Finding the physical parameters of the electrodynamic converter by the method of using the parameter BL and the method of mass added

Abstract

The task of finding the physical parameters of electrodynamic transducers is an integral part of the process of development and production of speakers [1,2]. The most popular method for this is the added mass method proposed by Neville Theel and Richard Small. This method is simple and reliable to use, does not require expensive technology and considerable computing power. But its biggest disadvantage is the direct addition of mass to the moving part of the converter, which can damage it and very often is practically impossible.The paper proposes a method of using the parameter BL (the product of the induction in the gap of the magnetic circuit and the inductance of the sound coil) is based on measuring the displacement of the moving part of the converter, as well as the current through the coil of the converter and the voltage at its terminals. These three characteristics make it possible to fully determine the parameters of the electrodynamic converter in the electrical and mechanical parts separately, ie to measure the total electrical impedance and the total mechanical impedance. Once the impedances have been determined, they can be handled individually, and different equivalent circuits can be applied to further determine directly the parameters of the converter model.To demonstrate the benefits of finding the physical parameters of the converter, using the BL parameter, an example of a typical three-inch wide-band electrodynamic converter was calculated. For detailed modeling of the electrical oscillation system, the model of John Vanderkoy was chosen, in which the complex resistance of the coil is the sum of the static resistance of the RDC, the frequency-dependent active resistance of the coil RVC (f) and the frequency-dependent inductance LVC (f). This allows the model to account for complex physical effects, such as eddy currents that occur in the metal parts of the magnetic system.A series of ten measurements were performed by each method and the mean for each physical parameter and the corresponding standard deviation were calculated.Simulation of the full electrical input impedance Ztot (f) using the BL parameter method shows that the results are closer to real measurements than the added mass method, especially at frequencies above resonance. Comparison using the BL optimization method and the Vanderkoy model for the magnetic system shows less error at high frequencies for both the full input impedance module and the phase. However, the parameters found by the classical method of added mass are close to those found by the method of the parameter BL, which proves its feasibility for rapid measurements in production.From a statistical point of view, the stability of the BL parameter utilization method, the high repeatability of the results, and the smaller statistical error compared to the added mass method were demonstrated. In addition, a significant advantage of the BL parameter method is the ability to use it for miniature converters or converters with very fragile membranes (RF converters). That is, in all cases where physical interference with the movable part (adding mass or volume) is practically impossible.