The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
The present invention utilizes a front-end device to measure the impedance frequency response of a microspeaker and utilizes a test-box method to obtain the impedance curve of the microspeaker. The electromechanical parameters of the microspeaker are calculated according to the impedance curve. After the electromechanical parameters have been identified, the performances of the microspeaker are evaluated, including: sound-pressure sensitivity, efficiency, total harmonic distortion, and inter-modulation distortion. Then, the analysis and design for optimizing the electromechanical parameters of the microspeaker are undertaken to obtain the best output performance of the microspeaker.
Refer to
wherein H(f) is the impedance frequency response of the resistor 14, and R is the impedance of the resistor 14.
After the impedance frequency response of the microspeaker has been obtained, the parameters of the microspeaker can be measured. Limited by the size of the microspeaker, the parameter identification is undertaken with a test-box method in the present invention, as shown in
Next, the process proceeds to Step 12. A first simulation circuit, which comprises a resistor, an inductor and a capacitor, is used to simulate the peak value of the outside-test box impedance frequency response curve of the microspeaker. A second simulation circuit, which also comprises a resistor, an inductor and a capacitor, is used to simulate the peak value of the inside-test box impedance frequency response curve of the microspeaker. The objective of the abovementioned simulation is to utilize a curve-fitting method to identify the mechanical system quality factor QMS and the closed-box system electrical quality factor QEC. The simulation steps comprise selecting appropriate resistance R, inductance M, and capacitance C so that the peak value of the frequency response curve of the first simulation circuit comprising said resistor, said inductor and said capacitor is the same as the peak value of the outside-test box impedance frequency response curve of the microspeaker; comparing the coefficients of the second order transfer function
of the inductor, resistor and capacitor with
the resonance frequency ωS and the mechanical system quality factor QMS of the microspeaker are then identified by utilizing Equation (1) to (3), as shown in Step 14, wherein Equations (1) to (3) are respectively expressed by:
Similarly, the inside-test box resonance frequency fc of the microspeaker and the closed-box system electrical quality factor QEC are obtained via comparing the coefficients of the second order transfer function of the second simulation circuit. After the closed-box system electrical quality factor QEC and the mechanical system quality factor QMS have been identified, the equivalent volume of the microspeaker can be calculated via the equation
wherein VT is the volume of the test box. The mechanical mass of the vibrating diaphragm MMD, the mass of the mechanical system of the vibrating diaphragm and air load MMS and the mechanical compliance of the vibrating diaphragm suspension CMS can be identified with Equations (4) to (6), which are expressed by:
wherein ρ0 is the air density; SD is the effective area of the vibrating diaphragm; M1 is the low-frequency air load impedance. The mechanical resistance of the vibrating diaphragm RMS and the motor constant B1 can be obtained with Equations (7) and (8), which are respectively expressed by:
The other important parameters, such as the acoustic compliance of vibrating diaphragm suspension CAS, the acoustic mass of the vibrating diaphragm and air load MAS, the acoustic resistance of suspension loss RAS, the capacitance driving the total displacement mass CMES, the inductance driving the mechanical compliance LCES, the acoustic resistance of suspension loss and electrical loss RAT, the total mechanical resistance of suspension loss and electrical loss RMT, and the mechanical mass of the vibrating diaphragm MMD, are respectively identified by:
wherein RAE is the acoustic resistance of electrical loss, and MA is the acoustic mass. The equivalent coil resistance and the equivalent coil inductance of the speaker can be identified with the following equations:
The values of n and Le can be worked out with the measured value ZVC and the following equation:
The calculation of the abovementioned parameters can be implemented with software having calculation function, such as Matlab GUI. After the outside-test box impedance response frequency of the microspeaker, the inside-test box impedance response frequency of the microspeaker and the size of the test box have been input, Matlab can automatically calculate the values of the abovementioned parameters. Therefore, the parameter identification method of the present invention can be presented in the form of a computer program.
Further, the present invention proposes an optimization method for the parameters of microspeakers. Since microspeakers are limited in volume and thickness, and the elements of a microspeaker are separately fabricated before assembled, it is hard to ensure that the elements are perfect matching, and the acoustic volume and quality of the microspeaker is hard to achieve the best performance. Thus, an optimization method is needed to fully achieve the designed performance of microspeakers. In the optimization method of the present invention, a target parameter and a limit parameter (used as a limiting condition) are selected from parameters; under the limiting condition, an optimization algorithm is used to perform optimization and find the maximum or minimum of the target parameter, as shown in Step 16. For example, when the target parameter is the axial sound pressure sensitivity psens1V, it is the value of the sound pressure sensitivity at the axial distance of 1 meter and under an input voltage eg=1 Vrms. The limiting condition may be the displacement of the vibrating diaphragm, the density of magnetic flux, the acoustic compliance, the resonance frequency, etc. The aim of the optimization is to obtain the maximum sound pressure sensitivity.
Refer to
wherein RAT=RAE+RAS. It can be observed from
In summary, the present invention provides a method of utilizing an external electronic circuit to measure the impedance frequency response of a microspeaker. The simple external electronic circuit serves as the front-end and replaces the conventional impedance analyzer. Further, the present invention proposes a method for parameter identification of a microspeaker, wherein the parameters of a microspeaker are identified via measurement procedures for identifying electromechanical constants. After the parameters of the microspeaker have been calculated, the optimal parameter design can be obtained so that the microspeaker can achieve the best acoustic performance with minimum harmonic distortion.
Those embodiments described above are to clarify the present invention to enable the person skilled in the art to understand, make and use the present invention. However, it is not intended to limit the scope of the present invention. Any equivalent modification and variation according to the spirit of the present invention is to be also included within the claims of the present invention stated below.
Number | Date | Country | Kind |
---|---|---|---|
95116064 | May 2006 | TW | national |