DBA decryption. Permissible noise standards in the apartment

Chapter from the book "Noise" by the English engineer Rupert Taylor, R. Taylor "Noise"

Nowadays, everyone has already heard something about "decibels", but almost no one knows what it is. The decibel seems to be something like the acoustic equivalent of a "candle" - a unit of luminous intensity - and seems to be associated with the ringing of bells (bell - translated from English means a bell). However, this is not at all the case: the decibel got its name in honor of Alexander Graham Bell - the inventor of the telephone.

The decibel is not only not a unit of measurement of sound, it is not a unit of measurement at all, at least in the sense of, for example, volts, meters, grams, etc. done in volts. Apparently, all this sounds a little strange, so let's try to provide an explanation. Probably no one will be surprised if I say that the distance from London to Inverness is twenty times the distance from my house to London. I can express any distance by comparing it to the distance from my home to London, say, to Piccadilly Circus The distance from London to John-o 'Trots is twenty-six times that last distance, and Australia is 500 times. does not mean that Australia is 500 units away from anything. All numbers are only ratios.

One of the measurable characteristics of sound is the amount of energy it contains; the intensity of sound at any point can be measured as the flow of energy per unit area, and expressed, for example, in watts per square meter (W / m 2). When trying to write in these units, the intensity of ordinary noise immediately becomes difficult, since the intensity of the quietest sound available to a person with the sharpest hearing is approximately 0.000 000 000 001 W / m 2. One of the loudest sounds, which we encounter, not without the risk of harmful consequences, is the noise of a jet plane flying at a distance of about 50 m. Its intensity is about 10 W / m2. And at a distance of 100 m from the launch site of the Saturn rocket, the sound intensity noticeably exceeds 1000 W / m 2. Obviously, it is very difficult to operate with numbers expressing sound intensities lying in such a wide range, regardless of whether we represent them in units of energy or even in the form of ratios. There is a simple, although not entirely obvious, way out of this difficulty. The intensity of the faintest audible sound is 0.000 000 000 001 W / m 2. Mathematicians would prefer to write this number in this way: 10 -12 W / m2. If someone is not accustomed to such a notation, recall that 10 2 is 10 squared, or 100, and 10 3 is 10 squared, or 1000. Similarly, 10 -2 means 1/10 2, or 1/100, or 0, 01, and 10 -3 is 1/10 3, or 0.001. Multiplying any number by 10 x means multiplying x times by 10.

Trying to find the most convenient way of expressing the intensities of sound, let's try to represent them in the form of ratios, taking the value of 10 -12 W / m2 as the reference intensity. In this case, we will note how many times the reference intensity must be multiplied by 10 in order to obtain a given sound intensity. For example, the noise of a jet plane is 10,000,000,000,000 (or 10 13) times higher than our standard, that is, this standard must be multiplied 13 times by 10. This way of expression can significantly reduce the values ​​of numbers expressing a gigantic range of sound intensities; if we denote a one-fold increase of 10 times as 1 bel, then we get "one" for expressing the relationship. Thus, the noise level of a jet plane corresponds to 13 bels. Bel turns out to be too big; it is more convenient to use smaller units, tenths of bel, which are called decibels. Thus, the noise intensity of a jet engine is 130 decibels (130 dB), but in order to avoid confusion with any other sound intensity standard, it should be stated that 130 dB is defined relative to a reference level of 10 -12 W / m 2.

If the ratio of the intensity of a given sound to the reference intensity is expressed by some less round number, for example 8300, the conversion to decibels will not be so easy. Obviously, the number of multiplications by 10 will be more than 3 and less than 4, but time-consuming calculations are required to accurately determine this number. How to get around this difficulty? It turns out to be quite simple, since all ratios expressed in units of "tenfold increases" have long been calculated - these are logarithms.

Any number can be represented as 10 to some extent: 100 is 10 2 and therefore 2 is the logarithm of 100 to base 10; 3 is the logarithm of 1000 base 10 and, less obviously, 3.9191 is the logarithm of 8300. There is no need to repeat "base 10" all the time, because 10 is the most common base of the logarithm, and if there is no other indication, this is what is meant base. In formulas, this value is written as log10 or lg.

Using the definition of a decibel, we can now write down the level of sound intensity in the form:

For example, with a sound intensity of 0.26 (2.6 × 10 -1) W / m 2, the intensity level in dB relative to the reference 10 -12 W / m 2 is

But the logarithm of 2.6 is 0.415; hence the final answer looks like this:

10 x 11.415 = 114 dB(accurate to 1 dB)

It should not be forgotten that decibels are not units of measurement in the sense of the word, such as, for example, volts or ohms, and that accordingly they have to be handled differently. If two batteries of 6 V (volts) are connected in series, then the potential difference at the ends of the circuit will be 12 V. What happens if you add 80 dB to the noise of 80 dB? Noise with a total intensity of 160 dB? Not at all - after all, when the number is doubled, its logarithm increases by 0.3 (with an accuracy of two decimal places). Then, when the sound intensity is doubled, the intensity level increases by 0.3 bela, that is, by 3 dB. This is true for any intensity level: doubling the sound intensity increases the intensity level by 3 dB. Table 1 shows how the intensity level, expressed in decibels, increases when sounds of different intensities are added.

