[hearing aids] hearing aids - reprint public network materials
This entry is reviewed by the "popular science China" science encyclopedia entry compilation and application project.
Hearing aid is a small loudspeaker, which expands the original inaudible sound, and then uses the residual hearing of the hearing impaired to send the sound to the auditory center of the brain and feel the sound. It brings great convenience to the hearing impaired.
catalogue
1 Introduction
2 types of hearing aids
3 structure of hearing aid
4 Classification of hearing aids
5 characteristics of cassette hearing aids
6 characteristics of in ear hearing aids
7 characteristics of deep ear canal hearing aid
What are the characteristics of ear back hearing aids
9 what are the characteristics of ear canal hearing aids
10 difference between bone guided hearing aid and air guided hearing aid
11 selection method of hearing aid
▪  Precautions for adults to choose hearing aids
▪  Precautions for children to choose hearing aids
12 extended reading:
brief introduction
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Sound is produced by the vibration of an object. It is the sound source of the object. Sound is just the movement of pressure waves through the air. Pressure waves vibrate the small bones of the inner ear (auditory bones). These vibrations are transformed into tiny electronic brain waves, which are the sounds we perceive. The principle of the inner ear is the same as that of the microphone capturing sound waves or the pronunciation of speakers. It is the relationship between the moving mechanical part and the air pressure wave. Naturally, when the sound wave is low in tone, long in wavelength and large enough, we can actually "feel" the pressure wave vibrating the body.
Schematic diagram of human ear structure
Types of hearing aids
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Hearing aid is mainly composed of microphone, amplifier, earphone, power supply and volume control. Hearing aids can be divided into air guided hearing aids and bone guided hearing aids according to the conduction mode; According to the way of use, they are classified into box type, glasses type, hairpin type, ear back type, inner ear type, ear canal type and deep ear canal type hearing aids.
Type of hearing aid - conduction mode
Types of hearing aids - Usage
Figure 2 Hearing aids with different use modes
Structure of hearing aid
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Since the electronic hearing aid was used in the early 20th century, the structure of the hearing aid has not changed much. It is still composed of microphone, amplifier, receiver and power supply. However, the volume of each part of the hearing aid is gradually reduced, the sound quality is gradually improved, and there are more selective controls.
1 microphone: collect sound and convert it into radio waves.
2 amplifier: increase the intensity of radio waves.
3 receiver: just opposite to the microphone, turn the increased electric energy back into sound waves.
4. Power supply: small battery.
5 enclosure: protect the internal structure.
Ear hanging hearing aid structure
Figure 3 Structure diagram of ear hanging hearing aid (Figure: 1. Headset, 2. Receiver, 3. Microphone, 4. Volume adjustment button, 5. Fine tuning potentiometer, 6. Amplifier, 7. Switch, 8. Battery base)
Inner ear hearing aid structure
Figure 4 Structure diagram of in ear hearing aid (Figure: 1. Volume regulator, 2. Microphone, 3. Amplifier, 4. Fine tuning potentiometer, 5. Housing, 6. Receiver)
Classification of hearing aids
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Hearing aid is an instrument to help improve hearing. In fact, it is a small semiconductor loudspeaker. Its function can make the weak sound transmitted to the earphone after amplification, so that the part with hearing loss can hear the sound with the help of amplification.
There are several types, but the function and principle are the same.
(1) From the external structure, it can be divided into box type, ear back type and inner ear type, and the inner ear type can be divided into ordinary inner ear type, ear canal type and deep ear canal type.
(2) From the electronic principle, it can be divided into: analog hearing aid; Programmable hearing aid, all digital hearing aid, wide dynamic language technology hearing aid, etc.
(3) Hearing aids can be divided into air guided hearing aids and bone guided hearing aids according to the conduction mode. Box type, ear back type and in ear type all belong to air guided hearing aids.
Classification of hearing aids
Figure 5 Appearance of several hearing aids
Characteristics of cassette hearing aids
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Box hearing aids are also called body mounted or pocket hearing aids. The shape is like a rectangular box the size of a small radio. The microphone, amplifier and battery of the hearing aid are assembled in it. The outside is connected with the earphone, earplug or special ear mold by a long wire. Usually in a pocket or a special pouch. This kind of hearing aid has a large volume and is suitable for the elderly and people with inconvenient finger movement. The microphone (microphone) of the hearing aid is far away from the receiver (earphone), so it is not easy to generate acoustic feedback. Therefore, the maximum output limit is small, the power can be large, and multiple manual adjustment knobs can be placed. The utility model has the advantages of low price and convenient maintenance. No. 5 or No. 7 batteries can be used, and rechargeable batteries can also be used. Body mounted hearing aids can also be made into binaural listening AIDS. Because of their large volume and poor concealment. The hearing aid adopts ordinary transistor elements, with high background noise. In addition, the friction between the hearing aid itself and the wire and the clothes makes the sound easy to be distorted and the sound quality reduced. At the same time, the earphone lead is easy to be damaged, which is unsafe for children to wear.
