Interesting acoustics

Гравюра Каміля Фламаріона із книги About the curiosity of acoustic phenomena have been written for a long time and a lot. Let’s start with the fact that we recall the sections “Sound and hearing. Wave-like movement “from the wonderful science-popular books of Jacob Perelman” Interesting physics “, which read many generations. Not even believe that the first book of Interesting Physics came back in 1913, and the second one in 1916! By the way, the term “science fiction” began to be used from the easy hand of J. Perelman, who corresponded with K. Tsiokolsky and S. Korolev. Later, acoustics was popularly written V. Morozov in the book “Interesting bioacoustics” and E. Waldman in the book “Interesting telegraphy and telephony. Today, too, you can meet enthusiasts who are already popularizing modern assignments in the field of electro-acoustics, and do it by modern means – we have, in particular, the site in mind Author’s non-commercial electronic journal on the sound of “Israeli electronics engineer Alexander Radzishevsky”. In general, thanks to the Internet you can find many useful and interesting information about acoustics and acoustic devices – to take at least The section “Sound and acoustics” of the site Або, якщо ви музикант та хочете одержати tips for mastering and editing – to your attention the WikiSound site... Thanks to the Internet, we also made our own collection of acoustic interesting things that we offer to your attention. At the same time, we adhered to the principle of “colorful”, trying to show as a possible broader list of applications acoustics. We hope that this will awaken new thoughts and encourage your own scientific and practical research in the field of acoustics …

Acoustic system for monitoring traffic flow

Патрік Мармаролі (Patrick Marmaroli)Postgraduate student at the Swiss Polytechnic School in Lausanne, Patrick Marmaroli, has developed a computer system with microphone sensors, which automatically controls traffic. This technology allows not only to determine the intensity of the traffic flow, but also can estimate the speed, size and even the type of vehicles. Two Swiss cities, Sion and Martini, have already shown interest in acquiring such systems.

The traffic noise is not just a noise. As Patrick Marmaroli has shown, traffic noise can also be a source of information.

While studying at the postgraduate course at the Swiss Polytechnic School in Lausanne, Patrick developed a computer system with a pair of microphones as sensors, which can be used to estimate the traffic intensity of the sound of tire rolling on asphalt. Moreover, you can also estimate the speed of individual cars and even their type.

Так зазвичай контролюють міський трафік (фото CITRAC)The system is extremely simple: two microphones and a laptop. “In the first tests, the laptop was used, but in the future we will apply a smaller overall system based on embedded digital processors,” explains Patrick. The area of ​​attention of microphones – only four meters, perpendicular to the direction of traffic on the highway. Each vehicle on the road is recognized and monitored in real time, while the speed of the car is also assessed. Moreover, the installation can determine the wheelbase of the vehicle, which allows us to draw conclusions about its overall dimensions. The error reaches 30 cm, but it is a bit comparing with the width of one tire. As a result, the system can recognize the belonging of the vehicle to the “car”, “freight” or “bus” classes.

Thus, the system has the rudiments of “artificial intelligence.” To filter out third-party noises, the installation uses tracking sounds similar to those embedded in the computer’s memory samples. As a result, the pedestrian steps and the sound of the hammers will not be confused with the noise of transport. If the system began to track one car moving at a speed of 80 km / h in one direction, the appearance of another identical noise (oncoming car) on the same section in the width of four meters will not ruin it with confusion. Computer “brain” of the device comes to the conclusion that the first car could not rotate directly behind the listening area and immediately accelerate to 80 km / h.

Спектрально-часове відображення шуму кількох автомобілів

As a result, the city traffic control center may not just find out the traffic of one or another route, but also determine the share of trucks or buses in such a load, as well as promptly take appropriate measures.

The advantages of the system do not need to paint: it does not have videos and cameras, radars, data collection center, it does not need operators. It is easy to install, its work is not complicated by poor visibility; Finally, it is comparatively cheaper than analogues. Two Swiss cities, Sion and Martini, have already shown interest in purchasing such systems and are taking part in negotiations on financing their production.

