Decibel is a relative unit of measurement, it is not similar to other known quantities, so it was not included in the system of generally accepted SI units. However, in many calculations it is allowed to use decibels along with absolute units of measurement and even use them as a reference value.
Decibels are determined by belonging to physical quantities, so they cannot be attributed to mathematical concepts. This is easy to imagine if we draw a parallel with percentages, with which decibels have much in common. They do not have specific dimensions, but they are very convenient when comparing 2 values of the same name, even if they are different in nature. Thus, it is not difficult to imagine what is measured in decibels.
History of occurrence
As it turned out as a result of long-term studies, susceptibility is not directly dependent on the absolutesound propagation level. It is a measure of power applied to a given unit of area, which is located in the zone of influence of sound waves, which is measured in decibels today. As a result, a curious proportion was established - the more space belongs to the usable area of the human ear, the better the perception of minimum power it is located.
Thus, the researcher Alexander Graham Bell managed to establish that the limit of perception of the human ear is from 10 to 12 watts per square meter. The resulting data covered too wide a range, which was represented by only a few values. This created some inconvenience and the researcher had to create his own measurement scale.
In the original version, the nameless scale had 14 values - from 0 to 13, where the human whisper had a value of "3", and colloquial speech - "6". Subsequently, this scale was widely used, and its units were called bels. To obtain more accurate data on a logarithmic scale, the original unit was increased by 10 times - this is how decibels were formed.
General information
First of all, it should be noted that a decibel is one tenth of a Bel, which is the decimal form of the logarithm that determines the ratio between 2 powers. The nature of the powers to be compared is chosen arbitrarily. The main thing is to respect the rule that represents the compared powers in equal units, for example, in Watts. Due to this feature, decibel designations are used in differentareas:
- mechanical;
- electric;
- acoustic;
- electromagnetic.
Since practical application showed that Bel turned out to be a rather large unit, for better clarity it was proposed to multiply its value by ten. Thus, a generally accepted unit appeared - the decibel, in which the sound is measured today.
Despite the vast scope, most people know that decibels are used to determine the degree of loudness. This value characterizes the intensity of the sound wave per square meter. Thus, increasing the volume by 10 decibels is comparable to doubling the volume of the sound.
In legislation, the decibel has been recognized as a design value for the amount of noise in a room. It was the defining characteristic for calculating the permissible noise level in residential buildings. This value makes it possible to measure the permissible noise level in decibels in an apartment and identify violations if necessary.
Scope of application
Today, telecommunication designers use the decibel as the base unit for comparing device performance on a logarithmic scale. Such opportunities are provided by the design feature of this value, which is a logarithmic unit of different levels used for attenuation or, conversely, power amplification.
Decibel is widely used in various fields of modern technology. What is measured in decibels today? These are different quantities that change inwide range that can be applied:
- in systems related to the transmission of information;
- radio engineering;
- optics;
- antenna technology;
- acoustics.
Thus, decibels are used to measure the characteristics of the dynamic range, for example, they can measure the volume of the sound of a certain musical instrument. It also opens up the possibility of calculating damped waves at the moment of their passage through an absorbing medium. Decibels allow you to determine the gain or fix the noise figure generated by the amplifier.
It is possible to use these dimensionless units both for physical quantities related to the second order - energy or power, and for quantities related to the first order - current or voltage. Decibels open up the possibility of measuring the relationship between all physical quantities, and besides, they compare absolute values with their help.
Sound volume
The physical component of the loudness of sound exposure is determined by the level of available sound pressure acting on a unit of contact area, which is measured in decibels. The noise level is formed from the chaotic fusion of sounds. A person reacts to low frequencies or, conversely, to high-frequency sounds as to quieter sounds. And mid-frequency sounds will be perceived as louder despite the same intensity.
Given the uneven perception of sounds of different frequencies by the human ear, on the electronicA frequency filter has been created in the base that is capable of transmitting the equivalent degree of sound with a unit of measure expressed in dBa – where “a” denotes the application of the filter. This filter, based on the results of measurement normalization, is able to simulate the weighted value of the sound level.
The ability of different people to perceive sounds is in the volume range from 10 to 15 dB, and in some cases even higher. The perceived limits of sound intensity are frequencies from 20 to 20 thousand Hertz. The easiest sounds to perceive are located in the frequency range from 3 to 4 kHz. This frequency is commonly used in telephones, as well as in broadcasting on medium and long waves.
Over the years, the range of perceived sounds narrows, especially in the high-frequency spectrum, where susceptibility can drop to 18 kHz. This results in a general hearing loss that affects many older people.
Permissible noise levels in residential premises
With the use of decibels, it became possible to determine a more accurate noise scale for ambient sounds. It reflects characteristics that are superior in accuracy compared to the original scale created at the time by Alexander Bell. Using this scale, the legislative bodies determined the noise level, the norm of which is valid within residential premises intended for recreation of citizens.
So a value of "0" dB means complete silence, which causes ringing in the ears. The next value of 5 dB also determines the totalsilence in the presence of a small sound background that drowns out the internal processes of the body. At 10 dB, fuzzy sounds become distinguishable - all kinds of rustling or rustling leaves.
A value of 15 dB is in the range of the quietest sounds, such as the ticking of a watch, being clearly audible. With a sound strength of 20 dB, you can make out the careful whisper of people at a distance of 1 meter. The 25 dB mark allows you to hear more clearly whispered conversations and the rustle of soft tissue friction.
