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 above 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 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.

Citizens, especially city dwellers, often complain about excessive noise in apartments and on the street. It is especially annoying (noise) on weekends and at night. Yes, and in the afternoon there is little joy from him, especially if there is a small child in the apartment.

Both experts and the Internet are united in their advice - you need to call the district police officer. But before contacting a law enforcement representative, it is necessary to at least roughly understand the noise levels at which such treatment is justified, and which is only an annoying factor, but does not fall under the ban.

Acceptable noise levels in residential premises

It is regulated by legislative acts, according to which the time of day is divided into periods and for each period the permissible noise level is different.

• 22.00 - 08.00 a period of silence, during which the specified level should not exceed 35-40 decibels, (it is in them that this indicator is considered).
• From eight in the morning to ten in the evening, according to the law, it refers to the daylight hours and you can make a little more noise - 40-50 dB.

Many are wondering why such a spread in dB. The thing is that the federal authorities gave only approximate values, and each region sets them independently. For example, in some regions, in particular, in the capital, there are additional periods of silence during the day. Usually this is the interval from 13.00 to 15.00. Failure to comply with silence during this period is a violation.

It is worth saying that the norms mean the level that cannot cause any harm to human hearing. But many do not understand what these indicators mean. Therefore, we give a comparison table with noise levels and with what to compare.

• 0-5 dB - nothing or almost nothing is heard.
• 10 - this level can be compared to a small rustle of leaves on a tree.
• 15 - rustle of foliage.
• 20 - barely audible human whisper (at an approximate distance of one meter).
• 25 - level when a person speaks in a whisper at a distance of a couple of meters.
• 30 decibels with what to compare? - a loud whisper, the clock on the wall. According to the SNiP standards, this level is the maximum permissible at night in residential premises.
• 35 - at about this level, the conversation is being conducted, however, in muted tones.
• 40 decibels is common speech. SNiP defines this level as acceptable for daytime.
• 45 is also a standard conversation.
• 50 is the sound of a typewriter (older generation will understand).
• 55 - what does this level compare to? Yes, the same as the top line. By the way, according to European standards, this level is the maximum permissible for class A offices.
• 60 is the level determined by law for ordinary offices.
• 65-70 - loud conversations at a distance of one meter.
• 75 - human scream, laughter.
• 80 - a working motorcycle with a muffler, this is also the level of a working vacuum cleaner with an engine of 2 kW or more.
• 90 - the sound emitted by a freight car when moving along a piece of iron and audible at a distance of seven meters.
• 95 is the sound of a subway car while driving.
• 100 - a brass band plays at this level, a chainsaw is working. A sound of the same power makes thunder. According to European standards, this is the maximum allowable level for the player's headphones.
• 105 - this level was allowed in passenger airliners until the 80s. last century.
• 110 - the noise emitted by a flying helicopter.
• 120-125 - the sound of a fender working at a distance of one meter.
• 130 - this is how many decibels a starting plane produces.
• 135-145 - a jet plane or a rocket takes off with such a noise.
• 150-160 - A supersonic aircraft crosses the sound barrier.

All of the above is conventionally divided according to the level of impact on human hearing:

• 0-10 - nothing or almost nothing is heard.
• 15-20 - barely audible.
• 25-30 - quiet.
• 35-45 is already quite noisy.
• 50-55 - clearly audible.
• 60-75 - noisy.
• 85-95 - very noisy.
• 100-115 - extremely noisy.
• 120-125 is an almost unbearable noise level for human hearing. Workers working with a jackhammer must wear special headphones, otherwise hearing loss is guaranteed.
• 130 is the so-called pain threshold, the sound higher for human hearing is already fatal.
• 135-155 - without protective equipment (headphones, helmets), a person has a contusion, brain injury.
• 160-200 - guaranteed rupture of the tympanic membranes and, attention, lungs.

Over 200 decibels can even be ignored, since this is a lethal sound level. It is at this level that the so-called noise weapon operates.

What else

But even lower rates can lead to irreversible injuries. For example, a long-term effect on hearing of sound in 70-90 decibels has a detrimental effect on a person, in particular on the central nervous system. For comparison - usually it is a loudly playing TV, the level of music in the car for some "amateurs", the sound in the player's headphones. If you also want to listen to loud music - be prepared for the fact that later on you will have to heal your nerves for a long time.

And if the noise exceeds 100 decibels, then hearing loss is almost guaranteed. And as practice shows, from music at this level there is more negativity than pleasure.

In Europe, it is forbidden to place a lot of office equipment in one room, especially if the room is not finished with sound-absorbing materials. Indeed, in a small room, two computers, a fax machine and a printer can raise the noise level up to 70 dB.

In general, at the workplace, the maximum noise level can be no more than 110 dB. If somewhere it exceeds 135, then any stay of a person, even a short one, is prohibited on this site.

If the noise level at the workplace exceeds 65-70 dB, it is recommended to wear special soft earplugs. If they are made with high quality, then they should reduce the external noise by 30 dB.

Isolating headphones available at home improvement stores not only provide maximum protection from virtually any noise, but also protect the temporal lobe of the head.

And in conclusion, let's say one interesting piece of news that might seem funny to someone. Statistics have shown that a city dweller living in a constant noise mode, once in a zone of complete silence, where the noise level does not exceed 20 dB, begins to experience discomfort. What can I say, he starts to get depressed. Here is such a paradox.

Noise is defined as a disorderly combination of different sounds with tones of varying strength and frequency. Noise levels are to be measured in quantities capable of expressing the degree of sound pressure produced. Such units of measurement of the noise level are associated with the names of two physicists - Alexander Bell and Heinrich Hertz.

Belami, and more often decibels, is the relative loudness of the sound. At its core, a decibel is ten times the logarithm of the ratio of the intensity of existing sound energy to its value. It is not directly a unit of measurement, but an expression of a relationship.

The measurable characteristic of sound is the amount of energy it contains. That is, its intensity as a flow of this energy. That is why, for example, the expression in watts per square meter (W / m2) acts as a quantitative characteristic. However, the values ​​obtained relative to the reference level of 10-12 W / m2 are so small and incomprehensible to most ordinary people that 1 bel was "adopted" to express the resulting ratios. For example, the noise level of a jet aircraft is on the order of 13 bels or, in smaller values, 130 decibels (dB). For the human ear, the normal noise range is 20 to 120 decibels. Sounds above this level can cause serious injury to the eardrum and contusion. And 160 dB can be fatal.

All people are faced with household noise. They consist of those that arise directly in the room and penetrate from the outside. In order to protect the health and the normal state of citizens, the norms of permissible penetrating noise have been adopted. This is 40 dB during the day and 30 at night. The average indicators of noise measurement units prove that in about 80% of cases, even with normal operation of radio and TV, conversations, noise coming from neighboring apartments is kept at a level of 40-45 dB, and sounds from the entrance (elevator movement, slaps of doors) reach 60 dB.

In addition to sound intensity, the human ear is sensitive to noise vibrations. Hertz is a unit C of frequency, equal to the frequency of the ongoing periodic process, in which one cycle of such a periodic process occurs in 1 second (that is, 1 oscillation). Therefore, for an objective characterization, it is necessary to use both of these units of measurement of the noise level. The human hearing aid is more sensitive to vibrations generated by high frequencies than by low frequencies. But in industrial and living conditions, everyone is under the influence of the entire spectrum. In this regard, when comparing the level of sound loudness, it is necessary, in addition to the characteristics of the strength and intensity of sound in decibels, to indicate the frequency of vibrations per second.