P.S .: PhD dissertation on this topic is protected on February 15, 2013.


A headset that makes phone conversations invisible to the surroundings

Another Ukrainian project – the Hushme headset – went to Kickstarter. Kievanin Roman Sakun, together with the design bureau ARTKB, has launched a company to raise funds for a headset design for smartphones that will make telephone conversations more confidential.

The idea to create a Hushme originated in 2015. The co-founder and top manager of the startup Roman Sakun sat with his friends at the cafe, and next to them the girl tried to talk on Skype using headphones. The girl spoke incessantly loudly, and the visitors began to look at her. No comments were made by the girl, but she felt uncomfortable and she had to interrupt an important conversation. So the idea was to make a device that solves this problem.

Experts from the design bureau ARTKB have joined Roman, who previously worked with such well-known Ukrainian startups as Petcube, iBlazr, Lametric, Hideez and others. In 2017, the prototype of the device presented at CES 2017, where the headset immediately attracted the attention of Western media. About Hushme wrote CNET, Daily Mail, Time, Telegraph, BBC, Mashable, Engadget, and also featured on Fox news and CNBS.

Гарнітура Hushme

When a user speaks on the phone with Hushme’s headset, the neighbors almost do not hear it, even if they are nearby. True, it should be expected that the headset will draw attention to the appearance of the user, because the muffler closing his mouth, reminds half-mask a bit of a futuristic look. Someone likes this kind of attention, someone is not very, but the main task of developers was to create a device that is useful for a certain layer of users.

First of all, Hushme focuses on office workers who do not want to interfere with colleagues by calling. But Hushme may also be needed by those on a business trip and wants to keep confidential their conversations, bloggers and writers who can dictate the text aloud without worrying home-made gamers so that their mother does not hear that some are still sleeping and playing in Dota 2 …

A video that advertises the features of the Hushme headset can be viewed at this link:

Як працює Hushme

And now – a little more about the headset.

In normal mode, the Hushme headset connects to your smartphone via Bluetooth and plays the role of an ordinary wireless headset that allows you to phone or listen to music.

In the passive camouflage mode, the brackets of the Hushme headset are fixed using special magnets located inside the mask to form a half-mask ring that shrinks the mouth. Due to the absorption of sound by this half-mask, the conversation is incomprehensible to people at a distance of one meter, but for those who are farther and almost inhumane.

The most interesting is the active voice cloaking mode provided by the electronics located inside the mask, and special software. When you click on the button, external loudspeakers located around the perimeter of the mask, which generate hidden masks, are activated. What this sounds for – the user can choose from the gallery Hushme. This may be the sound of rain, wind or sea, the cloak of the monkey or the breath of Darth Vader …

Команда розробників Hushme

It should be noted that students of the 4th year of the chair of acoustics and acoustoelectronics NTUU “KPI” – Andriy Vityk and Daniil Didenko – under the direction of Professor Arkady Prodeus contributed to the development of the software of the Hushme headset, investigating the effectiveness of masking the speech with synthetic noise.

For this purpose, a special software for the Matlab environment was developed. Using this software, the effectiveness of the proposed types of noise and their respective algorithms is evaluated experimentally. The assessment was performed by 10 masters of the department, and this assessment was performed within the framework of the educational process, in the form of a computer workshop. Thus, “without leaving the study”, quantitative assessments of the quality and legibility of the broadcast were obtained, depending on the intensity, color and type (stationary non-stationary) masking noise.

We note that these studies have attracted considerable interest from students. There are several reasons for this. First, students solved not some kind of “toy” task on “three land diggers digging a ditch”, but faced with a real challenge that has practical demand. Secondly, students are clearly familiar with the real difficulties faced by acoustic engineers when necessary subjectively, that is, using their own hearing system to evaluate such difficult factors as quality and intelligibility of speech. Finally, it is also important that such an assessment was organized at the highest modern level: the noisy signals were generated automatically in the computer, presented to the listeners in a random manner (that is, the listener did not know in advance what he was hearing), while the audible noises were done in headphones, which ensured the reliability of the results.

