A decibel is a relative unit of measure, it is not similar to other known quantities, therefore it was not included in the system of generally accepted SI units. However, in many calculations it is allowed to use decibels on a par with absolute units and even use them as a reference value.
Decibels are determined by belonging to physical quantities, so they can not 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 sizes, 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 absolute level of sound propagation. It is an indicator of power applied to a given unit of area, which is 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 useful area of the human ear, the better perception of minimum power it is located.
Thus, researcher Alexander Graham Bell was able to establish that the limit of perception of the human ear is from 10 to 12 watts per square meter. The data obtained encompassed too wide a range, which seemed to be just a few values. This created certain inconveniences 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 the value "3", and colloquial speech - "6". Subsequently, this scale found wide application, and its units were called whites. To obtain more accurate data on a logarithmic scale, the original unit was increased 10 times - this is how decibels were formed.
General information
First of all, it should be noted that the decibel is one tenth of Bela, which is the decimal form of the logarithm, which determines the relationship between 2 powers. The nature of the capacities to be compared is chosen arbitrarily. The main thing is to comply with the rule, representing the compared power in equal units, for example, in watts. Due to this feature, decibel designations are used in different areas:
- mechanical;
- electric;
- acoustic;
- electromagnetic.
Since practical application showed that Bel turned out to be a fairly large unit, for better clarity, it was proposed to multiply its value by ten. Thus, a common unit appeared - decibel, in which sound is measured today.
Despite the wide area of application, most people know that decibels are used to determine the degree of volume. This value characterizes the intensity of the sound wave per square meter. Thus, an increase in volume by 10 decibels is comparable to a double increase in sound power.
In the legislation, the decibel was recognized as the estimated noise level of the room. It was a defining characteristic for calculating the allowable noise power in residential buildings. This value makes it possible to measure the permissible noise level in decibels in the apartment and to identify violations if necessary.
Application area
Today, telecommunications designers use the decibel as the base unit to perform the comparative characteristics of devices reflected on a logarithmic scale. Such opportunities are provided by the design feature of this quantity, which is a logarithmic unit of different levels used in attenuation or, conversely, power amplification.
Decibel is widely used in various fields of modern technology. What is measured in decibels today? These are various quantities that vary over a wide range that can be applied:
- in systems related to the transmission of information;
- radio engineering;
- optics;
- antenna technology;
- acoustics.
Thus, decibels are used in measuring the characteristics of the dynamic range, for example, they can measure the sound volume of a particular musical instrument. And it also opens up the possibility of calculating the damped waves at the moment of their passage through the 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 strength or voltage. Decibels open up the possibility of measuring the relationship between all physical quantities, and in addition, with their help, absolute values are compared.
Sound volume
The physical component of the volume 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 merging of sounds. To low frequencies or, conversely, high frequency sounds, a person reacts as to quieter sounds. And the sounds of medium frequencies will be perceived as louder, despite the same intensity.
Given the uneven perception of sounds of different frequencies by the human ear, a frequency filter was created on the electronic base that can transmit an equivalent degree of sound with a unit of measure, which is expressed in dBA - where “a” indicates the use of the filter. This filter, according to the results of standardization of measurements, is able to simulate a weighted value of the sound level.
The ability of different people to perceive sounds is in the range of volume 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. It is customary to use such a frequency in telephones, as well as in broadcasting on medium and long waves.
Over the years, the range of perceived sounds narrows, especially for the high-frequency spectrum, where the susceptibility can be reduced to 18 kHz. This leads to a general hearing impairment, which affects many older people.
Permissible noise levels in residential premises
Using decibels, it became possible to define a more accurate noise scale for ambient sounds. It reflects superior accuracy characteristics compared to the original scale, created in due time by Alexander Bell. Using this scale, the legislative authorities determined the noise level, the norm of which is valid within residential premises intended for recreation of citizens.
Thus, the value “0” dB means complete silence, from which ringing in the ears. The next value of 5 dB also determines complete silence in the presence of a small sound background, drowning the internal processes of the body. At 10 dB, fuzzy sounds become apparent - all kinds of rustling or rustling leaves.
A value of 15 dB is in the range of clear audibility of the quietest sounds, such as the ticking of a wristwatch. With a sound power of 20 dB, you can make out the careful whisper of people at a distance of 1 meter. The mark of 25 dB allows you to hear more clearly the conversation in a whisper and rustle from the friction of soft tissues.
30 dB determines how many decibels are allowed in the apartment at night and is compared with a silent conversation or the ticking of a wall clock. At 35 dB, you can clearly hear muffled speech.
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 premises, watch TV or listen to music tracks. This mark determines how many decibels are allowed in an apartment during the day.
Noise level allowed under working conditions
Compared with the acceptable noise level in decibels in an apartment, in production and in office activities during working hours, other sound level standards are allowed. There are restrictions of a different order, clearly regulated for each occupation. The basic rule in these conditions is not to allow noise levels that can adversely affect human health.
