What sound does a person hear in hertz. Hearing range under normal conditions
Man is truly the most intelligent of the animals that inhabit the planet. However, our mind often deprives us of superiority in such abilities as the perception of the environment through smell, hearing and other sensory sensations. Thus, most animals are far ahead of us when it comes to auditory range. The human hearing range is the range of frequencies that the human ear can perceive. Let's try to understand how the human ear works in relation to the perception of sound.
Human hearing range under normal conditions
The average human ear can pick up and distinguish sound waves in the range of 20 Hz to 20 kHz (20,000 Hz). However, as a person ages, the auditory range of a person decreases, in particular, its upper limit decreases. In older people, it is usually much lower than in younger people, while infants and children have the highest hearing abilities. Auditory perception of high frequencies begins to deteriorate from the age of eight.
Human hearing in ideal conditions
In the laboratory, a person's hearing range is determined using an audiometer that emits sound waves of various frequencies and headphones adjusted accordingly. Under these ideal conditions, the human ear can recognize frequencies in the range of 12 Hz to 20 kHz.
Hearing range for men and women
There is a significant difference between the hearing range of men and women. Women were found to be more sensitive to high frequencies than men. The perception of low frequencies is more or less the same in men and women.
Various scales to indicate hearing range
Although the frequency scale is the most common scale for measuring human hearing range, it is also often measured in pascals (Pa) and decibels (dB). However, measurement in pascals is considered inconvenient, since this unit involves working with very large numbers. One µPa is the distance traveled by a sound wave during vibration, which is equal to one tenth of the diameter of a hydrogen atom. Sound waves in the human ear travel a much greater distance, making it difficult to give a range of human hearing in pascals.
Most soft sound, which can be recognized by the human ear, is approximately 20 µPa. The decibel scale is easier to use as it is a logarithmic scale that directly references the Pa scale. It takes 0 dB (20 µPa) as its reference point and continues to compress this pressure scale. Thus, 20 million µPa equals only 120 dB. It turns out that the range human ear is 0-120 dB.
The hearing range varies greatly from person to person. Therefore, to detect hearing loss, it is best to measure the range audible sounds in relation to the reference scale, and not in relation to the usual standardized scale. Tests can be performed using sophisticated hearing diagnostic tools that can accurately determine the extent and diagnose the causes of hearing loss.
For our orientation in the world around us, hearing plays the same role as vision. The ear allows us to communicate with each other using sounds; it has a special sensitivity to the sound frequencies of speech. With the help of the ear, a person picks up various sound vibrations in the air. Vibrations that come from an object (sound source) are transmitted through the air, which plays the role of a sound transmitter, and are caught by the ear. The human ear perceives air vibrations with a frequency of 16 to 20,000 Hz. Vibrations with a higher frequency are ultrasonic, but the human ear does not perceive them. The ability to distinguish high tones decreases with age. The ability to pick up sound with two ears makes it possible to determine where it is. In the ear, air vibrations are converted into electrical impulses, which are perceived by the brain as sound.
In the ear there is also an organ for perceiving the movement and position of the body in space - vestibular apparatus . The vestibular system plays an important role in the spatial orientation of a person, analyzes and transmits information about accelerations and decelerations of rectilinear and rotational movements, as well as changes in the position of the head in space.
ear structure
Based on the external structure, the ear is divided into three parts. The first two parts of the ear, outer (outer) and middle, conduct sound. The third part - inner ear- contains auditory cells, mechanisms for the perception of all three features of sound: pitch, strength and timbre.
outer ear- the protruding part of the outer ear is called auricle , its basis is a semi-rigid supporting tissue - cartilage. The anterior surface of the auricle has a complex structure and an inconsistent shape. It is made up of cartilage and fibrous tissue, except for the lower part - slices ( earlobe) made up of adipose tissue. At the base of the auricle, there is an anterior, superior, and posterior ear muscles, whose movements are limited.
In addition to the acoustic (sound-catching) function, the auricle performs protective role protecting the ear canal into the tympanic membrane from harmful effects environment(water, dust, strong air currents). Both the shape and size of the auricles are individual. The length of the auricle in men is 50–82 mm and the width is 32–52 mm; in women, the dimensions are slightly smaller. On a small area of the auricle, all the sensitivity of the body and internal organs is represented. Therefore, it can be used to obtain biologically important information about the state of any organ. The auricle concentrates sound vibrations and directs them to the external auditory opening.
External auditory canal serves to conduct sound vibrations of air from the auricle to the eardrum. The external auditory meatus has a length of 2 to 5 cm. Its outer third is formed by cartilage, and the inner 2/3 is bone. The external auditory meatus is arcuately curved in the upper-posterior direction, and easily straightens when the auricle is pulled up and back. In the skin of the ear canal are special glands secreting a secret yellowish color (earwax), whose function is to protect the skin from bacterial infection and foreign particles (insect ingress).