Of course, the great satisfaction from the conducted researches was received by their curator Arkady Prodeus. First, the results obtained are in good agreement with the projected estimates of the masking ability of stationary noise. And the study of the effect of non-stationary noise was generally up-to-date, and therefore twice as interesting and useful both from the scientific point of view and from the applied point of view.

The main customers of the conducted research – the top manager of the startup Roman Sakun and the founder of ARTKB Alex Nesterenko – also highly evaluated the results, both in view of the accuracy of the purpose of the research, and given the depth of work on the tasks.


Зображення: кадр із відеоThe acoustic camera allows you to see a source of incomprehensible noise in the car
South Korean engineers have created a compact “sound camera”, which allows you to see the source of any suspicious noise in engines, instrument panels, doors and other parts of the car.

It’s usually not easy to locate a source of buzz, creak and booty in cars. To solve this problem, Hyundai has commissioned engineering engineers to detect a source of sounds ranging from 200 herc to 20 kilohertz. The result was a manual “acoustic camera” SeeSV-S205. It represents dozens of inexpensive microelectromechanical (MEMS) microphones arranged in a spiral around the camcorder.

Signals coming from all microphones are treated in the same way as they do in radars – as a result, the direction of the source of sound is determined.

The device is compact and easy to operate. The real-time tool (25 frames per second) imposes a two-dimensional color soundcard on a video image, which allows you to quickly detect a sound source.



Noise isolation of the car with your own hands

Very often the comfort in the car interfere with extraneous noise. They not only “push” on the brains, but also cause some damage to the body. To get rid of this, car limousines often make noise isolation, which protects the driver and passengers from all scratches and foreign noises. The choice of material for noise insulation depends on the intended purpose, that is isolation for better sounding of music and noise reduction will be different.

Since in most cases the budget is limited, noise isolation in the whole machine is not worth it at once. Better to start with the door, and then go to the floor, trunk and so on. With regard to the set of tools, then necessarily required will be a construction hair dryer, padding roller (to attach the insulation material), scissors for cutting the material, solvent (to degrease the surface before putting on it noise isolation).

Materials: Vibroplates Silver, Gold, BiMast Bomb, Splenet 3004, Bitoplast 5, Accent 10, Madelin

Вібропласт Silver   Вібропласт БіМаст Бомб

Noise-isolation of the bonnet: If you make a noise isolation hood, then the engine will not “suffer” in winter from the cold. To do this, Accent 10 and Silver Silver Vibration will be required.

Soundproofing Doors: This type of insulation is aimed at getting rid of extraneous noise external environment as well as to music in the car sounded better. For this purpose it is enough to take the usual vibroplast “Silver” and “Gold”. Fill the material inside the door opposite the column. If a car is a good sound system, you need at least 4 layers of insulating the material to music in the cabin sounded good.

Матеріал для звукоізоляції Splen 3004   Матеріал-ущільнювач Бітопласт 5

Noise isolation of ceilings and roofs: Motorists handle the roof so that noise does not interfere with the outside: after the sound insulation, even the strongest rain will not “beat” on the head. For this type of isolation, the vibroplast of the above species is suitable.

Noise isolation of the floor: The main purpose of this type of insulation is to reduce the noise from the contact of the car with the road, as well as from the impact on the bottom of the car of small objects. The choice of materials is unlimited, but usually take the Bomest Bomb, and on top of it put Splen 8 or 4.

