The frequency of sound vibrations audible to humans. When to See a Doctor
February 7, 2018
Often people (even those who are well versed in the matter) have confusion and difficulty in clearly understanding how exactly a person hears frequency range sound is divided into general categories (low, mid, high) and narrower subcategories (upper bass, lower mids, etc.). At the same time, this information is extremely important not only for experiments with car audio, but also useful for general development. Knowledge will definitely come in handy when setting up an audio system of any complexity and, most importantly, it will help to correctly assess the strengths or weaknesses of a particular speaker system or the nuances of the room listening to music (in our case, the interior of the car is more relevant), because it has a direct impact on the final sound. If there is a good and clear understanding of the predominance of certain frequencies in the sound spectrum by ear, then it is elementary and quickly possible to assess the sound of a particular musical composition, while clearly hearing the influence of room acoustics on sound coloring, the contribution of the acoustic system itself to sound and more subtly to make out all the nuances, which is what the ideology of "hi-fi" sounding strives for.
Division of the audible range into three main groups
The terminology for dividing the audible frequency spectrum came to us partly from the musical, partly from the scientific worlds and in general view it is familiar to almost everyone. The simplest and most understandable division that can experience the frequency range of sound in general terms is as follows:
- low frequencies. The limits of the low frequency range are within 10 Hz (lower limit) - 200 Hz (upper limit). The lower limit starts exactly from 10 Hz, although in the classical view a person is able to hear from 20 Hz (everything below falls into the infrasound region), the remaining 10 Hz can still be partially heard, as well as felt tactilely in the case of deep low bass and even influence on mental attitude person.
The low-frequency range of sound has the function of enrichment, emotional saturation and final response - if the failure in the low-frequency part of the acoustics or the original recording is strong, then this will not affect the recognition of a particular composition, melody or voice, but the sound will be perceived poorly, impoverished and mediocre, while subjectively being sharper and sharper in terms of perception, since the mids and highs will bulge and dominate against the background of the absence of a good saturated bass region. 
Enough a large number of musical instruments reproduce sounds in the low frequency range, including male vocals can fall into the region of up to 100 Hz. The most pronounced instrument that plays from the very beginning of the audible range (from 20 Hz) can safely be called a wind organ. - Medium frequencies. The limits of the mid-frequency range are within 200 Hz (lower limit) - 2400 Hz (upper limit). The middle range will always be fundamental, defining and actually form the basis of the sound or music of the composition, therefore its importance cannot be overestimated.
This is explained in many ways, but mainly this feature human auditory perception is determined by evolution - it so happened over the many years of our formation that the hearing aid captures the mid-frequency range most sharply and clearly, because. within its limits is human speech, and it is the main tool for effective communication and survival. This also explains some non-linearity of auditory perception, which is always aimed at the predominance of medium frequencies when listening to music, because. our hearing aid is most sensitive to this range, and also automatically adjusts to it, as if "amplifying" more against the background of other sounds. 
In the middle range is the vast majority of sounds, musical instruments or vocals, even if a narrow range is affected from above or below, then the range usually extends to the upper or lower middle anyway. Accordingly, vocals (both male and female) are located in the mid-frequency range, as well as almost all well-known instruments, such as: guitar and other strings, piano and other keyboards, wind instruments, etc. - High frequencies. The boundaries of the high frequency range are within 2400 Hz (lower limit) - 30000 Hz (upper limit). The upper limit, as in the case of the low-frequency range, is somewhat arbitrary and also individual: the average person cannot hear above 20 kHz, but there are rare people with sensitivity up to 30 kHz.
Also, a number of musical overtones can theoretically go into the region above 20 kHz, and as you know, the overtones are ultimately responsible for the coloring of the sound and the final timbre perception of the whole sound picture. Seemingly "inaudible" ultrasonic frequencies can clearly affect psychological condition person, although they will not be tapped in the usual manner. Otherwise, the role of high frequencies, again by analogy with low ones, is more enriching and complementary. Although the high-frequency range has a much greater impact on the recognition of a particular sound, the reliability and preservation of the original timbre than the low-frequency section. High frequencies give music tracks "airiness", transparency, purity and clarity. 
Many musical instruments also play in the high frequency range, including vocals that can go into the region of 7000 Hz and above with the help of overtones and harmonics. The most pronounced group of instruments in the high-frequency segment are strings and winds, and cymbals and violin reach almost the upper limit of the audible range (20 kHz) more fully in sound.
In any case, the role of absolutely all frequencies in the range audible to the human ear is impressive, and problems in the path at any frequency are likely to be clearly visible, especially to a trained hearing aid. The goal of reproducing high-fidelity hi-fi sound of class (or higher) is to ensure that all frequencies sound as accurately and as evenly as possible with each other, as it happened at the time the soundtrack was recorded in the studio. The presence of strong dips or peaks in the frequency response of the acoustic system indicates that, due to its design features, it is not able to reproduce music in the way that the author or sound engineer originally intended at the time of recording. 
Listening to music, a person hears a combination of the sound of instruments and voices, each of which sounds in its own segment of the frequency range. Some instruments may have a very narrow (limited) frequency range, while others, on the contrary, can literally extend from the lower to the upper audible limit. It must be taken into account that despite the same intensity of sounds on different frequencies ah ranges, the human ear perceives these frequencies with different loudness, which again is due to the mechanism of the biological device of the hearing aid. The nature of this phenomenon is also explained in many respects by the biological necessity of adaptation mainly to the mid-frequency sound range. So in practice, a sound having a frequency of 800 Hz at an intensity of 50 dB will be perceived subjectively by ear as louder than a sound of the same strength, but with a frequency of 500 Hz.
Moreover, different audio frequencies flooding the audible frequency range of sound will have different threshold pain sensitivity! pain threshold
considered as a standard middle frequency 1000 Hz with a sensitivity of approximately 120 dB (may vary slightly depending on the individual). As in the case of uneven perception of intensity at different frequencies at normal volume levels, approximately the same dependence is observed with respect to the pain threshold: it occurs most quickly at medium frequencies, but at the edges of the audible range, the threshold becomes higher. For comparison, the pain threshold at an average frequency of 2000 Hz is 112 dB, while the pain threshold at a low frequency of 30 Hz will be already 135 dB. The pain threshold at low frequencies is always higher than at medium and high frequencies. 
A similar disparity is observed with respect to hearing threshold is the lower threshold after which sounds become audible to the human ear. Conventionally, the threshold of hearing is considered to be 0 dB, but again it is true for the reference frequency of 1000 Hz. If, for comparison, we take a low-frequency sound with a frequency of 30 Hz, then it will become audible only at a wave emission intensity of 53 dB.
The listed features of human auditory perception, of course, have a direct impact when the question of listening to music and achieving a certain psychological effect of perception is raised. We remember from that sounds with an intensity above 90 dB are harmful to health and can lead to degradation and significant hearing impairment. But at the same time, a sound of low intensity that is too quiet will suffer from strong frequency unevenness due to biological features auditory perception, which is non-linear in nature. Thus, a musical path with a volume of 40-50 dB will be perceived as depleted, with a pronounced lack (one might say a failure) of low and high frequencies. The named problem is well and long known, to combat it even a well-known function called loudness compensation, which, by equalization, equalizes the levels of low and high frequencies close to the level of the middle, thereby eliminating an unwanted drop without the need to raise the volume level, making the audible frequency range of sound subjectively uniform in terms of the degree of distribution of sound energy. 
