Hello! This publication is for finding and uniting like-minded people and enthusiasts in the difficult and costly business - creating a new type of acoustic devices. Namely discrete acoustic transducers.
Let us recall the recent history of technology. How electronics developed. Since the advent of the first triode vacuum tube amplifying tube in the early 20th century. And then it went and went. Radios, transmitters, amplifiers became more and more perfect. Then, in the 1950s, semiconductor devices appeared and the development of electronics accelerated even further.
Electronic devices became smaller in size and weight. Reliability and technical capabilities increased. By the late 1970s, analog electronics were very advanced. But after that, louder and louder, a new branch of electronics began to declare itself - digital electronics. Those tasks that were beyond the power of analog electronics are completely solved by the methods of digital electronics. We can safely say that with the advent of "digital" there was a powerful, qualitative breakthrough in the development of electronics, the possibilities of which are fantastic today.
The situation was approximately the same in the development of optics. Optics developed gradually. The first primitive glasses were found during excavations of the Egyptian pyramids. The submarine periscopes of World War II were, in the highest degree, the embodiment of the art of engineering in the field of optics. Everything developed linearly and measuredly. But that was before His Majesty Laser came to optics. With his appearance, as well as the methods of quantum optics, she received such a leap forward! Holography and optical methods of recording information alone evoke admiration and admiration.
But, for example, acoustics. Initially, by its nature, all its devices and methods are analog, but why is it worse than optics and electronics? There is a need for a similar leap here as well. Why are discrete, digital methods not used in acoustics?
I want to change this situation. When we talk, scream or sing, we modulate the air stream from the lungs with our vocal cords and, passing through the resonators in the oral cavity, emit sound vibrations. But at the same time, to reproduce sound through any technical devices, we often use a completely different method of obtaining sound - do we force a membrane, a string or a tuning fork to vibrate in the sound frequency range? The efficiency of devices with interruption of the air stream is obviously higher than that of devices with vibrating parts. Roughly speaking, a brass band, other things being equal, sounds louder than a string band.
The main sources of sound today are electrodynamic loudspeakers. They appeared almost simultaneously with the advent of Radio. That is, they have existed for over 100 years. Since then, their design has not fundamentally changed. In the field of a strong permanent magnet there is a coil through which an alternating current of an audio frequency flows. The coil is mechanically connected to the speaker cone. The coil vibrates - the diffuser vibrates with it - and we hear the sound. It's simple. But if the task is to increase the power of such a loudspeaker, then the designer is faced with a chain of insoluble contradictions. It is necessary to increase the power - it means you need to increase the current in the coil - therefore, a wire of a larger diameter is required. And when using a wire of a larger diameter, the mass of the coil inevitably increases.A massive coil degrades the frequency properties of an electrodynamic loudspeaker. A heavy winding cannot oscillate at a high frequency. In the chain "signal source - amplifier - acoustic system", the link "acoustic system" is the weakest. It is acoustics that most often limits the output of sound power. And what is typical for an electrodynamic loudspeaker is an extremely low efficiency of about 15%, like a steam locomotive. It is quite a feasible task for an electronic engineer to design an amplifier with an output power of 10 kW, and the corresponding electronic devices are readily available on the market. But for an acoustic engineer to design an electrodynamic loudspeaker of such power is a task from the realm of fantasy. To achieve high acoustic power, it is necessary to combine individual loudspeakers into acoustic systems.The most powerful of them are used to sound the concerts of famous rock stars. These are bulky, massive, and expensive structures that require a convoy of trucks to transport.
The attempt to create more powerful devices made acoustic engineers look towards pneumatic devices. So in the 20s of the 20th century, the pneumatic loudspeaker was invented. Pneumatic loudspeaker, acoustic emitter in which sound is created by changing (modulating) the compressed air flow. Its principle of operation is simple: Compressed air from the compressor is passed through a modulating device, in which the air flow passed through the damper. The damper, in turn, was driven by an electromagnetic system connected to the output of a relatively low-power low-frequency amplifier. The air flow rate was varied in accordance with the sound signal from the low frequency amplifier. At the output of the modulating device, air pressure fluctuations occurred, which generated sound waves.Pneumatic loudspeakers were used in the 30's and 40's. 20th century for the transmission of commands and messages in large harbors, river ports and other objects with an increased noise level. Pneumatic loudspeakers developed an acoustic power of up to 2 kW and reproduced sound vibrations with frequencies up to 2.5–3.5 kHz, with large intrinsic noise and significant nonlinear distortions. Because of these shortcomings, pneumatic loudspeakers are not used now.Because of these shortcomings, pneumatic loudspeakers are not used now.Because of these shortcomings, pneumatic loudspeakers are not used now.
