Kiat Ng, Poh, Kian Siong Jee, Li Wah Thong, and Jian Ai Yeow. “Design Innovation and Validation of a Non-Electric Hearing Aid for Improved Usability”. International Journal of Engineering & Technology 7, no. 3.7 (July 4, 2018): 90–94. Accessed May 3, 2024. https://sciencepubco.com/index.php/ijet/article/view/16220.