30 dB determines how many decibels are allowed in an apartment at night and is compared to a silent conversation or the ticking of a wall clock. At 35 dB, muffled speech can be clearly heard.
A level of 40 decibels determines the strength of the sound of a normal conversation. This is a sufficient volume that allows you to freely communicate within the room, watch TV or listen to music tracks. This mark determines how many decibels are allowed in the apartment during the day.
Noise level allowed under working conditions
Compared to the permissible noise level in decibels in an apartment, at work and in office activities, other sound level standards are allowed during working hours. There are restrictions of a different order, clearly regulated for each type of occupation. The main rule in these conditions is to avoid noise levels that can adversely affect human he alth.
In offices
A noise level of 45 dB is within easy audibility and is comparable to the sound of a drill orelectric motor. Noise of 50 dB is also within the limits of excellent audibility and is equal in strength to the sound of a typewriter.
The noise level of 55 decibels remains within excellent audibility, it can be represented by the example of the simultaneous sonorous conversation of several people at once. This indicator is taken as the upper mark acceptable for office space.
In animal husbandry and office work
Noise strength of 60 dB is considered high, such a level of noise can be found in offices where many typewriters are working at the same time. An indicator of 65 dB is also considered high and can be recorded when printing equipment is running.
Noise levels as high as 70 dB remain elevated and are found on livestock farms. The noise value of 75 dB is the limit value for increased noise levels, it can be noted in poultry farms.
In production and transport
With a mark of 80 dB comes the level of loud sound, prolonged exposure to which will result in partial hearing loss. Therefore, when working in such conditions, it is recommended to use ear protection. The noise level of 85 dB is also within the loud sound level, such readings can be compared with the operation of the equipment of a weaving factory.
A noise figure of 90 dB is kept within the loud sound, such a noise level can be registered when a train is moving. The noise level of 95 dB reaches the extreme limits of loud sound, such noise can befix in the rolling shop.
Noise limit
The noise level at 100 dB reaches the limits of an excessively loud sound, it can be compared to thunder. Work in such conditions is considered unhe althy and is performed within the framework of a certain length of service, after which the person is considered unfit for hazardous work.
The noise value of 105 dB is also in the range of excessively loud sound, the noise of such a force is created by a power cutter when cutting metal. The noise level of 110 dB remains within the limits of an excessively loud sound, such an indicator is recorded when a helicopter takes off. A noise level of 115 dB is considered the limit for the excessively loud sound that a sandblaster makes.
A noise level of 120 dB is considered unbearable, it can be compared to the work of a jackhammer. The noise level of 125 dB is also characterized by an unbearable noise level, this mark is reached by the aircraft at the start. The maximum noise level in dB is considered the limit at around 130, after which the pain threshold sets in, which not everyone can endure.
Critical noise level
Noise strength at around 135 dB is considered unacceptable, a person who finds himself in the zone of sound of such strength receives a shell shock. A noise level of 140 dB also leads to shell shock, the sound of a jet plane taking off. At a noise level of 145 dB, a fragmentation grenade explodes.
Achieves 150-155 dB rupture of a cumulative projectile on tank armor, the sound of such a force leads toconcussions and injuries. Beyond the 160 dB mark, the sound barrier sets in, sound exceeding this limit causes eardrum rupture, lung collapse, and multiple blast injuries, causing instant death.
The impact on the body of inaudible sounds
A sound whose frequency is below 16 Hz is called infrared, and if its frequency exceeds 20 thousand Hz, then such a sound is called ultrasound. The eardrums of the human ear are not able to perceive sounds of this frequency, so they are outside the range of human hearing. Decibels, which is how sound is measured today, also determine the meaning of inaudible sounds.
Low frequency sounds ranging from 5 to 10 Hz are poorly tolerated by the human body. Such an impact can activate malfunctions in the work of internal organs and affect brain activity. In addition, the intensity of low frequencies has an effect on bone tissue, provoking joint pain in people suffering from various diseases or injuries.
Everyday sources of ultrasound are various vehicles, they can also be thunder or the work of electronic equipment. Such effects are expressed in the heating of tissues, and the strength of their influence depends on the distance to the active source and on the degree of sound.
There are also certain restrictions for public places of work with sound sources in the inaudible range. The maximum intensity of infrared sound must be kept within 110dBa, and the strength of ultrasound is limited to 125 dBa. It is strictly forbidden even for a short time in areas where the sound pressure exceeds 135 dB of any frequency.
Effect of noise from office equipment and protection methods
Noise emitted by a computer and other organizational equipment can be higher than 70 dB. In this regard, experts do not recommend installing a large number of this equipment in one room, especially if it is not large. Noisy units are recommended to be installed outside the room in which people are.
To reduce the level of noise in finishing works, materials with noise-absorbing properties are used. In addition, you can use curtains made of dense fabric or, in extreme cases, ear plugs that cover the eardrums from exposure.
Today, in the construction of modern buildings, there is a new standard that determines the degree of sound insulation of premises. The walls and ceilings of buildings of apartment buildings are tested for resistance to noise. If the sound insulation level is below the acceptable limit, the building cannot be put into operation until the problems are fixed.
In addition, today they set limits on the strength of sound for various signaling and warning devices. For fire protection systems, for example, the sound strength of the warning signal should be between 75 dBa and 125 dBa.
