Hearing aid structure– The main components of the hearing aid
a small oneHearing aidAlthough it doesn’t look good, it’s very big. For some elderly people, or some friends with hearing impairments, hearing aids are the most convenient and helpful tool. This weapon can make the ambiguous sound pleasant and no longer worry because of hearing inconvenience. Obstacles to communicate with the outside world, help people in need to communicate freely, and even provide security when traveling. So how does the hearing aid work??HearingIntroduction to everyone:
It is an input transducer that converts sound energy into electrical energy and can be divided into an omnidirectional microphone and a directional microphone. An omnidirectional microphone that accepts sound in all directions in equal amounts. It is made of an insulating permanent polarized material, the sound enters the microphone, and the density change of the sound wave causes the negative metal diaphragm to vibrate, and then the sound energy is converted into mechanical energy, and the diaphragm vibrates on the electret. Pressure is generated and transmitted to the rear plate of the electret. Both the electret rear plate and the bottom of the diaphragm are connected to the field effect transistor preamplifier and have a terminal to the outside. When the diaphragm vibrates, the distance and space between the diaphragm and the electret rear plate changes, generating a voltage, and the mechanical energy is converted into electric energy through a field effect transistor fixed on the microphone, and then transmitted to the amplifier through the terminal. The electret microphone has a wide frequency response, high sensitivity and durability, and the diaphragm is the only part of its movement; the directional microphone: classified according to the polarity form, and the sound from the front is much more sensitive than the sound coming from the back. . The directional microphone has two openings at the ends of the diaphragm, one on each side. The vibration of the diaphragm depends on the phase relationship and depends on the pressure difference at both ends. A fine acoustic filter is placed on the front end of the rear sound hole to delay the sound, so that the sound from the back can reach the diaphragm from both front and rear sound holes and cancel, and the change of the sound source position can show different polarities. Figure.
That is, the signal processor integrates the signal processing method to amplify the power output from the microphone. The main function of the hearing aid is to process the sound that the hearing impaired person could not hear as audible as needed. The signal processing section includes amplification, frequency response adjustment, and input and output curve adjustment. These processes can be either analog or digital, and linear analog lines in conventional analog hearing aids are available.Class A, Class B, Class D. Amplifiers generally use multi-stage amplification and can be divided into preamplifiers and power amplifiers. In addition to pre-amplifying the signals provided by the microphones, the preamplifiers are subject to special adjustments based on different hearing loss conditions. The power amplifier, also known as the post-amplifier, mainly amplifies the preamplified boosted and modified microphone signal and drives the receiver to work.
In contrast to a microphone, the receiver converts the amplified electrical signal into a sound signal. The processed and amplified electrical signal is sent to the receiver, converted into a sound signal by the receiver, and output to the external auditory canal via the ear hook, the sound tube and the ear mold. The shape of the receiver is similar to that of a microphone, but the internal structure and working principle are completely different. The receiver is a transducer that uses an electromagnetic principle to convert an electrical signal into a sound signal. Figure34 clearly indicates the name and position of each component of the receiver. The soldering point is connected to the audio signal of the hearing aid and transmitted to the coil. The coil generates a changing magnetic field to cause the vibration of the reed. This vibration is transmitted to the diaphragm through the ejector pin. The vibration of the membrane causes the air chamber in the upper part to resonate to emit a sound, and the sound is transmitted through the sound outlet. The receiver can be divided into Class A, Class B, Class D, etc. in the same way as the amplifier, and the signal processing of the all-digital hearing aid is completed by the chip. Therefore, the Class A receiver is basically used. The receivers of the behind-the-ear and in-ear hearing aids are inside the machine, and the cassette receiver is externally attached to the earbuds or ear molds. In addition, there is a special type of receiver, the bone conduction receiver, which is suitable for the ear canal collapse or other conductive factors that can not use the ear mold, is the conversion of electrical energy into mechanical vibration.
4. Volume Governor VC:
Volume control is a variable resistor or potentiometer that regulates the current through the amplifier. The resistance is large, the current is less, the volume is small, and vice versa. Volume control is also a gain control. Most hearing aids have a roulette or button-type volume control that allows the wearer to adjust freely.VC.
The battery is an energy source that provides a hearing aid amplifier board to process sound signals. In general, the greater the gain and output of the hearing aid, the greater the battery energy required, and if the battery is not energetic, it will limit the output sound pressure of the hearing aid. Hearing aid battery In addition to the fifth battery used in the box machine, there are four types:
6. Inductive pickup coil:
In order to facilitate the hearing aid user to answer the phone, in addition to the microphone, the hearing aid is usually equipped with a telephone inductive pickup that picks up the telephone audio sensing signal (Telecoil). This is an induction coil made of a thin insulated wire. This current also produces a varying magnetic field around the telephone headset when the current in the phone drives the telephone headset to make a sound. If the hearing aid’s phone-sensing pickup is in this magnetic field, it can induce a voltage that is consistent with the sound. By switching the switch on the hearing aid (T-stop on the behind-the-ear 0-TM switch, or in-ear special T-stop switch), you can choose to send the microphone, phone inductive pickup, or a mixture of the two to the amplifier for amplification. The main technical parameter of a telephone-sensing pickup is its sensitivity. The sensitivity of a telephone-sensing pickup is characterized by the strength of the electromagnetic field it can receive, in milliamps per meter (mA/m). The electromagnetic pickup coil is used not only to answer the telephone (in fact, the current telephone headset does not generally emit a strong magnetic field for the hearing aid to pick up the sound, unless a dedicated hearing aid phone), and can also be used in some public places where the coil is arranged, Ear-hook coils, etc.
7. Audio signal input port:
In order to avoid the high frequency loss and the signal-to-noise ratio caused by the far-distance signal source when the hearing aid microphone directly picks up the signal, more and more people with hearing impairment use the audio signal. The most common form isFM system, which is a wireless transmitting and receiving system. The acoustic signal passes through the transmitter, and is replaced by an directional microphone with adjustable polarity, and then transmitted by the FM transponder to the FM receiver connected to the hearing aid. The electrical signal directly enters the amplifier of the hearing aid and passes the sound through the receiver. Restored, converted into an acoustic signal and finally output to the ear. In order to transmit the audio signal to the hearing aid, the battery compartment of the behind-the-ear hearing aid needs to be fitted with an audio shoe (the in-ear hearing aid cannot be connected to the audio shoe) and connected to the FM system by wire or wirelessly. Most of the behind-the-ear hearing aids have an audio signal input port that can be connected to the audio shoe and is compatible with the FM language trainer, and once the hearing aid detects the audio signal, the hearing aid automatically switches to the “audio input” state.
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