An echo occurs when sound waves traveling outward from a source (called incident waves) encounter a solid obstacle, such as the side of a mountain. Sound waves are reflected from such obstacles at an angle equal to the angle of their incidence.

The key factor for the occurrence of an echo is the distance of the obstacle from the sound source. When an obstacle is nearby, the reflected waves travel back quickly enough to mix with the original waves without producing an echo. If the obstacle is at least 15 meters away, the reflected waves return after the incident ones have been scattered. As a result, people will hear the sound repeated, as if it were coming from the direction of the obstacle. Acoustical engineers must design auditoriums and concert halls to account for echo generation by adding sound-absorbing elements and eliminating excessively reflective surfaces.

Reflection rule

In this experiment, low-frequency waves from a sound generator pass through glass tube A, are reflected from a mirror and enter tube B. The experiment proves that the angle of reflection of the wave is equal to the angle of its incidence.

During the day - faster

Sound travels faster in the warm air near the ground (picture below text) and slows down when it reaches the cooler upper atmosphere. This change in temperature leads to refraction (deflection) of the wave upward.

Slower at night

Lower nighttime air temperatures near the earth's surface slow down the passage of sound (figure below the text). In warmer overlying layers, the speed of sound increases.

Sound travels with the wind

Wind speeds at significant altitudes are much greater than near the ground. When sound waves travel from a land source, they travel with the wind. A windward listener will only hear a faint, barely audible sound; a downwind listener will hear the bell at a very great distance.

Even if you have never been to the mountains, you still probably know what an echo is and have encountered it more than once. The echo can lie in wait for us anywhere in the arch of a house, in an empty apartment, in the forest.

What is an echo and how can you hear it?

Echo is the reflection of sound. Echoes are taught in physics in the ninth grade, so everyone probably knows how it arises. Sound is reflected, sometimes even several times, from various surfaces and returns to us. The question arises: why do we not always hear an echo, but in some cases? Why don't we hear echoes in small rooms, for example?

The fact is that, firstly, things and furniture in the premises dampen reflected sounds, absorbing the echo. Secondly, in order for our brain to distinguish the reflected signal separately from the sent one, in the form of an echo, the difference between them must be at least six hundredths of a second.

It can be easily calculated, given that the speed of sound is approximately 340 m/s, that at a distance of three meters from the wall, the reflected sound will reach back in about two hundredths of a second. This time is not enough for the brain; it will not perceive these two sounds separately.

And in large rooms, where the signal is not damped by a large amount of furniture, and the distance to the walls is large, the sound may take more than six hundredths of a second to return to us reflected. In this case, we will hear an echo.

Where is the echo best heard?

High in the mountains, where there is no furniture, and the sound is easily reflected from the rocks, and the distance between the rocks is large, you can hear the echo of your cry more than once. Reflecting from the rocks located on at different distances, the sound arrives very late, so we hear a repeating echo.

Much the same thing happens in the forest, where sound is reflected from tree trunks. True, in a forest, sound is absorbed by leaves, grass and earth, but in the mountains there is often nothing to absorb sound, and therefore a loud scream can easily cause a collapse.

The vibrations of the sound wave are transmitted to the rocks, and stones and snow masses that are weakly held on the slopes can easily fall down from the resulting vibration. As they roll, they knock down new stones and snow along the way, causing an avalanche. Therefore, you should always remember in the mountains about the danger of a collapse and not shout unnecessarily.

The operating principle of the horn is based on the use of echo. The horn is an expanding round tube. A person speaks into the narrow end, the sound of his voice is reflected several times from the walls of the horn and comes out through the wide end in one direction, without scattering in all directions. Thus, its power is enhanced in a given direction, and the sound can travel a greater distance.

It happens sometimes, you are walking through the forest with your friends, you wander off in different directions and start cheerfully calling to each other.

Suddenly... what is this?

You hear that someone is pronouncing your same words, only in a muffled, quiet, even a little sad way. Echo!

Everyone really likes the echo, it’s funny to listen to it, and you start shouting to the whole forest: “Ay!..” - and call each other for a long time.

But what is this echo? Why does it happen?

You shouted - and the air vibrated, because every sounding body vibrates: the strings of a violin, harp, piano vibrate, your vocal cords vibrate when you speak. The sounding body vibrates, and from it a wave travels in all directions through the air, and when it reaches your ear, you hear the sound.