Taking into account interesting and unique features of human hearing, it is useful to note that with an increase in sound volume, the frequency non-linearity curve flattens out, and at about 80-85 dB (and higher), sound frequencies will become subjectively equivalent in intensity (with a deviation of 3-5 dB). Although the alignment is not complete and the graph will still be visible, albeit smoothed, but a curved line, which will maintain a tendency towards the predominance of the intensity of the middle frequencies compared to the rest. In audio systems, such unevenness can be solved either with the help of an equalizer, or with the help of separate volume controls in systems with separate channel-by-channel amplification.
Dividing the audible range into smaller subgroups
In addition to the generally accepted and well-known division into three general groups, sometimes it becomes necessary to consider one or another narrow part in more detail and in detail, thereby dividing the sound frequency range into even smaller "fragments". Thanks to this, a more detailed division appeared, using which you can simply quickly and fairly accurately indicate the intended segment of the sound range. Consider this division:
A small select number of instruments descend into the region of the lowest bass, and even more so sub-bass: double bass (40-300 Hz), cello (65-7000 Hz), bassoon (60-9000 Hz), tuba (45-2000 Hz), horns (60-5000Hz), bass guitar (32-196Hz), bass drum (41-8000Hz), saxophone (56-1320Hz), piano (24-1200Hz), synthesizer (20-20000Hz) , organ (20-7000 Hz), harp (36-15000 Hz), contrabassoon (30-4000 Hz). The indicated ranges include all the harmonics of the instruments.
Therefore, it is the upper bass that is responsible for the attack, pressure and musical drive, and only this narrow segment of the sound range can give the listener the feeling of the legendary "punch" (from the English punch - blow), when a powerful sound is perceived by a tangible and strong blow to the chest. Thus, it is possible to recognize a well-formed and correct fast upper bass in a musical system by the high-quality working out of an energetic rhythm, a collected attack, and by the well-formed instruments in the lower register of notes, such as cello, piano or wind instruments. In audio systems, it is most expedient to give a segment of the upper bass range to mid-bass speakers of a fairly large diameter 6.5 "-10" and with good power indicators, a strong magnet. The approach is explained by the fact that it is precisely these speakers in terms of configuration that will be able to fully reveal the energy potential inherent in this very demanding region of the audible range. 
But do not forget about the detail and intelligibility of the sound, these parameters are also important in the process of recreating a particular musical image. Since the upper bass is already well localized / defined in space by ear, the range above 100 Hz must be given exclusively to front-mounted speakers that will form and build the scene. In the segment of the upper bass, a stereo panorama is perfectly heard, if it is provided for by the recording itself.
The upper bass area already covers a fairly large number of instruments and even low-pitched male vocals. Therefore, among the instruments are the same ones that played low bass, but many others are added to them: toms (70-7000 Hz), snare drum (100-10000 Hz), percussion (150-5000 Hz), tenor trombone (80-10000 Hz), trumpet (160-9000 Hz), tenor saxophone (120-16000 Hz), alto saxophone (140-16000 Hz), clarinet (140-15000 Hz), alto violin (130-6700 Hz), guitar (80-5000 Hz). The indicated ranges include all the harmonics of the instruments.
In this range, the lower harmonics and overtones that fill the voice are concentrated, so it is extremely important for the correct transmission of vocals and saturation. It is also in the lower middle that the entire energy potential of the performer's voice is located, without which there will be no corresponding return and emotional response. By analogy with the transmission of the human voice, many live instruments also hide their energy potential in this segment of the range, especially those whose lower audible limit starts from 200-250 Hz (oboe, violin). The lower middle allows you to hear the melody of the sound, but does not make it possible to clearly distinguish the instruments. Accordingly, the lower middle is responsible for the correct design of most instruments and voices, saturating the latter and making them recognizable by timbre. Also, the lower middle is extremely demanding in terms of the correct transmission of a full-fledged bass range, since it "picks up" the drive and attack of the main percussion bass and is expected to properly support it and smoothly "finish", gradually reducing it to nothing. The sensations of sound purity and intelligibility of the bass lie precisely in this area, and if there are problems in the lower middle from an overabundance or the presence of resonant frequencies, then the sound will tire the listener, it will be dirty and slightly mumbling. 
If there is a shortage in the region of the lower middle, then the correct feeling of the bass and the reliable transmission of the vocal part, which will be devoid of pressure and energy return, will suffer. The same applies to most instruments that, without the support of the lower middle, will lose their "face", become incorrectly framed and their sound will become noticeably poorer, even if it remains recognizable, it will no longer be so full.
When building an audio system, the range of the lower middle and above (up to the top) is usually given to mid-range speakers (MF), which, without a doubt, should be located in the front part in front of the listener and build the stage. For these speakers, the size is not so important, it can be 6.5 "and lower, how important is the detail and the ability to reveal the nuances of sound, which is achieved by the design features of the speaker itself (diffuser, suspension and other characteristics). 
Also, correct localization is vital for the entire mid-frequency range, and literally the slightest tilt or turn of the speaker can have a tangible impact on the sound in terms of the correct realistic reproduction of the images of instruments and vocals in space, although this will largely depend on the design features of the speaker cone itself.
The lower middle covers almost all existing instruments and human voices, although it does not play a fundamental role, but is still very important for the full perception of music or sounds. Among the instruments there will be the same set that was able to win back the lower range of the bass region, but others are added to them that start already from the lower middle: cymbals (190-17000 Hz), oboe (247-15000 Hz), flute (240- 14500 Hz), violin (200-17000 Hz). The indicated ranges include all the harmonics of the instruments.
In the event of a failure in the middle, the sound becomes boring and inexpressive, loses its sonority and brightness, the vocals cease to fascinate and actually disappear. Also, the middle is responsible for the intelligibility of the main information coming from instruments and vocals (to a lesser extent, because consonants go in a higher range), helping to distinguish them well by ear. Most of the existing instruments come to life in this range, become energetic, informative and tangible, the same happens with vocals (especially female ones), which are filled with energy in the middle. 
The mid-frequency fundamental range covers the absolute majority of the instruments that have already been listed earlier, and also reveals the full potential of male and female vocals. Only rare selected instruments start their lives at medium frequencies, playing in a relatively narrow range initially, for example, a small flute (600-15000 Hz).
But overemphasizing this range has an extremely undesirable effect on the sound picture, because. it begins to noticeably cut the ear, irritate and even cause painful discomfort. Therefore, the upper middle requires a delicate and careful attitude with it, tk. due to problems in this area, it is very easy to spoil the sound, or, on the contrary, make it interesting and worthy. Usually, the coloring in the upper middle region largely determines the subjective aspect of the genre of the acoustic system. Thanks to the upper middle, vocals and many instruments are finally formed, they become well distinguished by ear and sound intelligibility appears. This is especially true for the nuances of the reproduction of the human voice, because it is in the upper middle that the spectrum of consonants is placed and the vowels that appeared in the early ranges of the middle continue. In a general sense, the upper middle favorably emphasizes and fully reveals those instruments or voices that are saturated with upper harmonics, overtones. In particular, female vocals, many bowed, stringed and wind instruments are revealed in a truly lively and natural way in the upper middle. 
