Laser interferometric characterization of a vibrating speaker system

Abstract

An experiment that combines opto-mechanical and electrical measurements for the characterization of a loudspeaker is presented. We describe a very simple laser vibrometer for evaluating the amplitude of the vibration ͑displacement͒ of the speaker cone. The setup is essentially a Michelson-type interferometer operated by an inexpensive semiconductor laser ͑diode laser͒. It is shown that the simultaneous measurements of three amplitudes ͑displacement, electrical current, and applied voltage͒, as functions of the frequency of vibration, allow us to characterize the speaker system. The experiment is easy to perform, and it demonstrates several useful concepts of optics, mechanics, and electricity, allowing students to gain an intuitive physical insight into the relations between mathematical models and an actual speaker system.

Experiments with a loudspeaker

“…The oscillation amplitude and the phase relationship between the driving force and the displacement were determined. Freschi et al (2003) measured the oscillations of a loudspeaker with a Michelson interferometer using the Doppler shift technique. From the measurements, electrical and mechanical parameters of the loudspeaker were calculated.…”

An inverse method for estimating the electromechanical parameters of moving-coil loudspeakers

“…(18) and (19) and substitute k 1 (t) and k 2 (t) into Eqs. (21) and (22) to obtain the gradient for the objective function rJ. Let c ð0Þ ¼ 0 when k ¼ 0; otherwise, use Eqs.…”

“…Furthermore, system identification methods [15][16][17][18][19][20][21] can be used to estimate electromechanical parameters by measuring the input voltage, voice-coil displacement, and voice-coil current. Optical linear displacement sensors 22,23 and the loudspeaker characteristics measurement technique proposed by can be used to measure voice-coil displacement, whereas currentmeasurement devices can be used to determine voice-coil current and input voltage.…”

A Model Updating Technique Based on the Constitutive Relation Error for In Situ Identification of Admittance Coefficient of Sound Absorbing Materials

“…The friction losses are described by a dissipation constant c P . The transfer function H V X between the complex displacement X(ω) and the complex voltage applied to the coil V (ω) is given by the expression [40]…”