Converting values from decibels to absolute values and power. Online decibel measurement. Construction and renovation work
When measuring the parameters of radio equipment, quite often one has to deal with relative values expressed in decibels [dB]. Decibels express sound intensity, voltage, current or power stage gain, transmission loss or signal attenuation, etc.
The decibel is a universal logarithmic unit. The widespread use of representing quantities in dB is due to the convenience of the logarithmic scale, and in calculations, decibels obey the laws of arithmetic - they can be added and subtracted if the signals have the same shape.
There is a formula for converting the ratio of two voltages into the number of decibels (a similar formula is valid for currents):
For example, if the output signal U2 has a level twice that of U1, then this ratio will be +6 dB (Ig2=0.301). If U2>U1 is 10 times, then the signal ratio is 20 dB (Ig10=1). If U1>U2, then the sign of the ratio changes by minus 20 dB.
For example, in a measuring generator, the attenuator for attenuating the output signal may have a graduation in dB. In this case, to convert a value from decibels to an absolute value, the result will be obtained faster if you use the already calculated table. 6; 1. It has a resolution of 1 dB (which is quite enough in most cases) and a range of values 0...-119 dB.
Table 6.1 can be used to translate the attenuator's decibels of attenuation into an output voltage level. For ease of use of the table, it is necessary to set the voltage level of 1 V (rms or amplitude) at the generator output in the absence of attenuation (0 dB at the attenuator). In this case, the corresponding desired value of the output voltage after setting the attenuation is located at the intersection of the horizontal and vertical graphs (the values in decibels are added arithmetically).
The output voltage in the table is indicated in microvolts (1 µV = 10-6 V). I
Using this table, it is not difficult to solve the inverse problem - using the required voltage, determine what signal attenuation should be set on the attenuator in decibels. For example, in order to obtain a voltage of 5 μV at the output of the generator, as can be seen from the table, you will need to set the attenuation to 100 + 6 = 106 dB on the attenuator. The ratio of the powers of two signals in decibels is calculated by the formula:
The formula for power is valid provided that the input and output impedances of the device are the same, which is often done in high-frequency devices to facilitate their matching with each other.
To determine the power, you can use the calculated table. 6.2
Often when practical use dB it is also important to know the absolute value of the ratio of two quantities, i.e. how many times the voltage or power at the output is greater than at the input (or vice versa). If the ratio of two quantities is designated: K=U2/U1 or K=P2/P1, then you can use the table. 6.3 to convert a value from dB to times (K) and vice versa.
For example, antenna amplifier provides signal power amplification of 28 dB. From the table 6.3 shows that the signal is amplified 631 times.
Literature: I.P. Shelestov - Useful diagrams for radio amateurs, book 3.
It is convenient to measure attenuation and gain coefficients in decibels:
Why logarithms? So, after all, human perception is logarithmic in nature! Imagine a shopping bag weighing 1 kg. If you add another liter kilogram to this mass, the change in mass will be very noticeable. If the same kilogram is added to the mass, say, 15 kg, then the weight gain will be noticeable, but will hardly be felt. And if this kilogram is added to a whole ton, then the increase will be completely unnoticeable. To push a car with and without a liter of juice, the same amount of force is required.
In addition, we recall the mathematics of logarithms and see how some calculations are simplified.
- Logarithm of the product equal to the sum logarithms
The signal power is attenuated in the line by 6.3 times; on the receiving side, the amplifier increases the power by 25 times. How many times will the signal power at the output of the amplifier be greater or less than at the output of the generator?
It doesn’t seem to be scary, but to calculate that the output signal will be almost 4 times stronger than at the input of the path, you will need a calculator.
Adding and subtracting is much easier! Again, we get the result that the signal power at the output of the path will be almost four times higher than at the input. That from the figure +5.9 dB it follows that the signal power is four times higher, we will see a little lower. In the meantime, let us remember one more consideration from the mathematics of logarithms
We have just calculated how many times the signal power at the output of the path differs from that supplied to the path. Surely I would like to know the magnitude of this power. Is it possible to express the values themselves in decibels? Of course you can! To do this, you need to divide the value by one.
Now remember a few statements:
- A 2-fold change in power is 3 dB
- A power change of 3 times is 4.8 dB
- A power change of 10 times is 10 dB
- A power change of 100 times is 20 dB
The correctness of these statements is easy to verify. And it is from this that it follows that an increase in the signal by 6 dB (2 times 3 dB) is an increase in power by 4 times (twice 2 times). And an increase in power by 20 times (10×2) is an increase of 13 dB (10 + 3)
. power change.
I deliberately wrote above only about capacities. Power has a quadratic dependence on voltage and current, and a change of 3 decibels is always and in all cases a change power 2 times. As we remember, power depends on the square of the voltage or the square of the current:
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- It all starts with Ohm's law:
Remember that the logarithm of an exponent is the product of the exponent and the logarithm of the base. The exponent is two, and you need to multiply not by 10, but by 20. Let's express 2 Volts in decibel-volts, and 3 decibel-volts in Volts:
Simple and not scary!
- In calculations of energy quantities (power) the number 10 appears
- In calculations of power quantities (voltage, current) the number 20 appears
A few calculations
Let’s solve a few calculation problems so that we can confidently navigate decibels.