The external auditory canal is separated from the middle ear by the tympanic membrane, which is always retracted inward. This is a thin connective tissue plate, covered on the outside stratified epithelium, and from the inside - the mucous membrane. The external auditory canal conducts sound vibrations to the tympanic membrane, which separates the outer ear from tympanic cavity(middle ear).
Middle ear, or tympanic cavity, is a small air-filled chamber that is located in a pyramid temporal bone and is separated from the external auditory canal by the tympanic membrane. This cavity has bony and membranous (eardrum) walls.
Eardrum is a 0.1 µm thick, sedentary membrane woven from fibers that go in different directions and are unevenly stretched in different areas. Due to this structure, the tympanic membrane does not have its own oscillation period, which would lead to amplification of sound signals that coincide with the frequency of natural oscillations. It begins to oscillate under the action of sound vibrations passing through the external auditory meatus. Through the hole in back wall the tympanic membrane communicates with the mastoid cave.
The opening of the auditory (Eustachian) tube is located in the anterior wall of the tympanic cavity and leads to the nasal part of the pharynx. Thereby atmospheric air may enter the tympanic cavity. normal hole eustachian tube closed. It opens during swallowing or yawning, helping to equalize air pressure on the eardrum from the side of the middle ear cavity and the external auditory opening, thereby protecting it from ruptures that lead to hearing loss.
In the tympanic cavity lie auditory ossicles. They are very small and are connected in a chain that extends from eardrum before inner wall tympanic cavity.
The outermost bone hammer- its handle is connected to the eardrum. The head of the malleus is connected to the incus, which is movably articulated with the head stirrup.
The auditory ossicles are so named because of their shape. The bones are covered with a mucous membrane. Two muscles regulate the movement of the bones. The connection of the bones is such that it increases the pressure of sound waves on the membrane oval window 22 times, which allows weak sound waves to set the liquid in motion in snail.
inner ear enclosed in the temporal bone and is a system of cavities and canals located in the bone substance of the petrous part of the temporal bone. Together, they form a bony labyrinth, inside of which is a membranous labyrinth. Bone labyrinth It is a bone cavity of various shapes and consists of the vestibule, three semicircular canals and the cochlea. membranous labyrinth consists of a complex system of the finest membranous formations located in the bony labyrinth.
All cavities of the inner ear are filled with fluid. Inside the membranous labyrinth is endolymph, and the fluid washing the membranous labyrinth from the outside is relymph and is similar in composition to cerebrospinal fluid. Endolymph differs from relymph (it has more potassium ions and less sodium ions) - it carries a positive charge in relation to relymph.
vestibule - central part bony labyrinth, which communicates with all its parts. Behind the vestibule are three bony semicircular canals: superior, posterior, and lateral. The lateral semicircular canal lies horizontally, the other two are at right angles to it. Each channel has an extended part - an ampoule. Inside it contains a membranous ampulla filled with endolymph. When the endolymph moves during a change in the position of the head in space, they are irritated nerve endings. The nerve fibers carry the impulse to the brain.
Snail is a spiral tube forming two and a half turns around a cone-shaped bone rod. She happens to be central part hearing organ. Inside the bony canal of the cochlea there is a membranous labyrinth, or cochlear duct, to which the ends of the cochlear part of the eighth cranial nerve Vibrations of the perilymph are transmitted to the endolymph of the cochlear duct and activate the nerve endings of the auditory part of the eighth cranial nerve.
The vestibulocochlear nerve consists of two parts. The vestibular part conducts nerve impulses from the vestibule and semicircular canals to the vestibular nuclei of the pons and medulla oblongata and further to the cerebellum. The cochlear part transmits information along the fibers that follow from the spiral (Corti) organ to the auditory trunk nuclei and then - through a series of switches in the subcortical centers - to the upper cortex temporal lobe cerebral hemispheres.
The mechanism of perception of sound vibrations
Sounds are produced by vibrations in the air and are amplified in the auricle. The sound wave is then conducted through the external auditory canal to the eardrum, causing it to vibrate. The vibration of the tympanic membrane is transmitted to the chain auditory ossicles: hammer, anvil and stirrup. The base of the stirrup is fixed to the window of the vestibule with the help of an elastic ligament, due to which the vibrations are transmitted to the perilymph. In turn, through the membranous wall of the cochlear duct, these vibrations pass to the endolymph, the movement of which causes irritation. receptor cells spiral organ. The resulting nerve impulse follows the fibers of the cochlear part of the vestibulocochlear nerve to the brain.
