely strong infrasound signals with a propagation speed of about 321 meters per second.

Tonga volcano eruption

It is worth mentioning that in addition to natural disasters or man-made explosions that can make loud noises, there are many animals in nature that also have the ability to "roar like a lion."

Loud animals

First, let’s talk about an animal that is very small but very loud, and that is the tiger pistol shrimp.

But don't get me wrong, this guy doesn't make sounds with his mouth, but uses his claws to shoot out water jets to create a bubble. When the bubble bursts, it can generate a shock wave greater than 200 decibels, killing certain creatures within 2 meters.

Tiger pistol shrimp with its own "bullets"

The second is the blue whale, which loves to sing in the sea. Sometimes their voices can even reach 188 decibels. If you happen to be next to a blue whale, you may be directly shattered by the sound.

Fortunately, whales only sing in the ocean, and we who live on land don’t often face “deafening” sounds.

The sound of a blue whale can travel up to 1,600 kilometers away

Finally, there are the cicadas that chirp non-stop in the trees every summer. I believe that many people’s childhood memories of the summer are filled with the chirping of cicadas.

Although everyone now says that it represents a memory, the piercing chirping of cicadas still makes people irritated. According to scientists' observations, the sound of cicadas can sometimes reach more than 100 decibels, which is no less than the intensity of music played on the speakers in KTV.

Male cicadas make sounds through the vocal organs in their abdomen.

In general, nature is indeed "embracing all rivers", with so many creatures with different characteristics living together here. Moreover, they seem to be separated by some kind of "barrier" and generally do not disturb each other. And it seems that even the universe is aware of this, so it has turned the universe into a vacuum, helping us shield the huge noise made by stellar activities.

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