WHAT ARE DECIBELS?

Universal logarithmic units decibels are widely used in quantitative estimates of the parameters of various audio and video devices in our country and abroad. In radio electronics, in particular, in wire communication, technology for recording and reproducing information, decibels are a universal measure.

Decibel is not a physical quantity, but a mathematical concept

In electroacoustics, the decibel is essentially the only unit for characterizing various levels - sound intensity, sound pressure, loudness, and also for evaluating the effectiveness of means of dealing with noise.

The decibel is a specific unit of measurement that is not similar to any of those that we have to meet in everyday practice. The decibel is not an official unit in the SI system, although, according to the decision of the General Conference on Weights and Measures, it can be used without restrictions in conjunction with the SI, and the International Chamber of Weights and Measures recommended its inclusion in this system.

The decibel is not a physical quantity, but a mathematical concept.

In this respect, decibels have some similarities with percentages. Like percentages, decibels are dimensionless and serve to compare two values ​​of the same name, in principle very different, regardless of their nature. It should be noted that the term "decibel" is always associated only with energy quantities, most often with power and, with some reservations, with voltage and current.

A decibel (Russian designation - dB, international designation - dB) is a tenth of a larger unit - bela 1.

Bel is the decimal logarithm of the ratio of the two powers. If two powers are known R 1 and R 2 , then their ratio, expressed in bels, is determined by the formula:

The physical nature of the compared powers can be any - electrical, electromagnetic, acoustic, mechanical - it is only important that both quantities are expressed in the same units - watts, milliwatts, etc.

Let us briefly recall what a logarithm is. Any positive 2 number, both whole and fractional, can be represented by another number to a certain extent.

So, for example, if 10 2 = 100, then 10 is called the base of the logarithm, and the number 2 - the logarithm of 100 and denote log 10 100 = 2 or lg 100 = 2 (read like this: "the logarithm of one hundred at base ten is two").

Base 10 logarithms are called decimal logarithms and are most commonly used. For numbers divisible by 10, this logarithm is numerically equal to the number of zeros per unit, and for other numbers it is calculated on a calculator or found from tables of logarithms.

Logarithms with base e = 2.718 ... are called natural. In computing, logarithms with base 2 are commonly used.

Basic properties of logarithms:

Of course, these properties are also valid for decimal and natural logarithms. The logarithmic way of representing numbers is often very convenient, since it allows you to replace multiplication by addition, division by subtraction, raising to a power by multiplication, and extracting a root by division.

In practice, bel turned out to be too large, for example, any power ratios in the range from 100 to 1000 fit within one bel - from 2 B to 3 B. Therefore, for greater clarity, we decided to multiply the number showing the number of bels by 10 and count the resulting product an indicator in decibels, i.e., for example, 2 B = 20 dB, 4.62 B = 46.2 dB, etc.

Usually, the power ratio is expressed immediately in decibels using the formula:

Operations with decibels are the same as operations with logarithms.

2 dB = 1 dB + 1 dB → 1.259 * 1.259 = 1.585;
3dB → 1.259 3 = 1.995;
4 dB → 2.512;
5 dB → 3.161;
6 dB → 3.981;
7 dB → 5.012;
8 dB → 6.310;
9 dB → 7.943;
10 dB → 10.00.

The → sign means “match”.

Similarly, you can create a table for negative decibels. Minus 1 dB characterizes a decrease in power by 1 / 0.794 = 1.259 times, that is, also by about 26%.

Remember that:

⇒ If R 2 = P 1 i.e. P 2 / P 1 = 1 , then N dB = 0 , because lg 1 = 0 .

⇒ If P 2 > P l , then the number of decibels is positive.

⇒ If R 2 < P 1 , then decibels are expressed in negative numbers.

Positive decibels are often referred to as gain decibels. Negative decibels usually characterize energy losses (in filters, dividers, long lines) and are called attenuation or loss decibels.

There is a simple relationship between the decibels of gain and damping: the opposite numbers of ratios correspond to the same number of decibels with different signs. If, for example, the relation R 2 /R 1 = 2 → 3 dB , then –3 dB → 1/2 , i.e. 1 / R 2 /R 1 = P 1 /R 2

⇒ If R 2 /R 1 represents a power of ten, i.e. R 2 /R 1 = 10 k , where k - any integer (positive or negative), then NdB = 10k , because lg 10 k = k .

⇒ If R 2 or R 1 is equal to zero, then the expression for NdB loses its meaning.

And one more feature: the curve, which determines the decibel values ​​depending on the power ratios, first grows rapidly, then its growth slows down.

Knowing the number of decibels corresponding to one power ratio, it is possible to recalculate for another - close or multiple ratio. In particular, for power ratios that differ by a factor of 10, the decibel number differs by 10 dB. This feature of decibels should be well understood and firmly remembered - it is one of the foundations of the entire system.

The advantages of the decibel system include:

⇒ versatility, that is, the ability to use in assessing various parameters and phenomena;

⇒ huge differences in converted numbers - from units to millions - are displayed in decibels as numbers of the first hundred;

⇒ natural numbers representing powers of ten are expressed in decibels as multiples of ten;

⇒ reciprocal numbers are expressed in decibels by equal numbers, but with different signs;

⇒ both abstract and named numbers can be expressed in decibels.

The disadvantages of the decibel system include:

⇒ low visibility: to convert decibels into ratios of two numbers or to perform the opposite actions, calculations are required;

⇒ Power ratios and voltage (or current) ratios are converted to decibels using different formulas, which sometimes leads to errors and confusion;

⇒ decibels can only be measured relative to a level that is not equal to zero; absolute zero, for example 0 W, 0 V, is not expressed in decibels.

Knowing the number of decibels corresponding to one power ratio, it is possible to recalculate for another - close or multiple ratio. In particular, for power ratios that differ by a factor of 10, the decibel number differs by 10 dB. This feature of decibels should be well understood and firmly remembered - it is one of the foundations of the entire system.

Comparing two signals by comparing their powers is not always convenient, since expensive and complex instruments are required to directly measure electrical power in the audio and radio frequency ranges. In practice, when working with equipment, it is much easier to measure not the power that is released at the load, but the voltage drop across it, and in some cases, the flowing current.

Knowing the voltage or current and resistance of the load, it is easy to determine the power. If measurements are carried out on the same resistor, then:

These formulas are very often used in practice, but note that if voltages or currents are measured at different loads, these formulas do not work and other, more complex dependencies should be used.

Using the technique that was used to compile the power decibel table, you can similarly determine what 1 dB is equal to the ratio of voltages and currents. A positive decibel will be 1.122, and a negative decibel will be 0.8913, i.e. 1 dB of voltage or current characterizes the increase or decrease of this parameter by about 12% with respect to the initial value.

The formulas were derived under the assumption that the load resistances are active and there is no phase shift between voltages or currents. Strictly speaking, one should consider the general case and take into account the presence of a phase angle for voltages (currents), and for loads not only active, but impedance, including reactive components, but this is significant only at high frequencies.

It is useful to remember some of the decibel values ​​that are often encountered in practice and the ratios of powers and voltages (currents) that characterize them, given in Table. one.

