Study On A New Approach And Instrument For Measuring Young’s Modulus And Loss Factor Of Loudspeaker Cone

The properties of loudspeaker cone, such as dynamic Young’s modulus, loss factor, acoustical velocity etc., are very important for a loudspeaker’s cone. These cone properties may have great impact on a loudspeaker’s acoustical performance. They are not only useful for designing and manufacturing loudspeaker system, but also helpful for choosing and optimization of raw materials in cone developing and quality control in cone making process.There are some limitations and errors in all the present methods for measurement of Young’s Modulus and Loss Factor of speaker cone. These present methods can only measure a straight shape sample with equal thickness. Since the speaker cone may have a curved shape often with non-uniform thickness the present testing method can directly evaluate the actual cone. Rather the present methods can only be used to measure raw materials by forming a flat paper strip. When measuring a speaker cone sample, there can be significant error and lack of repeatability. As it is known, Young’s Modulus and loss factor will change after raw cone material be made into a cone, So it is necessary to develop an instrument that can realistically measure Young’s Modulus and loss factor of speaker cone accuracy, repeatability and robustly.In this paper we research measuring Young’s Modulus and Loss Factor by the method of vibration reed. A measurement system for Young’s Modulus and Loss Factor (MSFYL) is developed. The MSFYL includes five sections:Controlling section, Excitation section, Detecting section, Software section and Operating section.The Control section consists of seven modules, they control the entire automated process. In the Excitation section, sine sweep signal was generated by a signal generator. The test sample is excited by the sound wave of the speaker. Meanwhile, vibration signal of the testing sample is detected by a laser sensor in a non-contact way and convert them into a digital data. The data was sent into CPU and analyzed by software, Young’s Modulus and Loss Factor is then determined. A monitor is used for operating the test process.The innovation of the MSFYL include two aspects:a three-dimensional automatic guide track is designed. Thus the laser sensor can move at a trajectory the same as the curve of the cone sample. Meanwhile, Young’s Modulus and Loss Factor is measured at each point from upper to the lower end of the sample in a successive automated manner. Then the testing values are transferred into an average, by this way we can modify the inaccuracy caused by non-uniform thickness of the cone sample. During the detecting process, at each particular detecting point, the laser sensor will automatically be adjusted to a place which is perpendicular to the testing sample. Hence, the testing inaccuracy caused by the curved shape of the testing cone sample will be avoided.The test result of MSFYL is proven in accordance with the standard Young’s modulus value that had been published in SCIENCE CHRONOLOGY published in Japan,1987(more detailed annotation needed). Experiments illustrate that the test results of MSFYL has high accuracy repeatability and dependability, and it can meet the practical need.