Chaotic state in an electrodynamic loudspeaker controlled by gas pressure

Abstract

An electrodynamic loudspeaker with resonant frequency f0=47.1 Hz has been driven in the far nonlinear regime, and f0 increases with increasing driving ac current I0. Landau cutoff of the vibration amplitude appears at frequency fc>f0, which is followed by the doubling of driving period 1/f and appearance of harmonic sequences at 1/2nf, 1/4nf, 3/4nf,.... By further increase of current the white noise spectrum appears, which is characteristic of the chaotic state. Electrodynamic loudspeaker is represented by an ordinary differential equation of motion describing an anharmonic forced oscillator, and it is possible to achieve an independent control of chaotic state by the gas pressure, since real RS and imaginary part XS of the gas acoustic impedance affect, respectively, friction and inertial terms in the equation. The used gas atmospheres (0.01<p<1 bar) were H2, D2, He4, Ne, Ar, CO2, SF6, and air. The cutoff frequency fc depends on the gas pressure and it was plotted against (p,I0), which in turn defines the surface in three-dimensional diagram. Values of parameters (p,I0) triggering chaotic state were chosen above this surface, and universality of some laws describing such state was tested against the gas density.