Design of directional loudspeaker : study of modulation techniques

• Main Author: Chang, Jia Yih.
• Other Authors: Chong Yong Kim
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio
• Online Access: http://hdl.handle.net/10356/49301
• Institution: Nanyang Technological University

Nonlinear interaction of ultrasound waves can be applied with parametric loudspeaker to generate audible sound. The audible sound reproduced using parametric loudspeaker has a special characteristic of high directivity. This phenomenon, known as the parametric array, is due to the self-demodulation property of finite amplitude ultrasonic waves. However, the demodulated signal from the parametric loudspeaker suffers from high distortion. To reduce the distortion in the reproduced signal, several pre-processing techniques of amplitude modulation is usually employed. This project is to provide theoretical studies and stimulation of the performance in decreasing the distortion from different amplitude modulation techniques. Objective measurement, such as sound pressure level, total harmonic distortion and intermodulation distortion are used to compare the performance of these pre-processing techniques. Practical constraint on the bandwidth of the ultrasonic emitter of the parametric loudspeaker is taken into consideration to determine the effectiveness of the techniques. Results have shown that distortion of the reproduced signal is significantly reduced with an orthogonal carrier.