An active control method for the spectral homogenization of airborne sound insulation laboratories at low frequencies

Abstract

Low frequency sound insulation measurements are affected by large uncertainties and inaccuracies due to the low modal density of small laboratory rooms. For this reason, an automated measuring system for the active spectral homogenization of enclosed spaces at low frequencies has been developed. The aim is to achieve a quasi-diffuse field, reducing the amplitude of room modes, in order to apply standard procedures for sound insulation measurements at low frequencies. The homogenization method is based on the active control of the interference spatial patterns of a system of two loudspeakers using a phase steering technique. The room response spectrum, as function of frequency-dependent phase difference between source signals, is measured in different positions in order to achieve the optimal spectral homogenization. Such technique allows to decrease the modal sound pressure level fluctuations in the source and receiving volumes in the frequency range between 30 Hz and 120 Hz. Based on this, sound insulation measurements at low frequencies on a high performance triple glazing and steel structure are performed and compared with standard ones.