The vast majority of instruments still play in the upper middle, although many are already represented only in the form of wraps and harmonicas. The exception is some rare ones, initially distinguished by a limited low-frequency range, for example, a tuba (45-2000 Hz), which ends its existence in the upper middle completely.
They practically do not play a role in terms of distinguishing instruments and recognizing voices, although the lower top remains a highly informative and fundamental area. In fact, these frequencies outline the musical images of instruments and vocals, they indicate their presence. In the event of a failure of the lower high segment of the frequency range, the speech will become dry, lifeless and incomplete, approximately the same thing happens with instrumental parts - the brightness is lost, the very essence of the sound source is distorted, it becomes distinctly incomplete and underformed. In any normal audio system, the role of high frequencies is assumed by a separate speaker called a tweeter (high frequency). Usually small in size, it is undemanding to the input power (within reasonable limits) by analogy with the middle and especially the bass section, but it is also extremely important for the sound to play correctly, realistically and at least beautifully. The tweeter covers the entire audible high-frequency range from 2000-2400 Hz to 20000 Hz. In the case of high-frequency drivers, almost by analogy with the mid-range section, the correct physical location and directionality is very important, since the tweeters are maximally involved not only in the formation of the sound stage, but also in the process of fine-tuning it. 
With the help of tweeters, you can largely control the scene, zoom in/out the performers, change the shape and flow of instruments, play with the color of the sound and its brightness. As in the case of adjusting midrange speakers, almost everything affects the correct sound of tweeters, and often very, very sensitively: turn and tilt of the speaker, its location vertically and horizontally, distance from nearby surfaces, etc. However, the success of the correct tuning and the finicky of the HF section depends on the design of the speaker and its polar pattern.
Instruments that play down to the lower highs, they do so predominantly through harmonics rather than fundamentals. Otherwise, in the lower high range, almost all the same ones that were in the mid-frequency segment "live", i.e. almost all existing ones. It is the same with the voice, which is especially active in the lower high frequencies, a special brightness and influence can be heard in the female vocal parts.
In fact, the presented segment of the range is comparable with increased clarity and detail of the sound: if there is no dip in the middle top, then the sound source is mentally well localized in space, concentrated at a certain point and expressed by a feeling of a certain distance; and vice versa, if there is a lack of lower top, then the clarity of the sound seems to be blurred and the images are lost in space, the sound becomes cloudy, clamped and synthetically unrealistic. Accordingly, the regulation of the lower high frequencies is comparable to the ability to virtually "move" the sound stage in space, i.e. move it away or bring it closer. 
The mid-high frequencies ultimately provide the desired presence effect (more precisely, they complete it to the fullest, since the effect is based on deep and soulful bass), thanks to these frequencies, the instruments and voice become as realistic and reliable as possible. We can also say about the middle tops that they are responsible for the detail in the sound, for numerous small nuances and overtones both in relation to the instrumental part and in the vocal parts. At the end of the mid-high segment, "air" and transparency begin, which can also be quite clearly felt and influence perception.
Despite the fact that the sound is steadily declining, the following are still active in this segment of the range: male and female vocals, bass drum (41-8000 Hz), toms (70-7000 Hz), snare drum (100-10000 Hz) , Cymbals (190-17000 Hz), Air Support Trombone (80-10000 Hz), Trumpet (160-9000 Hz), Bassoon (60-9000 Hz), Saxophone (56-1320 Hz), Clarinet (140-15000 Hz), oboe (247-15000 Hz), flute (240-14500 Hz), piccolo (600-15000 Hz), cello (65-7000 Hz), violin (200-17000 Hz), harp (36-15000 Hz) ), organ (20-7000 Hz), synthesizer (20-20000 Hz), timpani (60-3000 Hz).
In addition, in addition to the immediate audible part, the upper high region, smoothly turning into ultrasonic frequencies, can still have some psychological impact: even if these sounds are not heard clearly, but the waves are radiated into space and can be perceived by a person, while more at the level of mood formation. They also ultimately affect the sound quality. In general, these frequencies are the most subtle and gentle in the entire range, but they are also responsible for the feeling of beauty, elegance, sparkling aftertaste of music. With a lack of energy in the upper high range, it is quite possible to feel discomfort and musical understatement. In addition, the capricious upper high range gives the listener a sense of spatial depth, as if diving deep into the stage and being enveloped in sound. However, an excess of sound saturation in the indicated narrow range can make the sound unnecessarily "sandy" and unnaturally thin. 
When discussing the upper high frequency range, it is also worth mentioning the tweeter called the "super tweeter", which is actually a structurally expanded version of the conventional tweeter. Such a speaker is designed to cover a larger portion of the range in the upper side. If the operating range of a conventional tweeter ends at the expected limiting mark, above which the human ear theoretically does not perceive sound information, i.e. 20 kHz, then the super tweeter can raise this border to 30-35 kHz. The idea pursued by the implementation of such a sophisticated speaker is very interesting and curious, it came from the world of "hi-fi" and "hi-end", where it is believed that no frequencies in the musical path can be ignored and, even if we do not hear them directly, they are still initially present during the live performance of a particular composition, which means that they can indirectly have some kind of influence. The situation with the super tweeter is complicated only by the fact that not all equipment (sound sources/players, amplifiers, etc.) is capable of outputting a signal in the full range, without cutting frequencies from above. The same is true for the recording itself, which is often done with a cut in the frequency range and loss of quality.
Approximately in the way described above, the division of the audible frequency range into conditional segments looks like in reality, with the help of division it is easier to understand problems in the audio path in order to eliminate them or to equalize the sound. Despite the fact that each person imagines some exclusively his own and understandable only to him standard image of sound in accordance only with his taste preferences, the nature of the original sound tends to balance, or rather to the averaging of all sounding frequencies. Therefore, the correct studio sound is always balanced and calm, the entire spectrum of sound frequencies in it tends to a flat line on the frequency response (amplitude-frequency response) graph. The same direction is trying to implement uncompromising "hi-fi" and "hi-end": to get the most even and balanced sound, without peaks and dips throughout the entire audible range. Such a sound, by its nature, may seem boring and inexpressive, devoid of brightness and of no interest to an ordinary inexperienced listener, but it is precisely this sound that is truly correct in fact, striving for balance by analogy with how the laws of the very universe in which we live manifest themselves. .
One way or another, the desire to recreate some specific character of sound within your audio system lies entirely with the preferences of the listener. Some people like the sound with prevailing powerful lows, others like the increased brightness of the "raised" highs, others can enjoy the harsh vocals emphasized in the middle for hours ... There can be a huge variety of perception options, and information about the frequency division of the range into conditional segments will just help anyone who wants to create the sound of their dreams, only now with a more complete understanding of the nuances and subtleties of the laws that sound as a physical phenomenon obeys. 