Матеріал для звукової ізоляції Акцент 10   Декоративний ущільнюючий матеріал Madelin

Noise isolation of the trunk, arches and wheel niches: Protecting the trunk and the fifth door hatchback is extremely important, since it comes from there with most of the extra scratches and noises. If you want to put a subwoofer in the car, then do the noise isolation of the boot necessarily. All linings in the trunk must be covered with bitplast. Wheel niches are often pasted with vibroplast “Gold” or analogue.


Mufflers: from motorcycle and motorcycle – to armed
In modern cars one to five mufflers are installed, but for the most part there are two. The closest to the engine is the muffler called the previous (front) muffler or resonator. Behind him is the main, rear silencer (see drawings).

Передній глушник (резонатор)    Основний (задній) глушник

The above figures show quite clearly that on the path of the sound waves emitted by the motor, there appears a quite long range of different cameras of different sizes. The sound moves from camera to camera through various openings, repeatedly echoes from the walls of the muffler. In this case, the energy of sound vibrations is converted into heat energy, which achieves a reduction in noise. In addition, with a certain configuration of the silencer cameras, the sound waves can be superimposed on each other in the antiphase – and thus mutually destroyed. To summarize, we can say that in the automobile muffler the complex of noise reduction technologies is used:

  • expansion (narrowing) of the stream;
  • change of direction of flow;
  • interference of sound waves;
  • absorption of sound waves.
    The motorcycle muffler is much simpler. His scheme is shown in the following figure:

Мотоциклетний глушник

The front part of the muffler, from the intersection I to the intersection II, has the form of a long cone and acts as an acoustic transformer. The main part in the muffler is the rear part II-III, which serves to muffle the noise. This part contains an acoustic filter in the form of several cameras, passing through which, the sound waves lose their energy.

It is not surprising, but the muffler of a motorcycle is very similar to an armed muffler, which also has a number of expansion cameras, echoing cones, and so on. Several armed silencer schemes are listed below. On YouTube, you can even find videos where a simple one-chamber but very effective, muffler is made “on the knee” of a conventional aerosol can.

Простий однокамерний глушник               Багатокамерний глушник


Acoustic filters for hearing protection

Акустичні фільтри DUBS у вухахThe bottom of the application of electronic filters is to adjust the level of the acoustic signal at different frequencies. An example of such an application is equalizers, which are usually implemented by hardware-software (digital filters) or hardware (analog filters) way.

Акустичні фільтри DUBSHowever, there is one more variety of filters – these are acoustic filters, elements of which are mass, elasticity and geometry of physical objects. For example, an acoustic filter is any room. So, in a furnished room, language and music sound quite differently than in a room with bare walls. Another example is acoustic mufflers. It is about such a kind of acoustic filters that drown sound waves at certain frequencies, and this is the language here.

Частотна характеристика вушних акустичних фільтрів DUBS

The ear acoustic filters shown in the drawings are developed by DUBS and are intended to protect the human hearing system from noise, just as the sunglasses protect the visual system from excessive light. These filters look like a Bluetooth system, but in fact they do not contain any electronic elements.

Due to the design of the DUBS acoustic filters, both expansion chambers and Helmholtz resonators are used here.

Конструкція фільтрів DUBS

Analyzing the frequency response of DUBS acoustic filters (see graph), we see that these filters can successfully suppress both low frequencies (by 6 dB in the range of 100-400 Hz) and medium and high frequencies (by 24 dB in the range of 2- 8 kHz).

In the DUBS acoustic filters there is only one significant drawback – it’s a price ($ 25).


Automatic Speech Recognition System – Manually

Today, many have heard the news about the stunning  the results achieved by Microsoft in the field of automatic speech recognition:“Microsoft developers have taught neural networks to recognize human voice as well as people. In a report by a team of researchers in the field of artificial intelligence Speech & Dialog said that the speech recognition system is now erroneous as rarely as professional stenographers. In some cases, tells about writing your own programs in the programming language C ++.