1. Sound volume
The volume of sound is also measured in decibels. Remembering that a decibel is a measure of the ratio of two quantities, we always make sure to clarify in relation to what these decibels are measured, i.e. where is the origin of the countdown? And in in this case— in relation to the human hearing threshold: 2×10 -5 N/m 2 . Newton is a system unit of force, i.e. It is clearly a force quantity, so the number 20 appears in the calculations. Let’s calculate the force that sound pressure exerts on the eardrum in our ear, when a jet plane takes off and during a quiet conversation.
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What we know:
- Values in decibels are expressed relative to 2×10 -5 N/m 2
- The area of the human eardrum is about 55 mm 2, or 5.5 × 10 -5 m 2
- Tabular loudness of a jet aircraft at a distance of 5 m
- Table volume of a quiet conversation - 50 dB at a distance of 1 m
- Hooray! I found Newton!
Newton answers with a sly smile:
- I was wrong, smart guy! That's Newton per square meter! YOU FOUND PASCAL.
Let's calculate the sound pressure in Pascals, or Newtons per square meter:
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- Let's count our jet plane
Multiply the pressure in Pascals by the area in square meters, and we get the magnitude of the force in Newtons:
- For a jet plane
Let's convert Newtons into more tangible gram-forces:
0.0011 N × 102 gf/N = 0.1122 gf
0.N × 102 gf/N = 0.gf
As they say, feel the difference! And don’t forget that the mechanism of hearing is more complex, and we perceive sound not only through the eardrum in the depths of the ear!
2. Converting voltage level to signal power
At work, we often measure radio signal levels at the antenna input of a measuring receiver. And the measuring receiver in its metrological properties is close to a selective voltmeter, and the measured value is calculated in decibel-microvolts (dBμV). At the same time, radio measurements often operate on the signal power at the receiving point, often expressed in decibel-milliwatts (dBm). Let's count one into the other!
- Let us rewrite the expression connecting power and voltage once again:
Indeed, a signal with a level of 70 dBµV (3.16 mV) develops a power of 0.2 µV, or -37 dBm, at a load of 50 Ohms
And for greater happiness, I made an online calculator that converts voltage in decibel-microvolts into power in decibel-milliwatts and vice versa (I know, I know, there are countless of them on the Internet without me! :)
Online decibel calculator
The rules of use are simple to the point of disgrace. Change the value of any of the values, and all other values will be recalculated automatically.
Decibel Meter - a simple and fast noise level meter
Decibel Meter is a simple application for determining the noise level in decibels at its current, average and maximum value. It will be very useful if you want, for example, to find an area where the noise level is safe enough for nerves and hearing. All received values are recorded in a log, so you can later view them and compare them with the current situation.
The application is distributed free of charge, language simple interface English, Windows Phone 7.5 and 8 supported.
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Online decibel calculator
What is a decibel (dB)? It is a unit of measurement for the ratio of two quantities. Calculated using the formula:
Where A dB- value in decibels, A- measured physical quantity, A 0 is the value taken as the basis.
In sound engineering, decibels measure the level of sound signal relative to the nominal (0 dB), for example -6 dB, which corresponds to a level almost half the nominal. It is very easy to convert the sound level in decibels into percentages or “folds” using this online calculator:
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Indoor noise level: 3 measurement methods
Household appliances, cars on the street, neighbors - all this adds up to the total noise in the apartment. How to measure it? And how will the noise level change if a breather is installed in the room?
Professional sound level meters
These instruments have many similar names: sound level meters, noise meters, noise level meters, sound meters, sound level meters.
There is no point in spending money on your own sound level meter. Budget devices for rubles are not much different in accuracy from mobile applications and programs for measuring noise. And precision devices cost much more - rubles.
If you still managed to get a professional sound level meter, then remember important nuance. The “0 dBA” mark on the device display does not mean that there is absolute silence in your apartment. Zero on the screen indicates that the noise level in the room is so low or high that it is not within the operating range of this particular device.
Applications and programs
Essentially, to measure noise levels you need a microphone and a special analyzer program. Your laptop, tablet or smartphone has a microphone. TO desktop computer can be connected external microphone. All that remains is to download the analyzer program.
You can measure the noise level on a computer free program Decibel Reader. Also, sound level meters are available in many sound recording programs. For example, Audacity.
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The microphone on a smartphone or tablet is usually worse than an external microphone connected to a computer. But even with it you can make a fairly accurate measurement of the noise level. Calibration with professional instruments shows that the accuracy of measurements on a smartphone can differ from professional equipment by only 5 decibels. So mobile applications for operational work Even noise diagnostic specialists use it.
Smart Tools is one of the applications with a sound level meter function. Please note that the measurements are in dB, not dBA.
A “regular” decibel is dB, a unit of sound pressure. But our ear perceives the pressure of sounds of different frequencies differently. In order for a sound level meter to show the real noise level that a person hears, it must have a so-called frequency filter A. With it, dB turns into the same dBA.
IN Smart app Tools does not have a frequency filter, but even without it you can get a general idea of the noise level.
Other noise measurement applications:
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- MacOS: Decibel 10th, Decibel Meter Pro, dB Meter, Sound Level Meter
- Android: Sound Meter, Decibel Meter, Noise Meter, deciBel
- Windows: Decibel Meter Free, Cyberx Decibel Meter, Decibel Meter Pro
in specialized sound level meters (even the simplest ones), the parameters of the microphone and signal processor are consistent. This is not available in a smartphone, so the measurement accuracy mobile application will always be lower than with a special device.