Table No. 1

Now that we have solved the mystery of the decibel, here are some examples.

Noise level in decibels

Table 2 is a list of typical noises and their intensity levels in decibels.

Table No. 2

How can the intensity of a given sound be determined? This is a rather difficult task; it is much easier to measure pressure fluctuations in sound waves. Table 3 shows the sound pressure values ​​for sounds of different intensities. It can be seen from this table that the range of sound pressures is not as wide as the range of intensities: the pressure rises twice as slowly as the intensity. When the sound pressure is doubled, the energy of the sound wave must quadruple - then the speed of the particles of the medium will correspondingly increase. Therefore, if we measure the sound pressure, as well as the intensity, on a logarithmic scale and, in addition, we introduce a factor of 2, we get the same values ​​for the intensity level. For example, the sound pressure of the weakest audible sound is approximately 0.00002 N (Newton) / m2, and in the cabin of a diesel truck it is 2 N / m2, therefore, the noise intensity level in the cabin is

Table No. 3

When expressing the sound pressure level in decibels, remember that when the pressure is doubled, 6 dB is added. If the noise in the cabin of a diesel truck reaches 106 dB, the sound pressure doubles to 4 N / m 2, and the intensity quadruples and reaches 0.04 W / m 2.

We talked a lot about the measure of sound intensity, but did not touch on practical methods of measuring this quantity at all. The measurable characteristics of a sound wave include intensity, pressure, velocity, and particle displacement. All these characteristics are directly related to each other, and if it is possible to measure at least one of them, the rest can be calculated.

It is not difficult to see or feel the vibration of light objects caught in the path of the sound wave. The principle of operation of an oscilloscope - the oldest type of sound level meter - is based on this phenomenon. The oscilloscope consists of a diaphragm, to the center of which a thin thread is attached, a mechanical system to amplify the vibrations, and a pen that records the displacements of the diaphragm on paper tape. Such recordings are reminiscent of the "wavy lines" we talked about in the previous chapter.

This device was extremely insensitive and was only suitable for confirming the acoustic theories of scientists of that time. The inertia of the mechanical parts extremely limited the frequency response and accuracy of the instrument. Replacing the mechanical amplifier with an optical system and the use of a photographic method of recording signals made it possible to significantly reduce the inertia of the device. In the device improved in this way, the diaphragm thread was wound on a rotating drum fixed on an axis to which a mirror was attached, rotating with the drum. A ray of light fell on the mirror; when the mirror was turned in one direction or the other, which occurred as a result of membrane vibrations, the beam was deflected, and these deviations could be recorded on light-sensitive paper. It was only with the development of electronics that more or less accurate measuring instruments were developed, and in order to design a modern portable sound level meter, it was necessary to wait for the invention of transistors.

In essence, a modern sound level meter is an electronic analogue of an old mechanical device. The first step in the measurement process is the conversion of sound pressure into changes in electrical voltage; this conversion produces a microphone. Currently, microphones of various types are used in such devices: condenser, with a moving coil, crystal, ribbon, with a heated wire, with Rochelle salt - this is only a small part of all types of microphones. In our book, we will not consider the principles of their operation.

All microphones perform the same basic function, and most are equipped with a membrane, of one kind or another, which is vibrated by pressure changes in the sound wave. Diaphragm displacements cause corresponding voltage changes at the microphone terminals. The next step in the measurement is amplification, and then rectification of the alternating current and the final operation is to apply a signal to a voltmeter calibrated in decibels. In most of these devices, the voltmeter measures not the maximum, but the "rms values" of the signal, that is, the result of a certain type of averaging, which is used more often than the maximum values.

An ordinary voltmeter cannot cover a huge range of sound pressures, and therefore, in the part of the device where the signal is amplified, there are several circuits that differ in amplification by 10 dB, which can be switched on sequentially one after the other. However, an improved model of the old oscilloscope is still widely used. In an electron-beam oscilloscope, the problem of inertia inherent in a mechanical oscilloscope is completely eliminated, since the mass of the electron beam is negligible, and it is easily deflected by the electromagnetic field and draws on the screen a waveform of voltage fluctuations applied to the device.

The resulting oscillographic record is used for mathematical analysis of the sound waveform. Oscilloscopes are also extremely useful for measuring impulse noise. As we said, a conventional sound level meter continuously measures the rms values ​​of the signal. But, for example, a sonic clap or a gun shot do not generate continuous noise, but create a single, very powerful, sometimes dangerous to the ear pressure impulse, which is accompanied by gradually damping pressure fluctuations (Fig. 13). The initial pressure surge can damage hearing or break window glass, but since it is single and short-lived, the rms value will not be typical for it and can only lead to misunderstandings. Although there are special sound level meters for measuring impulse sounds, most of them will not be able to register the full RMS value of the impulse simply because they do not have time to trigger. This is where the oscilloscope demonstrates its benefits by instantly plotting an accurate pressure rise curve so that the maximum pulse pressure can be measured directly on the screen.