However, we can point out a slightly different approach to solving the same problem – using the HTK Toolkit application library. This approach is actively exploited by Ukrainian developers from

International scientific and educational center of information technologies (INNITS) Institute of Cybernetics named after. M. Glushkov Academy of Sciences of Ukraine.On one of the site pages of this center you will find 5 lessons, after which you will learn the skills you need.

The benefits of this approach are that you need to master the FAR File Manager controls to run self-developed automatic speech recognition programs in command line mode.

Perhaps you will be helped by useful information in the form of translations of individual sections of the book HTK BOOK, placed on the site of A. Prodeus, performed by him and his students. Separate (first two sections) translations were edited with the direct participation of V.Pilipenko, an employee of INNITS, to which the Chair of Acoustics and Acoustoelectronics is very grateful for the unselfish help in assimilating the foundations of such an uneasy industry as automatic speech recognition.


Noise, vibration and space flights

Американська ракета-носій The first Chinese cosmonaut, Jan Livay, told

that during his flight into space with a ship something obscure and mysterious was happening. Recall that Jan Liwei made a space flight on the ship “Shenzhou 5”, which was launched into orbit around the Earth as early as October 15, 2003. And during this flight, he heard extraordinary sounds. “The unusual situation in which I got into space was in the strange sound that arose from time to time. He was not coming from within the ship, it seemed that someone was striking the ship’s hull, the sound was like a wooden hammer in the iron The sound appeared for no reason, “- said the astronaut on the air of state television. Jan Liwei added that the sound was quite nervous in flight, he moved into the window to understand the cause, but did not find anything unusual.

One of the most important factors affecting the human body in space flight is noise and vibration. The designers of the first Chinese ships say that it took three years after the Shenzhou-6 ship to prepare for the Shenzhou-7 ship in order to resolve a number of problems, including excessive noise and vibration during the launch, which brought former carriers “a lot of trouble” . What this means is “considerable concern”, one can not only guess – today the practice of space flight allows a clear interpretation of the vague statements of the Chinese press.

Vibration and noise are mainly related to the phases of launching the spacecraft engines or their operation during the flight. Their sources are the work of rocket engines, their concussion, the displacement of fuel in tank tanks, atmospheric flows and turbulence of the atmosphere, as well as aerodynamic impact in overcoming the space barrier sound barrier.

Стартує ракета-носій корабля

Noise and vibration cause a feeling of discomfort, irritation, nausea and other unpleasant sensations. Characteristic appearance of a sense of anxiety and fear, strangulation, pain in the abdomen and spine, general fatigue, difficulty breathing, headache, itching and deafness. The normal flow of processes is violated both in separate cells and in the organs as a whole.

The harmful effects of vibrations are explained by the fact that the human body and its individual organs have their own resonance frequencies, which lie in the same range as the frequency of rocket carriers. Thus, the spacecraft “Apolon” with the Saturn-5 rocket carrier, depending on the flight phase, has the main resonance frequencies in the range of 4.5-9 Hz. A resonance frequencies of the human body are in the range of 3-12 Hz. When a spacecraft vibrates at any of these frequencies, vibration of the corresponding human organs resonantly increases, these bodies deform, shift and can be mechanically damaged.

In cosmonauts with strong vibrations not only there is a sense of discomfort. Pilots of the spaceship “Gemini” at a frequency of oscillations of 50 Hz could not even read the readings of the devices, because it is at this frequency that vibrations of eyeballs and eyes as if fastened with a curtain.

The colossal levels of noise generated by large space rockets can be judged by such figures. The Saturn-5 rocket generates nearly 200 million Watts of sound energy for 2 minutes, which is 0.3-0.8% of the total rocket power and four thousand times higher than the roaring of Boeing 707 jet aircraft engines.

Стартує ракета-носій китайського корабля

In terms of noise pollution, 160dB noise can cause mechanical damage and irreversible deafness as a result of the rupture of the tympanic membrane and the displacement of the auditory stones in the middle ear. At 140 dB, a person feels great pain, and prolonged noise exposure of 90-120 dB can lead to damage to the auditory nerve. Noise with a level greater than 60 dB causes inhibition of normal contractions of the stomach and intestine, reduces the secretion of gastric juice and saliva.