Comparative assessment
The approximate noise levels of a refrigerator, breather, vacuum cleaner, human speech and other common noise sources are known. The unit of measurement is acoustic decibels, dBA.
In fact, this method is not even a measurement, but comparative assessment. It gives a rough idea of how well the noise level in your home meets regulations.
First, try to reduce the noise level in the room as much as possible. Close windows and doors tightly to block out sounds from the street, entryway, and other rooms. Turn off everything: TV, computer and other “noisy” devices.
Take a regular metal needle and drop it on the floor. The volume of the sound you heard is approximately 15 dBA. Come close to a working refrigerator or breather. These devices operate at a volume of about BA.
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During the day background noise in the apartment it should be no louder than 40 dBA, and in the surrounding area no louder than 70 dBA. At night (from 23 to 7 o'clock) for the house and street there are different values - 30 and 60 dBA, respectively. This is a comfortable environment, and you should strive for it.
The volume of a quiet conversation is about BA. If you have to raise your voice to communicate due to noise in your apartment, the background noise level is twice as high as normal.
Crib
Finally, a custom noise test of the Tion O2 breather. The video shows that with the breather turned on and closed windows The noise level in the apartment is much lower than with open windows. A breather operating at first and second speeds does not actually change the level of background noise.
First, the computer turns on, you can hear how it accelerates the screws, then I turn on the breather, first to maximum, and then reduce it to minimum. Then I turn off the breezer and open the window.
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Unit converter
Sound level
Converter of values in decibels and ratios of amplitudes and powers
The ratio of amplitudes and powers must be a positive number.
How to improve mobile phone reception?
More about sound level
General information
Sound level determines its loudness and is used in acoustics - the science that studies the level and other properties of sound. When people talk about volume, they often mean sound level. Some sounds are very unpleasant and can cause a number of psychological and physiological problems, while other sounds, such as music, the sound of surf and birdsong, are calming, appealing to people and improve their mood.
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Table of values in decibels and ratios of amplitudes and powers
This table shows how the logarithmic scale allows you to describe very large and very small numbers representing ratios of powers, energies or amplitudes.
The human ear has very high sensitivity and is able to hear sounds from a whisper at a distance of 10 meters to the noise of jet engines. The sound power of a firecracker can be several times greater than the weakest sound that the human ear can hear (20 micropascals). This is very a big difference! Because the human ear can detect such a wide range of sound volumes, a logarithmic scale is used to measure sound intensity. On the decibel scale, the weakest sound, called the hearing threshold, is at 0 decibel level. A sound that is 10 times louder than the hearing threshold has a level of 20 decibels. If a sound is 30 times louder than the threshold of audibility, its level will be 30 decibels. Below are examples of the volume of different sounds:
- Hearing threshold - 0 dB
- Whisper - 20 dB
- Quiet conversation at a distance of 1 m - 50 dB
- Powerful vacuum cleaner at a distance of 1 m - 80 dB
- Sound that may cause hearing impairment with prolonged exposure - 85 dB
- Portable media player with full volume- 100 dB
- Pain threshold - 130 dB
- Fighter turbojet engine at a distance of 30 m - 150 dB
- Flash and sound M84 hand grenade at a distance of 1.5 m - 170 dB
Music
Music, according to archaeologists, has been decorating our lives for at least many years. It surrounds us everywhere - music is present in all cultures, and, according to scientists, it unites us with other people - in society, in the family, in an interest group. Mothers sing lullabies to their babies; people go to concerts; dances, both folk and modern, take place to the music. Music attracts us with its regularity and rhythm, as we often look for order and clarity in everyday life.
Noise pollution
Unlike music, some sounds cause very unpleasant sensations in us. Noise caused by human activities that disturbs people or harms animals is called noise pollution. It causes a number of psychological and physiological problems in humans and animals, such as insomnia, fatigue, disorders blood pressure, hearing loss with loud noise, and other problems.
Sources of noise
Noise can be caused by many factors. Transport is one of the main noise pollutants of the environment. Airplanes, trains and cars make a lot of noise. Equipment at various plants in the industrial area is also a source of noise. People living near wind turbines often complain about noise and related illnesses. Repair work, especially those involving the use of jackhammers, tends to produce a lot of noise. In some countries, people keep dogs, often for safety reasons. These dogs, most often those that live in the yard, bark if other dogs are nearby and strangers. This is not so noticeable during the day when there is already a lot of noise around, but it is very clearly audible at night. Noise in residential areas is also often caused by loud music in homes, bars and restaurants.
Wind turbines
The low-frequency noise they produce interferes with sleep and causes headaches and other symptoms in people living near the turbines, according to organizations that monitor companies that produce electricity from wind turbines. These problems are so serious that people often abandon their homes and move away to get away from this noise. Proponents of wind energy, on the other hand, argue that these problems are not caused by noise itself, but by a nocebo effect. That is, the problems are not caused by the sound itself, but by the expectation that these problems should appear. On this moment There are no long-term studies of this issue to understand who is right. Since the possibility of noise pollution is a real threat, it is necessary to begin research as soon as possible on the effect of this noise on people. Even if research shows that noise from turbines does not affect people's lives, this knowledge will help residents near wind turbines avoid the effects of the nocebo effect.
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Trains
Engineers are constantly trying to improve both the trains themselves and the tracks to reduce the noise caused by trains. Most of the noise is generated during vibrations generated when the wheels move along the rails. In addition, when turning, the wheels make noise due to the wheels slipping relative to the rails. The latter is inevitable, but the noise can be reduced. Experiments to reduce this noise are usually carried out on wheel and rail models. Often it is enough to reduce the vibration of the wheel and rails, which is achieved by improving their design. Improved brake design also helps reduce noise.