Rice. 13. Typical impulse noise

Perhaps one of the most significant issues in acoustics is the dependence of the behavior of sound on its frequency. The lower frequency limit of human perception of sound is about 30 Hz, and the upper one is not higher than 18 kHz; therefore, the sound level meter would have to register sounds in the same frequency range. But here a serious difficulty arises. As we will see in the next chapter, the sensitivity of the human ear for different frequencies is far from the same; so, for example, for sounds with a frequency of 30 Hz and 1 kHz to sound equally loud, the sound pressure level of the first of them should be 40 dB higher than the second. And therefore, the readings of the sound level meter by themselves are not yet worth much.

This problem was dealt with by electronics specialists, and modern sound level meters are equipped with corrective circuits consisting of separate chains, which can be connected to reduce the sensitivity of the sound level meter to low-frequency and very high-frequency sounds and thereby bring the frequency characteristics of the device closer to the properties of the human ear. Usually the sound level meter contains three correction loops, designated A, B and C; correction A is most useful; correction B is used only occasionally; Correction C has little effect on the sensitivity in the range of 31.5 Hz - 8 kHz. Some types of sound level meters also use the D correction, which allows you to read the instrument readings directly in PN dB units, used to measure aircraft noise. Calculating PN dB accurately is difficult, but for high noise levels the level in PN dB is equal to the level in dB measured by a D-weighted sound level meter plus 7 dB; in most cases, jet noise, expressed in PN dB, is approximately the same as the A-weighted sound level meter plus 13 dB.

Nowadays, almost everywhere, the noise level is taken equal to the level measured in dB using a sound level meter with correction A, and is expressed in units of dBA. Although the human ear perceives sound incomparably more subtly than a sound level meter, and therefore the sound levels expressed in dBA in no way correspond exactly to the physiological response, the simplicity of this unit makes it extremely convenient for practical use.

The most important disadvantage of measuring loudness in dBA is that our response to low-frequency sounds is underestimated and the increased sensitivity of the ear to the loudness of pure tones is completely neglected.

One of the advantages of the dBA scale is, in particular, the fact that here, as we will see in the next chapter, doubling the loudness roughly corresponds to an increase in the noise level by 10 dBA. However, even this scale gives no more than a rough indication of the role of the frequency composition of noise, and since this characteristic of noise is often extremely important, the results of measurements carried out with the help of a sound level meter have to be supplemented with data obtained using other devices.

Frequencies, like intensities, are measured on a logarithmic scale, based on the steps of doubling the number of oscillations per second. Since, however, the range of frequencies is less wide than the range of intensities, the number of tenfold increases is not counted, decimal logarithms are not used, and the frequencies of sound are always expressed in the number of vibrations, or cycles per second. The unit of frequency is one vibration per second, or 1 hertz (Hz). Determining the sound intensity for each frequency would require an infinite number of measurements. Therefore, as in musical practice, the whole range is divided by octaves. The highest frequency in each octave is twice the lowest. The first, the simplest stage of frequency analysis of sound - measuring the sound pressure level within each of 8 or 11 octaves, depending on the frequency range of interest to us; when measuring, the signal from the output of the sound level meter goes to a set of octave filters, or to an octave band-pass analyzer. The word "band" refers to a particular section of the frequency spectrum. The analyzer contains 8 or 11 electronic filters. These devices pass only those frequency components of the signal that lie within their bandwidth. By switching on the filters one at a time, you can sequentially measure the sound pressure level in each band directly using a sound level meter. But in many cases even octave analyzers do not give sufficient information about the signal, and then they resort to more detailed analysis, applying filters of half or one third of an octave. To obtain even more detailed analysis, narrow-band analyzers are used, which "cut" the noise into bands of constant relative width, for example, 6% of the center frequency of the band, or into bands with a width of a certain number of hertz, for example 10 or 6 Hz. If there are pure tones in the noise spectrum, which is often the case, their frequency and amplitude can be accurately determined using a discrete frequency analyzer.

Usually, sound-analyzing equipment is very cumbersome, and therefore its use is limited to the framework of laboratories. Quite often, the sound to be examined is recorded on a high-quality portable tape recorder through the microphone and amplifying circuits of the sound level meter, using test signals for calibration; then the recording is played back in the laboratory, sending a signal to the analyzer, which automatically traces the frequency spectrum on paper tape. In fig. 14 shows the spectra of typical noise obtained using octave, one-third octave and narrowband (6 Hz bandwidth) analyzers.

Rice. 14. Analysis of sound using octave and one-third octave filters and a filter with a bandwidth of 6 Hz.

However, in order to measure noise, it is not enough to know the volume level and frequency of the sound. If we talk about environmental noise, then it consists of many separate noises of various origins: these are the noises of traffic, aircraft, industrial noises, as well as noises arising from other types of human activities. If you try to measure the noise level on the street with a conventional sound level meter, it turns out that this is an extremely difficult task: the sound level meter needle will continuously fluctuate over a very wide range. What should be taken as the noise level? Maximum countdown? No, this figure is too high and not indicative. Average level? This would be possible, but it is extremely difficult to estimate the average value for a certain period of time, and in order to keep the arrow within the scale, you will have to continuously change the amplification steps of the sound level meter.

