The ears are one of the sensitive organs out of number of sensitive organs existing in the human body. They help in sensing the sound with different frequency at different intensity. The hearing of human ears ranges from 20 Hz to 20,000 Hz and intensity ranges from 0 dB to 120dB. Different definition of deafness stated by different organisation is found in the literature and they are.
As per the World Health Organization (WHO), the deafness refers to the complete hearing disability in one or two ears. The WHO definition of hearing impairment refers to both complete and partial loss of ability to hear. As per Rehabilitation Council of India Act 1992, hearing impairment of 70 dB and above in better ear or total loss of hearing in both ears. It is only applicable to the person having hearing impairment of 70 dB and above.
Globally there are 360 million people having disability of hearing and in India 63 million persons suffer from hearing loss. The national survey shows that hearing disability was the second most cases of disability. In the urban area 9 per cent and in the rural area it was 10 per cent. These numbers have been increased due the attitude of the modern civilisation. The three main types of hearing impairment are:
-Conductive hearing loss (inner ear)
-Sensorineural hearing loss (inner ear), and
-Mixed hearing loss.
They are subjected to various physical, medical and psychological ailments/diseases like; noise pollution (music, personal music systems, mobiles systems (to be on the safer side the sound intensity from these systems should be restricted to 50 dB; better if it is below 50 dB), vehicle noise, vehicles and their horns harsh sounds, industrial noise, celebrations, functions/religious sound systems and such other noise sources), some medical drugs effects, aging (especially persons above 65 years and as per literature, highest in South Asia, Asian Pacific and Sub–Saharan Africa) and water/cough entering the middle and the inner parts of the each ear or both the ears damage these organs and results in hearing loss of a range of ranking/grading of the ear hearing damages.
The damaged ear of the particular person in turn affects him of inability of understanding speech sound, lowers the capability to communicate, delay in language pick up, stigmatisation and social isolation. Some of the damages is difficult to treat or cannot be treated and correct deafness impairment or profound hearing impairment, some of the damages can be corrected by medical treatment and some of them can be treated by providing hearing aid. The table 1 details the different ranks and the corresponding data. The persons, especially in developing countries, in the rural areas and the remote areas who have been recommended to use hearing aids, have a number of difficulties of hearing aid systems and accessories due to the fact that these systems and their availability and price ranges. Hence there is significant demand for the easily available and economical hearing aid systems.
Earlier the persons with hearing impairment were using mechanical system devices to hear the speech by folding the palms into hollow cone. Further this method was improved by using the metallic/non-metallic hollow cones, lip reading, signing with palms and hands. Research and developments in electrical, electronics, mechanical, nano-engineering and material science lead to the development of HAS from ordinary handmade to smart ones.
It is understood that the hearing aid should be handy (as small as possible to hide the same form the public), best speech/sound hearing capacity and should be of highest comfortability. If one considers these features in hearing device, it is very difficult get for the persons in rural/remote places. To have an economical, simple, manageable and an average type of hearing device, some of the features have to be compromised.
A number of options exist to decide/select the appropriate design/configuration of the electronic circuit for the small transistor radio/one integrated chip (IC) (with pre amplifier and amplifier) and the electronic parts for constructing/manufacturing economical hearing aid. One can get required information and details of good one transistor amplifier circuit in electronics books, magazines, articles, company hand books, different web sites and such other sources, for building the amplifier for the hearing aid. Another option is to modify the old small conventional transistor radio (one to two transistors/one IC chip) or the conventional/ordinary mobile phone in to a hearing aid.
It is easy to construct the one transistor amplifier/one chip. Some of the amplifiers can be built without using printed circuit boards whereas modification of the old small conventional transistor radios or the small ordinary mobiles into the hearing aid is easy. In the case small transistor radio, the matching mike’s wires can be connected to the leads of volume control and disconnecting the antenna coil from circuit board, keeping other parts as it is on the circuit board. It is to be noted that earphone has to be used. In the case of ordinary small mobiles, the main thing is to know the circuit configuration used installed in the mobile. The study of the pre-amplifier, main amplifier, mike connections and earphone connection should be carried out in detail and accordingly the required modification should be made.
It is to be noted that the modification of small transistor radio or small ordinary mobile is the best option. With this innovative idea, the hearing aid device will be economical and affordable by almost all persons with hearing impairment, the e-waste will be reduced by reusing the discarded devices. Both the devices can be modified to work as the radio and the hearing aid by a two-way switch and in the similar way the small ordinary mobile can be modified. The modification cost will be less and at the same time the hearing aid will be small enough to keep it in the shirt pocket delivering good sound hearing and comfortable.
Subramanya Krishna Bhat
Permanent Member of ISTE,
Fellow of Institution of Engineers (India)