Characteristics of in ear hearing aids
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The in ear hearing aid is a micro shaped hearing aid, and the shell is customized according to the patient's ear. The amplifier, microphone and receiver are all placed in a custom housing and can all be placed in the ear nail cavity. The outside does not need wires or hoses, which is hidden and light. There are medium power, medium high power and high power in ear hearing aids. Because they need to be customized according to individual ear nail cavity, the price is high. Generally, middle-aged and young people choose more. For patients who are prone to sweating on the head, if they wear ear back hearing aids and are vulnerable to moisture damage, they can consider choosing intra ear hearing aids. Deaf children in growth and development stage are not suitable for wearing because their auricles are also developing.
Characteristics of deep ear canal hearing aids
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Deep ear canal hearing aid is the smallest and most concealed hearing aid. According to the user's ear canal, the sound amplification performance is closer to that of normal people. It is placed deep in the ear canal and can hardly be seen in the appearance, which greatly meets the requirements of users for their own appearance and image. In addition to the advantages of general ear canal hearing aids, more importantly, deep ear canal hearing aids placed in the ear canal can make full use of the self promotion effect of human ear canal structure on sound, especially the low-frequency part. Since the sound output port of the hearing aid is very close to the human eardrum, the sound output by the hearing aid can reach the eardrum immediately, so that the output gain and waveform are not attenuated, ensuring sufficient sound energy and sound quality fidelity. The scope of use is narrow. It is only suitable for mild and moderate deafness. The effect of hearing loss is the best within 65 dB. Children's ear canal is immature and not suitable for wearing.
What are the characteristics of ear back hearing aids
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Ear back hearing aids are widely used for all kinds of hearing loss. The microphone, amplifier, battery, volume adjustment, receiver, etc. are all installed in a small box in the shape of a long hook. The shape is slim. It depends on a hard plastic ear hook bent into a semicircular shape to hang behind the ear. The shell can be covered by the color of skin or hair. The amplified sound is transmitted to the sound hole of the ear mold through a plastic pipe through the ear hook. It is divided into different types such as low power, medium power and high power. It has high power, low noise, low distortion and easy to wear. The disadvantage is that the hearing aid will be damp due to the sweat of the user, accelerating the aging of components.
What are the characteristics of ear canal hearing aids
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Ear canal hearing aid is suitable for patients with mild, moderate and severe deafness. It is a high-precision personal hearing aid. The hearing aid shell is specially designed and manufactured according to the shape of the patient's ear, which is very close and tight when wearing, ensuring the sound tightness and comfortable when using; The volume of ear canal hearing aid is smaller than that of inner ear hearing aid, and there is no external wire, which can simulate the sound transmission process of human ear to the greatest extent. Because the ear canal hearing aid is placed in the ear canal, it is hidden and difficult to be noticed, which meets the user's image requirements for wearing the hearing aid. Children's ear canal is not mature and suitable for wearing; Patients with ear canal deformity, stenosis and ulcer should not wear it.
Difference between bone guided hearing aid and air guided hearing aid
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Normally, we listen to sound in at least two ways: bone conduction and air conduction. The so-called bone conduction mode is that the sound signal vibrates the skull and is not directly transmitted to the inner ear through the outer and middle ears; Air conduction refers to the transmission of sound through the outer and middle ears to the inner ear. In the two ways, the latter is absolutely dominant.
Usually, what we call box type, ear back type and in ear type are air guided hearing aids. The air conduction hearing aid transmits the amplified sound signal to the external auditory canal. Bone guided hearing aids are different. Strictly speaking, bone guided hearing aids ultimately produce not sound signals but vibration signals. Bone guided hearing aids do not have so-called "headphones" or earplugs. Instead, they are a vibrator that can produce vibration signals. The vibrator is pressed on the mastoid bone protruding behind the ear. The vibration of the vibrator will cause the vibration of the skull and transmit the signal directly to the inner ear through the outer and middle ears, which is the advantage of bone guided hearing aids. Because of this advantage, theoretically speaking, bone guided hearing aids are especially suitable for patients with conductive deafness (i.e. patients with problems in the outer and middle ears). However, this is not the case. Bone guided hearing aids are far less effective than expected. The reasons are as follows: first, bone guided hearing is far less effective than air guided hearing; Second, the output device of bone conduction hearing aid - vibrator is not only very unsightly, but also very uncomfortable, which is difficult to be accepted by users.
