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Amplifiers in hearing aids

Hear­ing aids are sound ampli­fiers placed in a plas­tic case. The micro­phone of the device per­ceives var­i­ous sounds that are in the envi­ron­ment and con­verts them into elec­tri­cal sig­nals trans­mit­ted to the ampli­fi­er of the device. The main func­tion of the ampli­fi­er is to increase the vol­ume of per­ceived sounds, to make them clear and under­stand­able for per­cep­tion.

There are two types of ampli­fiers:

• Lin­ear — it ampli­fies var­i­ous sounds at approx­i­mate­ly the same lev­el;
• non-lin­ear — sounds that are weak, poor­ly per­ceived by a hear­ing-impaired child are ampli­fied, and loud sounds can be sup­pressed so that they are com­fort­able for the ear. The change in sound inten­si­ty is con­trolled by a sys­tem equipped with a com­pres­sor.

The ampli­fied sig­nals are con­vert­ed into sounds through the loud­speak­er and trans­mit­ted to the audi­to­ry canal. For old­er chil­dren who can con­trol the device them­selves, there are devices with vol­ume con­trol — it can be reduced or increased by means of a han­dle or lever, remote con­trol. For babies, the device itself must adjust the vol­ume of sig­nals depend­ing on envi­ron­men­tal con­di­tions.

signal processing method

There are three types of hear­ing aids based on the way sound is processed. The choice of them is deter­mined by hear­ing loss, age and fam­i­ly capa­bil­i­ties.

Based on the way sound is processed, we divide hear­ing aids into three main types. The choice of device depends on the type of hear­ing loss, the age of the child, and the needs of the fam­i­ly.

• Ana­log Devices. These are the most inex­pen­sive and sim­ple devices that change the sound waves that enter the micro­phone into a con­tin­u­ous elec­tri­cal impulse, in which a dif­fer­ent volt­age lev­el, respec­tive­ly, will be a sound of dif­fer­ent inten­si­ty and fre­quen­cy. Ana­log sounds are processed min­i­mal­ly, so the sound qual­i­ty is dis­tort­ed and lost. The device has a micro­phone, an ampli­fi­er, con­trols (vol­ume) and a head­set that trans­mits sound to the ear.
• Pro­gram­ma­ble ana­logue instru­ment. This is a more advanced device that par­tial­ly process­es the sig­nal and has the abil­i­ty to choose the sound strength accord­ing to the sit­u­a­tion.
• dig­i­tal instru­ment. Due to the micro­com­put­er, the sounds are processed, the vol­ume and tim­bres are pre­served, unnec­es­sary noise is sup­pressed, the clar­i­ty and intel­li­gi­bil­i­ty of the trans­mit­ted sig­nals is increased. These devices give the most accu­rate sound qual­i­ty and allow chil­dren to hear almost like in nat­ur­al con­di­tions.

Good to know

What are the best hear­ing aids for adults?

According to the method of fixation

No less impor­tant is the method of fix­ing the device in the ear area. This is impor­tant so that the child is com­fort­able, and the device per­ceives the sur­round­ing sounds as much as pos­si­ble and trans­mits them to the audi­to­ry canal.

• Deep in-ear hear­ing aids, CIC-devices (from the Eng­lish Com­plete­ly-In-the-ear-Canal) are the small­est of the devices. They are com­plete­ly locat­ed inside the audi­to­ry canal, and are almost invis­i­ble from the out­side. They can only be used in old­er chil­dren and ado­les­cents, as the width of the chan­nel must be suf­fi­cient to accom­mo­date the device. Each ear will have its own device, select­ed with the fea­tures of the anato­my.
• in-ear hear­ing aids, ITC-devices (from the Eng­lish In-The-ear-Canal). These devices are larg­er than the pre­vi­ous ones, they are eas­i­er to use. They are suit­able for chil­dren with mild to mod­er­ate hear­ing loss. The case is select­ed indi­vid­u­al­ly and sep­a­rate­ly for each ear.
• in-the-ear hear­ing aids, ITE devices (from Eng­lish In-The-Ear). Larg­er, pro­vide high qual­i­ty sound, will help with all ranges of hear­ing loss. They are easy to use, are select­ed indi­vid­u­al­ly for the right and left ear.
• behind the ear hear­ing aids, BTE-devices (from the Eng­lish Behind-the-Ear). The body of the device is locat­ed behind the ear and is passed into the ear canal through a tube, at the end of which there is an indi­vid­u­al­ly select­ed insert. These devices are espe­cial­ly rec­om­mend­ed for chil­dren.
• Behind-the-ear hear­ing aids with ear­mould con­nec­tion cable, RITE-devices (from the Eng­lish Receiv­er-In-The-Ear). The most mod­ern behind-the-ear devices, instead of a tube, they have a thin wire con­nect­ed to an ear­mold in the ear canal.

A step-by-step guide to choosing a hearing aid

Before pur­chas­ing a hear­ing aid for a child, there are many dif­fer­ent fac­tors to con­sid­er. The choice of a spe­cif­ic type of hear­ing aid depends on the sever­i­ty of the pathol­o­gy, the per­son­al pref­er­ences of the child and his par­ents. The most key fac­tors that deter­mine the type of device:

• degree of hear­ing loss and vari­ant (uni­lat­er­al or bilat­er­al deaf­ness);
• anatom­i­cal fea­tures of the ear (some types of devices sim­ply do not fit in chil­dren’s ears);
• the age of the child, his skills and needs, abil­i­ties.
• appear­ance, aes­thet­ic char­ac­ter­is­tics;
• sound qual­i­ty.

Child’s age

One of the most impor­tant con­sid­er­a­tions when choos­ing a hear­ing aid is the age of the patient. Chil­dren under the age of six need a device with one mode of per­cep­tion, which is pro­grammed indi­vid­u­al­ly. This helps to quick­ly get used to the per­cep­tion of sound stim­uli. Such a device helps in teach­ing speech recog­ni­tion, learn­ing to read and pro­nounce all sounds.

Old­er chil­dren need hear­ing aids with dif­fer­ent set­tings. They need adap­tive devices to dif­fer­ent sound sit­u­a­tions. It helps in voca­tion­al train­ing and social­iza­tion.

Indications for the use of a hearing aid. Doctor’s advice

We dis­cussed the issues of choos­ing and wear­ing hear­ing aids for chil­dren with Vera Shinkarenko, otorhi­no­laryn­gol­o­gist, audi­ol­o­gist at JSC “Med­i­c­i­na” (Clin­ic of Aca­d­e­mi­cian Roit­berg), mem­ber of ISA (Inter­na­tion­al Soci­ety of Audi­ol­o­gy).