In a manned spacecraft, the strong noises damage not only because they negatively affect the body of the astronaut. At a noise level of 120 dB, serious deterioration occurs in speech communication and radio communications. Experiments show that the broadcast of the astronaut becomes much less legible if chaotic noise is added to vibration in the range of 10-30 Hz. Therefore, when creating the spacecraft “Apolon” sought to reduce the noise so that the maximum noise level after the phase of flight with the excluded engines did not exceed 55 dB in the range of frequencies 300-3800 Hz.


Music in the service of doctors and psychologists

Any music affects the human body. However, the special effect is produced by Mozart’s works. Numerous studies have shown the immense influence of this composer’s music on intellectual activity. And playing music of Mozart in places of accumulation of people (streets, squares, subways, etc.) dramatically reduces the level of crime. This phenomenon is not fully understood, but it has already received the title “The Mozart Effect.”

In France, the beneficial effect of music is used in its clinical practice by doctors of various specialties. In one of the Parisian hospitals, children can listen to different music and even play musical instruments in preparation for surgery. Harmonious and soothing sounds increase the efficiency of anesthesia, and after surgery help children recover faster.

Half an hour of classical music is a must-have daily rule, according to Florida State Law No. 660, for all children in Florida. The purpose of this law is to improve the sleep mode in children, stimulating the harmonious development of their brain.

However, it has been observed that some types of music reduce intellectual activity, and even encourage violence. In one experiment, students were asked to remember 20 numbers in a calm, quiet environment. Then the subjects for some time listened to “pop music” with simple words that are easily remembered. When repeating the experiment, it turned out that the students’ brain activity was significantly reduced, and some subjects only came in an hour. Also known is the number of cases when, after musical concerts, teens went out into the street and tore everything that fell on their arm.

An interesting experiment was held in Newcastle, England. The DJs of most radio stations have replaced rock music in their playlists in the composition of the baroque genre. After some time, vandalism and assaults have fallen by half! Since then, slow music has been used in this city to improve not only criminal but also medical statistics.

In the end, we will recall the research by scientist Robert Monroe, who showed that when listening to certain melodies, a person is able to feel “phantom” oscillations. For example, if one ear hears the sound at a frequency of 150 Hz, and the other – 157 Hz, then in the brain a “phantom” sound with a difference of 7 Hz oscillation frequency is formed. This phantom sound helps improve the functioning of the brain. But at the same time, we should not forget that not all such phantom frequencies are useful for our brain. For example, frequent listening of the same type of techno-music can lead to a drop in reaction speed, lower intellectual abilities.

Sources http: //
http: // music-na-cheloveka

Unusual loudspeakers
In 2008, Chinese scientists led by Kaili Jiang in the Nano Letters magazine published the article “Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers.” They described and demonstrated a thermoacoustic film made on the basis of carbon nanotubes. Such tubes are a kind of graphene, a new material, invented only recently, for which its authors, AK Game and KS Novoselov, received the 2010 Nobel Prize. An obscure, transparent plate with human hair under a microscope looks like a dense forest. Parallel to each other on silicon “earth” grow carbon “trees”. This “forest” works as the most powerful loudspeaker. Moreover, the film does not need to pull on the frame of the speaker and you can bend..

The secret of the powerful dynamics is that the transmission of the audio signal is not due to the vibration of the film, but on a fundamentally different mechanism. The nano-fiber loudspeaker sounds thanks to the thermoacoustic effect that occurs due to temperature fluctuations. The entire electric current is fed to each process: each pulse is heated by a nanotube, and it transfers heat to the environment. Heat the air and create a sound wave.

This effect was first described by Arnold (H.D.) and Crandal (Crandall I.B.) in 1917. They described the physical parameters that should have thermoacoustic material, and derived the formula of sound pressure. But at that time, the coconut tubes were simply unknown.

