Significance and reliability of absorption spectra of quiet pavements

The objectives and scope of the study described into this paper were to compare different methods to assess (measure or predict) the acoustic properties of a pavement in order to derive information about use in practical applications. To this end, in-lab Kundt tube, on-site Kundt tube, Adrienne device and theoretical modelling were used. Based on measurements, absorption spectra were derived. Analyses and results focused also on composite indicators, first-pick frequencies and objective functions. Based on results, when fitting experimental data through theoretical models the least square method is unsatisfactory and alternative algorithms are proposed. The on-site Adrienne method provides a good estimate of thickness, tortuosity, resistivity and maximum, while in-lab impedance tube, even if quite time consuming, seems to achieve the best accuracy. The on-site Kundt tube provides a satisfactory estimate of porosity and further investigations and analyses are recommended to investigate its use also for porous surfaces. Future research will address two competing needs which emerged from the study: i) the need for simplifying the procedures/methods; ii) the need for improving the quantity of information gathered (e.g., texture), through the same device.