But then the sound wave encounters some obstacle, like a sea wave on the shore, and returns back, and for the second time you hear your voice, but only a quiet one, because the wave gradually weakens.

You don’t always hear an echo and not everywhere. For this we need certain conditions: The obstacle that the sound wave encounters must be at a sufficient distance so that the wave does not have time to return in one tenth of a second, because our ear can perceive the same sound wave no less than after such a period of time.

That's what an echo is. That's why it happens.

Man understood the nature of the echo, understood its mechanics. And so, based on the laws of reflection of sound waves, man created a wonderful device - an echo sounder.

This device, installed on board a ship, sends a sound wave into the depths of the sea. The sound travels through the water, reaches the bottom and returns, and is picked up again by the device. Knowing the speed of sound in water and tracking how much time passed between the departure and reception of sound, scientists determine the depth of the sea in this place.

And if you send the sound not into the depths of the sea, that is, not vertically, but horizontally, then you can determine how far the ship is from the shore, or during fog, find out if there are any obstacles ahead that the ship risks running into: Is there a ship coming towards you, is there an iceberg floating? The sound wave encounters an obstacle and returns, it is picked up by a device called a sonar, and it reports the obstacle to the captain.

More than once, the white dolphin saved ships during severe storms, guiding them through dangerous reefs and underwater rocks. The sailors knew him well, fell in love and declared his life inviolable. They called the dolphin the “white pilot”, and pilots are specialists who guide ships along the waterway they have studied well, along the fairway to the ports.

This Bulgarian story tells about the life of various sea animals and about natural locators, thanks to which they swim freely in the depths of the sea, without fear of tearing their bellies on treacherous reefs, fleeing from enemies. The locator is a wonderful protective device. It is not only found in marine animals.

The bat also has a natural locator.

For a very long time, the behavior of these small animals, which fly freely in the dark, never bumping into any obstacles, always deftly avoiding them, has been a mystery to scientists. And on the fly they still manage to destroy mosquitoes and very tiny mosquitoes. Meanwhile, the eyes of bats are not distinguished by visual acuity; on the contrary, they see very poorly.

What's the matter?

Only recently, about thirty years ago, scientists unraveled this secret. It turns out that bats have their own locator. They emit sounds that we do not hear, our ear does not catch them; These sounds encounter an obstacle, come back, and the mice catch them with their huge ears. So, in general, they have no need for eyes: ears replace their eyes, they seem to illuminate them the world around us powerful sound headlights.

There is a wonderful invention created by man on the principle of reflecting a wave, only not a sound wave, but a radio wave.

Radio waves also have the ability to be reflected from objects that come in their way. And before the Second World War, scientists created a device capable of detecting enemy aircraft from afar, even before they appeared overhead. This device is called a radar, otherwise known as a radar.

The radar can detect enemy aircraft in the sky and enemy ships at sea, and determines both their distance and direction.

Radars are needed not only during war, but also in peacetime. They are great helpers. Meteorologists use them to determine the speed and direction of winds at high altitudes and detect the accumulation of thunderclouds. Astronomers, having sent a radio wave to our closest satellite, the Moon, were able to very accurately determine the distance to it. These are just two examples, but there are many that could be given.

Echo! The nature of this phenomenon has long been explained. But in ancient times it seemed mysterious and wonderful. And the ancient Greeks came up with a poetic legend about the forest echo.

...Once upon a time there lived in the forest a beautiful nymph named Echo. She frolicked freely, sang and danced, like her friends - the goddesses of meadows, streams, springs... But the poor little nymph Echo angered the formidable, powerful goddess Hera, and Hera punished her by forbidding her to speak. Nymph Echo could now only repeat other people's words.

That is why we sometimes hear the sad voice of the nymph Echo in the forest. And Pushkin, captivated by the poetry of the forest echo, created wonderful poems about it:

Whether an animal roars in the deep forest, Whether a horn blows, or thunder roars, Whether a maiden sings behind the hill - To every sound You suddenly give birth to your response in the empty air.

Echo. What do we know about this interesting physical phenomenon? Anyone who remembers a school physics course well will probably answer that an echo is a physical phenomenon, the essence of which is that the observer receives a wave that is reflected from some obstacle. However, echo is not as simple as it seems. This article will provide several interesting facts about this truly amazing physical phenomenon that you may not have known. So let's begin.