The design of the railway as a whole also affects noise. For example, installing noise barriers, similar to those around highways, can help reduce noise. Gravel mounds around the rails also absorb sound.
Some noise pollution associated with railways is inevitable. For example, an audible warning system at railway crossings is essential and helps prevent accidents. In conditions of poor visibility, it is thanks to it that pedestrians and drivers know that a train is approaching. This system is also necessary for people with poor vision.
Aircraft
Noise caused by aircraft is mainly generated during the operation of air-breathing jet and turbine-propeller engines. The problem of noise pollution exists both for passengers and crew, and for those who live near the airport. The noise in an airplane cabin when its engines are running at full power reaches 80 decibels. To reduce some of this noise, some passengers use active noise-canceling headphones, described below.
Laws in many countries do not require planes to fly below a certain altitude, even in residential areas. There are also few places where there is a limit on the total time an aircraft can remain over a given space. Typically, airspace is open to aircraft 24 hours a day, regardless of whether it is a residential area or not. When planning an airport, they often try to move it outside the city limits, but this is not always possible, especially in megacities. To help combat noise in some countries, collections of recommendations for reducing noise pollution are issued to airline companies.
Cars
Noise pollution caused by cars is a common problem, especially in cities. There are usually two reasons for noise. At high speeds it is caused by the movement of tires on the asphalt. Winter tires in the summer, or driving off-road vehicles on highways increases this problem. This is because winter and off-road tires are designed to provide maximum frictional force when driving, which in turn helps the tire have the traction needed on icy roads or off-road conditions. As the friction force increases, the noise increases accordingly.
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If, on the contrary, cars are moving slowly, then the noise is mainly caused by the engine. Car manufacturers are constantly trying to reduce this noise. It disturbs not only pedestrians and surrounding residents, but also the drivers themselves. Therefore, not only the overall sound emitted by the car is monitored, but also the sound penetrating into the cabin - especially in expensive cars. To achieve this, the cabin is soundproofed and an active noise reduction system is used. To suppress noise, sound waves are used that are in antiphase to the waves causing the noise. This method of active noise cancellation is also used in other applications, such as noise reduction in headphones. It is described in more detail below.
On large and high-speed highways, a soundproof barrier is often installed, which prevents the noise of passing cars from spreading beyond the highway. Some barriers are designed so well that a person standing on the other side of the road practically cannot hear passing cars. Unfortunately, not all barriers are so well made. Some block sound only at the ground floor level, and do not protect people living in multi-story buildings from noise at all.
Thanks to their design, electric vehicle engines are much quieter than gasoline-powered vehicles. Sometimes electric cars move so quietly that pedestrians cannot hear them, so for the safety of others, electric cars are sometimes equipped with a device that produces noise instead of the engine. This is necessary for traffic safety.
Construction and renovation work
Noise from construction and maintenance activities, such as highway and railroad repairs, often contributes to overall noise pollution. Repair work is especially often carried out at a time when the tracks or roads are used by the least number of people, that is, at night. The same noise at night disturbs people much more, not only because it is better heard in silence, but also because at this time most people are sleeping. In most cases, this noise cannot be controlled and is unavoidable. In many countries, the company that carries out construction or renovation work, must first obtain permission. It usually specifies working conditions, such as prohibiting work at night, on weekends, or on holidays.
Household and other noise
Noise in private homes is difficult to regulate by law, but city authorities generally regulate noise in in public places. For example, in some countries, private individuals are limited or completely prohibited from setting up fireworks. In some cases, fireworks are only allowed on certain holidays. Violators are usually fined. City authorities also sometimes restrict maximum noise pyrotechnic means. In some countries, authorities that monitor noise pollution in a city or region produce brochures advising residents on how to reduce the amount of household noise they make. For example, they advise informing neighbors in advance in case of upcoming noisy events or work. It is also advised to do repairs and other things that make a lot of noise at a time of day when most people are awake, as well as train dogs so that they bark less and install a noisy household appliances away from walls adjacent to the walls of neighbors. If the noise from neighboring houses and apartments is excessively loud, then in some countries it is considered normal to call the police with complaints.
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Sound insulation in some buildings, especially in apartment buildings, is poorly done, so when buying or renting a house or apartment, you need to carefully check how much sound from the street or from other apartments penetrates inside. To do this you can try the following:
- Ask your friend in advance to go out into the corridor and pretend that he is calling someone from his cell phone. This way you can find out how well the noise from the corridor can be heard in the apartment.
- Check if the floor is squeaking. If it creaks, then most likely the floorboards are poorly fitted to each other and will creak in other places, and also, probably, on the floor above.
- Try to go look at the apartment at the noisiest time of day. Since this time is different in each microdistrict, it is worth walking around the streets around the house several times a day. different time to understand when there is the most noise on the street.
- If there is a school nearby, then it will probably be in the morning and at the time when schoolchildren return home.
- If there is a large highway nearby, then during rush hour, or, conversely, early in the morning, when trucks and cars pass at high speed in the morning silence. Scanning the area at night will help you see if there are noisy businesses, such as bars, nearby.
