How Hearing Aids Work？

How hearing aids work

There are many different types of hearing aids, but the principle of all electronic hearing aids is the same.

A hearing aid converts an acoustic signal into an electrical signal, amplifies the electrical signal and then converts it into an acoustic signal to amplify the sound. In the process of energy conversion, the transducer function is realized by the microphone and the receiver.

The microphone is the input transducer that converts sound energy into electrical energy.

The amplifier amplifies the weak voltage converted by the microphone.

Third, the receiver is another transducer, just the opposite of the microphone, which converts the amplified electrical signal into an acoustic signal or mechanical vibration that is transmitted into the ear canal. Converted to acoustic signals for the receiver air-conducting receiver, converted to mechanical vibration of the receiver for the bone-conducting receiver.

Fourth, the volume control is a variable resistor or potentiometer to regulate the current through the amplifier, the volume varies with the resistance of the electrical signal. When the volume is turned up, more current is required; when the volume is turned down, the current through the amplifier is reduced, making the sound lighter.

Fifth, the fine-tuning potentiometer in programmable hearing aids, through the computer programming to carry out a variety of fine-tuning regulation, so that the regulation is more fine and accurate, can be more fine-tuning to compensate for hearing loss, including:

1, tone modulation, change the frequency response of the hearing aid;

2, peak clipping, can control the maximum output of the hearing aid;

3, Automatic gain compression regulation to control the sound within the comfortable loudness range;

4, gain control (GC): adjust the hearing aid gain.

Generally speaking, the greater the gain and output of the hearing aid, the greater the battery energy required, and the corresponding battery volume is also larger. If a battery has insufficient energy, it will limit the output sound pressure of the hearing aid.

The requirements for hearing aid batteries are: small size, constant voltage, reliable quality, long life, and environmental friendliness. Today's hearing aid batteries are all zinc air batteries (button batteries).

Accessories for hearing aids can include audio inputs and inductive coils:

1, Audio input:   Most hearing aids have a contact piece or jack for audio input, which is mainly used for listening to the radio or watching TV. Because the audio signal comes directly from the sound source, without the conversion of sound - electricity, electricity - sound, so the quality of the input signal is better than the signal converted by the microphone.

2, Anductance coil: inductance is a magnetic induction coil, can be leaked from the receiver on the telephone corresponding to the electromagnetic field, converted to electrical signals after amplification, so that the hearing aid can be used to listen to the phone. The advantages are no whistling, no interference, and a high signal-to-noise ratio in a noisy environment. Signal-to-noise ratio is the difference between the speech signal and the environmental noise, high signal-to-noise ratio is a strong speech signal, easy to distinguish.

Any hearing aid consists of six basic structures:

1, the microphone (microphone or microphone) to receive sound and convert it into electrical wave form, that is, the sound energy into electrical energy.

2, the amplifier amplifies the electrical signal (transistor amplification line)

3, headphones convert electrical signals into acoustic signals (i.e., convert electrical energy into acoustic energy).

4, ear mold (ear plugs) placed in the external ear canal.

5, volume control switch.

6, power supply for the amplifier with dry batteries.

In addition to the above 6 components, most models of hearing aids have 3 accessories, or 3 additional circuits (tone control, induction coil, output limiting control). A modern electronic hearing aid is an amplifier whose function is to increase the intensity of sound energy and transmit it into the ear with as little distortion as possible. Since the acoustic energy of sound cannot be amplified directly, it is necessary to convert it into an electrical signal, amplify it and then convert it into acoustic energy. The input transducer consists of a microphone (microphone or microphone), a magnetic induction coil and other parts. Its function is to convert the input acoustic energy into electrical energy to be transmitted to the amplifier. The amplifier amplifies the input electrical signal and then transmits it to the output transducer. The output transducer consists of a headset or a bone-conducting vibrator, and its function is to convert the amplified signal from electrical energy to acoustic or kinetic energy. The power supply is an indispensable part of the energy supply to the hearing aid, and there is also a peak clipping (PC) or automatic gain control (AGC) device to suit the needs of patients with different degrees of deafness.