Active shielding based on difference potentials

Active control of sound is a technique for altering acoustic fields to wanted onesin aimed domains by introducing controllable active secondary sound sources calledcontrols. This thesis describes an active shielding methodology based on differencepotentials for the control of noise and preservation of sound in domains. The mainfeature of this methodology is its ability to automatically preserve "wanted" soundwithin a domain while cancelling "unwanted" noise from outside the domain. Thismethod of preservation of the wanted sounds by active shielding control isdemonstrated with various broadband and realistic sound sources such as, humanvoice, music, etc in multiple domains in a one dimensional enclosure. Unlike manyother conventional active control methods, the proposed approach does not requirethe explicit characterisation of the wanted sound to be preserved. The controls aredesigned based on the measurements of the total field on the boundaries of theshielded domain only, which is allowed to be multiply connected, and thecontrols are placed on the boundaries only. The cancellation and preservationcan be achieved globally over a large area of the domain. The method is tested in avariety of experimental cases. The typical attenuation of the unwanted noise is foundto be about 20 dB over a large area of the shielded domain and the original wantedsound field is preserved with errors of around 1 dB and less below through a broadfrequency range up to 1 kHz. This thesis reports on the results of the validation forthe methodology in detail, with particular emphasis on the volumetric noisecancellation and wanted sound preservation offered by the proposed methodology,which are unique features compared to other techniques available in the literature