Table 1. Frequent decibel values ​​of power and voltage

Using this table and the properties of logarithms, it is easy to calculate what arbitrary values ​​of the logarithms correspond to. For example, 36 dB of power can be represented as 30 + 3 + 3, which corresponds to 1000 * 2 * 2 = 4000. We get the same result by representing 36 as 10 + 10 + 10 + 3 + 3 → 10 * 10 * 10 * 2 * 2 = 4000.

COMPARISON OF DECIBELS WITH PERCENTAGES

Earlier it was noted that the concept of decibels has some similarities with percent. Indeed, since the percentage is the ratio of a number to another, conventionally taken as one hundred percent, the ratio of these numbers can also be represented in decibels, provided that both numbers characterize power, voltage or current. For the power ratio:

For the ratio of voltages or currents:

You can also derive formulas for converting decibels to percentages of a ratio:

Table 2 is a translation of some of the most common values ​​of decibels in percentages of ratios. Various intermediate values ​​can be found on the nomogram in Fig. one.

Rice. 1. Converting decibels to percentages of ratios according to the nomogram

Table 2. Converting decibels to percentages

Let's look at two practical examples to illustrate the conversion of percentage to decibels.

Example 1. What is the harmonic level in decibels in relation to the level of the fundamental frequency signal corresponds to a THD of 3%?

Let's use fig. 1. Through the point of intersection of the vertical line of 3% with the "voltage" graph, draw a horizontal line until it crosses the vertical axis and we get the answer: –31 dB.

Example 2. What percentage of voltage attenuation does the –6 dB change correspond to?

Answer. 50% of the original value.

In practical calculations, the fractional part of the numerical value of decibels is often rounded to an integer, however, an additional error is introduced into the calculation results.

DECIBELS IN RADIO ELECTRONICS

Let's consider a few examples that explain the technique of using decibels in electronics.

Attenuation in the cable

Energy losses in lines and cables per unit length are characterized by the attenuation coefficient α, which, with equal input and output line resistances, is determined in decibels:

where U 1 - voltage in an arbitrary section of the line; U 2 - voltage in another section, spaced from the first by a unit of length: 1 m, 1 km, etc. For example, a high-frequency cable of the RK-75-4-14 type at a frequency of 100 MHz has an attenuation coefficient α = –0.13 dB / m, a twisted pair cable of category 5 at the same frequency has an attenuation of the order of –0.2 dB / m, and for a cable of category 6 it is slightly less. The signal attenuation plot in an unshielded twisted pair cable is shown in Fig. 2.

Rice. 2. A graph of the signal attenuation in an unshielded twisted pair cable

Fiber optic cables have significantly lower attenuation values ​​in the range from 0.2 to 3 dB at a cable length of 1000 m. All optical fibers have a complex attenuation dependence on wavelength, which has three "transparency windows" 850 nm, 1300 nm and 1550 nm ... "Window of transparency" means the smallest loss at the maximum signal transmission distance. The signal attenuation graph in fiber optic cables is shown in Fig. 3.

Rice. 3. Graph of signal attenuation in fiber optic cables

Example 3. Find what will be the voltage at the output of a piece of cable RK-75-4-14 length l = 50 m, if a voltage of 8 V at a frequency of 100 MHz is applied to its input. The load resistance and the characteristic impedance of the cable are equal, or, as they say, are matched with each other.

It is obvious that the attenuation introduced by a piece of cable is K = –0.13 dB / m * 50 m = –6.5 dB. This decibel value roughly corresponds to a voltage ratio of 0.47. This means that the voltage at the output end of the cable U 2 = 8V * 0.47 = 3.76V.

This example illustrates a very important point: losses in a line or cable grow extremely rapidly with increasing length. For a 1 km section of cable, the attenuation will already be –130 dB, that is, the signal will be attenuated more than three hundred thousand times!

The attenuation largely depends on the frequency of the signals - in the audio frequency range it will be much less than in the video range, but the logarithmic law of attenuation will be the same, and with a long line length, the attenuation will be significant.

Audio Amplifiers

In order to improve their quality indicators, negative feedback is usually introduced into audio amplifiers. If the open-loop voltage gain of the device is TO , and with feedback To OS then the number showing how many times the gain changes under the action of feedback is called depth of feedback ... It is usually expressed in decibels. In a working amplifier, the coefficients TO and TO OS determined experimentally, unless the amplifier is excited with an open feedback loop. When designing an amplifier, first calculate TO and then determine the value To OS in the following way:

where β is the transmission coefficient of the feedback circuit, i.e. the ratio of the voltage at the output of the feedback circuit to the voltage at its input.

The feedback depth in decibels can be calculated using the formula:

Stereo devices have to fulfill additional requirements compared to monaural ones. The surround sound effect is ensured only with good channel separation, that is, without the penetration of signals from one channel to another. In practical terms, this requirement cannot be fully satisfied, and mutual leakage of signals occurs mainly through nodes common to both channels. The channel separation quality is characterized by the so-called crosstalk damping a PZ A measure of the crosstalk in decibels is the ratio of the output powers of both channels when the input signal is applied to only one channel:

where R D - maximum output power of the operating channel; R SV is the free channel output power.

Good channel separation corresponds to a crosstalk of 60-70 dB, excellent –90-100 dB.

Noise and background

At the output of any receiving-amplifying device, even in the absence of a useful input signal, an alternating voltage can be detected, which is caused by the inherent noise of the device. The reasons that cause intrinsic noise can be both external - due to interference, poor filtering of the supply voltage, and internal, due to the intrinsic noise of radio components. Noise and interference arising in the input circuits and in the first amplifier stage are most affected, since they are amplified by all subsequent stages. Intrinsic noise degrades the actual sensitivity of the receiver or amplifier.

Noise is quantified in several ways.

The simplest one is that all noises, regardless of the cause and place of their occurrence, are recalculated to the input, i.e., the noise voltage at the output (in the absence of an input signal) is divided by the gain:

This voltage, expressed in microvolts, is a measure of the intrinsic noise. However, for evaluating a device from the point of view of interference, it is not the absolute value of the noise that is important, but the ratio between the useful signal and this noise (signal-to-noise ratio), since the useful signal must be reliably distinguished from the background of interference. The signal-to-noise ratio is usually expressed in decibels:

where R With - the specified or nominal output power of the useful signal together with noise; R w - output power of noise when the source of the useful signal is off; U c - signal and noise voltage across the load resistor; U Sh - noise voltage across the same resistor. So it turns out the so-called. "Unweighted" signal-to-noise ratio.

Often the signal-to-noise ratio is given in the parameters of audio equipment, measured with a weighting filter ("weighted"). The filter allows you to take into account the different sensitivity of a person's hearing to noise at different frequencies. The most commonly used filter is type A, in which case the designation usually indicates the unit of measurement "dBA" ("dBA"). The use of a filter usually gives better quantitative results than for unweighted noise (usually the signal-to-noise ratio is 6-9 dB higher), therefore (for marketing reasons) equipment manufacturers often indicate exactly the "weighted" value. For more information on weighing filters, see the Sound Meters section below.

Obviously, for the successful operation of the device, the signal-to-noise ratio must be higher than some minimum acceptable value, which depends on the purpose and requirements for the device. For Hi-Fi equipment, this parameter should be at least 75 dB, for Hi-End equipment - at least 90 dB.

Sometimes, in practice, they use the inverse ratio, characterizing the noise level relative to the useful signal. The noise level is expressed in the same decibels as the signal-to-noise ratio, but with a negative sign.

