From Big Medical Encyclopedia

HEARING AIDS — the electro-acoustic devices intended for reception, transformation, strengthening of audibles signal and transfer to their persons with the lowered hearing.

First S. and. appeared in the middle of 18 century; they represented acoustic concentrators of a sound (horns, loud-hailers) attached by the narrow end to outside acoustical pass. In the 30th 20 century S. of ampere-second electronic amplifiers appeared (on tiny lamps). In the 50th more portable transistor S. are created and. Modern S. and. are designed with use of integral chips that expands their functionality and considerably reduces dimensions and weight (weight) of the equipment.

Page and. consists of the microphone perceiving surrounding sounds and transforming them to electric signals, the electronic amplifier it is frequent with the self-adjustment of strengthening, manual volume control, the regulator of a timbre, the power supply (the accumulator or an element) and phone transforming the strengthened electric signal to acoustic.

Distinguish S. of ampere-second phones of air sound carrying out, in to-rykh the strengthened sound vibrations move in outside acoustical pass, and devices with phones of bone sound carrying out, in to-rykh the strengthened signal in the form of mechanical vibrations comes through a bone of a skull and soft tissues to a middle and inner ear.

Fig. 1. Pocket hearing aid: 1 — the case of the device with the microphone, the amplifier and the power supply; 2 — the switch of a duty; 3 — the regulator of loudness; 4 — phone of bone sound carrying out; 5 — phones of air sound carrying out with ear inserts.

On S.'s design and. share on zaushny, in a-point frame, pocket, and also executed in the form of ear inserts. Pocket S. and. (fig. 1) — the metal or plastic box placed, as a rule, in a breast pocket contains the microphone, the amplifier, the power supply and adjustment devices. Phone connects to the device a thin flexible cord and is densely inserted into outside acoustical pass by means of an ear insert.

Fig. 2. Zaushny hearing aid: 1 — the case of the device; 2 — a flexible sound wire with an ear insert: 3 — the regulator of loudness; 4 — the power supply.

Zaushny S. and. (fig. 2) thanks to miniaturization of the microphone, amplifier, phone, power supply and a special form of the case is located behind an ear of hearing-impaired and keeps in this situation with the help rigid, curved the star-koprovoda, the end to-rogo by means of an insert is inserted into an outside ear.

Fig. 3. The hearing aid in a-point frame: 1 — the nice fellow of points in whom the hearing aid is built in; 2 — regulators loudness and a timbre; 3 — a flexible sound wire with an ear insert.

In S. and. in a-point frame (fig. 3) the microphone, the amplifier, phone of air or bone sound carrying out and the power supply are placed in a handle of points from where by means of a sound wire the signal is given in an outside ear.

Page and. in the form of an insert represents tiny uniform constructive whole (the microphone, the amplifier, phone, the power supply and an insert), placed in an auricle and outside acoustical pass.

Main technical characteristics of the most widespread S. and. are presented by the following indicators: 1) acoustic strengthening — 30 — 50 dB for devices like an ear insert, 40 — 75 dB for zaushchny devices and established in a-point frame, 50 — 80 dB for pocket S. and.; 2) frequency range: the lower frequencies usually from 50 to 500 Hz, upper — from 3500 to 7000 Hz; a type of the frequency characteristic — uniform, with rise in low or high frequencies, frequency-selective etc.; 3) the maximum level of sound pressure — to 100 — 140 dB in zaushny devices and to 120 — 145 dB in pocket; 4) existence or lack of the self-adjustment of strengthening; 5) type of the power supply (an element, the accumulator) and time of continuous operation (the accumulator from 10 to 100 hours, an element 100 — 400 hours); 6) dimensions and weight (the ear insert usually has the mass from 3 to 5 g, zaushny devices 5 — 8 g, pocket 50 — 80 g). Besides, S. and. are characterized by coefficient of nonlinear distortions of a sound and adjustments of acoustic parameters differ by the form. Nek-ry hearing aids have the induction coil providing reception of signals of inductive communication, napr from the microreceiver of the telephone set, and also the device for connection to household radio - both the teleequipment and filters noise suppressors.

S.'s selection and. it is carried out on doctor's orders on points of hearing aid after the comprehensive investigation of a condition of hearing.

After S.'s selection and. hearing-impaired surely is trained by a surdopedagog (from several days to several weeks), in process to-rogo it adapts to conditions of perception of surrounding sounds through S. and. During the training in S.'s use and. use the so-called exercise machines of hearing representing the devices having wider functionality than S. and. Except the microphone, it is possible to connect to the amplifier of the exercise machine of hearing also other sources of a sound (the player, the tape recorder). The reverse channel to a surdopedagog allows to control possibilities of hearing of the patient. Range of adjustments in the amplifier allows to pick up the necessary loudness and a timbre of a sound and provides successful adaptation of perception of a sound, hearing-impaired to conditions, via hearing aids. Especially widely exercise machines of hearing are used for development of hearing and the speech in children.

Perspective of development of S. and. their further miniaturization, improvement of parameters and improvement of self-adjustments is.

See also Hearing aid .

Bibliography: M. M Efruss. Hearing aids and audiometers, M., 1975, bibliogr.

E. V, Kandaurov.