Functions of Hearing Aids And The Basic Parts
The basic parts of the latest hearing aid or hearing equipment include a microphone, an amplifier, a receiver, and a power supply.
A microphone is a transducer that converts the sound signal into electric energy.
The amplifier is a transformer that increases the amplitude of the electric signal that is sent to the receiver. The receiver then changes the altered electric signal back to sound energy that is directed into the ear.
A selection of microphones, amplifiers, and receivers are used, depending on the type and degree of hearing difficulties.
Hearing aid microphones are essentially electric devices that have good linear behaviour over a frequency range of 50-6000 Hz. This range can be changed to be more acceptable for precise hearing losses. Directional microphones have been developed that will alter with both the amplitude and the direction of the sound source relative to the microphone. They can cut back the sounds coming from the back of a hearing aid wearer compared to the sounds coming from the front by as much as fifteen dB. This change can significantly improve the signal-to-noise proportion of the listener and therefore the experience of speech in the presence of noise.
Hearing aid or hearing equipment amplifiers are transformers basically composed from transistors that are built into an integrated circuit. These transistors offer a current source and serve a number of functions. In these transistors, the first function of the amplifier is to extend the power of the electric signal received from the microphone.
Typically hearing aids have two or more stages of amplification. The 1st stage is the preamplifier, which is at the level of the microphone. The preamplifier aids to amplify the original input signal. At this level, the gain is comparatively low. Most amplification is supplied by the power amplifier. These amplifiers are typed in a selected class.
The commonest are known as class A, class B, and class D they are distinguished by their energy consumption, gain, and output capabilities. Each amplifier can be altered to restrict the maximum output of the hearing aid. For linear amplification, the amplifier might be restrained by top clipping.
This happens when the electric signal surpasses the maximum output of some part of the hearing aid circuit. This kind of limiting causes assorted forms of distortion that have been found to reduce the intelligibility and the subjective quality of speech. A hearing aid that has some form of level-dependent signal processing is named a nonlinear hearing aid. Most nonlinear hearing aids reduce gain as input or output levels increase. These helps generally use some kind of compression circuit that decreases the gain of the instrument when either the input to the device or the output of the device surpasses a destined level. This process ends up in a comfy amplification for the wearer and prevents the hearing aid from saturating. The hearing aid receiver is an output transducer and handles more power than a microphone. Receivers in hearing aids are minute due to cosmetic considerations. So , the little receivers on hearing aids might be taxed to their output capacities. The receiver must also be chosen to match its amplifier.
A mismatch in design produces limited output and increases distortion. Thanks to the receiver’s open position in the external ear canal, it is exposed to break from waste in the ear canal and from the aid being dropped. Makers confirm that roughly 40% of hearing aids returned for service have damage or blockage to the receiver.