Table No. 4

There are two generally accepted methods of accounting for fluctuations in the noise level, allowing this level to be expressed numerically. The first method uses a so-called statistical distribution analyzer. This device records the relative fraction of the time during which the measured noise level is within each of the scale steps located, for example, every 5 dB. The results of these measurements indicate for what fraction of the total time each of the sound levels was exceeded. By plotting the numbers presented in table. 4, by connecting the dots with a smooth line and setting the levels that were exceeded for 1, 10, 50, 90 and 99% of the time, we can give a satisfactory description of the "noise climate". The indicated levels are indicated as L1, L10, L50, L90 and L99. L1 gives an idea of ​​the maximum value of the noise level, L10 is a characteristic high level, while L90, as it were, shows the background noise, that is, the level to which the noise decreases when a temporary calm occurs. Of great interest is the difference between L10 and L90; it indicates the extent to which the noise level varies in each given place, and the greater the fluctuations in the noise, the stronger its irritating effect. However, L10 itself is a good indicator of traffic noise disturbance; this indicator is widely used in measuring and forecasting traffic noise, and, taking into account it, determine the amount of state compensation for victims of noise from new highways and roads (see Chapter 11). So L10 is the sound level, expressed in dBA, that is exceeded for exactly ten percent of the total measurement time.

Usually, traffic noise fluctuates in a quite definite way, so the L10 level serves as an independent fairly satisfactory indicator of noise, although it only partially represents the statistical picture of noise. If the noise changes randomly, as, for example, it happens when railway, industrial and sometimes aircraft noise is superimposed on each other, the distribution of noise levels fluctuates greatly from point to point. In such cases, it is also advisable to express all statistics in one number. Attempts have been made to devise a formula that includes the entire noise pattern, including the amplitude of the noise fluctuations. These indicators include the "traffic noise index" and "noise pollution level", but the most common indicator is a special kind of average value, denoted Leq. It characterizes the average value of the sound energy (as opposed to arithmetic averaging of levels expressed in dB); sometimes Leqv is called the equivalent continuous noise level, because numerically this value corresponds to the level of such a strictly stable noise at which the microphone would receive the same total amount of energy over the entire measurement period as it receives for all the irregularities, bursts and surges of the measured fluctuating noise. In the simplest case, Leq will be, for example, 90 dBA, if the noise level was always equal to 90 dBA, or if half of the measurement time the noise was 93 dBA, and the rest of the time was completely absent. Indeed, since doubling the intensity or energy of the noise leads to an increase in its level by 3 dB, in order to keep the total amount of energy constant when doubling the noise intensity, the time of its action should be halved. Similarly, we obtain the same value Leq = 90 dBA at a noise level of 100 dBA if it acts for one tenth of the same period of time. Measurement of electricity consumption using an electric meter is performed in the same way. In practice, periods of constant noise level and periods of its complete absence are not common, and therefore it is rather difficult to calculate Leq. This is where distribution tables like tabular come to the rescue. 4, or specially designed automatic counters. The Leq index has two disadvantages: when averaged, short bursts of high-level noise contribute more than periods of low-level noise; in addition, an increase in the number of maxima has little effect on the Leq value. For example, if averaging noise from 100 trains per day results in an equivalent level Leq = 65 dBA, then when the number of trains doubles, Leq increases by only 3 dBA. In order for the Leq value to increase in the same way as when the loudness was doubled (that is, when the level was increased by 10 dBA) of the noise generated by each of the trains, their number would have to be increased 10 times. And yet, despite some inferiority, the Leq scale is the best universal measure of noise from all currently available. In England, it will gradually gain the same distribution as it has on the continent. It is now being used in England to measure the dose of noise received by people employed in industry.

Another measure is also used, which is essentially much more similar to Leq than it might seem at first glance: this is the normalization noise index, unfortunately all too familiar to those who live near large airports. The scale of normalization noise indices is used to characterize the average maximum noise levels of aircraft, expressed in PN dB (the so-called "perceived sound level", see Acoustic Dictionary), and since it starts from 80 PN dB (about 67 dBA), the value 80 is subtracted from the average maximum level. Theoretically, if only one aircraft produces noise during the measurement, the value of this index will be exactly equal to the average maximum level in PN dB minus 80. For each doubling of the number of aircraft, 4.5 units should be added to this number, and not 3, as for the Leq scale. Although the formula for this index looks somewhat startling, we were able to describe it in full above. If the individual peak noise levels of aircraft differ by only a few dB, the average can be calculated arithmetically. Otherwise, the values ​​of the noise level, expressed in dB, will have to be converted back to the values ​​of intensity, and here you will need a table of logarithms and a bright head!

There are many other measures, scales and indices for measuring noise, including backgrounds, sones, noes, various derivatives of PN dB and a number of other criteria, not counting all international variants of the scale of normalization indices of noise. There is no need to deal with the description of other units and indicators. It should be noted that in the USA, the Leqv indicator is adopted to measure noise in the workplace, but when the time of exposure to noise is doubled, it does not add 3 dB to its value, as in Europe, but 5 dB. Otherwise, the indicators dBA, L10 and Leq are applied in the same way all over the world.

Excessive noise isn't just bad for your hearing. According to the WHO, about 2% of all deaths in the world are caused by diseases associated with excessive noise.