Translation of sounds perceived by the ear as pleasant and discomfort takes place in the brain. Irregular sound waves form sensations of noise, while regular, rhythmic waves are perceived as musical tones. Sounds propagate at a speed of 343 km/s at an air temperature of 15–16ºС.
The content of the article
HEARING, ability to perceive sounds. Hearing depends on: 1) the ear - outer, middle and inner - which perceives sound vibrations; 2) the auditory nerve, which transmits the signals received from the ear; 3) certain parts of the brain ( auditory centers), in which the impulses transmitted auditory nerves, cause awareness of the original sound signals.
Any source of sound - a violin string, which was drawn with a bow, a column of air moving in organ pipe, or vocal cords talking person- causes vibrations of the surrounding air: first, instantaneous compression, then instantaneous rarefaction. In other words, a series of alternating waves of increased and reduced pressure that spread rapidly in the air. This moving stream of waves forms the sound perceived by the hearing organs.
Most of the sounds we encounter every day are quite complex. They are generated by complex oscillatory movements of the sound source, creating whole complex sound waves. Hearing experiments try to choose as simple sound signals as possible so that it is easier to evaluate the results. A lot of effort is spent on ensuring simple periodic oscillations of the sound source (like a pendulum). The resulting stream of sound waves of one frequency is called a pure tone; it represents a regular, smooth change of high and low pressure.
The limits of auditory perception.
The "ideal" sound source described can be made to oscillate quickly or slowly. This allows us to clarify one of the main questions that arise in the study of hearing, namely, what is the minimum and maximum frequency of vibrations perceived by human ear like sound. The experiments showed the following. When the oscillations are very slow, less than 20 complete oscillations per second (20 Hz), each sound wave is heard separately and does not form a continuous tone. As the vibration frequency increases, a person begins to hear a continuous low tone, similar to the sound of the lowest bass pipe of an organ. As the frequency increases further, the perceived tone becomes higher and higher; at a frequency of 1000 Hz, it resembles the upper C of a soprano. However, this note is still far from upper bound human hearing. Only when the frequency approaches about 20,000 Hz does the normal human ear gradually stop hearing.
The sensitivity of the ear to sound vibrations of different frequencies is not the same. It is especially sensitive to medium frequency fluctuations (from 1000 to 4000 Hz). Here the sensitivity is so great that any significant increase in it would be unfavorable: at the same time, a constant background noise of the random movement of air molecules would be perceived. As the frequency decreases or increases relative to the average range, hearing acuity gradually decreases. At the edges of the perceived frequency range, sound must be very strong to be heard, so strong that it is sometimes felt physically before being heard.
Sound and its perception.
A pure tone has two independent characteristics: 1) frequency and 2) strength or intensity. The frequency is measured in hertz, i.e. is determined by the number of complete oscillatory cycles per second. Intensity is measured by the magnitude of the pulsating pressure of sound waves on any counter surface and is usually expressed in relative, logarithmic units - decibels (dB). It must be remembered that the concepts of frequency and intensity apply only to sound as an external physical stimulus; this is the so-called. acoustic characteristics of sound. When we talk about perception, i.e. O physiological process, the sound is judged as high or low, and its strength is perceived as loudness. In general, pitch - the subjective characteristic of sound - is closely related to its frequency; high frequency sounds are perceived as high. Also, in general, we can say that the perceived loudness depends on the strength of the sound: we hear more intense sounds as louder. These ratios, however, are not fixed and absolute, as is often assumed. The perceived pitch of a sound is affected to some extent by its strength, while the perceived loudness is affected by its frequency. Thus, by changing the frequency of a sound, one can avoid changing the perceived pitch by varying its strength accordingly.
"Minimum noticeable difference."
From both a practical and a theoretical point of view, determining the minimum ear-perceivable difference in frequency and strength of sound is a very important problem. How should the frequency and strength of the audio signals be changed so that the listener notices this? It turned out that the minimum noticeable difference determined by a relative change in the characteristics of the sound rather than an absolute change. This applies to both frequency and strength of sound.
Necessary for discrimination relative change frequencies are different both for sounds of different frequencies, and for sounds of the same frequency, but of different strengths. It can be said, however, that it is approximately equal to 0.5% in wide range frequencies from 1000 to 12000 Hz. This percentage (the so-called discrimination threshold) is slightly higher at higher frequencies and much higher at lower frequencies. Consequently, the ear is less sensitive to frequency change at the ends of the frequency range than at midrange, and this is often noticed by all piano players; the interval between two very high or very low notes seems to be shorter than that of notes in the middle range.
