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Comesana D.F.,Institute of Sound and Vibration Research ISVR | Garcia P.R.,Institute of Sound and Vibration Research ISVR | Torres-Guijarro S.,Laboratorio Oficial Of Metroloxia Of Galicia Lomg | Pena A.,University of Vigo
128th Audio Engineering Society Convention 2010 | Year: 2010

Directivity is one important parameter to define the behaviour of a loudspeaker. There are many techniques and standards about directivity measurements in anechoic chambers but in situ measurements of flush-mounted loudspeakers show some specific problems. This contribution develops a procedure to measure directivity under the special conditions of a non-environment listening room, introducing the techniques utilized, the problems found with the proposed solutions and discussing the limitations of the process. The existence of reections, baffling effects due to adjacent walls and a comparison to theoretical models of the radiation of a piston are discussed. Source

Narayanan S.,University of Southampton | Narayanan S.,Institute of Sound and Vibration Research ISVR | Joseph P.,University of Southampton | Joseph P.,Institute of Sound and Vibration Research ISVR | And 8 more authors.
20th AIAA/CEAS Aeroacoustics Conference | Year: 2014

This paper provides an experimental investigation into the use of leading edge serrations as a means of reducing the broadband noise generated due to the interaction between the aerofoil's leading edge (LE) and impinging turbulence. Experiments are performed on a flat plate in an open jet wind tunnel. Grids are used to generate isotropic homogeneous turbulence. The leading edge serrations are in the form of sinusoidal profiles of wavelengths, λ, and amplitudes, 2h. The frequency and amplitude characteristics are studied in detail in order to understand the effect of LE serrations on noise reduction characteristics and are compared with straight edge baseline flat plates. Noise reductions are found to be insignificant at low frequencies but significant in the mid frequency range for all the cases studied. The flat plate results are also compared to the noise reductions obtained on a serrated NACA-65 aerofoil with the same serration profile. Noise reductions are found to be significantly higher for the flat plates with a maximum noise reduction of around 8 dB compared with about 5 dB for the aerofoil. In general, it is observed that the sound power reduction level (ΔPWL) is sensitive to the amplitude, 2h of the LE serrations but much less sensitive to the serration wavelength, λ. Thus, this paper sufficiently demonstrates that the LE amplitude act as a key parameter for enhancing the noise reduction levels in flat plates and aerofoils. Source

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