But their high efficiency (about 80%) and the ability to create a huge amount of sound pressure remain indisputable; for all existing, today, loudspeakers, these figures are outrageous.
Again: Three significant disadvantages of pneumatic loudspeakers. Namely:
- High self-noise level due to air turbulence
- High level of harmonic distortion due to imperfect modulating device
- The limited frequency range due to the massiveness of the control element (damper) has led to the fact that at present these loudspeakers are only mentioned in acoustics reference books and in the Encyclopedia.
All available today designs of pneumatic loudspeakers contain one major fundamental drawback. Namely - in them, the air flow is controlled according to the same law in time as the oscillations emitted by them. All attempts to improve such loudspeakers are doomed to failure in advance.
If the above problems are solved, then it is possible to build an effective sound radiator of great power. Let us consider in more detail the disadvantages of existing pneumatic loudspeakers:
1) The high level of intrinsic noise of a pneumatic loudspeaker. The movement of the air flow through any irregularities inevitably causes all kinds of eddies and turbulence. It is impossible to silently release air through any opening.
The main way to reduce the noise from an air jet is to break it up into many small ones. Almost all exhaust silencers in pneumatic systems work according to this principle. Attempts in this way to reduce the intrinsic noise in pneumatic loudspeakers (so-called modulation gratings were made) did not have much success.
2) High level of harmonic distortion in pneumatic loudspeaker. The fact is that when an electrodynamic loudspeaker is operating, the sound pressure that it creates is directly proportional to the Ampere's force acting on its diffuser through the voice coil.
And, in turn, the Ampere force is directly proportional to the current in the coil of an electrodynamic loudspeaker. Therefore, an electrodynamic loudspeaker has a fairly low level of nonlinear distortion. The situation is completely different with a pneumatic loudspeaker. In the process of converting the energy of an air stream into the energy of sound waves, many nonlinearities arise. The main one looks like this: according to Bernoulli's law, the pressure in the air stream is inversely proportional to the square of its speed. The dependence of the air flow speed on the valve opening is also nonlinear.
3) The limited frequency range of existing designs of pneumatic loudspeakers, in my opinion, is due to the fact that with a high damage to its own noise, high-frequency sounds are masked by noise. Also, the desire of the designers of pneumatic loudspeakers to reduce their noise by crushing the air stream into many small jets, made them create bulky modulation gratings. These gratings could not vibrate at a high frequency - and this reduced the upper operating frequency of existing structures at the time.
I have been thinking about ways to improve the pneumatic loudspeaker for a long time. And now I can confidently say that there is a real opportunity to create a device free from the main shortcomings of previous similar designs. It is possible to create a device that is unique in its characteristics, significantly surpassing all existing designs. It is realistic to build a loudspeaker installation with a capacity of 10 acoustic kilowatts, with signal quality parameters commensurate with the best examples of powerful electrodynamic acoustic systems. Moreover, it turns out to be quite compact - it is quite possible to place it on a cargo, off-road vehicle chassis or on a helicopter and at the same time sound huge territories. Under favorable conditions, this loudspeaker will be heard loudly at a distance of 8 km and beyond.Potential customers of such a product are serious organizations. This is primarily the Ministry of Emergency Situations - the product can be used to organize search and rescue activities, to alert the population about special situations. Ministry of Internal Affairs - use to influence the crowd during riots on the streets. MO - propaganda in the enemy troops across the front line during the war, imitation of the noise of military equipment to misinform the enemy.
The aspect of international prestige is also important - the Russian Federation will become a country where the world's most powerful loudspeakers are being built.
Power electronics are now progressing at a tremendous rate. For some twenty years, electronic devices for controlling powerful electrical loads (electric motors, heaters, etc.) have turned from an expensive and unreliable exotic into actually working products with capacities of hundreds of kilowatts.
In all such devices - frequency converters, soft starters of electric motors, power regulators, etc., the method of pulse width modulation (PWM) is widely used. The essence of this method is quite simple - the regulating element thyristor or transistor has no intermediate states, it is either completely open or completely closed (this is extremely beneficial from an energy point of view). Closing - opening occurs with a frequency several orders of magnitude higher than the frequency of change of the controlled variable. The amount of power delivered by such a regulator is directly proportional to the open time or the open pulse width of the electronic device of the regulator.
I am confident that the pulse width modulation method can be successfully applied to a new pneumatic loudspeaker design. I propose to abandon the method of modulating the air stream with a continuous low frequency signal. It is proposed to apply the principle of pulse-width modulation - PWM in a pneumatic loudspeaker.