The minimum noticeable difference in terms of sound strength is somewhat different. Discrimination requires a rather large change in the pressure of sound waves, about 10% (i.e., about 1 dB), and this value is relatively constant for sounds of almost any frequency and intensity. However, when the intensity of the stimulus is low, the minimum perceptible difference increases significantly, especially for low frequency tones.
Overtones in the ear.
A characteristic property of almost any sound source is that it not only produces simple periodic oscillations (pure tone), but also performs complex oscillatory movements that give several pure tones at the same time. Typically, such a complex tone consists of harmonic series (harmonics), i.e. from the lowest, fundamental, frequency plus overtones whose frequencies exceed the fundamental by an integer number of times (2, 3, 4, etc.). Thus, an object vibrating at a fundamental frequency of 500 Hz can also produce overtones of 1000, 1500, 2000 Hz, etc. The human ear in response to sound signal behaves in a similar way. Anatomical features The ears provide many opportunities for converting the energy of an incoming pure tone, at least partially, into overtones. So, even when the source gives a pure tone, an attentive listener can hear not only the main tone, but also barely perceptible one or two overtones.
The interaction of two tones.
When two pure tones are perceived by the ear simultaneously, the following variants of their joint action can be observed, depending on the nature of the tones themselves. They can mask each other by mutually reducing the volume. This most often occurs when the tones do not vary greatly in frequency. Two tones can connect with each other. At the same time, we hear sounds corresponding either to the difference in frequencies between them, or to the sum of their frequencies. When two tones are very close in frequency, we hear a single tone whose pitch roughly matches that frequency. This tone, however, gets louder and quieter as the two slightly mismatched acoustic signals continually interact, amplifying and canceling each other out.
Timbre.
Objectively speaking, the same complex tones can differ in the degree of complexity, i.e. composition and intensity of overtones. The subjective characteristic of perception, which generally reflects the peculiarity of sound, is timbre. Thus, the sensations caused by a complex tone are characterized not only by a certain pitch and loudness, but also by a timbre. Some sounds are rich and full, others are not. First of all, thanks to differences in timbre, we recognize the voices of various instruments among a variety of sounds. An A note played on a piano can be easily distinguished from the same note played on a horn. If, however, one manages to filter and muffle the overtones of each instrument, these notes cannot be distinguished.
Sound localization.
The human ear not only distinguishes between sounds and their sources; both ears, working together, are able to determine quite accurately the direction from which the sound is coming. Since the ears are located on opposite sides of the head, the sound waves from the sound source do not reach them at the same time and act with slightly different strengths. Due to the minimal difference in time and strength, the brain quite accurately determines the direction of the sound source. If the sound source is strictly in front, then the brain localizes it along horizontal axis with an accuracy of several degrees. If the source is shifted to one side, the localization accuracy is slightly less. Distinguishing sound from behind from sound in front, as well as localizing it along the vertical axis, is somewhat more difficult.
Noise
often described as an atonal sound, i.e. consisting of various frequencies that are not related to each other and therefore do not repeat such an alternation of high and low pressure waves consistently enough to get any particular frequency. However, in fact, almost any "noise" has its own height, which is easy to see by listening and comparing ordinary noises. On the other hand, any "tone" has elements of roughness. Therefore, the differences between noise and tone are difficult to define in these terms. The current trend is to define noise psychologically rather than acoustically, calling noise simply an unwanted sound. Noise reduction in this sense has become a pressing modern problem. Although permanent loud noise, no doubt leads to deafness, and working in a noisy environment causes temporary stress, yet it is probably less durable and strong effect than is sometimes attributed to him.
Abnormal hearing and hearing in animals.
The natural stimulus for the human ear is sound propagating in the air, but the ear can be affected in other ways. Everyone, for example, is well aware that sound is heard under water. Also, if a vibration source is applied to the bone part of the head, a sensation of sound appears due to bone conduction. This phenomenon is very useful in some forms of deafness: a small transmitter applied directly to the mastoid process (the part of the skull located just behind the ear) allows the patient to hear the sounds amplified by the transmitter through the bones of the skull due to bone conduction.
Of course, humans are not the only ones with hearing. The ability to hear arises early in evolution and already exists in insects. Different types Animals perceive sounds of different frequencies. Some people hear a smaller range of sounds than a person, others a larger one. Good example- a dog whose ear is sensitive to frequencies beyond human hearing. One use for this is to produce whistles that are inaudible to humans but sufficient for dogs.
It is known that 90% of information about the world around a person receives with vision. It would seem that there is not much left to hear, but in fact, human organ hearing aid is not only a highly specialized sound vibration analyzer, but also a very powerful tool communications. Doctors and physicists have long been concerned about the question: is it possible to accurately determine the range of human hearing in different conditions, does hearing differ between men and women, are there "particularly outstanding" record holders who hear inaccessible sounds, or can produce them? Let's try to answer these and some other related questions in more detail.