Only high-tech speakers require only electrodes. Accordingly, and the speakers can be used as it pleases: put on a table, hang on the ceiling or wrap them a laptop. You can create singing curtains, diapers and flags. However, such “squatters” are suitable not only for entertainment, but also for entirely targeted use. For example, for even sounding music, it’s not necessary to place speakers around the perimeter of the halls. It is enough to hang one thermal acoustic sphere in the center (instead of a chandelier, for example).

And scientists from the University of Texas at Dallas (Dallas University) have come up with a way to use thermoacoustics for state security. According to researchers, if such material is “covered” by a submarine, it will become invisible to enemy radar.


Acoustic gun – LRAD
Early on the 5th of November, on Saturday 5th of November 2005, passengers of the cruise ship “Siborn Spirits” woke up under the noise of shots. The ship was 160 km from the Somali coast. The pirates were attacked on the liner. The attackers fired the ship and were preparing to go on board, when they responded from the liner with a gun from the acoustic gun. Confused pirates left the gun and eyed their eyes, trying to find salvation from an unknown terrible pain. Thus the crew and passengers of the liner succeeded in escaping. After this incident, world-wide trade companies literally sacked the American manufacturer of acoustic weapons orders. So the acoustic gun went through baptism and proved its effectiveness.

During the Iraq war, the LRAD system was used by the Americans as a means of deterrence, as soldiers often had to deal with angry crowds of people. An acoustic gun was also tested during the dispersal of demonstrators in Tbilisi in 2007. Nowadays, the American police use such guns to curb the participants of overly loud parties and parties, which can not be settled in another way …

The weapon, which was developed in 2000 by the American Technology Corporation, was named “LRAD” – “Long Range Acoustic Device,” ie, “Long Range Acoustic Device.” First, the gun was designed for ships, since there is almost no obstacle on the high seas that would reflect acoustic waves back – it was a danger to the ship’s team. However, over time, the scope of the use of acoustic guns was distributed to land and even to city quarters, as the police or the military were able to protect their ears in one way or another, while the crowd of rebels was not yet ready.

In the end, LRAD can be used for peaceful purposes, for example, serving as a powerful megaphone for transmitting messages at a distance of hundreds or even thousands of meters, which is very important in distress areas.

A few words about the physiological effect of an acoustic gun. At a distance of one meter, the installation can develop a sound pressure of 162 dB. For example, the sound of a fire siren is only 80-90 dB. Taking into account that the human pain threshold is 120-130 dB, such a weapon can both destroy the tympanic membranes and damage internal organs of a person. If a special way to modulate the radiating sound, you can exercise influence on the psyche of a person who feels unmotivated fear and rushes away to flee. A person who stands outside the sound beam will also experience the sound effect, but it is much smaller. In addition, operators of installations also use means of protection of own hearing.

Concerning the principle of acoustic gun, at first glance, the structure of the installation is simple: instead of one super-powerful radiating element, a large number of small piezoelectric emitters are used, which allows the output of the LRAD to receive a sharp directional sound beam. However, this simplicity is deceptive. Suffice it to say that the development of the LRAD system lasted 8 years and cost $ 40 million. With regard to the mass-dimensional indicators, the LRAD gun is a relatively compact device and has a weight of 20 kg with a diameter of the radiating disk of 83 cm.

Today Woody Norris, inventor of the acoustic gun, turned 78 years old. When asked about his motto, he likes to answer: “There is nothing that can not be improved.”


Acoustic simulation of black holes
The black hole is not really a hole. This is a massive object that has such a huge force of gravity that even the light can not escape beyond its limits.

Such a cosmic object that absorbs everything, to which it will reach its gravitational claws. The boundary to which these clauses reach are called “horizon of events”. That is, everything that crosses the horizon of events will never break its limits. So, it can be argued that the black hole is enormous