Airborne noise calculation for single-layer partitions with the concentrated parameters method

The article considers an approach to the calculation of sound insulation for building partitions with the method of concentrated parameters at the standard frequency range, which is specified in regulatory documents. The concepts of “reduced” and “concentrated” masses are introduced for objects that are sound conductors. It is noted that the physical model of sound insulation in the three conditionally allocated frequency ranges of the standard spectrum has differences. The calculated equations of sound insulation for three frequency ranges are given. Systems of equations for obtaining the calculation formulas at the first and the second frequency ranges are used. The systems consist of equations for the conservation of the amount of motion and the conservation of kinetic energy. The influence of the damping effect of air and resonant phenomena in the plate on the final value of sound insulation is described. The nature of sound propagation in the third frequency range is considered, in which, unlike the first two sections of the frequency spectrum, where the propagation of flexural waves is mainly recorded in the plate, shear and dilatational vibrations have a predominant influence on the sound insulation level. Examples of graphs for massive partitions obtained by the considered method are given. The accuracy of the proposed method is evaluated in comparison with the normative code’s method and the method based on the theory of self-matching of sound fields. A general algorithm for calculating sound insulation in the entire standard frequency range is presented.

Wear and Airborne Noise Interdependency at Asperitical Level: Analytical Modelling and Experimental Validation

Generation of wear and airborne sound is inevitable during friction processes. Previously, the relationship between the wear and the sound has only been determined experimentally. Analytical models do exist, but they remain rare and do not fully account for the wear and the airborne sound generation especially at the asperitical level. This model attempts to fill the gap by providing a quantifiable relationship at an asperitical level between the wear generated and the sound emitted in a simple pin-on-disc setup. The model was validated for three materials (iron, mild steel, and aluminium T351) under two loads (10 N and 20 N) at 300 RPM. The theoretical model agrees with the experimental results with a varying error of 10 to 15% error in iron and aluminium. However, a larger error is observed in the case of mild steel. The model could be refined to improve the accuracy as it assumes point impacts on the asperities where a distributed impact would be more suitable. Furthermore, the pin is assumed a single asperity to simplify the model at the expense of accuracy. Overall, the experimental results are in good correlation with the theoretical results and this model provides the first step in quantifying wear using only the recorded sound pressure.

Loudspeaker-based sound reproduction for evaluating noise transmission into the car cabin

Virtual and laboratory-based design techniques can accelerate the development process over conventional prototype-and-field-test procedures. In car acoustics, the transmission of outside airborne noise into the cabin needs to be understood and managed. Here, we evaluate the accuracy of sound field recording and reproduction techniques for investigating the transmission of airborne noise into the driver's cabin of a car. Reference measurements of a real sound field, generated by a truck with idling engine to create a realistic scenario, were carried out in a semi-anechoic chamber. The reference sound field was recorded inside and around a test car. Additionally, a spatial recording of the reference sound field was carried out and used to reproduce the reference sound field over a loudspeaker array in a different, fully anechoic chamber, where the sound field was again measured inside and around the same test car. A comparison of the measured loudness inside the test car shows that this key parameter for sound quality could be reproduced rather faithfully over a loudspeaker array in a controlled testing facility.

Gauge repeatability and reproducibility study of airborne sound isolation measurements

A gauge repeatability and reproducibility study (GRR) uses analysis of variations (ANOVA) on an appropriately designed experiment to separate and quantify the components of the overall uncertainty. The authors have previously presented results of GRR studies of the measurement of airborne and impact insulation of floor-ceiling and demising wall assemblies in several apartment buildings, in which the uncertainty in the measurement method and the variability of the nominally-identical assemblies were compared. The results of two additional GRR studies on measurements of airborne noise isolation of wood stud demising walls are presented. The first study, like previous studies, evaluates the components of variance attributable to operator, repeatability, and part. The second study uses a fixed operator and part, and evaluates the variance due to loudspeaker type, position, and level on the measured noise reduction. The measurement standard (ASTM E336) gives limited guidance on the type and location of the loudspeaker used on the source side, and this study can inform whether changes in the standard with regards to the loudspeakers could reduce the uncertainty in measurement.

Noise Reduction by Rail Damper Tunable for Individual Rails in Curve

Tuned mass rail dampers are cost effective for the mitigation of the airborne noise and vibration with the ability to be tuned for individual site. TMDs have been developed and installed at a single rail in a curve tunnel and achieve more than 4dB(A) noise reduction in many cases. According to the on-site noise reduction performance during damper installation, half, one, two or three dampers can be installed at each spacing between two baseplates. TMDs with only half-installation provides more than 10dB reduction at vertical pin-pin resonance (~1kHz). With the standard installation, they provide the strong damping to half the corrugation growth rate. The stick-slip phenomena which causes the corrugation will be affected by the damping effect from TMDs. On the other hand, they can also be tuned to the low-frequency (p2 resonance) for grandborne noise control. The high reduction of the grand borne noise proved our claim for effectiveness of the TMDs besides many other studies on the other parameters like the type of the baseplates or the soil types. According to the test results TMDs achieve strong performance in different range of the frequencies.

Predictions of airborne noise between unit cabins by developing a cavity transfer matrix

The unit cabin has been used to construct internal ship space for improved efficiency and to reduce budgetary costs in shipbuilding. Because the cavity is placed between unit cabins, the noise of one room is transmitted through the sound insulating panel, the cavity, and the opposite sound-insulating panel. In this study, by developing a transfer matrix of the cavity between structures, airborne noise between unit cabins was predicted. A sandwich panel, which is usually used in ships, was employed to construct a double panel, and the sound insulation performance was confirmed by changing the thickness of the cavity. To improve the reliability of numerical results, they were compared with those from experiments conducted. The results showed that as the cavity size increases, the overall sound insulation performance improves. A parameter study was also conducted on the density, Young's modulus, thickness, and thickness ratio of the core of the sandwich panel. To improve the sound insulation performance, increasing the density of the core is preferable to increasing the core thickness. The panel thickness ratio should be increased to avoid performance degradation as a result of the resonance frequency.