Optimal Boundary Conditions and Driving Methods in the Design of Flat Plane Speakers

Abstract

The flat plane speaker has wide sound radiation area making its tone characteristics preferable to the conventional type speakers. However, the main defect is its multiresonance of the vibrating membrane. After the analysis of flat membrane vibrations, a new driving method is proposed for eliminating the multiresonances, that is, if the membrane were driven by the distributed force proportionate to the fundamental mode amplitude, no multiresonance would take place. Mean while within some restricted frequency range, the uniresonance is expected from some discrete concentrated driving points. In the preceding paper, this driving method has been applied to the cases having easily analizable boundary conditions. On the contrary, this paper includes the application to three complicated problems, entirely clamped, free and mode degenerated. Comparing them, the entirely free boundary condition is found theoretically best, however, the problem is how to hold the free membrane in the space. As the result of various experiments, the boundary condition almost the same as the free boundary but having a small viscous damping element which makes it possible to solve the suspension problem is found.