Modern medicine considers loud sounds to be one of the formidable enemies of human health. In ecology, there is even the concept of "noise pollution". In addition to hearing disorders, cardiovascular diseases and hypertension may occur. The metabolism, the activity of the thyroid gland and the brain are disturbed. Reduced memory, performance. From noise stress insomnia appears, appetite disappears. High noise levels can cause peptic ulcer disease, gastritis, and mental illness.

Noise through the pathways of the sound analyzer affects various centers of the brain, as a result of which the work of various body systems is disrupted. According to the Austrian scientist Griffith, noise causes premature aging in 30 cases out of 100 and shortens the life of people in large cities by 8-12 years. WHO experts consider sound 85 dB safe for health, acting on a person every day for no more than 8 hours.

25-30 decibels

T Which noise level is considered comfortable for humans. This is a natural sound background, without which life is impossible.

By the way…

In terms of loudness, this is comparable to the rustle of leaves on trees - 5-10 dB, wind noise - 10-20 dB, whispering - 30-40 dB. And also with cooking on the stove - 35-42 dB, filling the bath - 36-58 dB, elevator movement - 34-42 dB, refrigerator noise - 42 dB, air conditioner - 45 dB.

The house shouldn't be too quiet. When there is deathly silence around, we subconsciously experience anxiety. The noise of the rain, the rustle of foliage, the chime of the bells hanging in the doorway, the ticking of the clock have a pacifying effect on us and even have a healing effect.

We used to think that silence is the absence of sounds, but as it turned out, our brain clearly hears it and perceives it in the same way as other sounds. This was found by scientists from the University of Oregon in the United States.

60-80 decibels

Such noise, acting regularly, causes disorders of the autonomic nervous system in a person and is tiring even with short exposure.

By the way…

Large store - 60 dB, washing machine - 68 dB, vacuum cleaner - 70 dB, playing the piano - 80 dB, crying - 78 dB, car - up to 80 dB.

The noise level is perceived subjectively, addiction is possible. But in relation to developing vegetative reactions, adaptation is not observed.

Continuous traffic noise (65 dB) leads to hearing loss. Street noise disrupts the hearing center in the brain and negatively affects behavior. This conclusion was made by scientists from the University of California at San Francisco.

90-110 decibels

The sound is perceived as excruciating. Leads to hearing loss. With an intense noise exposure of 95 dB and above, a violation of vitamin, carbohydrate, protein, cholesterol and water-salt metabolism is possible. At a sound power of 110 dB, the so-called "noise intoxication" occurs, and aggression develops.

By the way…

Motorcycle, truck engine and Niagara Falls - 90 dB, apartment redevelopment - 90-100 dB, lawn mower - 100 dB, concert and disco - 110-120 dB.

According to GOSTs, production with such a noise level is harmful, employees must regularly undergo medical examinations. People working in such conditions are 2 times more likely to suffer from hypertension. Workers in noisy professions are advised to take vitamins of group B and C.

If the player is turned on at full power, then the ears are affected by the sound of about 110 dB. The risk of developing hearing loss (deafness) is high.

115-120 decibels

This is the "pain threshold", when the sound as such is practically not heard anymore, the pain in the ears is felt.

By the way…

The leaders in creating this noise are airports and train stations. The volume of a freight train when driving is more than 100 dB. When the train approaches the platform, the noise level on the platform is slightly less - 95 dB. Even a kilometer from the runway, the noise level from a liner taking off or landing is more than 100 dB.

The noise level in the metro can reach 110 dB at stations and 80-90 dB in carriages.

Don't get too carried away with karaoke. At the same time, the acoustic load level exceeds the permissible limits, reaching 115 dB. After such extreme vocals, hearing is temporarily reduced by 8 dB.

140-150 decibels

The noise is practically intolerable, loss of consciousness is possible, eardrums can burst.

By the way…

When starting jet engines of aircraft, the noise level fluctuates from 120 to 140 dB, the noise of a working drill is 140 dB, the launch of a rocket is 145 dB, a salute salute, a rock concert next to a huge powerful speaker, a car with a "punctured" silencer is 120-150 dB ...

180 decibels or more

Fatal to humans. Even metal begins to deteriorate.

By the way…

The shock wave from a supersonic aircraft is 160 dB, a shot from a 122 mm howitzer is 183 dB, a powerful volcano explosion is 180 dB.

According to research by American experts, the loudest sound in the animal kingdom is emitted by a blue whale - 189 dB.

Big city problems

According to experts, up to 70% of Moscow's territory is subject to excessive noise from various sources. The magnitude of the excess reaches the following values:

• 20-25 dB - near highways;
• up to 30-35 dB - for apartments in houses facing large highways (without soundproof glazing);
• up to 10-20 dB - near railways;
• up to 8-10 dB - in areas subject to periodic exposure to aircraft noise;
• up to 30 dB - in case of non-compliance with the established requirements for the conduct of construction work at night.

