Further experiments with a loudspeaker

A common moving-coil (dynamic) loudspeaker is a device very suitable for teaching the general features of oscillating systems. As an addition to a previous paper (Kraftmakher 2009), this paper includes the following topics: (i) a new design of the optical sensor for measuring the cone oscillations; (ii) positive feedback and self-excited oscillations; (iii) the determination of the loudspeaker parameters without direct measurements of the cone oscillations; and (iv) the loudspeaker in a vacuum chamber. The measurements are performed without a lock-in amplifier. The tight connection between the mechanical and electrical parameters of a loudspeaker is confirmed. The experiments are well related to the university courses of electricity and magnetism and can be used in undergraduate laboratories.