Understanding the process of saturation with certain frequencies of the sound range (filling it with energy in each of the sections) in practice will not only facilitate the tuning of any audio system and make it possible to build a scene in principle, but will also give invaluable experience in assessing the specific nature of the sound. With experience, a person will be able to instantly identify the shortcomings of the sound by ear, moreover, very accurately describe the problems in a certain part of the range and suggest a possible solution to improve the sound picture. Sound correction can be done various methods, where you can use an equalizer as "levers", for example, or "play" with the location and direction of the speakers - thereby changing the nature of the early reflections of the wave, eliminating standing waves, etc. This will already be a "completely different story" and a topic for separate articles.
The frequency range of the human voice in musical terminology
Separately and separately in music, the role of the human voice as a vocal part is assigned, because the nature of this phenomenon is truly amazing. The human voice is so multifaceted and its range (compared to musical instruments) is the widest, with the exception of some instruments, such as the pianoforte. 
Moreover, at different ages a person can make sounds of different heights, in childhood up to ultrasonic heights, in adulthood a male voice is quite capable of falling extremely low. Here, as before, the individual characteristics of the human vocal cords are extremely important, because. there are people who can amaze with their voice in the range of 5 octaves!
- Baby
- Alto (low)
- Soprano (high)
- Treble (high in boys)
- Men's
- Bass profundo (extra low) 43.7-262 Hz
- Bass (low) 82-349 Hz
- Baritone (medium) 110-392 Hz
- Tenor (high) 132-532 Hz
- Tenor altino (extra high) 131-700 Hz
- Women's
- Contralto (low) 165-692 Hz
- Mezzo-soprano (medium) 220-880 Hz
- Soprano (high) 262-1046 Hz
- Coloratura soprano (extra high) 1397 Hz
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 (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 of different frequency and intensity, and the value of the minimum sound that the patient hears is marked with dots. 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, tone threshold audiometry is most often used, which determines the minimum hearing threshold (the quietest sound that a person hears, measured in decibels (dB)) at various frequencies (usually 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, mood, etc., and on 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 are depicted separately and signed (most often the right ear is on the left, and the left ear is 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 - 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 can be at the level of conducting a 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. Exist various calculations degree of deafness. However, the most widely used is the 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 (125 Hz, 250 Hz) give the effect of vibration and the subject may take this sensation as auditory. Therefore, it is necessary to be critical of the air-bone interval at these frequencies, especially with severe degrees of 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 in the development of the outer and middle ear (microotia, atresia of the outer 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 the 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 on the left is indicative. 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.
Audiogram at mixed hearing loss 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. As a rule, to establish the final diagnosis, a comprehensive audiological study is required, which, in addition to audiometry, includes acoustic impedancemetry, otoacoustic emission, auditory evoked potentials, hearing tests 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.
Psychoacoustics - a field of science bordering between physics and psychology, studies data on the auditory sensation of a person when a physical stimulus - sound - acts on the ear. A large amount of data has been accumulated on human reactions to auditory stimuli. Without this data, it is difficult to gain a correct understanding of the operation of audio frequency signaling systems. Consider the most important features of human perception of sound.
A person feels changes in sound pressure occurring at a frequency of 20-20,000 Hz. Sounds below 40 Hz are relatively rare in music and do not exist in spoken language. At very high frequencies, musical perception disappears and a certain indefinite sound sensation arises, depending on the individuality of the listener, his age. With age, the sensitivity of hearing in humans decreases, especially in the upper frequencies of the sound range.
But it would be wrong to conclude on this basis that the transmission of a wide frequency band by a sound reproducing installation is unimportant for older people. Experiments have shown that people, even barely perceiving signals above 12 kHz, very easily recognize the lack of high frequencies in a musical transmission.
Frequency characteristics of auditory sensations
The area of sounds audible by a person in the range of 20-20000 Hz is limited in intensity by thresholds: from below - audibility and from above - pain sensations.
The threshold of hearing is estimated by the minimum pressure, more precisely, by the minimum increment of pressure relative to the boundary; it is sensitive to frequencies of 1000-5000 Hz - here the threshold of hearing is the lowest (sound pressure is about 2-10 Pa). In the direction of lower and higher sound frequencies, the sensitivity of hearing drops sharply.
The pain threshold determines the upper limit of the perception of sound energy and corresponds approximately to a sound intensity of 10 W / m or 130 dB (for a reference signal with a frequency of 1000 Hz).
With an increase in sound pressure, the intensity of the sound also increases, and the auditory sensation increases in jumps, called the intensity discrimination threshold. The number of these jumps at medium frequencies is about 250, at low and high frequencies it decreases and, on average, over the frequency range is about 150.
Since the range of intensity variation is 130 dB, then the elementary jump of sensations on average over the amplitude range is 0.8 dB, which corresponds to a change in sound intensity by 1.2 times. At low levels of hearing, these jumps reach 2-3 dB, at high levels they decrease to 0.5 dB (1.1 times). An increase in the power of the amplifying path by less than 1.44 times is practically not fixed by the human ear. With a lower sound pressure developed by the loudspeaker, even a twofold increase in the power of the output stage may not give a tangible result.
Subjective characteristics of sound
The quality of sound transmission is evaluated on the basis of auditory perception. Therefore, it is possible to correctly determine the technical requirements for the sound transmission path or its individual links only by studying the patterns that connect the subjectively perceived sensation of sound and the objective characteristics of sound are pitch, loudness and timbre.
The concept of pitch implies a subjective assessment of the perception of sound in the frequency range. Sound is usually characterized not by frequency, but by pitch.
Tone is a signal of a certain height, having a discrete spectrum (musical sounds, vowels of speech). A signal that has a wide continuous spectrum, all frequency components of which have the same average power, is called white noise.
gradual increase frequencies of sound vibrations from 20 to 20,000 Hz are perceived as a gradual change in tone from the lowest (bass) to the highest.
The degree of accuracy with which a person determines the pitch by ear depends on the sharpness, musicality and training of his ear. It should be noted that the pitch to some extent depends on the intensity of the sound (at high levels, sounds of greater intensity seem lower than weaker ones..
The human ear is good at distinguishing two tones that are close in pitch. For example, in the frequency range of approximately 2000 Hz, a person can distinguish between two tones that differ from each other in frequency by 3-6 Hz.
The subjective scale of sound perception in terms of frequency is close to the logarithmic law. Therefore, a doubling of the oscillation frequency (regardless of the initial frequency) is always perceived as the same change in pitch. The pitch interval corresponding to a frequency change of 2 times is called an octave. The frequency range perceived by a person is 20-20,000 Hz, it covers approximately ten octaves.
An octave is a fairly large pitch change interval; a person distinguishes much smaller intervals. So, in ten octaves perceived by the ear, one can distinguish more than a thousand gradations of pitch. Music uses smaller intervals called semitones, which correspond to a frequency change of approximately 1.054 times.