But before you understand how many hertz the human ear hears, you need to understand such a fundamental concept as sound, and in general, understand what exactly is measured in hertz.
Sound vibrations are unique way transfer of energy without the transfer of matter, they are elastic oscillations in any medium. When it comes to ordinary human life, such an environment is air. It contains gas molecules that can transmit acoustic energy. This energy represents the alternation of bands of compression and tension of the density of the acoustic medium. In absolute vacuum, sound vibrations cannot be transmitted.
Any sound is a physical wave, and contains all the necessary wave characteristics. This is the frequency, amplitude, decay time, if we are talking about a damped free oscillation. Consider it on simple examples. Imagine, for example, the sound of the open G string on a violin when it is drawn with a bow. We can define the following characteristics:
- quiet or loud. It is nothing but the amplitude, or power of the sound. More loud sound corresponds to a large amplitude of oscillations, and a quiet sound - a smaller one. A sound of greater strength can be heard at a greater distance from the place of origin;
- sound duration. Everyone understands this, and everyone is able to distinguish the peals of a drum roll from the extended sound of a choral organ melody;
- pitch, or frequency of a sound wave. It is this fundamental characteristic that helps us to distinguish "beeping" sounds from the bass register. If there were no frequency of sound, music would only be possible in the form of rhythm. Frequency is measured in hertz, and 1 hertz is equal to one oscillation per second;
- timbre of sound. It depends on the admixture of additional acoustic vibrations - formant, but to explain it in simple words very easy: even with eyes closed we understand that it is the violin that sounds, and not the trombone, even if they have exactly the same characteristics listed above.
The timbre of sound can be compared with numerous taste shades. In total, we have bitter, sweet, sour and salty tastes, but these four characteristics are far from exhausting all kinds of taste sensations. The same thing happens with timbre.
Let us dwell in more detail on the height of the sound, since it is on this characteristic that the most hearing acuity and the range of perceived acoustic vibrations. What is a range audio frequencies?
Hearing range in ideal conditions
The frequencies perceived by the human ear under laboratory or ideal conditions are in a relatively wide band from 16 Hertz to 20,000 Hertz (20 kHz). Everything above and below - the human ear can not hear. These are infrasound and ultrasound. What it is?
infrasound
It cannot be heard, but the body can feel it, like the work of a large bass speaker - a subwoofer. These are infrasonic vibrations. Everyone knows very well that if you constantly weaken the bass string on the guitar, then, despite the continued vibrations, the sound disappears. But these vibrations can still be felt with the fingertips by touching the string.
Many people work in the infrasonic range. internal organs human: there is a contraction of the intestine, expansion and narrowing of blood vessels, many biochemical reactions. Very strong infrasound can cause serious disease state, even waves of panic horror, the action of infrasonic weapons is based on this.
Ultrasound
On the opposite side of the spectrum are very high sounds. If the sound has a frequency above 20 kilohertz, then it stops "beeping" and becomes inaudible to the human ear in principle. It becomes ultrasonic. Ultrasound has great application in the national economy, based on it ultrasound diagnostics. With the help of ultrasound, ships navigate the sea, bypassing icebergs and avoiding shallow water. Thanks to ultrasound, specialists find voids in all-metal structures, for example, in rails. Everyone saw how workers rolled a special flaw detection trolley along the rails, generating and receiving high-frequency acoustic vibrations. Ultrasound is used the bats to find an unmistakable path in the dark without bumping into cave walls, whales and dolphins.
It is known that with age, the ability to distinguish high-pitched sounds decreases, and children can hear them best. Modern research show that already at the age of 9-10 years, the range of hearing in children begins to gradually decrease, and in older people the audibility of high frequencies is much worse.
To hear how older people perceive music, you just need to use the multi-band equalizer in the player of your cell phone turn down one or two rows of high frequencies. The resulting uncomfortable "mumbling, like from a barrel," and will be a great illustration of how you yourself will hear after the age of 70 years.
in hearing loss important role plays malnutrition, drinking and smoking, postponing cholesterol plaques on the walls of blood vessels. ENT statistics - doctors claim that people with the first blood group more often and faster come to hearing loss than the rest. Approaches hearing loss overweight, endocrine pathology.
Hearing range under normal conditions
If we cut off the “marginal parts” of the sound spectrum, then not so much is available for a comfortable human life: this is the interval from 200 Hz to 4000 Hz, which almost completely corresponds to the range of the human voice, from deep basso-profundo to high coloratura soprano. However, even when comfortable conditions, a person's hearing is constantly deteriorating. Usually, the highest sensitivity and susceptibility in adults under the age of 40 is at the level of 3 kilohertz, and at the age of 60 years or more it drops to 1 kilohertz.