I suggest applying PWM to airflow control in a pneumatic loudspeaker. With PWM, the time of transient processes when opening - closing the air flow tends to zero. Accordingly, the intrinsic noise of such a loudspeaker is sharply reduced. Nonlinear distortions should also be significantly reduced, since in this case the function for air pressure waves is not the flow rate, but the time of the channel open state - and this dependence is linear.
In practice, such a loudspeaker can be realized, for example, by radically altering the long-known Seebeck siren. Or in some other way. The main thing is to be able to control the duration of the air pressure pulses in accordance with the sound vibrations. During the operation of the device, parasitic ultrasonic vibrations are inevitably formed; they can be suppressed by special acoustic low-frequency filters based on Heimholtz resonators. The capacity of the device will be limited only by the capacity of the compressor unit, the mechanical strength of the modulating device and safety for the environment.
This version of a high-power pneumatic loudspeaker has been well thought out by me and for this design I have filed a patent for invention RU No. 2 653 089.
I see it as promising, also another way to improve the design of a pneumatic loudspeaker. Namely, bandpass vocoders have long been used in speech coding technology.
In a typical band-pass vocoder, the original speech signal is analyzed by a bank of band-pass filters, typically 16-25, non-uniformly overlapping a range essential for speech perception (typically 0 to 3 kHz). Oscillations at the outputs of the bandpass filters are detected and pass through the low-pass filter, the output signals of which to one degree or another represent the envelope of the speech spectrum. The parameters characterizing the source of excitation are obtained using a tone-to-noise detector that determines whether the sound is voiced (vocal cords vibrate) or deaf. In the first case, the main tone selector determines the basic frequency of vibration of the ligaments. Sixteen channel signals, tone-to-noise signal and pitch value are encoded and transmitted over the communication channel to the receiver.
Let's assume the transmission is error free. Then the task of the receiver is reduced to speech reconstruction based on the transmitted parameters. The excitation source is either a pulse generator, the frequency of which is synchronized by a signal, or a noise generator. Depending on the tone-to-noise signal, one of them is connected to a bank of filters, identical to those of the analyzer, and excites them. The detected spectral envelope signals are used to modulate the oscillations at the outputs of the corresponding bandpass filters, thereby creating sound power in each of the frequency bands. The synthesized speech signal is obtained after the summation of all the modulated band-pass oscillations - this is, in short, the principle of the band-pass vocoder operation.
When applied to a pneumatic loudspeaker, it is quite possible to implement its operation on the principle of the receiving part of a bandpass vocoder. Namely: As a harmonic source, you can use a multifrequency, specially modified Seebeck siren. Use either a specially designed pneumatic acoustic noise generator or the same Seebeck multifrequency siren as a noise signal source. Bandpass acoustic filters can be implemented based on acoustic Heimholtz resonators. To form the desired frequency response of the filter system, you can use high-speed pneumatic valves controlled by electronics.
So, in general terms, I see the ways in which it is necessary to improve the design of a pneumatic loudspeaker.
I tried to implement my idea on my own, but immediately stopped these attempts. It turns out a very complex and expensive product - one person cannot do it. I have thought out the design to the level of flowcharts and rough sketches. I cannot calculate and bring to the level of decent drawings alone - for this I do not have enough special knowledge, effort and time. But I have a good idea of how the product will look and see in which direction the work should be done. We need persistent, purposeful research and development activities. We need a small but strong, efficient team.
Required: Practical engineer, acoustics specialist, good programmer who can write analysis programs - synthesis of sound signals, electronic circuit engineer, engineer - specialist in coding and speech recognition, mechanical engineer, specialist in the latest composite materials and you may still need people ...
I will repeat myself - the device I proposed is a rather new and complex thing. Complex because it contains both precision mechanics and smart electronics, and also has several parts that will need to be made from the latest composite materials. And like anything new, creating it will most likely have to face unforeseen difficulties. Therefore, to build a prototype, you need to carry out a complex of research and design work. Some financial and human resources will be required. I won't be able to calculate exactly how much is needed. Due to the high degree of novelty, there is a high risk of unforeseen problems during the implementation of this project. I am a lone inventor. I contacted many interested organizations, but in response either silence or condescending - approving responses. I will be sincerely glad,if among the readers of the channel there are people who manage the activities of design bureaus that develop complex, high-tech electronic and mechanical products, aerospace, or close to this, profile. And they will be interested in this direction. This topicmy site is also dedicated .
Best regards, Igor Zharikov pentagrid88@yandex.ru