If, despite a thorough check, you find after moving that the apartment is noisy, then try the following to reduce the noise:
- Fabrics, carpets, tapestries, and other sound-absorbing materials improve sound insulation and silence in rooms. They should cover the floor, walls, and, if possible, the ceiling. You can also hang curtains not only on the windows, but also on the walls - they will not only reduce noise, but will also serve as a decoration for the room.
- Noise is easily transmitted through solid objects as a result of their vibration. Therefore, when purchasing, it is better to choose upholstered furniture. To reduce noise, you must also limit the movement of solid objects. For example, furniture can be covered with a cloth or tablecloth.
- To reduce wall vibration, you can place heavy objects against them, such as bookcases or sideboards.
In some rental apartments, owners require residents to have carpeted floors in all rooms. If your upstairs neighbors are making a lot of noise and you suspect they don't have carpets, you might want to contact your landlord to check.
Noise legislation
In some countries noise is regulated by relevant laws. Violations usually result in fines. In this case, residents can complain about noise in the surrounding area to the authorities responsible for maintaining order. The complaint will usually be reviewed and, if possible, the source of the noise will be checked. In some countries, apartment buildings also often have noise regulations, such as whether and at what times musical instruments can be played.
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In many cities, in order to build or open a restaurant, bar, nightclub, or other establishment in a residential area that plays loud music, you must obtain a license. It often specifies what sound level is acceptable and at what time. In some areas, the construction of such establishments is prohibited, or allowed, but on the condition that the building be soundproofed. Zoning also helps with noise pollution, that is, dividing the city into zones such as bedroom, industrial, and others. In this case, areas with the greatest noise pollution, for example, industrial zones with enterprises and factories, try to be located as far as possible from residential areas, hospitals and schools.
Sound level measurement
Sound levels are measured to ensure they are within normal limits and are appropriate for the job at hand, such as that microphones provide sufficient volume during an event. Such measurements are also necessary to ensure safe noise levels in the workplace.
Sound level meters
If ambient noise exceeds 85 decibels, there is a high likelihood of hearing damage, especially when a person is exposed to such noise for a long time. A person's pain threshold starts at 115 decibels, but for some people it can be as high as 140 decibels. That is, even if the sound level threatens hearing loss, people do not notice it. This is why in situations where people are exposed to loud sound for a long time, the sound level is measured special devices to make sure that this level does not exceed the norm. Usually these are sound level meters. Most of them are portable and can be purchased at an affordable price.
Sound dosimeters
If it is necessary to measure not only the current sound level, but also the total dose of noise exposure over a certain period of time, sound dosimeters are used. Since long-term exposure to loud sounds often causes hearing damage, dosimeters can help determine whether people working in loud noise environments need to wear hearing protection or earplugs. It is also convenient to use dosimeters if the sound level is not the same throughout the day. Typically, dosimeters are attached to the clothing of the workers themselves, but not everyone welcomes the use of dosimeters in the workplace, since many problems are associated with them. For example, workers can easily distort data, either intentionally or accidentally, especially when they see an audio level indicator. Dosimeters also often interfere with operation and can even get caught and fall into equipment. This risks not only broken equipment, but also likely accidents to workers. For this reason, sound level meters can be used instead of dosimeters, measuring sound levels at different times and in different places. Using this information, a noise map is created that gives a rough idea of the noise pollution in different areas of the workspace. This is especially useful to know if employees work in the same places every day. Recently, dosimeter manufacturers have also been trying to combat the above problems by producing dosimeters smaller size, with short wires or no wires at all, and often without a display so that the worker cannot influence the operation of the device based on current noise information.
Ways to deal with noise
In factories, airports and other noisy workplaces, it is necessary to not only measure but also control the amount of noise workers hear to protect their hearing and prevent hearing loss. Noise not only impairs hearing, but also makes it difficult for people to concentrate. This interferes with their work and exposes them to additional danger because if they are not careful, they may not hear the hazard warning lights due to the noise, which could lead to an accident. In addition, it is unpleasant to be and work in a noisy room, so the sound is also controlled for the comfort of workers. It is not always possible to use a sound level meter. In such a situation, a simple rule applies: if you have to shout in order to be heard, this means that the room is too noisy, and this noise needs to be reduced.
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There are two main ways to deal with noise: noise insulation or noise reduction using counteracting noise. The first method is passive, and the second is active. Which of the two methods to use is decided depending on the situation, and sometimes both are used at once. You can also use several methods of passive noise reduction or noise blocking at the same time. For example, ground teams Maintenance Airports often use earplugs and passive noise-canceling headphones at the same time.
Sometimes factories and factories also use sound absorbers. They prevent sound from being amplified in the room and reflected from walls and other surfaces. For this purpose, sound absorbers are made from materials that absorb sound well.
Passive Noise Cancellation
For passive noise reduction, materials that absorb sound well are used. Most of the above tips for reducing noise in an apartment are based on this principle. The sound-absorbing materials used in headphones are foamed polymers.
Active Noise Cancellation
Active noise cancellation can reduce ambient noise by about 20 decibels. The principle of active sound cancellation is that an incoming sound wave is canceled by an outgoing sound wave with the same amplitude but opposite phase. The outgoing noise is generated by headphones.
What happens to sound in this case can be demonstrated using the example of a swing. When one person pushes the swing forward, and another, with the same amplitude, begins to swing it back, then these pushes will be in antiphase. When two waves are out of phase, they total amount equal to zero. That is, in the case of a swing, it will stop swinging.
