Targeted energy transfer from a resonant room to a hybrid electro-acoustic nonlinear membrane absorber: Numerical and experimental study

We present the first real size evidence of targeted energy transfer in a concrete building, with an efficient action on low frequency noise reduction. It is achieved by the means of a hybrid Electro-Acoustic Nonlinear Energy Sink (EA-NES). The EA-NES action is based on targeted energy transfer. As in previous works the EA-NES is made of two elements: a membrane with a nonlinear dynamics, and an active system based on a loudspeaker which controls the pressure applied to the rear face of the membrane. We study here a proportional feedback control law driving the loudspeaker in current mode, and compare it with the voltage mode command law. The experiment is fully modeled. A singular perturbation method around a 1:1 resonance is used to find the slow critical manifold of the system and its dependence on the control loop gain for the two driving modes, in view of finding conditions allowing Strongly Modulated Regime (SMR). A good quantitative agreement is found between the model and the experiments. In the experimental study we observe a range in the excitation level corresponding to SMR where the sound level in the room is limited. We study the influence of its parameters on the thresholds of the working range of the EA-NES. We measure up to 8 dB of attenuation around 43 Hz.