In the descriptions of receiving and amplifying equipment, the term background level sometimes appears, which characterizes in decibels the ratio of the components of the background voltage to the voltage corresponding to a given nominal power. The background components are multiples of the mains frequency (50, 100, 150 and 200 Hz) and during measurement are isolated from the total interference voltage using band-pass filters.

The signal-to-noise ratio does not allow, however, to judge which part of the noise is directly caused by the elements of the circuit, and which is introduced as a result of imperfections in the design (pickup, background). To assess the noise properties of radio components, the concept is introduced noise factor ... Noise figure is rated in terms of power and is also expressed in decibels. This parameter can be characterized as follows. If at the input of the device (receiver, amplifier) ​​a useful signal with a power R With and noise power R w , then the signal-to-noise ratio at the input will be (R With /R w ) in After strengthening the attitude (R With /R w ) out will be less, since the amplified intrinsic noise of the amplifying stages will also be added to the input noise.

The noise figure is the ratio expressed in decibels:

where TO R is the power amplification factor.

Therefore, noise figure represents the ratio of the output noise power to the amplified input noise power.

Meaning Rsh.in determined by calculation; Psh.out measured and TO R usually. known from calculation or after measurement. An ideal amplifier in terms of noise should only amplify useful signals and should not introduce additional noise. As follows from the equation, for such an amplifier, the noise figure is F Sh = 0 dB .

For transistors and ICs intended for operation in the first stages of amplifying devices, the noise figure is regulated and given in the reference books.

The self-noise voltage also determines another important parameter of many amplifying devices - the dynamic range.

Dynamic range and adjustments

Dynamic range is the ratio of the maximum undistorted output power to its minimum value, expressed in decibels, at which the admissible signal-to-noise ratio is still ensured:

The lower the noise floor and the higher the undistorted output power, the wider the dynamic range.

The dynamic range of sound sources - orchestra, voice, is determined in a similar way, only here the minimum sound power is determined by the background noise. In order for the device to transmit both the minimum and maximum amplitudes of the input signal without distortion, its dynamic range must be no less than the dynamic range of the signal. In cases where the dynamic range of the input signal exceeds the dynamic range of the device, it is artificially compressed. This is done, for example, when recording.

The effectiveness of the manual volume control is checked at two extreme positions of the control. First, with the regulator in the maximum volume position, a voltage of 1 kHz is applied to the input of the audio frequency amplifier, such that a voltage corresponding to a certain specified power is established at the amplifier output. Then the volume control knob is turned to the minimum volume, and the voltage at the amplifier input is raised until the output voltage again becomes equal to the initial one. The ratio of the input voltage with the knob in the minimum volume position to the input voltage at the maximum volume, expressed in decibels, is an indication of how the volume control is operating.

The given examples are far from being exhausted practical cases of application of decibels to the estimation of parameters of radioelectronic devices. Knowing the general rules for the application of these units, one can understand how they are used in other conditions not considered here. Faced with an unfamiliar term, defined in decibels, one should clearly imagine the ratio of which two quantities it corresponds to. In some cases, this is clear from the definition itself, in other cases, the relationship between the components is more complicated, and when there is no clear clarity, one should refer to the description of the measurement procedure in order to avoid serious errors.

When operating with decibels, you should always pay attention to the ratio of which units - power or voltage - each specific case corresponds to, i.e. what coefficient - 10 or 20 - should come before the sign of the logarithm.

LOGARITHMIC SCALE

The logarithmic system, including decibels, is often used when constructing amplitude-frequency characteristics (AFC) - curves depicting the dependence of the transfer coefficient of various devices (amplifiers, dividers, filters) on the frequency of external influences. To construct the frequency response, a number of points characterizing the output voltage or power at a constant input voltage at different frequencies are determined by calculation or experiment. The smooth curve connecting these points characterizes the frequency properties of the device or system.

If numerical values ​​are plotted along the frequency axis in a linear scale, i.e., in proportion to their actual values, then such a frequency response will be inconvenient for use and will not be visual: in the region of lower frequencies it is compressed, and in the region of higher frequencies it is stretched.

Frequency characteristics are usually plotted on the so-called logarithmic scale. On the frequency axis, in a scale convenient for work, values ​​are plotted that are proportional not to the frequency itself f , and the logarithm lgf / f o , where f O - the frequency corresponding to the origin. Values ​​are labeled against axis marks f ... To build logarithmic frequency response, a special logarithmic graph paper is used.

When carrying out theoretical calculations, they usually use more than just the frequency f , and the value ω = 2πf which is called the circular frequency.

Frequency f O , corresponding to the origin, can be arbitrarily small, but cannot be equal to zero.

On the vertical axis, the ratio of the transmission coefficients at different frequencies to its maximum or average value is plotted in decibels or in relative numbers.

The logarithmic scale allows a wide range of frequencies to be displayed on a small section of the axis. On such an axis, equal ratios of two frequencies correspond to sections of equal length. The interval characterizing the tenfold increase in frequency is called decade ; twice the frequency ratio corresponds octave (this term is borrowed from music theory).

Frequency range with cutoff frequencies f H and f V occupies a strip in decades f B / f H = 10m , where m - the number of decades, and in octaves 2 n , where n - number of octaves.

If the bandwidth of one octave is too wide, then intervals with a lower frequency ratio of half an octave or a third of an octave can be used.

The average frequency of an octave (half-octave) is not equal to the arithmetic mean of the lower and higher frequencies of the octave, but is equal to 0.707 f V .

Frequencies found in this way are called rms.

For two adjacent octaves, the mid frequencies also form octaves. Using this property, one and the same logarithmic frequency series can be considered either as octave boundaries or as their average frequencies, if desired.

On logarithmic forms, the center frequency bisects the octave series.

On the frequency axis in a logarithmic scale, for every third of an octave there are equal axis segments, each one third of an octave long.

When testing electroacoustic equipment and performing acoustic measurements, it is recommended to use a number of preferred frequencies. The frequencies of this series are members of a geometric progression with a denominator of 1.122. For convenience, some frequencies have been rounded to within ± 1%.

The interval between the recommended frequencies is one-sixth of an octave. This was not done by chance: the series contains a sufficiently large set of frequencies for different types of measurements and picks up the series of frequencies at intervals of 1/3, 1/2 and a whole octave.

And one more important property of a number of preferred frequencies. In some cases, not an octave, but a decade is used as the main frequency interval. So, the preferred range of frequencies can be considered equally as binary (octave) and decimal (decade).

The denominator of the progression on the basis of which the preferred frequency range is built is numerically equal to 1 dB of voltage, or 1/2 dB of power.

REPRESENTATION OF NAMED NUMBERS IN DECIBELS

Until now, we assumed that both the dividend and the divisor under the sign of the logarithm have an arbitrary value and to perform the decibel conversion it is important to know only their ratio, regardless of the absolute values.

In decibels, you can also express specific values ​​of powers, as well as voltages and currents. When the value of one of the terms under the logarithm sign in the previously considered formulas is given, the second term of the ratio and the number of decibels will uniquely determine each other. Therefore, if you set any reference power (voltage, current) as a conditional comparison level, then another power (voltage, current), compared with it, will correspond to a strictly defined number of decibels. In this case, a power equal to the power of the conditional comparison level corresponds to zero decibels, since at N P = 0 R 2 = P 1 therefore this level is usually referred to as zero. Obviously, at different zero levels, the same specific power (voltage, current) will be expressed in different decibels.

where R is the power to be converted to decibels, and R 0 - zero power level. The magnitude R 0 is put in the denominator, while the power is expressed in positive decibels P> P 0 .