What is an echo?

As mentioned above, an echo is a sound wave reflected from some obstacle (however, it can also be electromagnetic, but you, of course, will not hear such an echo). Reflected sound waves return to the observer (the noise source), who can sometimes hear them much later. It is this sound reflected from obstacles that is called echo.

About the origin of the word echo

This word has a rather interesting history. It came into Russian from the German word echo. This word came into the German language, like many other words in Western European languages, from Latin - ēсhō. And Latin adopted this word from Greek - ἠχώ , which meant “echo.”

Conditions for the existence of an echo

Several conditions are required for an echo to appear. Have you ever wondered why echo is not heard in an apartment or a store, but at the same time it is extremely easy to hear in the mountains? The fact is that the human ear hears an echo only when the reflected sound sounds separately from the spoken sound, and does not “layer” on it. To create such an effect, it is necessary that the time elapsed between the influence of the sound itself and the reflected wave on the ear must be at least 0.06 seconds. In a normal environment (for example, in an apartment) this will not happen due to short distance and various objects that also absorb sound.

Sometimes the echo is suppressed

There is a term called echo cancellation. It is used in telephony. The process of echo cancellation is the removal of echo that is unnecessary in a connection, which degrades the quality of communication. Echo cancellation is needed not only to improve sound quality, but also to increase bandwidth at the communication channel.

There is a room where there is no echo at all. It's called an anechoic chamber. There are two types of anechoic chambers. Each type serves to “jam” one or another type of echo. Simply put, in such a chamber, sound (or radio waves) simply do not reflect from the walls. The first is the acoustic type. It, as the name implies, serves to suppress ordinary sound echo. The second, accordingly, is radio frequency and is necessary to suppress the reflection of radio waves.

Light echo is an astronomical term. This phenomenon occurs when there is a sharp flash of light (for example, during the outbreak of novae). With such a flash, light is reflected from objects and reaches the observer much later.

World echo

World echo, also known as “long delay echo,” is a special effect associated with radio waves. This special type of echo is a sound that sometimes occurs in the range short waves, which returns some time after the signal is transmitted. This unusual and difficult to explain phenomenon was discovered in 1927 by Scandinavian Jorgen Hals.

Ancient Greek myth about the nature of echoes

The ancient Greeks explained many natural phenomena with myths. Echo was no exception. The myth about the birth of the echo goes something like this: one day, the jealous wife of Zeus, Hera, punished the beautiful nymph Echo, forbidding her to answer questions - Echo could only repeat last words addressed to her. Echo saw the beautiful Narcissus walking through the forest. He heard the rustling and exclaimed:

• -Who's here?
• -Here! – Echo shouted back.
• -Come here!
• -Here! – Echo answered joyfully, running towards Narcissus, but he pushed her away, because he believed that only he himself was worthy of his love. So now the beautiful nymph hides in the forests and mountains, occasionally repeating the words of the travelers.

About echolocation

Everyone knows that bats and dolphins use echolocation to navigate in space. However, few people can answer the question “how does it all work?” And it works something like this. First of all, the mouse emits ultrasound. Then she catches the echo of the same sound emitted to her, reflected from objects. The bat has the ability to recognize ultra-short intervals that pass from emission sound signal until the echo returns. In this way, the mouse determines the distance between trees or other objects, and also “sees” how far this or that insect is from it. What is surprising is that the bat perfectly distinguishes the echo from a static (immovable) object from a moving object.

Echolocation was discovered in dolphins more than half a century ago. Dolphins, like bats, use ultrasound, mainly frequencies 80-100 gHz. The signals emitted by dolphins are incredibly powerful: for example, they can “see” a school of fish more than one kilometer away!

Small interesting facts

• If the distance from the noise source to the nearest obstacle (wall or rock), then no echo is formed.
• The famous German river Rhine is full of surprises. For example, there is a place where the echo repeats 20 times
• In the city of Verdun, in France, there are two towers. If you shout while standing between them, you will hear the echo of your voice up to 11 times.
• The ear of Dionysus is a real record holder in the field of echo. This is a grotto in Syracuse, shaped like a human ear. But that’s not what makes him interesting. Due to its shape, the grotto makes the echo incredibly strong. Throwing a stone or a simple clap will echo out of the darkness with real thunder