What is noise? Types of noise and noise levels. Red noise Noise can be
Sounds surround us everywhere - only in rare cases can a modern person be completely immersed in silence. In this regard, the importance of regulating noise parameters increases. At workplaces, for example, special requirements are imposed on the organization of working conditions. The list of such requirements certainly includes optimal indicators of sound exposure. However, noise research may be required in other situations - in a medical facility, in public places and, of course, at home. For this purpose, special devices are used - sound level meters. But first, it’s worth understanding the very nature of sound.
Sound sources
Most of the sources of urban noise are formed by anthropogenic factors, for example, vehicles, air flows that pass between buildings, engineering systems, etc. As a rule, the causes of noise of this kind are negative in nature, since they are dominated by low frequencies, as well as chaotic changes accents across the entire spectrum. This can be judged especially by the work of industrial enterprises and
Of course, the most favorable conditions, from an acoustic point of view, are found outside the city. In this case, the source is nature itself. One of the most soothing and relaxing is the sound of the sea, which is characterized by periodic and pronounced vibrations. The unhurried and monotonous sound creates a unique and attractive marine rhythm that helps strengthen the nervous system.
Device design
In the modern market of sound level meters, digital devices are popular today. They are small in size and have a reliable plastic case, which is complemented by a microphone - however, this element can be integrated inside the device. The device also includes an amplifier, filtering elements, an indicator and a detector. Actually, the human ear has many parts that are similar in functionality. In turn, special equipment allows you to study noise while recording several parameters simultaneously. Filters capture sounds with different frequencies, and information about the measurements taken is reflected on the screens in decibels. As for power supply, most sound level meters are powered by a battery, the charge of which can vary from 50 to 70 hours.
Principle of operation
As for the principle of operation, in this case it is more appropriate to compare the device with a microphone. The main difference will be that the sound level meter interacts during the measurement process with a voltmeter, calibrated in decibels. Since the electrical flow signal output from the microphone is equivalent to the original noise, an addition to the level of acoustic pressure that acts on the membrane will cause a similar increase in current voltage when entering the voltmeter. The noise measurement is based on this principle, the indicators of which are reflected on the display. To measure indicators, the signal is passed through special filters - this is done at the moment when it is on the way from the microphone to the voltmeter.
Since the ability of the ear to perceive sound is determined not only by the frequency properties of noise, but also by its intensity, the devices provide several types of filtering elements. The choice of a specific device depends on the characteristics of the permissible noise at the measurement site. Filters make it possible to simulate the amplitude-frequency spectrum under conditions of a given noise power.
Technical and operational characteristics
Manufacturers strive to distinguish between models designed exclusively for measuring loudness and devices for universal measurements. Nevertheless, the volume level remains one of the key characteristics of almost all sound level meters - this indicator varies from 30 to 130 dB. It is important to note one feature of noise meters. Some models, when operating in conditions where the sound coefficient exceeds the maximum level of the scale, do not conduct a noise study at all due to limitations in their capabilities. The next characteristic is measurement accuracy. This quality is determined by the error, which can range from 1 to 1.5 dB. Accordingly, the smaller the deviation in the sound level meter measurements, the higher its accuracy. The operation of devices may be affected by temperature conditions. For example, if the range from 0 to 40 °C is indicated, then the device can be used in open areas.
Manufacturers
On the market you can find devices from specialized manufacturers of measuring equipment, as well as products from well-known construction brands. The first category includes Testo models, which can be called the best in class. They are distinguished by wide-capacity batteries and a wide range of decibel measurements. However, devices of this brand are the most expensive - on average from 20 to 30 thousand rubles. If you plan to study noise in a domestic environment, you can pay attention to Geo-Fennel and ADA products. Firstly, the models of these manufacturers provide good measurement accuracy, and secondly, they are affordable - on average, such devices cost 3-4 thousand rubles.
Noise level measurements
To understand whether noise level is a physical quantity, you need to understand what a decibel is, which measures sound itself. By the way, this quantity got its name in honor of Alexander Graham Bell, who invented the telephone, and had nothing to do with the sound pressure level. But historically this is how it happened.
Noise level in dB
So it is believed that a decibel is a unit of measurement for noise. Although this is not true. Why? The thing is that a sound wave can be measured by several parameters, one of which is the energy per area. That is, noise is measured, or more precisely, its intensity in watts per square meter W/m². But with this unit of measurement, difficulties arise.
