Abstract:

Loudspeaker drive units are conventionally modeled as linear devices. Evidence is presented that shows that this assumption leads to unacceptable modeling errors for practical conditions of use. This paper presents new techniques for accurate, nondestructive measurement of linear and nonlinear electromechanical parameters. These parameters are used in more complete models which improve accuracy of frequency response and distortion estimates. The measurement workstation uses pneumatic pressure to displace the diaphragm in order for position-dependent parameters to be measured over the full excursion range. Suspension compliance and mechanical damping are measured under conditions which simulate normal operation, thereby capturing the influence of creep, aerodynamic drag, and other second-order characteristics which are not measured separately at present. Moving mass and force factor measurements utilize a magnetic position servo and gravity to obtain data without displacing the suspension. Conventionally, maximum diaphragm displacement, x[inf max] is calculated from voice-coil and magnet geometry. This ignores the magnetic fringe field and the effect of suspension nonlinearities. An improved value of x[inf max] is derived from the new measurement data.