Hearing range for men and women
Currently, sexual segregation is not welcome, but men and women really perceive sound differently: women are able to hear better in the high range, and the age-related involution of sound in the high frequency region is slower, and men perceive high sounds somewhat worse. It would seem logical to assume that men hear better in the bass register, but this is not so. The perception of bass sounds in both men and women is almost the same.
But there is unique women on the "generation" of sounds. Thus, the voice range of the Peruvian singer Yma Sumac (almost five octaves) extended from the sound “si” of a large octave (123.5 Hz) to “la” of the fourth octave (3520 Hz). An example of her unique vocals can be found below.
At the same time, men and women have quite a big difference in work speech apparatus. Women produce sounds from 120 to 400 hertz, and men from 80 to 150 Hz, according to the average data.
Various scales to indicate hearing range
At the beginning, we talked about the fact that pitch is not the only characteristic of sound. Therefore, there are different scales, according to different ranges. The sound heard by the human ear can be, for example, quiet and loud. The simplest and most clinically acceptable sound loudness scale is the one that measures the sound pressure perceived by the eardrum.
This scale is based on the smallest energy of sound vibration, which is capable of transforming into a nerve impulse and causing a sound sensation. This is the threshold of auditory perception. The lower the perception threshold, the higher the sensitivity, and vice versa. Specialists distinguish between sound intensity, which is a physical parameter, and loudness, which is a subjective value. It is known that the sound of strictly the same intensity healthy man, and a person with hearing loss will be perceived as two different sound, louder and quieter.
Everyone knows how in the ENT doctor's office the patient stands in a corner, turns away, and the doctor from the next corner checks the patient's perception of whispered speech, uttering separate numbers. This is the simplest example of the primary diagnosis of hearing loss.
It is known that the barely perceptible breath of another person is 10 decibels (dB) of sound pressure intensity, a normal conversation in home environment corresponds to 50 dB, the howling of a fire siren is 100 dB, and a jet aircraft taking off near, near pain threshold- 120 decibels.
It may be surprising that the entire enormous intensity of sound vibrations fits on such a small scale, but this impression is deceptive. This is a logarithmic scale, and each successive step is 10 times more intense than the previous one. According to the same principle, a scale for assessing the intensity of earthquakes is built, where there are only 12 points.
Today we understand how to decipher an audiogram. Svetlana Leonidovna Kovalenko, a doctor of higher education, helps us with this. qualification category, chief pediatric audiologist-otorhinolaryngologist of Krasnodar, candidate of medical sciences.
Summary
The article turned out to be large and detailed - in order to understand how to decipher an audiogram, you must first get acquainted with the basic terms of audiometry and analyze examples. If you do not have time to read and understand the details for a long time, in the card below - summary articles.
An audiogram is a graph of the patient's auditory sensations. It helps diagnose hearing loss. There are two axes on the audiogram: horizontal - frequency (the number of sound vibrations per second, expressed in hertz) and vertical - sound intensity (relative value, expressed in decibels). The audiogram shows bone conduction(sound that in the form of vibrations reaches the inner ear through the bones of the skull) and air conduction (sound that reaches the inner ear in the usual way - through the outer and middle ear).
During audiometry, the patient is given a signal different frequency and intensity and mark with dots the value of the minimum sound that the patient hears. Each dot indicates the minimum sound intensity at which the patient hears at a particular frequency. By connecting the dots, we get a graph, or rather, two - one for bone sound conduction, the other for air.
The norm of hearing is when the graphs are in the range from 0 to 25 dB. The difference between the schedule of bone and air sound conduction is called the bone-air interval. If the schedule of bone sound conduction is normal, and the schedule of air is below the norm (there is an air-bone interval), this is an indicator of conductive hearing loss. If the bone conduction graph repeats the air conduction graph, and both lie below normal range This is indicative of sensorineural hearing loss. If the air-bone interval is clearly defined, and both graphs show violations, then the hearing loss is mixed.
Basic concepts of audiometry
To understand how to decipher an audiogram, let's first dwell on some terms and the audiometry technique itself.
Sound has two main physical characteristics: intensity and frequency.
Sound intensity is determined by the strength of sound pressure, which is very variable in humans. Therefore, for convenience, it is customary to use relative values, such as decibels (dB) - this is a decimal scale of logarithms.
The frequency of a tone is measured by the number of sound vibrations per second and is expressed in hertz (Hz). Conventionally, the sound frequency range is divided into low - below 500 Hz, medium (speech) 500-4000 Hz and high - 4000 Hz and above.
