Localization and characterization of sound sources

 

This research area aims to solve the problem of isolating the acoustic contribution and position of one or more sources when there is a sound field generated by multiple sources.  To resolve this problem at the LEAM we have developed systems based on the use of microphone arrays.

 

What is a microphone array?

A microphone array is a set of microphones arranged at different points in space, simultaneously measuring the acoustic field. Simultaneous measurements in different parts of a sound field can locate the sources that have generated the sounds and account for the contribution each makes.

 

 

Measuring noise levels

Acoustic photograph of a train fuselage

 

Fields of action

Microphone array measurements are performed when measurements are needed in unfavorable environments, such as those with a high level of background noise which could otherwise falsify the results. The use of integrated acoustic antennas for various microphones (arrays) allows, apart from separating signals from the unwanted effects of environmental sources, locating sound sources that generate a particular acoustic field.

 

On the one hand the LEAM applies this technique to localize sound sources in industrial machinery such as wind turbines [1] or trains.  In these cases the signal processing used is based on the difference between the time of arrival at each microphone in order to locate and quantify the contribution of the source. Examples of this application are the projects "Design and construction of a microphone array for the detection of acoustic radiation of wind turbine blades" done in collaboration with the companies SENER and GAMESA and" Development and application of a methodology for the determination of noise sources in high speed trains " together with the company SENER.

  

Acoustic photograph of wind turbine blades

 

Likewise, this technique has been applied to monitoring aircraft around airports. For this purpose we have developed two systems: one based on the difference between the arrival times of sound to the different signals of a lineal array of microphones with a length of 3 meters [2,3], and another based on the change of frequency caused by the Doppler effect in the different signals from a microphone array distributed over an area of kilometers around the airport [4]. An example of this application is in the project "Application of array technique to measure airplane noise" produced for the Boeing Company, the two national patents entitled "Método de medida de ruido de aeronaves en sobrevuelo y eliminación automática de ruido no procedente de las aeronaves" and "Sistema para la medida de ruido y localización de una fuente móvil en presencia de ruido de fondo".

 

Monitoring aircraft using microphone antenna

 

[1] M. Genescà, J. Romeu, T. Pàmies and J. Solé, On the use of a linear microphone array to measure wind turbine aerodynamic noise, Wind Energy (Accepted for publication).

[2] M. Genescà, J. Romeu, T. Pàmies, A. Sánchez, Aircraft noise monitoring with linear microphone arrays, IEEE A&E Systems Magazine (2010).

[3] M. Genescà, J. Romeu, T. Pàmies, A. Sánchez, Real time aircraft fly-over noise discrimination, Journal of Sound and Vibration (2009).

[4] M. Genescà, J. Romeu, T. Pàmies, A. Balastegui, Passive acoustic method for tracking moving sound sources, Acta Acústica united with Acústica (2011).