DESIGN, DEVELOPMENT AND PERFORMANCE • EVALUATION OF AN INDUCTION LOOP SYSTEM FOR THE DEAF

Abstract

The hearing impaired children in a class room face a lot of difficulty in distinguishing the sound of their teacher due to presence of noise and interferring signals. The interferences produced by acoustical signals makes the situation worse. The induction loop system along with efficient microphones, amplifiers, loop transformer and hearing aids are used in the class rooms to improve upon the situation. But it has been often found that poor performance of audio amplifier and improper laying down of the loop wire creates lot of problems in a real class room situation. Thus there is a necessity to develop a high performance induction loop system. This dissertation deals with a high performance induction loop system which has been designed and developed for a classroom of deaf children. The system has been tested in the real class room situation. On the basis of its performance evaluation, further improvements have been made in both the system components and overall induction loop system.) The dissertation deals with the characteristics of sound, thresholds and hearing fields, definition of deafness and its causes, human hearing systems and help for hearing impaired. In addition to dealing with individual components of the induction loop system, the dissertation includes the details of principles of induction loop system, basic magnetic theory, design criteria, power rating, current design criteria, current rating, loop location and its size) An example has been taken to indicate the procedure of selection of various parameters i,e current rating,power rating and the best configuration of the loop. The overall amplifier system consists of a pre amplifier, power amplifier, filters, power supply, tone and volume control. (The power amplifier, being an important part of the induction loop system, has been dealt in detail. A brief discussion on sources of noise has also been in-cluded) The waveforms at various stages are taken at 1 KHz, since the most of the energy in the voice signal lies around this frequency. The performance evaluation of the various configuration of the loops has also been carried out. Overall performance of the developed induction loop system is satisfactory...