Study On The Life Time Test System Of Micro Loudspeaker

With the increasing demand for high volume of audio equipment such as mobile phones,manufacturers will increase the volume of loudspeakers by some algorithms.These algorithms can output as high volume as possible,and at the same time,they will prevent the mechanical damage of the diaphragm and the thermal damage of the coil.In order to verify the effectiveness of diaphragm protection and coil temperature protection algorithm used in intelligent power amplifier,it is necessary to carry out LTT test on batch of miniature loudspeakers.The existing LTT test scheme cannot monitor the diaphragm amplitude and coil temperature during the test process.In this paper,a voltage amplitude model is proposed to monitor the amplitude of loudspeaker,and the modeling and parameter calculation method of the model are given.The diaphragm amplitude can be calculated only by measuring the voltage at both ends of the loudspeaker.An improved Goertzel algorithm is proposed to calculate the amplitude of low frequency signal and then calculate the coil temperature.The software and hardware of the LTT test system are designed,and the related experimental verification and testing are carried out according to the proposed LTT test process.Before and after the test,the speaker was tested,and the impedance characteristics,frequency response characteristics and THD characteristics of the loudspeaker were recorded.The results showed that the listening results were normal,and the changes of impedance characteristics,frequency response characteristics and THD characteristics before and after the test were not more than 10%.Before the test,the amplitude measured by laser is compared with the amplitude calculated by LTT system,and the temperature set by the incubator is compared with the coil temperature calculated by LTT system.The results show that the amplitude error of LTT system is less than 5%,and the coil temperature calculation error of LTT system is less than 2%.In the test process,eight micro loudspeakers of the same model and the designed sound source were used to test the amplitude protection and temperature protection for 72 hours in the constant temperature environment of 25 ? and 55 ?.The voltage and current at both ends of the loudspeaker were measured by the designed lower computer system,and the amplitude was calculated by the differential equation model of the loudspeaker in the upper computer software,and the improved Goertzel algorithm was used to calculates the impedance characteristics of the loudspeaker under the condition of 50 Hz low frequency,and then obtains the coil temperature;the results show that both the amplitude and the coil temperature do not exceed the set threshold,which indicates that the intelligent power amplifier can realize amplitude protection and temperature protection when the output volume is as high as possible.Combined with the test results before and after the test,it is concluded that the amplitude protection and coil temperature protection algorithm are effective.The proposed LTT test system solves the problem that the existing LTT test system does not have the function of amplitude and coil temperature measurement.The proposed modeling and parameter calculation method solves the difficulty of applying the loudspeaker model to calculate the amplitude,and reduces the cost of amplitude monitoring for batch loudspeakers.The flexibility of coil temperature measurement is improved by the proposed method.The whole system can meet the life test requirements of intelligent power amplifier for micro loudspeaker.