Audiometry is a measurement of hearing acuity. This technique is subjective and requires feedback with the patient. The examiner (the one who conducts the study) gives a signal using an audiometer, and the subject (whose hearing is being examined) lets know whether he hears this sound or not. Most often, for this, he presses a button, less often he raises his hand or nods, and the children put the toys in a basket.
Exist different kinds audiometry: tonal threshold, suprathreshold and speech. In practice, the most commonly used tone threshold audiometry, which determines the minimum hearing threshold (the quietest sound that a person hears, measured in decibels (dB)) at different frequencies(as a rule, in the range of 125 Hz - 8000 Hz, less often up to 12,500 and even up to 20,000 Hz). These data are noted on a special form.
An audiogram is a graph of the patient's auditory sensations. These sensations may depend both on the person himself, his general condition, arterial and intracranial pressure, moods, etc., and from external factors- atmospheric phenomena, noise in the room, distractions, etc.
How an audiogram is plotted
Air conduction (through headphones) and bone conduction (through a bone vibrator placed behind the ear) are measured separately for each ear.
Air conduction- this is directly the patient's hearing, and bone conduction is the hearing of a person, excluding the sound-conducting system (outer and middle ear), it is also called the cochlea (inner ear) reserve.
Bone conduction due to the fact that the bones of the skull capture the sound vibrations that come to the inner ear. Thus, if there is an obstruction in the outer and middle ear (any pathological conditions), then the sound wave reaches the cochlea due to bone conduction.
Audiogram blank
On the form of an audiogram, most often the right and left ear depicted separately and signed (most often right ear on the left, and the left ear on the right), as in figures 2 and 3. Sometimes both ears are marked on the same form, they are distinguished either by color (the right ear is always red, and the left ear is blue), or by symbols (the right circle or square (0-- -0---0), and the left one is a cross (x---x---x)). Air conduction is always marked with a solid line, and bone conduction with a broken line.
Hearing level (stimulus intensity) is marked vertically in decibels (dB) in steps of 5 or 10 dB, from top to bottom, starting from -5 or -10, and ending with 100 dB, less often 110 dB, 120 dB. Frequencies are marked horizontally, from left to right, starting from 125 Hz, then 250 Hz, 500 Hz, 1000 Hz (1 kHz), 2000 Hz (2 kHz), 4000 Hz (4 kHz), 6000 Hz (6 kHz), 8000 Hz (8 kHz), etc., can be some variation. At each frequency, the level of hearing in decibels is noted, then the points are connected, a graph is obtained. The higher the graph, the better the hearing.
How to transcribe an audiogram
When examining a patient, first of all, it is necessary to determine the topic (level) of the lesion and the degree of auditory impairment. Correctly performed audiometry answers both of these questions.
Hearing pathology may be at the level of conduction sound wave(the outer and middle ear are responsible for this mechanism), such hearing loss is called conductive or conductive; at the level of the inner ear (the receptor apparatus of the cochlea), this hearing loss is sensorineural (neurosensory), sometimes there is a combined lesion, such hearing loss is called mixed. Very rarely there are violations at the level of the auditory pathways and the cerebral cortex, then they talk about retrocochlear hearing loss.
Audiograms (graphs) can be ascending (most often with conductive hearing loss), descending (more often with sensorineural hearing loss), horizontal (flat), and also of a different configuration. The space between the bone conduction graph and the air conduction graph is the air-bone interval. It determines what kind of hearing loss we are dealing with: sensorineural, conductive or mixed.
If the audiogram graph lies in the range from 0 to 25 dB for all studied frequencies, then it is considered that the person has normal hearing. If the audiogram graph goes down, then this is a pathology. The severity of the pathology is determined by the degree of hearing loss. There are various calculations of the degree of hearing loss. However, the most wide use received an international classification of hearing loss, which calculates the arithmetic mean hearing loss at 4 main frequencies (the most important for speech perception): 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz.
1 degree of hearing loss- violation within 26-40 dB,
2 degree - violation in the range of 41-55 dB,
3 degree - violation 56−70 dB,
4 degree - 71-90 dB and over 91 dB - zone of deafness.
Grade 1 is defined as mild, grade 2 is moderate, grades 3 and 4 are severe, and deafness is extremely severe.
If bone conduction is normal (0-25 dB), and air conduction is impaired, this is an indicator conductive hearing loss. In cases where both bone and air sound conduction is impaired, but there is a bone-air gap, the patient mixed type hearing loss(violations both on average and in inner ear). If bone conduction repeats air conduction, then this sensorineural hearing loss. However, when determining bone conduction, it must be remembered that low frequencies(125Hz, 250Hz) give the effect of vibration and the subject can take this sensation as auditory. Therefore, it is necessary to be critical of the air-bone interval at these frequencies, especially when severe degrees hearing loss (3-4 degrees and deafness).