Impact of loud noise
For example, the noise intensity of the quietest conversation is 0.000000000001 W/m². but the sound of a rocket taking off is 1000 W/m². that is, it turns out to be a fairly wide range, which is simply inconvenient to record. Therefore, scientists adopted a completely different measuring unit, which denoted a ratio, where the standard or nominal value was that very low conversation, which can be mathematically designated as 10 −12 W/m 2 . If we compare this value with the noise of a rocket launch, it turns out that the latter is 15 times higher than the standard one. So the change in the indicator by 10 became known as white. And its tenths of decibels. That is, any change in noise intensity is its ratio to the reference indicator.
Important. Decibels are not a value like, for example, volts or amperes, kilometers and centimeters. In order to understand this, it is necessary to give an example. If you add 20 m to 1 km, the total will be 1.02 km or 1020 m. If you add the same amount to 10 dB, you will not get 20 dB. It's essentially a logarithmic function, so when you double a number, it only increases by 0.3. That is, the total will be not 20 dB, but 13 dB.
That is why, when choosing a soundproofing material, it is necessary to measure the noise level and then compare it with the indicator of the material. And one moment. For comparison, let's give an example. Soundproofing boards ISOPLAAT, the model line of which includes panels with a thickness of 10 and 25 mm. So, the first one has a sound protection value of 22 dB, the second one has a value of 26 dB. This again comes to the question of why the sound (noise) level is not determined in direct proportion to the auxiliary criteria.
It is quite difficult to determine the level or intensity of noise, so pressure fluctuations in the sound flow are measured. In this case, one can trace the pattern that the sound pressure range is much smaller than the intensity limits. Hence the conclusion: the pressure grows much slower than the intensity, almost twice as much. That is, if you double the sound pressure, the noise level or intensity will quadruple.
We can leave the scientific proceedings at this point. Let's move on to the main issue of the topic - the permissible noise level.
Maximum permissible noise level standards
Why were these indicators introduced? The whole matter, as always, depends on human health. There are special hygienic standards that clearly define how loud the noise should be (of a long-term nature) so that it does not harm a person’s hearing system. So here it is:
- during the day, the permissible noise level should not exceed 55 dB;
- at night 40 dB.
To make it easier for you to navigate various noises, we suggest that you familiarize yourself with the table, which describes all kinds of noises, as well as their values in decibels (dB):
Noise intensity
What conclusion can be drawn from looking at the table presented? All noises that we hear every day exceed the maximum permissible norm. But these are almost all natural sounds, from which it is very difficult to hide in our everyday life. And there are also those that we can control. For example, noise from a TV or stereo system. With a strong sound, there is more harm than the pleasure that both devices bring.
- 70-90 dB with prolonged exposure sharply reduces hearing.
- Above 100 dB can cause complete deafness.
How to measure sound (noise) level
There are certain maximum permissible standards that guarantee the protection of people living in cities in apartment buildings. So this document clearly states that the maximum permissible background sound level at night should not exceed 30 dB. But if your neighbor is carrying out repairs, and careless craftsmen work at night, then you can measure the pressure level of the noise emitted in order to bring both the neighbor and the craftsmen to justice with a fine.
How can this be done, what equipment is needed for this? To find out, you need:
- Call a specialist who has a special device. This device comes with a very sensitive microphone that records sounds and transfers them to a monitor that shows the level in decibels. Such a service is not cheap, as is the device itself.
- Use a computer, tablet, iPhone and other gadgets. To do this, you need to download a special application from the Internet. There are several of them. Some are paid, some are free. Since there is no need for high accuracy in determining the maximum permissible sound pressure, an approximately taken measurement already guarantees a certain success in your endeavor. So this is the simplest and most affordable option. The main thing, as always, is to understand and use the device correctly.
How to calculate sound (noise) level
It is impossible to independently calculate the noise level (its pressure) if you are not a specialist in this matter. Why? Because for the calculation it is necessary to take into account a fairly large number of various conditions. Eg:
- The noise source itself, as well as all its characteristics and properties, are determined.
- The noise in each room is measured separately, for which a professional device is used.
- The points where the calculation will be performed are selected.
After which the specialist will need other data.
- Indicators of the room (dimensions, what material it is built from, etc.).
- Sound pressure spectrum.
- Are there any barriers to noise propagation and their characteristics?
- The distance from the calculated point where the measuring device will be installed to the sound source.
What is included in the calculations? In principle, this is a fairly voluminous and serious document.
- Collected data and their analysis.
- List of sources.
- Calculation of sound pressure.
- Calculation of sound power.