In offices
The value of the noise level of 45 dB is within good hearing and is comparable to the noise of the drill or motor. Noise of 50 dB is also characterized by excellent audibility limits and matches the strength of a typewriter.
The noise level of 55 decibels remains within the limits of excellent audibility, it can be represented by the example of simultaneous sonorous conversation of several people at once. This indicator is taken as the upper mark acceptable for office premises.
In livestock and clerical activities
Noise power of 60 dB is considered to be increased, this level of noise can be found in offices where many typewriters work simultaneously. An indicator of 65 dB is also considered to be increased and it can be fixed during the operation of printing equipment.
The noise level, reaching 70 dB, remains high and is found on livestock farms. The noise value of 75 dB is the limit value of the increased noise level, it can be noted at poultry farms.
In production and transport
With a mark of 80 dB, a loud sound level sets in, prolonged exposure of which will result from partial hearing loss. Therefore, when working in such conditions, it is recommended to use protective headphones. The noise power of 85 dB is also within the loud sound level, such readings can be compared with the work of the equipment of the weaving factory.
A noise figure of 90 dB is kept within a loud sound, such noise power can be registered when the train is moving. The noise level of 95 dB reaches the extreme limits of loud sound, such a force of noise can be fixed in a metal rolling workshop.
Noise limit
The noise level at around 100 dB reaches the limits of an excessively loud sound, it can be compared with peals of thunder. Work in such conditions is considered harmful to health and is carried out within a certain length of service, after which a person is considered unsuitable for harmful work.
The noise value of 105 dB is also within the limits of an excessively loud sound; noise of such a force creates a gas cutter when cutting metal. The noise power of 110 dB remains within the boundaries of an excessively loud sound, such an indicator is fixed when the helicopter takes off. The noise level of 115 dB is considered the limit for the boundaries of excessively loud sound, such noise emits a sandblasting device.
The noise level of 120 dB is considered unbearable, it can be compared with the work of a jackhammer. The noise mark of 125 dB is also characterized by an unbearable noise level, the aircraft reaches this level at the start. The maximum noise level in dB is considered the limit at around 130, after which there is a pain threshold, which not everyone can tolerate.
Critical noise level
Noise power at 135 dB is considered unacceptable, a person who is in the zone of action of sound of such strength receives a concussion. The noise level of 140 dB also leads to a concussion, this sound is accompanied by the start of a jet aircraft. With a noise value of 145 dB, a fragmentation grenade explodes.
Reaches the level of 150-155 dB rupture of the cumulative projectile on the tank armor, the sound of such a force leads to shell shock and injury. After the 160 dB mark, a sound barrier sets in, sound exceeding this limit leads to rupture of the eardrum, collapse of the lungs and multiple injuries caused by the shock wave, which causes instant death.
The impact on the body of inaudible sounds
Sound whose frequency is lower than 16 Hz is called infrared, and if its frequency exceeds 20 thousand Hz, then such sound is called ultrasound. The tympanic membranes of the human ear are not able to perceive sounds of this frequency, so they are beyond the limits of human hearing. The decibels in which sound is measured today also determine the meaning of inaudible sounds.
Sounds of low frequency, ranging from 5 to 10 Hz, are poorly tolerated by the human body. Such an effect can activate malfunctions in the work of internal organs and affect brain activity. In addition, the intensity of low frequencies affects bone tissue, provoking joint pain in people suffering from various diseases or having suffered injuries.
Various vehicles are everyday sources of ultrasound, and they can also be thunder or electronic equipment. Such effects are expressed in tissue heating, and the strength of their influence depends on the distance to the current source and the degree of sound.
There are certain restrictions on public workplaces that have sources of inaudible range of sounds . The maximum strength of infrared sound should be kept within 110 dBa, and the strength of ultrasound is limited to 125 dBA. It is strictly forbidden even to stay in areas where the sound pressure exceeds 135 dB of any frequency.
The effect of noise coming from office equipment, and methods of protection
The noise that a computer and other organizational equipment makes may be higher than 70 dB. In this regard, experts do not recommend installing a large amount of this equipment in one room, especially if it is not large. Noisy units are recommended to be installed outside the premises in which people are located.
To reduce the level of noise in the finishing work, materials are used that have sound-absorbing properties. In addition, you can use curtains made of dense fabric or, in extreme cases, birushi, covering the eardrum from exposure.
Today, in the construction of modern buildings, there is a new norm that determines the degree of sound insulation of rooms. Walls and ceilings of buildings of apartment buildings are checked for resistance to noise. If the sound insulation level is below the permissible limit, the building cannot be commissioned until troubleshooting.
In addition, today they set limits on the strength of sound for various signaling and warning devices. For fire-fighting systems, for example, the sound power of the warning signal should be in the range from 75 dBa to 125 dBa.