An octave is divided into half octaves and a third of an octave. For the latter, the following range of frequencies has been standardized: 1; 1.25; 1.6; 2; 2.5; 3; 3.15; 4; 5; 6.3:8; 10, which are the boundaries of one-third octaves. If these frequencies are placed at equal distances along the frequency axis, then a logarithmic scale will be obtained. Based on this, all frequency characteristics of sound transmission devices are built on a logarithmic scale.
The transmission loudness depends not only on the intensity of the sound, but also on the spectral composition, the conditions of perception and the duration of exposure. So, two sounding tones of medium and low frequency, having the same intensity (or the same sound pressure), are not perceived by a person as equally loud. Therefore, the concept of loudness level in backgrounds was introduced to denote sounds of the same loudness. The level of sound pressure in decibels of the same volume of a pure tone with a frequency of 1000 Hz is taken as the sound volume level in phons, i.e. for a frequency of 1000 Hz, the volume levels in phons and decibels are the same. At other frequencies, for the same sound pressure, sounds may appear louder or quieter.
The experience of sound engineers in recording and editing musical works shows that in order to better detect sound defects that may occur during work, the volume level during control listening should be kept high, approximately corresponding to the volume level in the hall.
With prolonged exposure to intense sound, hearing sensitivity gradually decreases, and the more, the higher the volume of the sound. The detectable reduction in sensitivity is related to the hearing response to overload, i.e. with its natural adaptation, After a break in listening, hearing sensitivity is restored. To this it should be added that the hearing aid, when perceiving high-level signals, introduces its own, so-called subjective, distortions (which indicates the non-linearity of hearing). Thus, at a signal level of 100 dB, the first and second subjective harmonics reach levels of 85 and 70 dB.
A significant volume level and the duration of its exposure cause irreversible phenomena in the auditory organ. It is noted that in recent years, the hearing thresholds have sharply increased among young people. The reason for this was the passion for pop music, characterized by high sound levels.
The volume level is measured using an electro-acoustic device - a sound level meter. The measured sound is first converted by the microphone into electrical vibrations. After amplification by a special voltage amplifier, these oscillations are measured with a pointer device adjusted in decibels. To ensure that the readings of the device correspond as closely as possible to the subjective perception of loudness, the device is equipped with special filters that change its sensitivity to the perception of sound of different frequencies in accordance with the characteristic of hearing sensitivity.
An important characteristic of sound is timbre. The ability of hearing to distinguish it allows you to perceive signals with a wide variety of shades. The sound of each of the instruments and voices, due to their characteristic shades, becomes multicolored and well recognizable.
Timbre, being a subjective reflection of the complexity of the perceived sound, does not have a quantitative assessment and is characterized by terms of a qualitative order (beautiful, soft, juicy, etc.). When a signal is transmitted through an electro-acoustic path, the resulting distortions primarily affect the timbre of the reproduced sound. The condition for the correct transmission of the timbre of musical sounds is the undistorted transmission of the signal spectrum. The signal spectrum is a set of sinusoidal components of a complex sound.
The so-called pure tone has the simplest spectrum, it contains only one frequency. The sound of a musical instrument turns out to be more interesting: its spectrum consists of the fundamental frequency and several "impurity" frequencies, called overtones (higher tones). Overtones are multiples of the fundamental frequency and are usually smaller in amplitude.
The timbre of the sound depends on the distribution of intensity over the overtones. The sounds of different musical instruments differ in timbre.
More complex is the spectrum of combination of musical sounds, called a chord. In such a spectrum, there are several fundamental frequencies along with the corresponding overtones.
Differences in timbre are shared mainly by the low-mid frequency components of the signal, therefore, a large variety of timbres is associated with signals lying in the lower part of the frequency range. The signals related to its upper part, as they increase, lose their timbre coloring more and more, which is due to the gradual departure of their harmonic components beyond the limits of audible frequencies. This can be explained by the fact that up to 20 or more harmonics are actively involved in the formation of the timbre of low sounds, medium 8 - 10, high 2 - 3, since the rest are either weak or fall out of the region of audible frequencies. Therefore, high sounds, as a rule, are poorer in timbre.
Almost all natural sound sources, including sources of musical sounds, have a specific dependence of the timbre on the volume level. Hearing is also adapted to such a dependence - for it it is natural definition intensity of the source according to the color of the sound. Loud sounds are usually more harsh.
Musical sound sources
Big influence on the sound quality of electroacoustic systems a number of factors characterizing the primary sources of sounds.
The acoustic parameters of musical sources depend on the composition of the performers (orchestra, ensemble, group, soloist and type of music: symphonic, folk, pop, etc.).
The origin and formation of sound on each musical instrument has its own specifics associated with the acoustic features of sound formation in a particular musical instrument.
An important element of musical sound is attack. This is a specific transient process during which stable sound characteristics are established: loudness, timbre, pitch. Any musical sound goes through three stages - beginning, middle and end, and both the initial and final stages have a certain duration. The initial stage is called the attack. It lasts differently: for plucked, percussion and some wind instruments 0-20 ms, for bassoon 20-60 ms. An attack is not just an increase in sound volume from zero to some steady value, it can be accompanied by the same change in pitch and timbre. Moreover, the characteristics of the attack of the instrument are not the same in different parts of its range with different playing styles: the violin is the most perfect instrument in terms of the richness of possible expressive methods of attack.
One of the characteristics of any musical instrument is the frequency range of the sound. In addition to the fundamental frequencies, each instrument is characterized by additional high-quality components - overtones (or, as is customary in electroacoustics, higher harmonics), which determine its specific timbre.
It is known that sound energy is unevenly distributed over the entire spectrum of sound frequencies emitted by the source.
Most instruments are characterized by amplification of the fundamental frequencies, as well as individual overtones in certain (one or more) relatively narrow frequency bands (formants), which are different for each instrument. The resonant frequencies (in hertz) of the formant region are: for trumpet 100-200, horn 200-400, trombone 300-900, trumpet 800-1750, saxophone 350-900, oboe 800-1500, bassoon 300-900, clarinet 250-600 .
Another characteristic property of musical instruments is the strength of their sound, which is determined by a larger or smaller amplitude (span) of their sounding body or air column (a larger amplitude corresponds to a stronger sound and vice versa). The value of peak acoustic powers (in watts) is: for large orchestra 70, bass drum 25, timpani 20, snare drum 12, trombone 6, piano 0.4, trumpet and saxophone 0.3, trumpet 0.2, double bass 0.( 6, piccolo 0.08, clarinet, horn and triangle 0.05.
The ratio of the sound power extracted from the instrument when performing "fortissimo" to the sound power when performing "pianissimo" is commonly called the dynamic range of the sound of musical instruments.
The dynamic range of a musical sound source depends on the type of performing group and the nature of the performance.
Consider the dynamic range of individual sound sources. Under the dynamic range of individual musical instruments and ensembles (orchestras and choirs of various composition), as well as voices, we understand the ratio of the maximum sound pressure created by a given source to the minimum, expressed in decibels.