- Full analysis of the situation.
Advice. Such calculations are much easier to carry out at the design stage of a building, at the stage of major repairs or before carrying out soundproofing work.
Conclusion
Everything related to noise level, with the concept of sound pressure measured in decibels, it is necessary to understand that both measurement and calculation are carried out according to special standards. It is their accounting that allows us to determine what kind of atmosphere we live in. And if the indicators exceed the maximum permissible norms, then this situation will have to be dealt with. How? Firstly, the market offers a huge range of different soundproofing materials for this purpose. Secondly, this is the topic of another article.
We have already noted that there are two types of noise based on the nature of its distribution in the room: airborne and structural. In airborne noise, vibrations created by, for example, the speakers of a running TV set produce sound waves in the form of air vibrations. This type of noise predominates outdoors. The first of the tables below shows the most common sources in everyday life, the noise from which exceeds the standard level (40 dBA during the day, 30 dBA at night - according to SNiP II-12-77).
A mechanical action, such as hammering a nail into a wall or moving furniture across the floor, can also be a source of noise. This noise is called structural noise, and it is generated in this way: vibration of the floor from footsteps is transmitted to the wall, and its vibrations are heard in the next room. The most unpleasant structural noise is the impact type. Most often it spreads over long distances from the source. The same knock on the central heating pipe on one floor is clearly audible on all the others and is perceived by residents as if its source was in their room. In the second table you can see the sources of structural noise.
Table 2. Household noise sources |
||
A. Air | ||
№ | Noise source | Noise level, dBA |
1 | TV | 70 |
2 | Music Center | 85 |
3 | Conversation (calm) | 65 |
4 | baby crying | 78 |
5 | Piano playing | 80 |
6 | Vacuum cleaner operation | 75 |
7 | -//- washing machine | 68 |
8 | -//- refrigerator | 42 |
9 | -//- electric shavers | 60 |
10 | -//- electric polisher | 83 |
11 | -//- forced ventilation | 42 |
12 | -//- air conditioner | 45 |
13 | Cooking on the Stove | 35-42 |
14 | Filling the bath | 36-58 |
15 | Filling the tank in the bathroom | 40-67 |
16 | Water flowing from a tap | 44-50 |
B. Structural | ||
№ | Noise source | Noise level, dBA |
1 | Elevator movements | 34-42 |
2 | The sound of the elevator door closing | 44-52 |
3 | The sound of a garbage chute closing | 42-58 |
4 | Knocking on the central heating pipe | 45-60 |
There are also household appliances that are sources of both types of noise. These include a forced ventilation system. Airborne noise enters the room through air ducts, and structural noise occurs due to vibration of the walls of the fan protective casing and the air ducts themselves.
Sound and noise
So, sound is a physical process caused by the oscillatory movement of particles in the medium. Sound vibrations have a certain amplitude and frequency. A person is able to hear sounds that differ in amplitude tens of millions of times. Well, the frequencies perceived by our ear are in the range of 16-20,000 Hz. The energy of sound is characterized by intensity (W/m2), or sound pressure (Pa). From birth we have the ability to hear both the rumble of thunder and the slightest rustle of leaves. To be able to compare such different sounds, the following were adopted: the sound intensity level indicator L and the unit of measurement - decibels (dB). The human hearing threshold corresponds to a sound pressure of 2 10 -5 Pa, or 0 dB. In turn, noise is a chaotic, discordant mixture of sounds that has a negative effect on the nervous system.
The decibel is used to measure sound.
This is a relative logarithmic unit of measurement of quantities associated with sound intensity (power, amplitude, signal voltage or current, gain/attenuation, etc.). Hearing sensitivity is logarithmic in nature - an increase in intensity in the form of a power function is perceived by the ear as a linear increase in volume, therefore in some cases it is more convenient to use logarithmic rather than linear units. The decimal logarithm of the ratio of a certain quantity to its reference value – lg ( X/X E) is called white (B), and its tenth part is lg ( X/X E) / 10 – decibel (dB). Measuring in decibels is also convenient because the human ear can distinguish a relative change in intensity of approximately 1 dB.
When measuring absolute sound intensity (W/m2), the reference value is the level of the hearing threshold for a sinusoidal signal with a frequency of 1 kHz – 10 to the power of –12 (10 –12) W/m2. In this case, the hearing threshold is determined by an intensity of 0 dB, and the intensity at which pain begins (pain threshold) is about 140 dB. The intensity of a quiet whisper is about 35 dB, a loud voice is about 95 dB, forte fortissimo orchestra - about 100 dB, orchestral tutti (sound of all instruments) - about 120 dB.
