JMC method applied to active control of sound: Theoretical extensions and new source configurations: Dissertation

The active control of sound can be used to control the acoustics of interior spaces, to reduce the sound radiation of machines and equipment, to decrease and even to refine noise in a more comfortable form in, e.g., ducts and vehicles.The JMC method, developed by Jessel, Mangiante and Canévet, is a systematic tool in the active control of sound.It is applied mostly by using scalar weighting, in which all the first-order field quantities and primary source strengths are weighted similarly.In this thesis, a modified JMC method is developed, in which the primary sources remain unchanged in all cases, the situation being more similar to a practical one.On the basis of the modified JMC method, the vector and dyadic weightings are defined, the former weighting the sound pressure and particle velocity independently, and the latter also changing the direction of the particle velocity.These new weightings increase the possibilities in field reshaping.In the JMC method, three types of secondary sources are needed: monopoles, dipoles and quadripoles.It is found that in multi-source configurations, the last ones are automatically generated by the dependence of the dipole distribution on the lateral coordinates.Four three-unit approximations of the JMC element (i.e., detector-actuator combination according to the JMC method) are developed, in which one of either the primary field quantities or the secondary source quantities is approximated by the help of a field impedance function.For waveguides (e.g., ducts), ideal unidirectional three-element and two-element JMC source configurations and their approximations are discovered.The inter-channel delay in the control structure of the two-element actuators may be optimized downstream or upstream, or omitted altogether.Especially the last case turns out to be advantageous in the practical implementation of digital control systems.The adaptive JMC structures for the new ideal two-element solutions are presented.The results of this thesis enlarge the possibilities in the active control of sound and facilitate more useful applications to be realized in ducts and three-dimensional spaces.