In practice, when determining the dynamic range of a sound source, one usually operates only with sound pressure levels, calculating or measuring their corresponding difference. For example, if the maximum sound level of an orchestra is 90 and the minimum is 50 dB, then the dynamic range is said to be 90 - 50 = = 40 dB. In this case, 90 and 50 dB are the sound pressure levels relative to the zero acoustic level.
The dynamic range for a given sound source is not constant. It depends on the nature of the performed work and on the acoustic conditions of the room in which the performance takes place. Reverb expands the dynamic range, which usually reaches its maximum value in rooms with a large volume and minimal sound absorption. Almost all instruments and human voices have a dynamic range that is uneven across the sound registers. For example, the volume level of the lowest sound on the "forte" of the vocalist is equal to the level of the highest sound on the "piano".
The dynamic range of a musical program is expressed in the same way as for individual sound sources, but the maximum sound pressure is noted with a dynamic ff (fortissimo) shade, and the minimum with pp (pianissimo).
The highest volume, indicated in notes fff (forte, fortissimo), corresponds to an acoustic sound pressure level of approximately 110 dB, and the lowest volume, indicated in notes prr (piano-pianissimo), approximately 40 dB.
It should be noted that the dynamic shades of performance in music are relative and their connection with the corresponding sound pressure levels is to some extent conditional. The dynamic range of a particular musical program depends on the nature of the composition. Thus, the dynamic range of classical works by Haydn, Mozart, Vivaldi rarely exceeds 30-35 dB. The dynamic range of variety music usually does not exceed 40 dB, while dance and jazz - only about 20 dB. Most works for Russian folk instruments orchestra also have a small dynamic range (25-30 dB). This is true for the brass band as well. However, the maximum sound level of a brass band in a room can reach a fairly high level (up to 110 dB).
masking effect
The subjective assessment of loudness depends on the conditions in which the sound is perceived by the listener. In real conditions, the acoustic signal does not exist in absolute silence. At the same time, extraneous noises affect the hearing, making it difficult sound perception, masking to a certain extent the main signal. The effect of masking a pure sinusoidal tone by extraneous noise is estimated by a value indicating. by how many decibels the threshold of audibility of the masked signal rises above the threshold of its perception in silence.
Experiments to determine the degree of masking of one sound signal by another show that the tone of any frequency is masked by lower tones much more effectively than by higher ones. For example, if two tuning forks (1200 and 440 Hz) emit sounds with the same intensity, then we stop hearing the first tone, it is masked by the second one (having extinguished the vibration of the second tuning fork, we will hear the first one again).
If there are two complex sound signal, consisting of certain spectra of sound frequencies, then the effect of mutual masking occurs. Moreover, if the main energy of both signals lies in the same region of the audio frequency range, then the masking effect will be the strongest. Thus, when transmitting an orchestral work, due to masking by the accompaniment, the soloist's part may become poorly legible, indistinct.
Achieving clarity or, as they say, "transparency" of sound in the sound transmission of orchestras or pop ensembles becomes very difficult if the instrument or individual groups of instruments of the orchestra play in the same or close registers at the same time.
When recording an orchestra, the director must take into account the peculiarities of disguise. At rehearsals, with the help of a conductor, he sets a balance between the sound power of the instruments of one group, as well as between the groups of the entire orchestra. The clarity of the main melodic lines and individual musical parts is achieved in these cases by the close location of the microphones to the performers, the deliberate selection by the sound engineer of the most important instruments in a given place, and other special sound engineering techniques.
The phenomenon of masking is opposed by the psycho-physiological ability of the hearing organs to single out one or more sounds from the general mass that carry the most important information. For example, when the orchestra is playing, the conductor notices the slightest inaccuracies in the performance of the part on any instrument.
Masking can significantly affect the quality of signal transmission. A clear perception of the received sound is possible if its intensity significantly exceeds the level of interference components that are in the same band as the received sound. With uniform interference, the signal excess should be 10-15 dB. This feature of auditory perception is practical use, for example, when evaluating the electroacoustic characteristics of carriers. So, if the signal-to-noise ratio of an analog record is 60 dB, then the dynamic range of the recorded program can be no more than 45-48 dB.
Temporal characteristics of auditory perception
The hearing aid, like any other oscillatory system, is inertial. When the sound disappears, the auditory sensation does not disappear immediately, but gradually, decreasing to zero. The time during which the sensation in terms of loudness decreases by 8-10 phon is called the hearing time constant. This constant depends on a number of circumstances, as well as on the parameters of the perceived sound. If two short sound pulses arrive at the listener with the same frequency composition and level, but one of them is delayed, then they will be perceived together with a delay not exceeding 50 ms. For large delay intervals, both pulses are perceived separately, an echo occurs.
This feature of hearing is taken into account when designing some signal processing devices, for example, electronic delay lines, reverbs, etc.
It should be noted that thanks to special property hearing, the sensation of the volume of a short-term sound impulse depends not only on its level, but also on the duration of the impact of the impulse on the ear. So, a short-term sound, lasting only 10-12 ms, is perceived by the ear quieter than a sound of the same level, but affecting the ear for, for example, 150-400 ms. Therefore, when listening to a transmission, the loudness is the result of averaging the energy of the sound wave over a certain interval. In addition, human hearing has inertia, in particular, when perceiving non-linear distortions, he does not feel such if the duration of the sound pulse is less than 10-20 ms. That is why in the level indicators of sound-recording household radio-electronic equipment, instantaneous signal values are averaged over a period selected in accordance with the temporal characteristics of the hearing organs.
Spatial representation of sound
One of the important human abilities is the ability to determine the direction of the sound source. This ability is called the binaural effect and is explained by the fact that a person has two ears. Experimental data shows where the sound comes from: one for high-frequency tones, the other for low-frequency ones.
The sound travels a shorter path to the ear facing the source than to the second ear. As a result, the pressure of sound waves in ear canals differs in phase and amplitude. Amplitude differences are significant only at high frequencies, when the sound wave length becomes comparable to the size of the head. When the amplitude difference exceeds the 1 dB threshold, the sound source appears to be on the side where the amplitude is greater. The angle of deviation of the sound source from the center line (line of symmetry) is approximately proportional to the logarithm of the amplitude ratio.
To determine the direction of the sound source with frequencies below 1500-2000 Hz, phase differences are significant. It seems to a person that the sound comes from the side from which the wave, which is ahead in phase, reaches the ear. The angle of deviation of sound from the midline is proportional to the difference in the time of arrival of sound waves to both ears. A trained person can notice a phase difference with a time difference of 100 ms.
The ability to determine the direction of sound in the vertical plane is much less developed (about 10 times). This feature of physiology is associated with the orientation of the hearing organs in the horizontal plane.
Specific Feature spatial perception of sound by a person is manifested in the fact that the hearing organs are able to feel the total, integral localization created with the help of artificial means of influence. For example, two speakers are installed in a room along the front at a distance of 2-3 m from each other. At the same distance from the axis of the connecting system, the listener is located strictly in the center. In the room, two sounds of the same phase, frequency and intensity are emitted through the speakers. As a result of the identity of the sounds passing into the organ of hearing, a person cannot separate them, his sensations give an idea of a single, apparent (virtual) sound source, which is located strictly in the center on the axis of symmetry.