When measuring quantities with which intensity is related by a quadratic dependence - voltage, current and sound pressure - in the expression for decibel, the factor of 10 changes to 20 (the two is taken out from the logarithm of the ratio of the squares).
When measuring relative quantities, any value of the quantity is taken as the reference level. For example, when estimating gain, it is taken to be unity gain (signal transmission without change) equal to 0 dB. In this case, 60 dB corresponds to an amplification of 1000 times (60 = 20lg 1000), and –20 dB corresponds to a weakening of 10 times. The decibel per octave (dB/octave) unit is also used to describe the characteristics of amplifiers and filters, indicating the change in gain when the frequency changes by a factor of two.
In acoustics, it is customary to measure loudness in dB. SPL(Sound Pressure Level). Doubling the sound intensity results in a 3 dB increase in intensity level.
When expressing the sound pressure level in decibels, it should be remembered that when the pressure doubles, 6 dB is added.
There are types of measurements: dBA,dBB,dBC,dBD– reference levels are selected according to the frequency characteristics of “weight filters” in accordance with equal loudness curves.
Acoustic decibel
A unit of noise level measurement with a filter applied to the meter that takes into account the peculiarity of noise perception by the human hearing aid (nonlinearity of the frequency response of the ear). dBA value - The sound pressure level measured in dB by a sound level meter containing a correction circuit that reduces the sensitivity of the device at low and very high frequencies in order to more closely simulate the sensitivity of the human ear and provide a reading that gives some indication of loudness, unpleasantness or acceptability sound. The dBA value is usually 10 units higher than the equivalent value of the normalized noise index for a given sound.
In digital processing, the concept of dB is calculated from zero and down into the region of negative values. Zero is the maximum level representable by a digital circuit.
IN dBFS(Full Scale– “full scale”) – the reference voltage corresponds to the full scale of the device; for example, “the recording level is −6 dBFS" For linear digital code, each digit corresponds to 6 dB, and the maximum possible recording level is 0 dBFS.
Noise is a chaotic combination of sounds of varying strength and frequency. Sound as a physical phenomenon is a wave-like movement in an elastic medium, caused by the oscillatory movements of a sounding body and perceived by the organ of humans and animals. From the physical side, sound is characterized by the sound pressure level, measured in decibels, and the vibration frequency, expressed in hertz (Hz - 1 vibration per second). A person perceives sound vibrations with a frequency from 16 to 20,000 Hz. The strength of sound pressure does not completely determine the degree of its perception by the hearing organ, since the nervous apparatus of the inner ear, which perceives sound, is more sensitive to high-frequency sounds. To compare the degree of perception of sounds of different frequencies, a special unit of volume was introduced - “background” (the volume level of a standard tone with a frequency of 1000 Hz, the sound pressure strength of which is 1 dB).
The noise level is measured using special devices - sound level meters. Determination of the noise spectrum (the frequencies of its constituent sounds and the part of the total sound energy attributable to individual frequencies) is carried out using noise spectrum analyzers.
Noise has an adverse effect on the human body and can cause various kinds of painful conditions, including (see) deafness. Under the influence of noise, breathing becomes more frequent and energy consumption increases. Long-term exposure to noise has a harmful effect on the central nervous system and human psyche. As a result of exposure to noise, a person develops symptoms of fatigue and exhaustion of the nervous system. On the mental side, there is a depressed mood, decreased attention, intellectual processes are delayed, and nervous excitability increases. Noise reduces efficiency and productivity, interferes with normal rest and... Under the influence of significant noise, a change in the normal activity of various organs and systems is observed (changes in the secretion of gastric juice, increased blood pressure, etc.).
Measures to combat noise in populated areas are: rational planning, landscaping, streamlining street traffic, replacing noisy types of urban transport with less noisy ones, prohibiting sound signals from transport, soundproofing residential buildings, reducing the noise of engineering equipment built into buildings (elevators, pumps, engines, fans, etc.), limiting household noise. Measures to reduce or eliminate noise in production are: changes in the technological process, noise metric control of new types of industrial equipment, sound insulation of production premises with noisy processes and noise sources, the use of sound absorbers, supervision of operating equipment. Machines that produce loud noise are installed on special foundations, separated from other structures by air layers made of elastic materials. In noisy workshops, personal protective equipment for workers is used (see). Workers in noisy workshops undergo a preliminary medical examination by a neurologist, otorhinolaryngologist and therapist. Contraindications are persistent hearing loss, internal diseases and, in some cases, organic diseases of the central nervous system and diseases.
