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Thursday, July 11 • 10:40 - 11:00
NUMERICAL AND EXPERIMENTAL STUDY OF A HYBRID ELECTRO-ACOUSTIC NONLINEAR SOUND ABSORBER IN A RESONANT ROOM

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We present a hybrid Electro-Acoustic Nonlinear Energy Sink (EA-NES) coupled to a resonant room. It is made of a baffled nonlinear membrane with its front face exposed to the noise in the room, and the rear face enclosed. The enclosure includes a feedback loop associating a microphone and a loudspeaker that control the acoustic pressure applied to the rear face of the membrane. The dimensions of the setup correspond to applications in building acoustics for resonant rooms, at low frequencies and high sound levels. The EA-NES action is based on the concept of Targeted Energy Transfer resulting from the nonlinear coupling between the absorber and an acoustic mode (primary system). The model includes the electrical control loop of the EA-NES in its stable range, the nonlinear dynamics of the EA-NES membrane, and the dynamics of the first acoustic mode of the room. The asymptotic study shows the possible existence of relaxation oscillations, which are affected by the gain level of the control loop and by the driving mode of the loudspeaker. The experimental study shows that a hybrid EA-NES can work in a concrete building. For an optimal excitation level, it can limit the sound level in the room up to 8 dB at 43 Hz for a footprint of 0.2% of the room volume. Different regimes are observed. They correspond well to previous observations for passive NES absorbers: some responses are harmonic, and there is a range in frequencies and excitation levels where the responses exhibit a Strongly Modulated Regime (SMR), and where the vibration of the degree of freedom localized in the room is limited below a threshold. The SMR responses can be simulated with a good agreement. The gain level and the control loop command laws are explored, showing how the EA-NES performance can be controlled electrically.


Thursday July 11, 2019 10:40 - 11:00 EDT
Westmount 3
  T02 Act. noise & vib. cntrl., SS03 Active meta-materials