Adaptive minimization of radiated sound power from lightweight structures with anti-noise

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One well-known application of anti-noise is the noise cancellation in an active headset. Here, sound immission (noise acting at the users ear) is reduced by anti-noise. In noise emission (thus noise emitting from a source) passive sound insulation such as insulation mats are used mostly. Weight and installation space limit the application at frequencies below 300 Hz. This gap can be closed by active noise treatments. The planned research project concerns with this task.Reduction of the radiation of structure-borne sound is both applied in free sound fields (e.g. noise radiated by electrical transformers) as well as in indoor space (e.g. noise within an aircraft cabin). Here, an adaptive control system generates actuation signals for anti-noise loudspeakers to minimize the sound pressure at microphones. Due to the spatial dependence of the sound field, a global noise reduction is possible only by the use of many microphones.The global noise reduction with a local arrangement of electromechanical and -acoustic transducers has long been discussed in the literature. Solutions for global active noise control (ANC) require the observability of global acoustic quantities such as the total potential sound energy in a weakly damped volume or the total radiated sound power into the free sound field. The feasibility of a local ANC system with unknown radiation impedance of the vibrating structure, while simultaneously controlling the total radiated sound power, has been poorly studied up to now.This approach offers the possibility of significantly reducing the quantity as well as the effort for position optimization of transducers in an ANC system. Preparatory work of the apprentices working group proves that adaptive minimization of total sound power is possible.This leads to the aim of the research project, that is the adaptive minimization of the total radiated sound power of a periodically-actuated plate structure in the frequency range between 80 Hz and 300 Hz with locally arranged loudspeakers and sensorsAnalytical and numerical methods as well as experimental investigations on a plate structure are the consequent step to the own preliminary work and already gained knowledge from the literature. The planned investigations form the basis for this research project and for the extension of the principle to a real lightweight structure. Thus fundamental experience about global noise reduction of sound emitting structures by a non-contact with electro acoustic actuators will be generated and prepared for applicability.