I can not hear

The human ear can only hear vibrations, the frequency of which ranges from 16 to 20,000 Hz. Oscillations with a frequency of up to 16 Hz are called infrasound, more than 20,000 Hz - ultrasound, and the human ear does not perceive them. The ear's highest sensitivity to sounds is in the frequency range 1000-4000 Hz. The higher the tonality of a sound or noise, the stronger its adverse effect on the organ of hearing. Infra and ultrasound can be harmful to human health. However, the degree of their influence depends on the frequency and time of exposure.

Let me sleep!

The sensitivity of hearing during sleep increases by 10-14 dB. According to WHO guidelines, cardiovascular disease can occur if a person is constantly exposed to noise levels of 50 dB or higher at night. To get insomnia, 42 dB of noise is enough, to just get irritable - 35 dB.

In the last article, we touched on the topic of cleaning the ears with cotton swabs. It turned out that, despite the prevalence of such a procedure, self-cleaning of the ears can lead to perforation (rupture) of the tympanic membrane and a significant decrease in hearing, up to complete deafness. However, improper ear cleaning is not the only thing that can ruin our hearing. Excessive noise exceeding health standards, as well as barotrauma (injury due to pressure drop) can also lead to hearing loss.

To have an idea of ​​the danger that noise poses to hearing, you need to familiarize yourself with the permissible noise standards for different times of the day, as well as find out what level of noise in decibels certain sounds produce. In this way, you can begin to understand what is safe for hearing and what is dangerous. And with understanding, the ability to avoid the harmful effects of sound on the ear will come.

According to sanitary standards, the permissible noise level, which does not harm hearing even with prolonged exposure to the hearing aid, is considered to be 55 decibels (dB) in the daytime and 40 decibels (dB) at night. These values ​​are normal for our ear, but, unfortunately, they are very often violated, especially within large cities.

Noise level in decibels (dB)

Indeed, the normal noise level is often significantly exceeded. Here are examples of just some of the sounds that we encounter in our life and how many decibels (dB) these sounds actually contain:

• Spoken speech ranges from 45 decibels (dB) to 60 decibels (dB), depending on the volume of the voice;
• Car horn reaches 120 decibels (dB);
• Heavy traffic noise - up to 80 decibels (dB);
• Baby crying - 80 decibels (dB);
• The noise of a variety of office equipment, vacuum cleaner - 80 decibels (dB);
• Noise of a running motorcycle, trains - 90 decibels (dB);
• Nightclub Dance Music Sound - 110 decibels (dB);
• Airplane noise - 140 decibels (dB);
• Renovation noise - up to 100 decibels (dB);
• Cooking on the stove - 40 decibels (dB);
• Forest noise 10 to 24 decibels (dB);
• The level of noise that is lethal for a person, the sound of an explosion is 200 decibels (dB).

As you can see, most of the noises that we encounter literally every day are significantly higher than the acceptable threshold of the norm. And these are just natural noises that we cannot do anything about. But there is also the noise from the TV, loud music, which we ourselves expose our hearing aids to. And with our own hands we inflict great harm on our hearing.

What level of noise is harmful?

If the noise level reaches 70-90 decibels (dB) and continues for quite a long time, then such noise with prolonged exposure can lead to diseases of the central nervous system. And prolonged exposure to noise levels of more than 100 decibels (dB) can lead to significant hearing loss, up to complete deafness. Therefore, we get much more harm from loud music than pleasure and benefit.

What happens to hearing when exposed to noise?

Aggressive and prolonged noise exposure to the hearing aid can lead to perforation (rupture) of the tympanic membrane. The consequence of this is hearing loss and, as an extreme case, complete deafness. Although a perforation (rupture) of the tympanic membrane is a reversible disease (i.e., the tympanic membrane can heal), the recovery process is long and depends on the severity of the perforation. In any case, the treatment of perforation of the tympanic membrane takes place under the supervision of a physician, who chooses a treatment regimen after examination.

The physical characteristic of sound loudness is the sound pressure level, in decibels (dB). "Noise" is a disorderly mixture of sounds.

The maximum permissible sound levels (LAmax, dBA) are 15 decibels more than "normal" ones. For example, for living rooms of apartments, the permissible constant sound level in the daytime is 40 decibels, and the temporary maximum is 55.

Inaudible noise - sounds with frequencies less than 16-20 Hz (infrasound) and more than 20 kHz (ultrasound). Low-frequency vibrations of 5-10 hertz can cause resonance, vibration of internal organs and affect the functioning of the brain. Low-frequency acoustic vibrations increase aching pain in bones and joints in sick people. Sources of infrasound: cars, wagons, thunder from lightning, etc. High-frequency vibrations cause tissue heating. The effect depends on the strength of the sound, the location and properties of its sources.

Powerful fans can make a lot of noise in bakeries, mills and other enterprises where an exhaust hood is used, and the wind blows from their side - it increases the propagation range in waves. A possible cause of their noise is improper installation and the design itself, broken bearings, misalignment, elementary wear and tear of equipment. You can be fined for this.

High-frequency sound and ultrasound with a frequency of 20-50 kilohertz, modulated by several hertz, are used to scare away birds from airfields, animals (dogs, for example) and insects (mosquitoes, midges).

At workplaces, the maximum permissible equivalent sound levels for intermittent noise: the maximum sound level should not exceed 110 dBA, and for impulse noise - 125 dBAI. Even a short stay in areas with sound pressure levels exceeding 135 dB in any octave band is prohibited.

