An in situ method of determining sound-insulation properties of locally responding materials

The paper presents a new method for determining sound insulation that is based on insonifying the test material with a point sound source and measuring acoustic field directly above the test material using a microflown capable of simultaneously recording pressure and velocity, and acoustic pressure on the hard base on which the material is placed. The local response requirement for the material proceeds from limitations of the transfer matrix method, which is used for calculating sound insulation. Since the material does not require any special processing, while the measurements are taken with material staying in its natural position on a hard wall, such method of study is known as an in situ method (performed on site). The results of tests on such materials as foam rubber used for aeronautical applications and Lamkotek demonstrated that sound-insulation curves obtained using the proposed method were in good agreement with experimental data obtained in an impedance tube and theoretical calculations of sound insulation of the materials in the frequency range of the materials local response. It is worth noting that the proposed method provides a much better approximation of the sound-insulation curve of the materials than experimental data obtained using the method of two loads in an impedance tube, attributed to the absence of shear waves in the material that appear when the material is clamped between the walls of the tube to provide sealing, and that is where the key advantage of the in situ method lies.