Normally, there are in use certain technologies of reduction of noise named passive, in the cancellation of the noise produced by industrial machinery. These technologies can be applied directly on the source (use of absorbers, mufflers and closings), in the way of transmission (as isolations, acoustic barriers, materials of absorption and acoustic sounders), or in the recipient (as the acoustic conditioning of locals or ear protective ).
In this thesis, there is applied a technology different from that of passive type, named active control of noise, centring his use on the field of the industrial machinery.The active control is based on the attenuation or elimination of a acoustic wave by destructive interference. Though nowadays the active control of noise is in use commercial in some applications like air ducts, elements of auditory personal protection, cabins of planes ¿, it is occasionally used in industrial buildings, where the machines are in the habit of issuing serious and strongly tonal noise, what a priori, they are the suitable conditions for the utilization of the above mentioned control. The problem is that the industrial machinery places inside industrial buildings of big dimensions and therefore of high modal density. Normally passive technologies can be applied encasing totally the source with panels of absorbent and insulating material. But to low frequencies, to encase is not synonymous of reducing the level of noise in the exterior, since these materials in the range of low frequencies have very under performance of attenuation and enclosed to the resonance frequencies of the capsule is possible to come to increase the sonorous level in the exterior. If the active control is realized there is not obtained a global reduction (in the whole space) but punctually near the microphones of control. This doctoral thesis tries to demonstrate that, introducing a noise source in a suitable capsule is achieved to diminish the modal density of his acoustic field, and therefore, it is possible to obtain the global cancellation for active control of the noise generated by this one in an enclosure of big dimensions, where of direct form it would be totally impossible to realize it for other means. There has carried out the theoretical model of the acoustic field produced in an enclosure for an encased source and has been validated by means of level measurements of sonorous pressure in the interior and exterior of the encapsulamiento for a loudspeaker. With these equations the active control and his parameters have been studied for an ideal cancellation depending on different situations and applications. There have been realized tests of active control of an electrical encased engine, the results have been analyzed them comparing to the obtained ones with the theoretical model, a loudspeaker or the own engine without encasing, so much inside the capsule as in the exterior enclosure, corroborating the kindness of the active capsule. There has been realized a practical application of this theory in the cancellation by active control of the noise of a ventilator of a personal computer.