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To properly block sound, noise canceling devices must first detect the amplitude and frequency of incoming sound waves so they can then create similar waves in antiphase. Such devices work well with monotonous, repetitive sound that is easy to predict. If the sound is spontaneous and changes all the time, then noise-cancelling devices are ineffective. Incoming audio is received in devices such as headphones using the built-in microphone. Except cabins latest models cars and household headphones, active noise cancellation used in some ear protection for airport workers.
Maintaining protective equipment in working order
Although employers in many countries are required to provide their employees with personal hearing protection, such as headphones and earplugs, it is always best to check them before use to ensure they are in working order and are not cracked anywhere. This is especially important because errors sometimes occur and faulty equipment may not be noticed when it is inspected.
Unit Converter articles were edited and illustrated by Anatoly Zolotkov
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Acoustics - sound
Sound level
Sound is elastic waves propagating in an elastic medium (solid, liquid or gas) and creating mechanical vibrations in it. Sound waves are one example of many oscillatory processes.
A decibel (dB) is a unit of measurement of sound levels, power levels, or amplitudes of electrical signals by comparing them to a given level and applying a logarithmic scale to the resulting ratio. More broadly, the decibel can be defined as a logarithmic dimensionless unit of the ratio of levels to some reference level, as well as attenuation and gain. A value expressed in decibels is numerically equal to the decimal logarithm of the dimensionless ratio of a physical quantity to the physical quantity of the same name, taken as the original, multiplied by ten. A decibel is equal to one tenth of a bel, which is rarely used. A change in power of 100 times is represented as a change of 20 dB. A change of 3 dB approximately corresponds to a change in power by a factor of two. In science and technology, in particular in electronics and radio engineering, the decibel is used to measure the ratio of certain quantities - “energy” (power, energy, power flux density) or “amplitude” (current, voltage, sound).
In acoustics, the decibel is commonly used to indicate the loudness of a sound relative to 0 decibel level, which is defined as a sound pressure level of 20 micropascals. Typically this ratio is specified for power.
Neper (Np) - logarithmic dimensionless unit measuring the ratio of two levels, attenuations or gains. Napier is not included in the SI system of units. The difference between bels and nepers is that the ratio of quantities expressed in bels or decibels involves the use of decimal logarithms, while the ratios in nepers use natural logarithms (base e).
Using the Sound Level Converter
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The Internet is full of similar calculators, but I also wanted to make my own. I’m sure I won’t surprise anyone by saying that it works here too JavaScript, and all the computing load falls on your browser. If there empty fields, this means that your browser does not work with JavaScript-ohm, and the calculations won't work :(
19 Dec 2017 an EMC unit converter has appeared. Perhaps it better suits your needs?
Terms of use simple as hell. Change the value of any of the values, and all other values will be recalculated automatically.
Converting the ratio of incident and reflected power to SWR:
Just in case, a hint for use:
Recalculate dBµV V dBm(dBμV to dBm) In the “Voltage, dBμV” field, enter the voltage value in decibel-microvolts. If you have a value in decibel-millivolts (dBmV), just add 60 dB to it (0 dBmV ≡ 60 dBmV). Don't forget that to convert voltage into power, you also need to know the load resistance! dBm V dBµV Recalculate (dBm in dBμV) In the “Power, dBm” field, enter the power value in decibel-milliwatts. If you have a value in decibel-watts, just subtract 30 dB from it (0 dBW ≡ 30 dBm). Don't forget that to convert power into voltage, you also need to know the load resistance! Convert decibels by times Enter in the table the change in level in decibels, and the calculator will show how many times the voltage and power will change. The calculator doesn't like it
Unit Bel expresses not the quantity itself, but the ratio of one quantity to another. Bel is a logarithmic unit. More often this unit is used with the decimal prefix “ deci-", i.e. "tenth part" It is convenient to measure attenuation and gain coefficients in decibels:
Why logarithms? So, after all, human perception is logarithmic in nature! Imagine a shopping bag weighing 1 kg. If you add another liter kilogram to this mass, the change in mass will be very noticeable. If the same kilogram is added to the mass, say, 15 kg, then the weight gain will be noticeable, but will hardly be felt. And if this kilogram is added to a whole ton, then the increase will be completely unnoticeable. To push a car with and without a liter of juice, the same amount of force is required.
In addition, we recall the mathematics of logarithms and see how some calculations are simplified.
This already makes life easier. Let's solve a simple problem:The signal power is attenuated in the line by 6.3 times; on the receiving side, the amplifier increases the power by 25 times. How many times will the signal power at the output of the amplifier be greater or less than at the output of the generator?
We have just calculated how many times the signal power at the output of the path differs from that supplied to the path. Surely I would like to know the magnitude of this power. Is it possible to express the values themselves in decibels? Of course you can! To do this, you need to divide the value by one.
Now calculate the signal power at the output of the path, expressed in dBW, is not difficult. For example, if the input power was 0.25 W (-6 dBW), then the signal power at the path output
About 1 W, as you might guess. Let's convert to watts: 
Now remember a few statements:
- Power change 2 times- This 3 dB
- Power change 3 times- This 4.8 dB
- Power change 10 times- This 10 dB
- Power change 100 times- This 20 dB
...power change...
I deliberately wrote above only about capacities. Power has a quadratic dependence on voltage and current, and a change of 3 decibels is always and in all cases a change power 2 times. As we remember, power depends on the square of the voltage or the square of the current:
Remember that the logarithm of an exponent is the product of the exponent and the logarithm of the base. The exponent is two, and you need to multiply not by 10, but by 20. Let's express 2 Volts in decibel-volts, and 3 decibel-volts in Volts: 
Simple and not scary!