Requirements for noise levels are established in accordance with the Hygienic Standards for Permissible Sound Pressure Levels and Sound Levels in Workplaces No. 1004-73 (approved by the Chief Sanitary Doctor of the USSR on January 12, 1973) and the Sanitary Standards for Permissible Noise in Residential and Public Buildings and on residential area No. 872-70.
Noise (noises) are random non-periodic vibrations of various physical natures.
Noise intensity is assessed by the ratio of the generated sound pressure to the pressure taken as a unit of comparison, which corresponds approximately to the threshold for the human ear to perceive a tone with a frequency of 1000 Hz.
Since the ratio of sound pressures from the perception threshold (2·10 -5 n/m2) to the pain threshold (20 n/m2) changes millions of times, it is customary to measure noise intensity in logarithmic units - decibels, which significantly reduces the measurement scale. In hygienic practice, the measurement scale is limited to the range from 20 to 140 dB. The set of frequencies that make up noise is called the noise spectrum.
Based on the nature of the change in total intensity over time, noise is divided into stable, with a change in intensity over time of no more than 5 dB, and pulsed (shock) with a sharp increase and subsequent decrease in intensity.
Based on the width of the spectrum, they distinguish between narrowband noise, consisting of a limited number of adjacent frequencies, and broadband noise, including almost all frequencies of the audible range. Based on the predominance of intensities in the spectrum in the frequency range up to 300 Hz, noise is considered low-frequency, above 1000 Hz - high-frequency, from 300 to 1000 Hz - mid-frequency. Based on the time of exposure to noise on the human body, they are distinguished: long-term, lasting for 4 hours or more, and short-term noise - less than 4 hours per work shift. Noise is measured using sound level meters - instruments that determine the overall noise intensity. Combined with them, octave or narrower filters can measure intensity in individual sound ranges, thereby determining the spectrum of a particular noise.
The sources of noise in production are equipment: machines with electric, pneumatic and motor drives, lifting and transport mechanisms; auxiliary engineering equipment - compressors, pumps, fans, transformers, as well as technological operations for processing materials. The noisiest areas of production are: in mechanical engineering - cutting areas of foundries, stamping and pressing shops, testing shops of all types of engines, straightening and punching sections of preparatory shops, assembly shops with pneumatic riveting sections, ball shops of bearing factories; in the metallurgical industry - hardware production; in the forestry industry - woodworking shops; in the textile industry - weaving workshops, especially with shuttle looms.
Noise is a biological irritant that affects all organs and systems and mainly through the auditory analyzer on the central nervous system.
Comprehensive characteristics of noise are a noise sound pressure level gram, showing the change in the energy of the oscillatory process over time, and a noise spectrogram, indicating the distribution of oscillation energy over the frequency range at a given time.
The organ of hearing is most sensitive to high-frequency sounds (over 1000 Hz), which cause the earliest hearing fatigue and disruption of the relationship between the main processes in the central nervous system. Long-term exposure to noise on the body can lead to occupational hearing loss (see Acoustic trauma, Hearing loss) and general disorders (hypertension, hypotension, heartburn, headaches, etc.), as well as aggravate chronic diseases.
The fight against industrial noise is a national task.
The State Sanitary Standards in force in the USSR for limiting noise in production establish maximum permissible noise levels in workplaces, which should be taken into account when designing machines and other equipment and when placing them in production premises. An equally important link in the prevention of the harmful effects of noise is the supervision of operating machinery and equipment, the identification of areas and workshops with noise levels significantly exceeding the permissible ones, and the development of a set of preventive measures to reduce noise in the workplace.
The greatest effect in the prevention complex is provided by technical means of combating noise, namely: reducing noise at the source of its formation by constructive, technological and operational measures; reduction of noise along the path of its propagation by means of sound insulation and sound absorption.
In the absence of the technical ability to reduce noise to safe limits, personal protective equipment against noise is used - noise suppressors (see), which, with the correct selection of type and systematic use, significantly reduce the risk of adverse effects of noise on the body.
Medical preventive measures in the fight against noise are preliminary and periodic medical examinations of persons working in noise conditions; in particular, professional selection (see) upon entry to work and early diagnosis of possible noise disorders are provided.
A properly developed set of all measures (technical, medical, organizational) can completely prevent the harmful effects of noise on the body.