The conditional power level with which the comparison is made, in principle, can be anything, but not everyone would be convenient for practical use. Most often, a power of 1 mW is selected as the zero level, dissipated across a 600 ohm resistor. The choice of these parameters occurred historically: initially, the decibel as a unit of measurement appeared in the technology of telephone communication. The characteristic impedance of overhead two-wire copper lines is close to 600 ohms, and a power of 1 mW is developed without amplification by a high-quality carbon telephone microphone on a matched load impedance.

For the case when R 0 = 1 mW = 10 –3 W: P R = 10 lg P + 30

The fact that the decibels of the presented parameter are reported relative to a certain level is emphasized by the term "level": noise level, power level, loudness level

Using this formula, it is easy to find that with respect to the zero level of 1 mW, the power of 1 W is defined as 30 dB, 1 kW as 60 dB, and 1 MW is 90 dB, i.e., almost all the powers that you have to meet fall into within the first hundred decibels. Powers less than 1 mW will be expressed in negative decibels.

Decibels, specified with respect to 1 mW level, are called decibel-milliwatts and stand for dBm or dBm. The most common values ​​for zero levels are summarized in Table 3.

Similarly, you can present formulas for expressing voltages and currents in decibels:

where U and I - voltage or current to be converted, a U 0 and I 0 - zero levels of these parameters.

The fact that the decibels of the presented parameter are reported relative to a certain level is emphasized by the term "level": noise level, power level, loudness level.

Microphone sensitivity , i.e. the ratio of the electrical output to the sound pressure acting on the diaphragm, is often expressed in decibels by comparing the power delivered by a microphone at its nominal load impedance to a standard zero power level P 0 = 1 mW ... This microphone parameter is called standard microphone sensitivity ... Typical test conditions are considered to be a sound pressure of 1 Pa with a frequency of 1 kHz, a load resistance for a dynamic microphone - 250 Ohm.

Table 3. Zero levels for measuring named numbers

Designation		Description
int.	Russian
dBc	dBc	the reference is the level of the carrier or fundamental harmonic in the spectrum; for example, “distortion is –60 dBc”.
dBu	dBu	a reference voltage of 0.775 V, corresponding to a power of 1 mW at a load of 600 ohms; for example, the standardized signal level for professional audio equipment is +4 dBu, i.e. 1.23 V.
dBV	dBV	reference voltage 1 V at rated load (for household appliances usually 47 kOhm); for example, the standardized signal level for consumer audio equipment is –10 dBV, i.e. 0.316 V
dBμV	dBμV	reference voltage 1mkV; for example, “the sensitivity of the receiver is –10dBμV”.
dBm	dBm	reference power of 1 mW, corresponding to a power of 1 milliwatt at a nominal load (in telephony 600 Ohm, for professional equipment usually 10 kOhm for frequencies less than 10 MHz, 50 Ohm for high-frequency signals, 75 Ohm for television signals); for example, "the sensitivity of a cell phone is -110 dBm"
dBm0	dBm0	the reference power in dBm at the reference point. dBm - The reference voltage corresponds to the thermal noise of an ideal 50 ohm resistor at room temperature in a 1 Hz bandwidth. For example, "the noise level of the amplifier is 6 dBm0"
dBFS		(English Full Scale - "full scale") the reference voltage corresponds to the full scale of the device; for example, "the recording level is –6 dBfs"
dBSPL		(English Sound Pressure Level - "sound pressure level") - reference sound pressure of 20 μPa, corresponding to the audibility threshold; for example, "volume 100 dBSPL". dBPa - reference sound pressure 1 Pa or 94 dB sound scale dBSPL; for example, “for a volume of 6 dBPa, the mixer was set to +4 dBu, and the recording control was –3 dBFS, the distortion was –70 dBc”.
dBA, dBB, dBC, dBD		reference levels are selected in accordance with the frequency characteristics of standard "weight filters" of type A, B, C or D, respectively (filters reflect curves of equal loudness for different conditions, see below in the section "Sound level meters")

The power delivered by a dynamic microphone is naturally extremely low, much less than 1 mW, and the sensitivity level of the microphone is therefore expressed in negative decibels. Knowing the standard level of microphone sensitivity (it is given in the passport data), you can calculate its sensitivity in voltage units.

In recent years, to characterize the electrical parameters of radio equipment, other quantities have also begun to be used as zero levels, in particular 1 pW, 1 μV, 1 μV / m (the latter is used to assess the field strength).

Sometimes it becomes necessary to recalculate the known power level P R or voltage P U given relative to one zero level R 01 (or U 01 ) another R 02 (or U 02 ). This can be done using the following formula:

The ability to represent both abstract and named numbers in decibels leads to the fact that the same device can be characterized by different decibel numbers. This duality of decibels must be borne in mind. A clear understanding of the nature of the parameter being determined can serve as protection against errors.

To avoid confusion, it is advisable to state the reference level explicitly, eg –20 dB (relative to 0.775 V).

When converting power levels to voltage levels and vice versa, it is imperative to take into account the resistance that is standard for this task. In particular, the dBV for a 75 ohm TV circuit is (dBm – 11dB); dBμV for 75 ohm TV circuit corresponds to (dBm + 109dB).

Decibels in acoustics

Until now, speaking of decibels, we have operated in electrical terms - power, voltage, current, resistance. Meanwhile, logarithmic units are widely used in acoustics, where they are the most frequently used unit in quantitative assessments of sound quantities.

Sound pressure R represents the excess pressure in the medium in relation to the constant pressure that exists there before the appearance of sound waves (unit of measurement - pascal (Pa)).

An example of a sound pressure (or sound pressure gradient) receiver is most types of modern microphones that convert this pressure into proportional electrical signals.

The intensity of sound is related to the sound pressure and the vibrational speed of air particles by a simple relationship:

J = pv

If a sound wave propagates in free space, where there is no sound reflection, then

v = p / (ρc)

here ρ is the density of the medium, kg / m3; With - the speed of sound in the medium, m / s. Product ρ c characterizes the environment in which the propagation of sound energy occurs, and it is called specific acoustic resistance ... For air at normal atmospheric pressure and a temperature of 20 ° С ρ c = 420 kg / m2 * s; for water ρ c = 1.5 * 106 kg / m2 * s.

You can write that:

J = p 2 / (ρс)

everything that has been said about converting electrical quantities to decibels applies equally to acoustic phenomena

If you compare these formulas with the previously derived formulas for cardinality. current, voltage and resistance, it is easy to find an analogy between the individual concepts that characterize electrical and acoustic phenomena, and the equations describing the quantitative relationships between them.

Table 4. The relationship between electrical and acoustic performance

The analogue of electrical power is acoustic power and sound intensity; the analogue of voltage is sound pressure; the electric current corresponds to the vibrational speed, and the electrical resistance - to the specific acoustic resistance. By analogy with Ohm's law for an electrical circuit, we can talk about the acoustic Ohm's law. Consequently, everything that has been said about the conversion of electrical quantities into decibels applies equally to acoustic phenomena.

