Nonlinear distortions of loudspeakers allow absorbing sound

Nonlinear distortions are not favored in audio systems, except in the cases where they contribute to the DNA of music genres (eg. heavy metal or electronic music). However, nonlinear membrane sound absorbers are known to allow absorbing acoustic energy through a physical phenomenon known as Targeted Energy Transfer. When triggered by high enough sound pressure levels, energy can be transferred from the incident sound pressure to higher harmonics vibration components of the membrane, leading to a net loss of energy in the acoustic domain, as thoroughly described in the literature on Nonlinear Energy Sinks. This is exactly the aim of the Nonlinear ElectroAcoustic Resonators (NEAR) presented in our paper, published in Physical Review Applied [1], where a loudspeaker is used as an active membrane absorber, through an hybrid active impedance control scheme. Such device tweaks the loudspeaker to act as an “active” nonlinear membrane resonator, mimicking the behavior of a cubic stiffness, exhibiting Target Energy Transfer phenomena even for excitation levels that are 1’000 times lower than the one reported in the literature. This study paves the way to a new generation of Active Nonlinear Energy Sinks, outperforming the existing concepts so far, for better sound absorption at low frequencies.