The noise emitted by a computer, printer and fax in a room without sound-absorbing materials - can exceed the level of 70 db. Therefore, it is not recommended to place a lot of office equipment in one room. Equipment that is too noisy should be removed outside the premises where the workplaces are located.

You can reduce the noise level if you use sound-absorbing materials as decoration of the room and curtains made of thick fabric. Anti-noise earbuds will also help.

When erecting buildings and structures, in accordance with modern, more stringent sound insulation requirements, technologies and materials must be used that can provide reliable protection against noise.

For fire alarm: the sound pressure level of the useful audio signal provided by the siren must be at least 75 dBA at a distance of 3 m from the siren and not more than 120 dba at any point in the protected area (clause 3.14 of NPB 104-03).

A siren of high power and a ship's howler - pressures more than 120-130 decibels.

Special signals (sirens and "crackers" - Air Horn) installed on service vehicles are regulated by GOST R 50574 - 2002. Sound pressure level of the signaling device when a special sound is applied. signal, at a distance of 2 meters along the horn axis, must be at least:

116 dB (A) - when installing a sound emitter on the roof of a vehicle;

122 dBA - when installing the beam in the engine compartment of the vehicle.

Changes to the fundamental frequency should be between 150 and 2000 Hz. The duration of the cycle is from 0.5 to 6.0 s.

The horn of a civil car, according to GOST R 41.28-99 and UNECE Regulation No. 28, must emit a continuous and monotonous sound with an acoustic pressure level of no more than 118 decibels. This order is the maximum permissible values ​​- and for car alarms.

If a city dweller, accustomed to constant noise, finds himself in complete silence for a while (in a dry cave, for example, where the noise level is less than 20 db), then he may well experience depressive states instead of rest.

The device is a noise meter for measuring the level of sound, noise.

To measure the noise level, a sound level meter is used, which is produced in different modifications: household (approximate price - 3-4 thousand rubles, measurement ranges: 30-130 dB, 31, 5 Hz - 8 kHz, filters A and C), industrial ( integrating, etc.) The most common models: SL, octave, svan. Wide-range sound level meters are used to measure infrasonic and ultrasonic noise.

Low and high pitched sounds appear quieter than midrange sounds of the same intensity. Taking this into account, the uneven sensitivity of the human ear to sounds of different frequencies is modulated with the help of a special electronic frequency filter, obtaining, as a result of normalization of measurements, the so-called equivalent (in energy, "weighted") sound level with the dimension dBA (dB (A), then yes - with filter "A").

A person can hear sounds with a volume of 10-15 dB and above. The maximum frequency range for the human ear is 20 to 20,000 Hz. Better audible sound with a frequency of 2-3 kHz (common in telephones and on the radio on the MW and LW ranges). With age, the audible range of sounds narrows, especially for high-frequency sounds, decreasing to 18 kilohertz or less.

In the absence of sound-absorbing materials (carpets, special coatings) on the walls of the premises, the sound will be louder due to multiple reflections (reverberation, that is, echoes from walls, ceilings and furniture), which will increase the noise level by several decibels.

Noise scale (sound levels, decibels), in the table

Sound volume - noise level.

WHO experts consider sound 85 dB safe for health, acting on a person every day for no more than 8 hours. 25-30 decibels This level of noise is considered comfortable for humans. This is a natural sound background, without which life is impossible. By the way ... In terms of volume, this is comparable to the rustle of leaves on trees - 5–10 dB, wind noise - 10–20 dB, whispering - 30–40 dB. And also with cooking on the stove - 35–42 dB, filling the bath - 36–58 dB, elevator movement - 34–42 dB, refrigerator noise - 42 dB, air conditioner - 45 dB. The house shouldn't be too quiet. When there is deathly silence around, we subconsciously experience anxiety. The noise of the rain, the rustle of leaves, the ringing of bells hanging in the doorway, the ticking of a clock have a pacifying effect on us and even have a healing effect.

A collection of answers to your questions

If during a thunderstorm you saw a strong lightning and after 12 seconds heard the first thunderclaps, this means that the lightning struck four kilometers from you (340 * 12 = 4080 m.) In approximate calculations, it is accepted - three seconds per kilometer of distance ( in airspace) to the sound source. The line of propagation of sound waves deviates in the direction of decreasing the speed of sound (refraction on the temperature gradient), that is, on a sunny day, when the air at the surface of the earth is warmer than the overlying one - the line of propagation of sound waves bends upward, but if the upper layer of the atmosphere turns out to be warmer than the surface layer, then the sound will go back down from there and it will be heard better. Diffraction of sound - wave bending around an obstacle when its size is comparable to the wavelength or less.

Noise pollution: how to protect yourself?