The use of decibels in acoustics is very convenient. The intensities of sounds that have to be dealt with in modern conditions can differ hundreds of millions of times. Such a huge range of changes in acoustic quantities creates great inconvenience when comparing their absolute values, and when using logarithmic units, this problem is removed. In addition, it was found that the loudness of a sound when assessed by ear increases approximately in proportion to the logarithm of the sound intensity. Thus, the levels of these quantities, expressed in decibels, correspond fairly closely to the loudness perceived by the ear. For most people with normal hearing, a change in the volume of a 1 kHz sound is felt when the sound intensity changes by about 26%, that is, by 1 dB.

In acoustics, by analogy with electrical engineering, the definition of decibels is based on the ratio of two powers:

where J 2 and J 1 - acoustic powers of two arbitrary sound sources.

Likewise, the ratio of two sound intensities is expressed in decibels:

The last equation is valid only if the acoustic impedances are equal, in other words, the constancy of the physical parameters of the medium in which the sound waves propagate.

The decibels determined by the above formulas are not related to the absolute values ​​of acoustic values ​​and are used to evaluate sound attenuation, for example, the effectiveness of sound insulation and noise suppression and suppression systems. The unevenness of the frequency characteristics is expressed in a similar way, i.e. the difference between the maximum and minimum values ​​in a given frequency range of various emitters and receivers of sound: microphones, loudspeakers, etc. range) relative to the value at a frequency of 1 kHz.

In the practice of acoustic measurements, however, as a rule, one has to deal with sounds, the values ​​of which must be expressed in specific numbers. The equipment for carrying out acoustic measurements is more complex than the equipment for electrical measurements, and in terms of accuracy it is significantly inferior to it. In order to simplify the measurement technique and reduce the error in acoustics, preference is given to measurements relative to reference, calibrated levels, the values ​​of which are known. For the same purpose, to measure and study acoustic signals, they are converted into electrical ones.

The absolute values ​​of powers, intensities of sounds and sound pressures can also be expressed in decibels, if in the above formulas you specify the values ​​of one of the terms under the sign of the logarithm. By international agreement, the reference level of sound intensity (zero level) is considered to be J 0 = 10 –12 W / m 2 ... This negligible intensity, under the influence of which the amplitude of the vibrations of the tympanic membrane is less than the size of an atom, is conventionally considered to be the hearing threshold of the ear in the frequency range of the highest hearing sensitivity. It is clear that all audible sounds are expressed with respect to this level only in positive decibels. The actual hearing threshold for people with normal hearing is slightly higher and is equal to 5-10 dB.

To represent the intensity of sound in decibels relative to a given level, use the formula:

The intensity value calculated by this formula is usually called sound intensity level .

The sound pressure level can be expressed in a similar way:

In order for the levels of sound intensity and sound pressure in decibels to be numerically expressed in one quantity, the value must be taken as the zero sound pressure level (sound pressure threshold):

Example. Let us determine what level of intensity in decibels is created by an orchestra with a sound power of 10 W at a distance of r = 15 m.

The sound intensity at a distance r = 15 m from the source will be:

Intensity level in decibels:

The same result will be obtained if you convert not the intensity level to decibels, but the sound pressure level.

Since the sound intensity level and the sound pressure level are expressed in the same number of decibels at the place of sound reception, in practice the term “level in decibels” is often used without specifying which parameter these decibels refer to.

Having determined the level of intensity in decibels at any point in space at a distance r 1 from a sound source (by calculation or experiment), it is easy to calculate the intensity level at a distance r 2 :

If the sound receiver is simultaneously influenced by two or more sound sources and the sound intensity in decibels produced by each of them is known, then to determine the resulting value of the decibels should be converted into absolute values ​​of the intensity (W / m2), added them, and this sum again converted into decibels. In this case, it is impossible to add decibels at once, since this would correspond to the product of the absolute values ​​of the intensities.

If there is n several identical sound sources with the level of each L J , then their total level will be:

If the intensity level of one sound source exceeds the levels of the others by 8-10 dB or more, only this one source can be taken into account, and the effect of the rest can be neglected.

In addition to the considered acoustic levels, sometimes you can also find the concept of the sound power level of a sound source, determined by the formula:

where R - sound power of the characterized arbitrary sound source, W; R 0 - initial (threshold) sound power, the value of which is usually taken equal to P 0 = 10 –12 W.

VOLUME LEVELS

The ear's sensitivity to sounds of different frequencies is different. This dependence is quite complex. At low sound intensity levels (up to about 70 dB), the maximum sensitivity is 2-5 kHz and decreases with increasing and decreasing frequency. Therefore, sounds of the same intensity, but of different frequencies, will seem to the ear to be different in volume. With an increase in sound power, the frequency response of the ear flattens out and at high intensity levels (80 dB and above) the ear reacts approximately the same to sounds of different frequencies of the sound range. It follows from this that the intensity of sound, which is measured by special broadband devices, and the loudness, which is recorded by the ear, are not equivalent concepts.

The loudness level of sound of any frequency is characterized by the value of the level equal in loudness to sound with a frequency of 1 kHz

The volume level of sound of any frequency is characterized by the value of the level equal in volume to a sound with a frequency of 1 kHz. Loudness levels are characterized by so-called equal loudness curves, each of which shows what level of intensity at different frequencies the sound source must develop in order to give the impression of equal loudness with a tone of 1 kHz of a given intensity (Fig. 4).

Rice. 4. Curves of equal loudness

Equal loudness curves represent essentially a family of ear frequency responses on a decibel scale for different intensity levels. Their difference from the usual frequency response is only in the way of construction: the "blockage" of the characteristic, that is, a decrease in the transmission coefficient, is shown here by an increase, not a decrease in the corresponding section of the curve.

The unit characterizing the loudness level, in order to avoid confusion with the decibels of intensity and sound pressure, has been assigned a special name - background .

The sound volume level in backgrounds is numerically equal to the sound pressure level in decibels of a pure tone with a frequency of 1 kHz, equal to it in volume.

In other words, one hum is 1 dB SPL of a 1 kHz tone, corrected for the frequency response of the ear. There is no constant relationship between the two, these units: it changes depending on the volume of the signal and its frequency. Only for currents with a frequency of 1 kHz, the numerical values ​​for the loudness level in backgrounds and the intensity level in decibels coincide.

Referring to Fig. 4 and to trace the course of one of the curves, for example, for a level of 60 background, it is easy to determine that to ensure equal loudness with a tone of 1 kHz at a frequency of 63 Hz, a sound intensity of 75 dB is required, and at a frequency of 125 Hz, only 65 dB.

High quality audio amplifiers use manual volume controls with loudness, or, as they are also called, compensated controls. Such controls, simultaneously with the adjustment of the input signal value in the direction of decrease, provide an increase in the frequency response in the low-frequency region, due to which a constant sound timbre is created for the hearing at different sound reproduction volumes.

Studies have also found that a twofold change in sound volume (as estimated by ear) is approximately equivalent to a change in volume level by 10 phon. This dependence is used as the basis for assessing the sound loudness. For a unit of loudness called dream , conventionally adopted a volume level of 40 background. The doubled loudness, equal to two sleep, corresponds to 50 phon, four sleep - 60 phon, etc. The conversion of loudness levels into loudness units is facilitated by the graph in Fig. 5.

Rice. 5. Relationship between volume and volume

Most of the sounds that you have to deal with in everyday life are noisy in nature. Characterizing the loudness of noise based on comparison with pure 1 kHz tones is straightforward, but results in the perceived noise by ear may be at odds with the readings of the measuring instruments. This is explained by the fact that at equal levels of noise loudness (in backgrounds), the most annoying effect on a person is produced by noise components in the range of 3-5 kHz. Noises can be perceived as equally unpleasant, although their loudness levels are not equal.