- In calculations of energy quantities (power) the number 10 appears
- In calculations of power quantities (voltage, current) the number 20 appears
A few calculations
Let’s solve a few calculation problems so that we can confidently navigate decibels.
1. Sound volume
The volume of sound is also measured in decibels. Remembering that a decibel is a measure of the ratio of two quantities, we Necessarily We always clarify in relation to what these decibels are measured, i.e. where is the origin of the countdown? And in this case - in relation to the human hearing threshold: 2×10 -5 N/m 2. Newton is a system unit of force, i.e. It is clearly a force quantity, so the number 20 appears in the calculations. Let’s calculate the force that sound pressure exerts on the eardrum in our ear, when a jet plane takes off and during a quiet conversation.
What we know:
- Values in decibels are expressed relative to 2×10 -5 N/m 2
- The area of the human eardrum is about 55 mm 2, or 5.5 × 10 -5 m 2
- Table volume of a jet aircraft - 120 dB at a distance of 5 m
- Table volume of quiet conversation - 50 dB at a distance of 1 m
Einstein, Newton and Pascal played hide and seek. It fell to Einstein to drive. Pascal ran into the bushes, disguised himself, the man is not visible at all, but Newton just stands there. He drew a square around himself and stood there. Einstein counted to one hundred, turns around, sees Newton and shouts:
- Hooray! I found Newton!
Newton answers with a sly smile:
- I was wrong, smart guy! That's Newton per square meter! YOU FOUND PASCAL!!!
Let's calculate the sound pressure in Pascals, or Newtons per square meter:
We multiply the pressure in Pascals by the area in square meters to get the force in Newtons:
Let's convert Newtons into more tangible gram-forces:
- Jet plane exerts pressure
0.0011 N × 102 gf/N = 0.1122 gf - The sound of a quiet conversation presses on the eardrum with silo
0.0000003479 N × 102 gf/N = 0.000035 gf
As they say, feel the difference! And don’t forget that the mechanism of hearing is more complex, and we perceive sound not only through the eardrum in the depths of the ear!
2. Converting voltage level to signal power
At work, we often measure radio signal levels at the antenna input of a measuring receiver. And the measuring receiver in its metrological properties is close to a selective voltmeter, and the measured value is calculated in decibel-microvolts ( dBµV). At the same time, radio measurements often operate on the signal power at the receiving point, often expressed in decibel-milliwatts ( dBm). Let's count one into the other!
And for greater happiness, I made an online calculator that converts voltage in decibel-microvolts into power in decibel-milliwatts and vice versa (I know, I know, there are countless of them on the Internet without me! :))
Online decibel calculator
Terms of use simple as hell. Change the value of any of the values, and all other values will be recalculated automatically.
| Voltage, mV: | ||
| Voltage, dBμV: | ||
| Power, dBm: | ||
| Power, mW: |
Very often, beginners are faced with such a concept as decibel. Many of them intuitively know what it is, but most still have questions.
Relative logarithmic Bela units (decibels) are widely used in quantifying parameters various audio, video, measuring devices. The physical nature of the powers being compared can be anything - electrical, electromagnetic, acoustic, mechanical - it is only important that both quantities are expressed in the same units - watts, milliwatts, etc. Bel expresses the ratio of two values of an energy quantity by the decimal logarithm of this ratio, and Energy quantities mean: power, energy.
By the way, this unit got its name in honor of Alexander Bell (1847 - 1922) - an American scientist of Scottish origin, the founder of telephony, the founder of the world famous companies AT&T and Bell Laboratories. It is also interesting to recall that in many modern mobile phones(smartphones) there is always a selectable ringing sound (notification), called “bell”. However, Bel refers to units not included in International system units (SI), but in accordance with the decision of the International Committee of Weights and Measures, it is allowed to be used without restrictions in conjunction with SI units. Mainly used in telecommunications, acoustics, and radio engineering.
Formulas for calculating decibels
Bel (B) = log (P2/P1)
Where
In practice, it turned out that it is more convenient to use the Bel value reduced by 10 times, i.e. decibel, therefore:
decibel (dB) = 10 * log(P2/P1)
Strengthening or weakening power in decibels expressed by the formula:
Where
P 1 - power before amplification, W
P 2 - power after amplification or attenuation, W
Bel, decibel values can be with a “plus” sign if P2 > P1 (signal amplification) and with a “minus” sign if P2< P1 (ослабление сигнала)
In many cases, comparing signals by measuring powers may be inconvenient or impossible - it is easier to measure voltage or current.
In this case, if we compare voltages or currents, the formula will take a different form:
Where
N dB - gain or loss of power in decibels
U 1 is the voltage before amplification, V
I 1 - current strength before amplification, A
I 2 - current strength after amplification, A
Here is a small plate that shows the basic voltage ratios and the corresponding number of decibels:
The fact is that the operations of multiplication and division on numbers in the usual basis are replaced by the operations of addition and subtraction in the logarithmic basis. For example, we have two cascaded amplifiers with gains K1 = 963 and K2 = 48. What is the total gain? That's right - it is equal to the product K = K1 * K2. Can you quickly calculate 963*48 in your head? Me not. I can estimate K = 1000*50 = 50 thousand, no more. And, if we know that K1 = 59 dB and K2 = 33 dB, then K = 59+33 = 92 dB - it wasn’t difficult to add up, I hope.