For the octahertz frequency, these emitting points are located on the opposite side of the globe, from the source of the electromagnet. waves. At 14 hertz - along the triangle. Local, highly ionized regions in the lower layers of the ionosphere (sporadic layer Es) and plasma reflectors - can be interconnected or spatially coincide. How to preserve your hearing Prolonged exposure to noise with a level of more than 80-90 decibels can lead to partial or complete hearing loss (at concerts, the power of acoustic systems can reach tens of kilowatts).
Also, in this case, pathological changes can occur in the cardiovascular and nervous system. Only sounds with a volume of up to 35 dB are safe. The reaction to prolonged and strong noise exposure is "tinnitus" - ringing in the ears, "noise in the head", which can develop into progressive hearing loss.

Noise level.

Modern medicine considers loud sounds to be one of the formidable enemies of human health. In ecology, there is even the concept of "noise pollution". In addition to hearing disorders, cardiovascular diseases and hypertension may occur.

The metabolism, the activity of the thyroid gland and the brain are disturbed. Reduced memory, performance. From noise stress insomnia appears, appetite disappears. High noise levels can cause peptic ulcer disease, gastritis, and mental illness.

Noise through the pathways of the sound analyzer affects various centers of the brain, as a result of which the work of various body systems is disrupted. According to the Austrian scientist Griffith, noise causes premature aging in 30 cases out of 100 and shortens the life of people in large cities by 8-12 years.

Noise norm in decibels in the apartment

The sound is perceived as excruciating. Leads to hearing loss. With an intense noise exposure of 95 dB and above, a violation of vitamin, carbohydrate, protein, cholesterol and water-salt metabolism is possible. At a sound power of 110 dB, the so-called "noise intoxication" occurs, and aggression develops.
By the way ... Motorcycle, truck engine and Niagara Falls - 90 dB, redevelopment in the apartment - 90–100 dB, lawn mower - 100 dB, concert and disco - 110–120 dB. According to GOSTs, production with such a noise level is harmful, employees must regularly undergo medical examinations. People working in such conditions are 2 times more likely to suffer from hypertension.

Workers of noisy professions are advised to take vitamins of group B and C. If the player is turned on at full power, then the sound affects the ears of about 110 dB. The risk of developing hearing loss (deafness) is high.

In the "household" may come in handy

This is the "pain threshold", when the sound as such is practically not heard anymore, the pain in the ears is felt. By the way ... Leaders in creating such noise are airports and train stations. The volume of a freight train when driving is more than 100 dB.

When the train approaches the platform, the noise level on the platform is slightly less - 95 dB. Even a kilometer from the runway, the noise level from a liner taking off or landing is more than 100 dB. The noise level in the metro can reach 110 dB at stations and 80–90 dB in carriages.

Don't get too carried away with karaoke. At the same time, the acoustic load level exceeds the permissible limits, reaching 115 dB. After such extreme vocals, hearing is temporarily reduced by 8 dB. 140–150 decibels The noise is practically unbearable, loss of consciousness is possible, eardrums can burst.

403 forbidden

However, this is not the case. In this case, this power is the instantaneous impedance power. Simplifying all the features of harmonic oscillations - this is the power that occurs at a certain frequency in an extremely short period of time. This is also called "Chinese kilowatts". In fact, the power is hundreds of times less.

• Design.

  If a system doesn't win in volume, it might win in design. Unlike loudness, this parameter cannot be measured and is highly subjective.

• Practicality. At the moment, the record for the loudness of a car audio system is more than 180db.

  
  This is a lethal level. Hence, a natural question follows, why such a system is needed?

As in any tournaments and contests, there are also awards. Such events are sponsored by representatives of giant companies in the audio industry, such as Pioneer, Alpine and others.
Sources of sound 0 Nothing is heard 5 Almost inaudible 10 The quiet rustle of leaves is almost inaudible 15 The rustle of leaves is barely audible 20 A person's whisper is barely audible (at a distance of 1 meter). 25 Quietly whispering of a person (1m) 30 Quietly whispering, ticking of a wall clock. The maximum permissible according to the norms for living quarters at night, from 23 to 7 hours (SNiP 23-03-2003 "Protection against noise"). 35 Quite audible muffled conversation 40 Quite audible ordinary speech. The norm for living quarters during the day, from 7 to 23 o'clock. Read more in Rossiyskaya Gazeta 45. Normal conversation is quite audible 50. Conversation is audible, typewriter 55. class A (according to European standards) 60 Noisy Norm for offices 65 Noisy loud conversation (1m) 70 Noisy loud conversations (1m) 75 Noisy screaming, laughing (1m) 80 Very noisy screaming, motorcycle with a silencer, noise of a vacuum cleaner (with high engine power - 2 kilowatts).
Sound frequency ranges Sub-ranges of the audio frequency spectrum to which the filters of two- or three-band acoustic systems are tuned: low-frequency - oscillations up to 400 hertz; mid-frequency - 400-5000 Hz; high-frequency - 5000-20000 Hz Sound speed and range of its propagation Approximate speed of audible, mid-frequency sound (with a frequency of about 1-2 kHz) and the maximum range of its propagation in various environments: in air - 344.4 meters per second (at a temperature of 21.1 on the Celsius scale) and about 332 m / s - at zero degrees; in water - about 1.5 kilometers in second; in a tree of hard varieties - about 4-5 km / s along the fibers and one and a half times less - across. At 20 ° C., The speed of sound in fresh water is 1484 m / s (at 17 ° - 1430), in sea water - 1490 m / s.