Generally speaking, as long as air guided hearing aids can be used, air guided hearing aids should be selected first. Patients with external auditory canal malformation or repeated pus after external and middle ear infection and unable to wear earplugs, ear molds or in ear hearing aids can consider using bone guided hearing aids.
Selection method of hearing aid
Precautions for adults to choose hearing aids
Hearing aids on the market are divided into box type, ear back type, in ear type and ear canal type. [1]
1。 The box type hearing aid is also called pocket type or pocket type, which is slightly larger than the matchbox. The body is connected with the earphone with a wire. When in use, the earphone is inserted into the external auditory canal, and the box is placed in the chest pocket. The utility model has the advantages of small interference, large power, convenient use, easy adjustment, long service time and low price, and can meet the needs of people with severe deafness. However, when the hearing aid box is placed in the pocket, it will produce friction sound and affect language discrimination. It is very conspicuous when wearing, so it sometimes feels inconvenient.
2。 The shape of the ear back hearing aid is 3 ~ 4cm long hook shape, which is placed behind the auricle and sends the sound into the ear canal through a sheep horn ear hook and plastic tube. The utility model has the advantages of no wire, small volume, concealment and small interference. The induction coil can be installed to increase the function of listening to the phone. The disadvantage is that an ear mold needs to be specially prepared, which is not used at the beginning and inconvenient to adjust.
3。 Inner ear and canal hearing aids belong to small hearing aids, which have the advantages of miniaturization, concealment, no wire, no need to make another ear mold, good sound listening effect and improving hearing; However, the adjustment is inconvenient and expensive. It needs to be customized according to each person's ear canal and concha cavity. Due to the low power, it is only suitable for moderate deafness and not suitable for severe and very severe deafness.
When selecting hearing aids, it is best to go to the hospital for a comprehensive examination of hearing, accurately evaluate the degree of deafness with electrical audiometry and other instruments, and then select hearing aids. If there is no local hospital with corresponding conditions, the selection of hearing loss degree and hearing aid power can be estimated according to oral test. For example, people who can't hear whispers have a hearing loss of 30 ~ 40 dB, and people who can't hear whispers have a hearing loss of about 40 ~ 50 dB. At this time, it's appropriate to buy low-power and medium-power hearing aids; The hearing loss of people who can't hear ordinary speech is about 50 ~ 60 dB, and the hearing loss of people who can't hear loud speech is 60 ~ 70 dB. Medium power and high-power hearing aids can be selected; For those who can't hear loud shouting, the hearing loss is 70 ~ 80 dB, and medium and high-power hearing aids shall be selected; The hearing loss of people who can't hear the cry with all their strength is about 80 ~ 90 dB or higher. It can be equipped with high-power and extra high-power hearing aids.
Precautions for children to choose hearing aids
Children's "deafness" is often divided into curable and incurable cases. Curable deafness, such as otitis media and ear cerumen embolism, can be cured only by anti-inflammatory injection or cleaning the ear canal. If hearing aids are hard equipped, the amplified sound of hearing aids will cause damage to the child's hearing.
Be sure to make a clear diagnosis before wearing a hearing aid. Because children's expression ability is weak, it is not easy to cooperate in the examination. In addition, children's hearing sometimes fluctuates, so it is not easy to draw a conclusion in one examination. Parents should take their children to do more examinations. Only after doing relevant examinations at least twice in regular hospitals can they decide whether to equip their children with hearing aids. When wearing hearing aids, don't just consider beauty. I think children don't look good when wearing older hearing aids. In fact, the selection of inappropriate hearing aids will affect children's listening and pronunciation. After wearing hearing aids for 1 ~ 2 months, be sure to go to the hospital for hearing test, so as to adjust in time. After wearing a hearing aid, the child has a process of slowly adapting from the silent world to hearing sound. Parents should insist on language training for the child, but don't be eager for success. After training, the child generally starts to learn to speak after wearing it for 3 ~ 4 months.