The annoying effect of noise is more accurately assessed by another parameter, the so-called perceived noise level ... A measure of the perceived noise is the sound level of uniform noise in an octave band with an average frequency of 1 kHz, which, under given conditions, is judged by the listener as equally unpleasant with the noise being measured. Perceived noise levels are expressed in PNdB or PNdB units. Their calculation is carried out according to a special method.

Further development of the noise estimation system is the so-called effective levels of perceived noise, expressed in EPNdB. The EPNdB system allows for a comprehensive assessment of the nature of the influencing noise: the frequency composition, discrete components in its spectrum, as well as the duration of the noise exposure.

By analogy with the unit of loudness sleep, the unit of noise has been introduced - Noah .

For one Noah adopted noise level of uniform noise in the 910-1090 Hz band at a sound pressure level of 40 dB. In other respects, nois are similar to dreams: a twofold increase in noise corresponds to an increase in the perceived noise level by 10 RNdB, i.e. 2 noi = 50 RNdB, 4 noi = 60 RNdB, etc.

When working with acoustic concepts, it should be borne in mind that the intensity of sound is an objective physical phenomenon that can be accurately determined and measured. It really exists regardless of whether anyone hears it or not. The loudness of the sound determines the effect that the sound produces on the listener, and is, therefore, a purely subjective concept, since it depends on the state of the human hearing organs and his personal properties for the perception of sound.

NOISE METERS

To measure all kinds of noise characteristics, special devices are used - sound level meters. The sound level meter is a self-contained portable device that allows you to measure directly in decibels levels of sound intensity over a wide range relative to standard levels.

The sound level meter (Fig. 6) consists of a high-quality microphone, a broadband amplifier, a sensitivity switch that changes the gain in 10 dB steps, a frequency response switch and a graphical indicator, which usually provides several options for presenting the measured data - from numbers and tables to graphs.

Rice. 6. Portable digital sound level meter

Modern sound level meters are very compact, which allows measurements in hard-to-reach places. From domestic sound level meters, one can name the device of the company "Octava-Electrodesign" "Octava-110A" (http://www.octava.info/?q=catalog/soundvibro/slm).

Sound level meters allow the determination of both general sound intensity levels in measurements with a linear frequency response and sound levels in backgrounds when measured with frequency responses similar to those of the human ear. The measurement range of sound pressure levels is usually in the range from 20-30 to 130-140 dB relative to the standard sound pressure level of 2 * 10-5 Pa. With interchangeable microphones, the measurement level can be expanded up to 180 dB.

Depending on the metrological parameters and technical characteristics, domestic sound level meters are divided into the first and second classes.

The frequency characteristics of the entire path of the sound level meter, including the microphone, are standardized. There are five frequency characteristics in total. One of them is linear within the entire operating frequency range (symbol Lin), four others approximately repeat the characteristics of the human ear for pure tones at different volume levels. They are named by the first letters of the Latin alphabet. A, B, C and D ... The form of these characteristics is shown in Fig. 7. The frequency response switch is independent of the range switch. For sound level meters of the first class, characteristics are required A, B, C and Lin ... Frequency response D - additional. Sound level meters of the second class must have the characteristics A and WITH ; the rest are allowed.

Rice. 7. Standard frequency characteristics of sound level meters

Characteristic A simulates the ear at about 40 fon. This characteristic is used when measuring weak noise - up to 55 dB and when measuring loudness levels. In practical conditions, the frequency response with correction is most often used. A ... This is explained by the fact that, although the perception of sound by a person is much more complicated than a simple frequency dependence that determines the characteristic A , in many cases the instrument's measurements are in good agreement with hearing noise estimates at low volume levels. Many standards - domestic and foreign - recommend the assessment of noise by the characteristic A regardless of the actual sound intensity level.

Characteristic V repeats the characteristic of the ear at level 70 background. It is used when measuring noise in the range of 55-85 dB.

Characteristic WITH uniform in the range 40-8000 Hz. This characteristic is used when measuring significant loudness levels - from 85 phon and above, when measuring sound pressure levels - regardless of the measurement limits, as well as when connecting devices to a sound level meter for measuring the spectral composition of noise in cases where the sound level meter does not have a frequency response Lin .

Characteristic D - auxiliary. It represents the average of the ear at about 80 phon, taking into account the increase in its sensitivity in the band from 1.5 to 8 kHz. When using this characteristic, the readings of the sound level meter more accurately than according to other characteristics correspond to the level of perceived noise by a person. This characteristic is mainly used when assessing the irritating effect of high-intensity noise (aircraft, high-speed cars, etc.).

The sound level meter also includes a switch Fast - Slow - Pulse , which controls the time characteristics of the device. When the switch is in position Quickly , the device manages to monitor rapid changes in sound levels, in the position Slowly the instrument shows the average value of the measured noise. Time characteristic Pulse used for recording short sound impulses. Some types of sound level meters also contain an integrator with a time constant of 35 ms, which simulates the inertia of human sound perception.

When using a sound level meter, the measurement results will differ depending on the set frequency response. Therefore, when recording readings, to avoid confusion, the type of characteristic at which the measurements were made is also indicated: dB ( A ), dB ( V ), dB ( WITH ) or dB ( D ).

To calibrate the entire path of the microphone - meter, the sound level meter kit usually includes an acoustic calibrator, the purpose of which is to create uniform noise of a certain level.

According to the currently valid instruction "Sanitary standards for permissible noise in residential and public buildings and on the territory of residential development", the normalized parameters of constant or intermittent noise are sound pressure levels (in decibels) in octave frequency bands with average frequencies of 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz. For intermittent noise, such as noise from passing vehicles, the standardized parameter is the sound level in dB ( A ).

The following total sound levels have been established, measured on the A scale of the sound level meter: living quarters - 30 dB, auditoriums and classrooms of educational institutions - 40 dB, residential areas and recreation areas - 45 dB, working premises of administrative buildings - 50 dB ( A ).

For a sanitary assessment of the noise level, corrections from –5 dB to +10 dB are introduced into the sound level meter readings, which take into account the nature of the noise, the total time of its action, the time of day and the location of the object. For example, in the daytime, the allowable noise norm in residential premises, taking into account the amendment, is 40 dB.

Depending on the spectral composition of the noise, the approximate norm of the maximum permissible levels, dB, is characterized by the following figures:

High frequency from 800 Hz and above	75-85
Medium frequency 300-800 Hz	85-90
Low frequency below 300 Hz	90-100

In the absence of a sound level meter, an approximate assessment of the loudness levels of various noises can be carried out using the table. 5.

Table 5. Noises and their assessment

Loudness rating aurally	Level noise, dB	Source and location of noise measurement
Deafening	160	Damage to the tympanic membrane.
	140-170	Jet engines (close up).
	140	Noise Tolerance Limit.
	130	Pain threshold (sound is perceived as pain); piston aircraft engines (2-3 m).
	120	Thunder overhead.
	110	High-speed powerful motors (2-3 m); riveting machine (2-3 m); very noisy workshop.
Very loud	100	Symphony orchestra (loudness peaks); woodworking machines (in the workplace)
	90	Outdoor loudspeaker; noisy street; metal-cutting machines (in the workplace).
	80	Radio receiver loudly (2m)
Loud	70	Bus salon; scream; a policeman's whistle (15 m); medium noisy street; noisy office; large store hall
Moderate	60	Calm conversation (1 m).
	50	Light car (10-15 m); calm office; living quarters.
Weak	40	Whisper; reading room.
	60	Rustle of paper.
	20	Hospital ward.
Very weak	10	Quiet garden; radio center studio.
	0	Hearing threshold

1 A. Bell is an American scientist, inventor and businessman of Scottish descent, the founder of telephony, the founder of the Bell Telephone Company, which determined the development of the telecommunications industry in the United States.
2 Logarithms of negative numbers are complex numbers and will not be considered further.

