Theoretical Analysis and Experimental Measurements on the Characteristics for Diaphragm and the Noise of Port

With the continuous improvement and rapid development of technology, the demand for high quality of loudspeaker are increased. Electro-acoustic industry particularly focus on the development of speakers, to make products much smaller, thinner, and easy to carry. Though the working principle of speakers is considerably uncomplicated and the technology of speakers has been developed for a long time. However manufacturing a high-quality speaker with sweet-sounding voice and low distortion is still a difficult issue. Preference for voice is distinct for people, thus the task about designing a perfect speaker to satisfy different users is worthy of being discussed. The main purpose of this research focuses on theoretical analysis, numerical analysis and experimental measurements on the influence of dynamic characteristics for diaphragm, and port in loudspeaker system. The content of this thesis is divided into two parts. The content of this thesis is ranged into two parts. The first topic of this thesis is to The first topic of this thesis is to research the mechanical characteristics of materials for diaphragms by experimental measurement, and design fixtures to provide fine boundary condition. The stiffness of the diaphragm is measured by the Nano-indentation and air pressure pushing of the thin film for diaphragms. The damping ratio of the diaphragm in distinct exciting frequency is determined by measuring the dynamic signals of the different thickness and material of diaphragm on the basis of vibration theory by laser displacement sensor. The second topic of this thesis is to perform the analysis to appraise the characteristics of broad-band noise generated from small bass-reflex loudspeaker. To begin with, we find the Bandwidth with stronger noise from system to obtain exciting frequencies. The noise strength of different diameter and length for port by the finite element analysis, consequently we can get principal direction to design port. Furthermore, the correctness of simulation is verified by experiment. We compare resonant frequency of chuffing for different port by experiment, simulation and standing wave theory. Finally, we change the shape of port to attempt to reduce the noise strength.by above-mentioned step.