Dr.-Ing. André Jakob

Improvement of sound insulation of machine housings by active means

Often sound insulation of machine housings is poor at low frequencies. In the project an enclosure for a combustion engine used for stationary applications shall be acoustically improved with active noise control inside the enclosure.

Supported by BMWi/AiF
Duration of Project:   1/2009 – 12/2010

Non-linear high intensity sound sources for active noise control applications

Active noise control is an important and appropriate addition to traditional passive sound reduction methods. Passive methods are suitably mainly for the mid and high frequency region. Whereas the suppression of low frequency noise is often limited due to the high requirements concerning additional mass and/or space. Active methods are potentially suitably for the low frequency region. It exists especially for exhaust systems, e.g. in cars or trucks, the hope, that anti-sound will help to lower noise pollution. Despite the most questions are already solved for a rather long time, the practical realization fails at present, because of the neccessary high sound levels at low frequencies, which are to high demands for conventional loudspeakers. In the current project alternative sound sources are developed. Mainly are here considered the so-called compressed-air loudspeakers, which use a modulated airstream for the sound generation. Those sound sources are potentially nonlinear. Thus in this project they either shall be linearized with some electronic pre-distortion or the nonlinearities shall be used directly to cancel the unwanted harmonic components of the primary disturbance. Those new sound sources and algorithms to be developed will be tested experimentally. This project was sponsored by the DFG, Deutsche Forschungsgemeinschaft, project name: "Nichtlineare Antischallquellen".

Enhancement of sound insulation of double panels by active means

Double panels are used for double-glazing windows, for aircraft fuselage shells or in car-bodies. They are distinguished by high acoustic transmission loss for the high- and mid-frequency range but are weak in the low-frequency range. The acoustic insulation is poor especially around the mass-spring-mass resonance frequency of the panel-cavity-panel system. Active methods have the potential to increase the poor transmission loss at low frequencies. Minimization of the cavity sound field between the panels and/or minimization of the panel vibration are both possibilities to enhance the transmission loss of the double panel. Both methods will be investigated experimentally using both feedforward and feedback controllers.
This project was sponsored by the DFG, Deutsche Forschungsgemeinschaft, project name: "Aktive Doppelschalen".

Active minimization of sound radiation from vibrating plates

The sound radiation of vibrating plates (e.g. flat parts of chassis or separators such as windows) is to be minimized by means of secondary forces (Active Structural Acoustics Control - ASAC). Studies have shown that minimizing the plate vibration (i.e. mean square velocity) does not necessarily result in the best reduction of the sound radiation. Better results can be achieved by changing the local distribution of the velocity. The principles of sound reduction expressed in terms of change of the modal amplitudes were investigated. Algorithms were developed with the goal of minimizating the sound radiation of the plate by only measuring the plate vibration itself.
This project was sponsered by the Technical University of Berlin within the interdisciplinary project "Digitale Filter", Project number IFP 12/21.

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