If we now reduce the volume of one speaker, then the apparent source will move towards the louder speaker. The illusion of sound source movement can be obtained not only by changing the signal level, but also by artificially delaying one sound relative to another; in this case, the apparent source will shift towards the speaker, which emits a signal ahead of time.
Let us give an example to illustrate integral localization. The distance between speakers is 2m, the distance from the front line to the listener is 2m; in order for the source to shift as if by 40 cm to the left or right, it is necessary to apply two signals with a difference in intensity level of 5 dB or with a time delay of 0.3 ms. With a level difference of 10 dB or a time delay of 0.6 ms, the source will "move" 70 cm from the center.
Thus, if you change the sound pressure generated by the speakers, then the illusion of moving the sound source arises. This phenomenon is called total localization. To create a total localization, a two-channel stereophonic sound transmission system is used.
Two microphones are installed in the primary room, each of which works on its own channel. In the secondary - two loudspeakers. Microphones are located at a certain distance from each other along a line parallel to the placement of the sound emitter. When the sound emitter is moved, different sound pressure will act on the microphone and the arrival time of the sound wave will be different due to the unequal distance between the sound emitter and the microphones. This difference creates the effect of total localization in the secondary room, as a result of which the apparent source is localized at a certain point in space located between the two loudspeakers.
It should be said about the binoural sound transmission system. With this system, called the "artificial head" system, two separate microphones are placed in the primary room, positioned at a distance from each other equal to the distance between the ears of a person. Each of the microphones has an independent sound transmission channel, at the output of which telephones for the left and right ears are switched on in the secondary room. With identical sound transmission channels, such a system accurately reproduces the binaural effect created near the ears of the "artificial head" in the primary room. The presence of headphones and the need to use them for a long time is a disadvantage.
The organ of hearing determines the distance to the sound source by a number of indirect signs and with some errors. Depending on whether the distance to the signal source is small or large, its subjective assessment changes under the influence of various factors. It was found that if the determined distances are small (up to 3 m), then their subjective assessment is almost linearly related to the change in the volume of the sound source moving along the depth. An additional factor for a complex signal is its timbre, which becomes more and more "heavy" "as the source approaches the listener. This is due to the increasing strengthening of the overtones of the low compared to the overtones of the high register, caused by the resulting increase in volume level.
For average distances of 3-10 m, the removal of the source from the listener will be accompanied by a proportional decrease in volume, and this change will apply equally to the fundamental frequency and to the harmonic components. As a result, there is a relative amplification of the high-frequency part of the spectrum and the timbre becomes brighter.
As the distance increases, the energy loss in the air will increase in proportion to the square of the frequency. Increased loss of high register overtones will result in a reduction in timbre brightness. Thus, the subjective assessment of distances is associated with a change in its volume and timbre.
Under conditions of an enclosed space, the signals of the first reflections, which are delayed by 20–40 ms relative to the direct one, are perceived by the ear as coming from different directions. At the same time, their increasing delay creates the impression of a significant distance from the points from which these reflections originate. Thus, according to the delay time, one can judge the relative remoteness of secondary sources or, which is the same, the size of the room.
Some features of the subjective perception of stereo broadcasts.
A stereophonic sound transmission system has a number of significant features compared to a conventional monophonic one.
The quality that distinguishes stereophonic sound, surround, i.e. natural acoustic perspective can be assessed using some additional indicators that do not make sense with a monophonic sound transmission technique. These additional indicators include: the angle of hearing, i.e. the angle at which the listener perceives the sound stereo image; stereo resolution, i.e. subjectively determined localization of individual elements of the sound image at certain points in space within the angle of audibility; acoustic atmosphere, i.e. the effect of making the listener feel present in the primary room where the transmitted sound event occurs.
About the role of room acoustics
The brilliance of sound is achieved not only with the help of sound reproduction equipment. Even with good enough equipment, the sound quality can be poor if the listening room does not have certain properties. It is known that in a closed room there is a phenomenon called reverberation. By affecting the hearing organs, reverberation (depending on its duration) can improve or degrade the sound quality.
A person in a room perceives not only direct sound waves created directly by the sound source, but also waves reflected by the ceiling and walls of the room. Reflected waves are still audible for some time after the termination of the sound source.
It is sometimes believed that reflected signals play only a negative role, interfering with the perception of the main signal. However, this view is incorrect. certain part The energy of the initial reflected echo signals, reaching the ears of a person with short delays, amplifies the main signal and enriches its sound. On the contrary, later reflected echoes. the delay time of which exceeds a certain critical value, form a sound background that makes it difficult to perceive the main signal.
The listening room should not have a long reverberation time. Living rooms tend to have low reverberation due to their limited size and the presence of sound-absorbing surfaces, upholstered furniture, carpets, curtains, etc.
Barriers of different nature and properties are characterized by the sound absorption coefficient, which is the ratio of the absorbed energy to the total energy of the incident sound wave.
To increase the sound-absorbing properties of the carpet (and reduce noise in the living room), it is advisable to hang the carpet not close to the wall, but with a gap of 30-50 mm).
Deafness is pathological condition characterized by hearing loss and difficulty in understanding spoken language. It occurs quite often, especially in the elderly. However, today there is a trend towards more early development hearing loss, including among young people and children. Depending on how weakened hearing is, hearing loss is divided into different degrees.
What are decibels and hertz
Any sound or noise can be characterized by two parameters: height and sound intensity.
Pitch
The pitch of a sound is determined by the number of vibrations of the sound wave and is expressed in hertz (Hz): the higher the hertz, the higher the tone. For example, the very first white key on the left on a conventional piano (“A” subcontroctave) produces a low sound at 27.500 Hz, while the very last white key on the right (“up to” the fifth octave) produces 4186.0 Hz.
The human ear is able to distinguish sounds within the range of 16–20,000 Hz. Anything less than 16 Hz is called infrasound, and anything over 20,000 is called ultrasound. Both ultrasound and infrasound are not perceived by the human ear, but can affect the body and psyche.
All in frequency audible sounds can be divided into high, medium and low frequencies. Low-frequency sounds are up to 500 Hz, mid-frequency - within 500-10,000 Hz, high-frequency - all sounds with a frequency of more than 10,000 Hz. human ear with the same impact force, it is better to hear mid-frequency sounds, which are perceived as louder. Accordingly, low- and high-frequency sounds are “heard” quieter, or even “stop sounding” altogether. In general, after 40–50 years, the upper limit of audibility of sounds decreases from 20,000 to 16,000 Hz.
sound power
When exposed to the ear loud sound there may be a break eardrum. In the picture below - a normal membrane, above - a membrane with a defect.Any sound can affect the organ of hearing in different ways. It depends on its sound strength, or loudness, which is measured in decibels (dB).
Normal hearing is able to distinguish sounds ranging from 0 dB and above. When exposed to loud sound more than 120 dB.
The most comfortable human ear feels in the range up to 80-85 dB.
