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Hier finden Sie wissenschaftliche Publikationen aus den FraunhoferInstituten. Optimal shape of the reflex tube of a bass loudspeaker
 Sas, P. ; Katholieke Universiteit Leuven, Departement Werktuigkunde: Noise and vibration engineering. Proceedings of ISMA 2004. CDROM : Leuven, 2004 September 20  22; International Conference on Noise and Vibration Engineering Leuven: Katholieke Universiteit Leuven, 2004 ISBN: 9073802822 ISBN: 9789073802827 pp.38773890 
 International Conference on Noise and Vibration Engineering (ISMA) <2004, Leuven> 

 English 
 Conference Paper 
 Fraunhofer ITWM () 
Abstract
If a strong sinusoidal signal is sent to a vented bass loudspeaker we do not only hear the fundamental frequency, but also higher harmonics not present in the original signal. This nonlinear distortion is partially due to the response of the electromechanical components and partially due to the transfer behavior of the enclosed air. Here, we investigate the latter effect. In particular, we show how to design a reflex tube in order to reduce the induced first overtone to a minimum. Obviously, the problem cannot be formulated in the framework of linear acoustics. On the other hand, solving the full Euler equations in each step of a shape optimization is impracticable. Therefore, we propose a correction to the linear Helmholtz equation. In contrast to the classical second order equation of nonlinear acoustics it consists just in a second inhomogeneous Helmholtz equation for the first harmonic and an algebraic equation for the radiation pressure. The system of linear PDEs may be solved sequentially. A Lagrangian description takes into account moving boundaries in a natural way and pressure is chosen as unknown rather than the velocity potential, which cannot be measured.