An experimental investigation into cooperation phenomena is presented, which in this case can be described as the contribution of energy from a random signal to the energy of a periodic signal under certain conditions. Previously cooperation phenomena have been described mainly from a theoretical point of view. However, well-known practical examples exist. For the present experiment a loudspeaker was used that had a slightly rubbing voice coil subjected simultaneously to excitation from a random signal and from a periodic signal. Test results clearly show the influence of cooperation on both the random and the periodic signals. The random signal acquires additional "agility," allowing some of its energy to be transferred to the periodic signal. Experimental results are compared with theoretical analysis based on limit cycles and Van der Pol's oscillators. The application of limit cycles is then extended to friction-induced phenomena. The subject matter is of general interest in the dynamics of nonlinear systems and of more specific interest in the behavior and testing of loudspeakers.
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