For comparison:
- winter forest in calm weather - about 0 dB,
- rustling of leaves in the forest, park - 20-30 dB,
- ordinary colloquial speech, office work - 40-60 dB,
- noise from the engine in the car - 70-80 dB,
- loud screams - 85-90 dB,
- thunder rolls - 100 dB,
- a jackhammer at a distance of 1 meter from it - about 120 dB.
Degrees of hearing loss relative to loudness
The following degrees of hearing loss are usually distinguished:
- Normal hearing - a person hears sounds in the range from 0 to 25 dB and above. He distinguishes the rustling of leaves, the singing of birds in the forest, the ticking of a wall clock, etc.
- Hearing loss:
- I degree (mild) - a person begins to hear sounds from 26-40 dB.
- II degree (moderate) - the threshold for the perception of sounds starts from 40–55 dB.
- III degree (severe) - hears sounds from 56-70 dB.
- IV degree (deep) - from 71–90 dB.
- Deafness is a condition when a person cannot hear a sound louder than 90 dB.
An abbreviated version of the degrees of hearing loss:
- Light degree - the ability to perceive sounds less than 50 dB. Man understands colloquial speech almost completely at a distance of more than 1 m.
- Medium degree - the threshold for the perception of sounds begins at a volume of 50–70 dB. Communication with each other is difficult, because in this case a person hears speech well at a distance of up to 1 m.
- Severe degree - more than 70 dB. Speech of normal intensity is no longer audible or unintelligible near the ear. You have to scream or use a special hearing aid.
In everyday practical life, specialists can use another classification of hearing loss:
- Normal hearing. A person hears conversational speech and whispers at a distance of more than 6 m.
- Mild hearing loss. A person understands conversational speech from a distance of more than 6 m, but he hears a whisper no more than 3-6 meters away from him. The patient can distinguish speech even with extraneous noise.
- Moderate degree of hearing loss. A whisper distinguishes at a distance of no more than 1-3 m, and ordinary conversational speech - up to 4-6 m. Speech perception can be disturbed by extraneous noise.
- Significant degree of hearing loss. Conversational speech is heard no further than at a distance of 2-4 m, and a whisper - up to 0.5-1 m. There is an illegible perception of words, some individual phrases or words have to be repeated several times.
- Severe degree. Whisper is almost indistinguishable even at the very ear, colloquial speech, even when screaming, is hardly distinguished at a distance of less than 2 m. Reads lips more.
Degrees of hearing loss relative to pitch
- I group. Patients are able to perceive only low frequencies in the range of 125–150 Hz. They only respond to low and loud voices.
- II group. In this case, higher frequencies become available for perception, which are in the range from 150 to 500 Hz. Usually, simple colloquial vowels "o", "y" become distinguishable for perception.
- III group. Good perception of low and medium frequencies (up to 1000 Hz). Such patients already listen to music, distinguish the doorbell, hear almost all vowels, catch the meaning simple phrases and individual words.
- IV group. Become accessible to the perception of frequencies up to 2000 Hz. Patients distinguish almost all sounds, as well as individual phrases and words. They understand speech.
This classification of hearing loss is important not only for the correct selection of a hearing aid, but also for determining children in a regular or specialized school for.
Diagnosis of hearing loss
Audiometry can help determine the degree of hearing loss in a patient. The most accurate reliable way to identify and determine the degree of hearing loss is audiometry. For this purpose, the patient is put on special headphones, into which a signal of appropriate frequencies and strength is applied. If the subject hears a signal, then he lets know about it by pressing the button of the device or by nodding his head. Based on the results of audiometry, an appropriate auditory perception curve (audiogram) is built, the analysis of which allows not only to identify the degree of hearing loss, but also in some situations to get a more in-depth understanding of the nature of hearing loss.
Sometimes, when performing audiometry, they do not wear headphones, but use a tuning fork or simply pronounce certain words at some distance from the patient.
When to See a Doctor
It is necessary to contact an ENT doctor if:
- You began to turn your head towards the one who is speaking, and at the same time strain to hear him.
- Relatives living with you or friends who have come to visit make a remark about the fact that you turned on the TV, radio, player too loudly.
- The doorbell is now not as clear as before, or you have stopped hearing it altogether.
- When talking on the phone, you ask the other person to speak louder and more clearly.
- They began to ask you to repeat what you were told again.
- If there is noise around, then it becomes much more difficult to hear the interlocutor and understand what he is talking about.
Despite the fact that, in general, the sooner the correct diagnosis is made and treatment is started, the better the results and the more likely it is that hearing will persist for many years to come.
Audio topics worth talking about human hearing a little more. How subjective is our perception? Can you test your hearing? Today you will learn the easiest way to find out if your hearing is fully consistent with the table values.
It is known that the average person is able to perceive acoustic waves in the range from 16 to 20,000 Hz (16,000 Hz depending on the source). This range is called the audible range.
| 20 Hz | A hum that can only be felt but not heard. It is reproduced mainly by top-end audio systems, so in case of silence, it is she who is to blame |
| 30 Hz | If you can't hear it, it's most likely a playback problem again. |
| 40 Hz | It will be audible in budget and mainstream speakers. But very quiet |
| 50 Hz | hum electric current. Must be heard |
| 60 Hz | Audible (like everything up to 100 Hz, rather tangible due to reflection from the auditory canal) even through the cheapest headphones and speakers |
| 100 Hz | End of bass. Beginning of the range of direct hearing |
| 200 Hz | Mid frequencies |
| 500 Hz | |
| 1 kHz | |
| 2 kHz | |
| 5 kHz | Beginning of the high frequency range |
| 10 kHz | If this frequency is not audible, it is likely serious problems with hearing. Need a doctor's consultation |
| 12 kHz | The inability to hear this frequency may indicate the initial stage of hearing loss. |
| 15 kHz | A sound that some people over 60 can't hear |
| 16 kHz | Unlike the previous one, almost all people over 60 do not hear this frequency. |
| 17 kHz | Frequency is a problem for many already in middle age |
| 18 kHz | Problems with the audibility of this frequency - the beginning age-related changes hearing. Now you are an adult. :) |
| 19 kHz | Limit frequency of average hearing |
| 20 kHz | Only children hear this frequency. Is it true |
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This test is enough for a rough estimate, but if you do not hear sounds above 15 kHz, then you should consult a doctor.
Please note that the problem of hearing low frequencies is most likely related to.
Most often, the inscription on the box in the style of "Reproducible range: 1–25,000 Hz" is not even marketing, but an outright lie on the part of the manufacturer.
Unfortunately, companies are not required to certify not all audio systems, so it is almost impossible to prove that this is a lie. Speakers or headphones, perhaps, reproduce the boundary frequencies ... The question is how and at what volume.
Spectrum problems above 15 kHz are quite a common age phenomenon that users are likely to encounter. But 20 kHz (the very ones that audiophiles are fighting for so much) are usually heard only by children under 8-10 years old.
It is enough to listen to all the files sequentially. For more detailed study you can play samples, starting with the minimum volume, gradually increasing it. This will allow you to get a more correct result if the hearing is already slightly damaged (recall that for the perception of some frequencies it is necessary to exceed a certain threshold value, which, as it were, opens and helps the hearing aid to hear it).
Do you hear the entire frequency range that is capable of?