The apartment is our fortress, our harbor of peace and comfort. But very often extraneous noise prevents us from calmly relaxing and resting after a hard day at work. Especially often, residents of large cities suffer from such problems, whom even new soundproof plastic windows do not save from the penetration of street noise into the room. The problem is aggravated by the summer heat, when it is not possible to close the window in a residential building or apartment, because not everyone has air conditioners. And if in the daytime the noise can still be somehow tolerated, then at night it is simply impossible to deal with it. But there are also neighbors who, looking at night, begin to drill, knock, sort things out, have fun with guests and listen to music loudly. And on the other side of the house there is a round-the-clock construction project, compared to which the noise from the neighbors seems to be a minute of silence.

What law protects citizens from increased noise in residential premises? What sanitary standards must be observed? What level in dB is acceptable in an apartment? Who should complain about a noisy cafe or construction near your home? What noise level will not violate the established standards and harm your health? Yes, you heard right. Constant presence in a noisy room is quite harmful for the human ear and the whole body as a whole. Is it possible to measure the noise level at home and to which competent authority to contact if the sanitary standard dB for residential premises is exceeded? How can you influence neighbors to stop making noise? All these pressing questions are asked to themselves every day by about seventy percent of city dwellers. The Internet will help you little with your search for answers. It is better to immediately contact experienced professionals who have experience in solving such problems.

The consultants of our website are ready to help you competently, quickly and, which is very important, free of charge at any time.

In order to give answers to the above questions, you must first understand the basic concepts of the topic. What is noise, most likely, is clear to every person, so now we will not give it a scientific basis. But the loudness of a sound is understood as the level of its (in the sense of sound) pressure in units of measurement, which are dB (decibels). The maximum noise level in an apartment means an increase in the norm by 15 dB. That is, if the law establishes a sanitary standard of 40 dB during the daytime, then the permissible level will be 55 dB. At night, the maximum rate in residential apartments is 40 decibels and cannot be exceeded. Why does the law set different indicators for premises at night and day? Because at night the ears become the main organ of perception, there is even such a thing as light sleep. The noise susceptibility level increases by about 10-15 dB. This means that sharp, loud sounds interfere with sleep.

Continuous violation of noise boundaries in decibels can lead to disruption of the normal functioning of your body. Regular noise in the apartment, for example from the actions of neighbors, in the amount of 70 dB will already negatively affect your health (the nervous system does not rest, irritability appears, headaches, etc.). In some cases, you don't even want to stay in residential premises for a long time due to the increased background noise. There is no need to try to argue with the people responsible for the rumble and screams. You can always find justice for neighbors, builders, and even for the management of a nearby cafe, who violate the law on permissible noise in the daytime and at night. To get started, contact the specialists and they will tell you the algorithm of actions according to the law and justice.

Noise levels by example

It is not enough to measure dB in living quarters. It is also necessary to understand how much exceeding the permissible sound can affect your health and what degree of violation of the law is observed in this case (with a standard rate of 40 sound units).

Comparative list of sound vibrations (the unit of measurement here will naturally be dB):

• from 0 to 10 almost nothing is audible, it can be compared with a very quiet rustle of foliage;
• from 25 to 20 barely audible sound, can be compared with a human whisper in residential apartments at a distance of one meter;
• from 25 to 30 quiet sound (ticking of a clock, for example);
• from 35 to 45 the noise effect from a quiet (possibly even muffled) conversation, for residential buildings the standard is 40 dB;
• from 50 to 55 a distinct sound wave, acceptable for non-residential premises, for example, for offices or workrooms using technical means (typewriters, fax, printer, etc.);
• from 60 to 75 a noisy room can be compared to loud conversations, laughter, shouts, etc. I would like to remind you that 70 dB is already dangerous for your health;
• from 80 to 95 very noisy sounds, in residential premises a powerful vacuum cleaner can work this way, in non-residential (including on the street) such sounds are emitted by the subway, the roar of a motorcycle, very loud screams, etc.;
• from 100 to 115 maximum sound for headphones, thunderclap, helicopter, chainsaw, etc .;
• 130 - the sound pressure level falling under the pain threshold (for example, the sound of the aircraft engines when it starts);
• from 135 to 145 this sound pressure can lead to concussion;
• from 150 to 160, such sound pressure can lead not only to contusion, but also to injury, as well as to the introduction of a person into a state of shock;
• over 160 rupture is possible not only of the eardrums, but also of the human lungs.

In addition to audible sounds, health is also influenced by those inaudible by the ear (ultrasound, infrasound). For details, you can contact our consultants.

Anti-noise legislation

In our country, there is no specific law protecting the peace of citizens during the day and night. For example, the standards for maximum sound pressures (40 and 50 dB) are not established by civil or criminal proceedings, but by sanitary norms. You will not find a definition of noise of 70 dB as harmful to health in modern legislation either. And people themselves do not respect each other's needs for rest. Regardless of age (a neighbor can turn on music loudly at night, even if he is 18, at least 40, at least 70) and social status. Construction work is also carried out day and night, bypassing the law by obtaining permission from the deputy bodies. Fighting neighbors is easier. At night, you can call the police and hold them accountable for disturbing public order. In the daytime, if someone bothers you, and you are sure that you are right, you can call the employees of the SES or Rospotrebnadzor, who are required to measure the noise level and record your complaint.

There are provisions on which premises are considered residential and allowable living conditions are prescribed in it. There you can find information about the violation of sound pressure standards in the daytime as well.

In order not to get into a mess when calling the police, you need to understand what day and night time means. So, the norms of SanPiN tell us that the daytime is from 7.00 am to 23.00 pm, respectively, the night lasts from 23.00 to 7.00. in accordance with the Federal Law on maintaining normal living conditions, for violations of these very norms, administrative responsibility is threatened.

Also, the law prohibits construction work that violates noise standards at night. If construction in a residential area is still underway, you can contact the municipal authorities or Rospotrebnadzor. Each situation is individual and therefore, before doing anything, contact the experts for advice.

Hearing preservation

In order not to harm your hearing, you must follow certain rules:

• no need to drown out extraneous noise from the outside with loud music in headphones, you can only make it worse;
• if you need to spend a lot of time in noisy places (or at work), use special earplugs (they are called earplugs);
• noise reduction in the room is possible with the use of special materials for sound insulation;
• follow the safety rules when diving, skydiving, flying on an airplane, practicing in a shooting range, etc.;
• take care of your ears if you get a runny nose or get rhinitis (all actions listed in the line above are prohibited);
• even with a great love for loud music, you do not need to listen to it for days on end;
• Give your hearing a break if you can't avoid noisy places.

Take care of your health, because no one except you and your loved ones will do this. And in case of difficult situations, if you need legal assistance, please contact our lawyers. This can be done on the site without leaving your home and without any financial costs.