Conductive hearing loss is rarely severe, more often grade 1-2 hearing loss. The exceptions are chronic inflammatory diseases middle ear after surgical interventions on the middle ear, etc., congenital anomalies development of the outer and middle ear (microotia, atresia of the external auditory canals etc.), as well as with otosclerosis.
Figure 1 - an example of a normal audiogram: air and bone conduction within 25 dB in the entire range of studied frequencies on both sides.
Figures 2 and 3 show typical examples of conductive hearing loss: bone sound conduction is within the normal range (0−25 dB), while air conduction is disturbed, there is a bone-air gap.
Rice. 2. Audiogram of a patient with bilateral conductive hearing loss.
To calculate the degree of hearing loss, add 4 values - the sound intensity at 500, 1000, 2000 and 4000 Hz and divide by 4 to get the arithmetic mean. We get on the right: at 500Hz - 40dB, 1000Hz - 40dB, 2000Hz - 40dB, 4000Hz - 45dB, in total - 165dB. Divide by 4, equals 41.25 dB. According to international classification, this is the 2nd degree of hearing loss. We determine the hearing loss on the left: 500Hz - 40dB, 1000Hz - 40dB, 2000Hz - 40dB, 4000Hz - 30dB = 150, divided by 4, we get 37.5 dB, which corresponds to 1 degree of hearing loss. According to this audiogram, the following conclusion can be made: bilateral conductive hearing loss on the right of the 2nd degree, on the left of the 1st degree.
Rice. 3. Audiogram of a patient with bilateral conductive hearing loss.
We perform a similar operation for Figure 3. Degree of hearing loss on the right: 40+40+30+20=130; 130:4=32.5, i.e. 1 degree of hearing loss. On the left, respectively: 45+45+40+20=150; 150:4=37.5, which is also the 1st degree. Thus, we can draw the following conclusion: bilateral conductive hearing loss of the 1st degree.
Figures 4 and 5 are examples of sensorineural hearing loss. They show that bone conduction repeats air conduction. At the same time, in Figure 4, hearing in the right ear is normal (within 25 dB), and on the left there is sensorineural hearing loss, with a predominant lesion of high frequencies.
Rice. 4. Audiogram of a patient with sensorineural hearing loss on the left, the right ear is normal.
The degree of hearing loss is calculated for the left ear: 20+30+40+55=145; 145:4=36.25, which corresponds to 1 degree of hearing loss. Conclusion: left-sided sensorineural hearing loss of the 1st degree.
Rice. 5. Audiogram of a patient with bilateral sensorineural hearing loss.
For this audiogram, the absence of bone conduction left. This is due to the limitations of the instruments (the maximum intensity of the bone vibrator is 45−70 dB). We calculate the degree of hearing loss: on the right: 20+25+40+50=135; 135:4=33.75, which corresponds to 1 degree of hearing loss; left — 90+90+95+100=375; 375:4=93.75, which corresponds to deafness. Conclusion: bilateral sensorineural hearing loss on the right 1 degree, deafness on the left.
The audiogram for mixed hearing loss is shown in Figure 6.
Figure 6. Both air and bone conduction disturbances are present. The air-bone interval is clearly defined.
The degree of hearing loss is calculated according to the international classification, which is the arithmetic mean of 31.25 dB for the right ear, and 36.25 dB for the left, which corresponds to 1 degree of hearing loss. Conclusion: bilateral hearing loss 1 degree mixed type.
They made an audiogram. What then?
In conclusion, it should be noted that audiometry is not the only method for studying hearing. Typically, to establish final diagnosis a comprehensive audiological study is needed, which, in addition to audiometry, includes acoustic impedancemetry, otoacoustic emission, auditory evoked potentials, hearing testing using whispered and colloquial speech. Also, in some cases, the audiological examination must be supplemented with other research methods, as well as with the involvement of specialists from related specialties.
After diagnosing hearing disorders, it is necessary to address the issues of treatment, prevention and rehabilitation of patients with hearing loss.
The most promising treatment for conductive hearing loss. The choice of the direction of treatment: medication, physiotherapy or surgery is determined by the attending physician. In the case of sensorineural hearing loss, improvement or restoration of hearing is possible only in its acute form (with a duration of hearing loss of not more than 1 month).
In cases of persistent irreversible hearing loss, the doctor determines the methods of rehabilitation: hearing aids or cochlear implantation. Such patients should be observed at least 2 times a year by an audiologist, and in order to prevent further progression of hearing loss, receive courses of drug treatment.