However, the relevance of such calculations was great in the era when the concept of Bel was introduced and when there were not only iPhones, but also electronic calculators. Now it’s enough to open the calculator on your gadgets and quickly calculate what is what. Well, in order not to worry every time when converting dB into several times, the most convenient way is to find an online calculator on the Internet. Yes, at least here.
Weber-Fechner law
Why decibels? Everything comes from the Weber-Fechner law, which tells us that the intensity of the sensation of human feelings is directly proportional to the logarithm of the intensity of any stimulus.
So a lamp with eight light bulbs seems to us as much brighter than a lamp with four light bulbs as a lamp with four light bulbs is brighter than a lamp with two light bulbs. That is, the number of light bulbs should double each time so that it seems to us that the increase in brightness is constant. That is, if we add one more light bulb to our 32 light bulbs on the graph, we won’t even notice the difference. In order for the difference to be noticeable to our eyes, we must add another 32 light bulbs to the 32 light bulbs, etc. Or in other words, in order for us to feel like our lamp is gradually gaining brightness, we need to light twice as many light bulbs each time as the previous value.
Therefore, the decibel is indeed more convenient in some cases, since it is much easier to compare two values in small numbers than in millions and billions. And since electronics is a purely physical phenomenon, decibels are not spared.
Decibels and amplifier frequency response
As you remember in the previous example with an op-amp, our non-inverting amplifier amplified the signal 10 times. If you look at our plate, it turns out to be 20 dB relative input signal. Well yes, that's how it is:
Also in dB on some frequency response graphs the slope of the frequency response characteristic is indicated. It might look something like this:
In the graph we see the frequency response of the bandpass filter. Signal change +20 dB per decade(dB/dec, dB/dec) tells us that for every increase in frequency by 10 times, the signal amplitude increases by 20 dB. The same can be said about the signal decay of -20 dB per decade. With each increase in frequency by 10 times, the amplitude of the signal will decrease by -20 dB. There are also similar characteristic dB per octave(dB/oct, dB/oct). Here, almost everything is the same, only the signal changes with each increase in frequency by 2 times.
Let's look at an example. We have a filter high frequencies(HPF) of the first order, assembled on an RC circuit.
Its frequency response will look like this (click for full opening)
We are now interested in the inclined straight line of the frequency response. Since its slope is approximately the same up to a cutoff frequency of -3 dB, you can find its slope, that is, find out how many times the signal increases for each increase in frequency by 10 times.
So let's take the first point at a frequency of 10 Hertz. At a frequency of 10 Hertz, the signal amplitude decreased by 44 dB, this can be seen in the lower right corner (out: -44)
We multiply the frequency by 10 (decade) and get the second point of 100 Hertz. At a frequency of 100 Hertz our signal decreased by approximately 24 dB
That is, in one decade our signal increased from -44 to -24 dB per decade. That is, the slope of the characteristic was +20 dB/decade. If +20 dB/decade is converted to dB per octave, you get 6 dB/octave.
Quite often, discrete attenuators (dividers) of the output signal measuring instruments(especially on generators) are graduated in decibels:
0, -3, -6, -10, -20, -30, -40 dB. This allows you to quickly navigate the relative level of the output signal.
What else is measured in decibels?
Also very often expressed in dB (signal-to-noise ratio, abbreviated SNR)
Where
U c is the effective value of the signal voltage, V
U sh - effective value of noise voltage, V
The higher the signal/noise value, the more clear sound provided by an audio system. For musical equipment, it is desirable that this ratio be at least 75 dB, and for Hi-Fi equipment at least 90 dB. The physical nature of the signal does not matter, it is important that the units are in the same dimensions.
As a unit of the logarithmic ratio of two like physical quantities neper (Np) is also used - 1 Np ~ 0.8686 B. It is based not on the decimal (lg), but on the natural (ln) logarithm of the ratios. Currently rarely used.
In many cases, it is convenient to compare not arbitrary values with each other, but one value relative to another, called conventionally reference (zero, base).
In electrical engineering, a power value equal to 1 mW allocated across a resistor with a resistance of 600 Ohms is chosen as such a reference or zero value.
In this case, the base values when comparing voltages or currents will be 0.775 V or 1.29 mA.
For sound power, this basic value is 20 microPascal (0 dB), and the threshold of +130 dB is considered painful for a person:
More details about this are written on Wikipedia at this link.
For cases when certain specific quantities are used as basic values, even special designations units of measurement:
dbW (dBW)- here the countdown is relative to 1 Watt (W). For example, let the power level be +20 dBW. This means that the power has increased 100 times, that is, by 100 watts.
dBm- here we are already counting relative to 1 milliwatt (mW). For example, a power level of +30dBm will be correspondingly equal to 1 W. Don’t forget that these are energy decibels, so the formula will be valid for them
The following characteristics- these are already amplitude decibels. The formula will be valid for them
dBV- as you guessed, the reference voltage is 1 Volt. For example, +20dBV will give - this is 10 Volts
From dBV other types of decibels with different prefixes also follow:
dBmV— reference level 1 millivolt.
dBuV (dBμV)— reference voltage 1 microvolt.
Here I have given the most commonly used special types of decibels in electronics.
Decibels are also used in other industries, where they also show the ratio of any two measured quantities on a logarithmic scale.
With input from Jeer
