Measurements Of Sound Reduction Index Research Articles

Vibroacoustic metamaterial for enhanced Sound Transmission Loss with variable frequency range designed for serial production

Recently, vibroacoustic metamaterials have been broadly investigated, especially for noise and vibration mitigation. By creating a band gap effect in flexural wave propagation in a base element, metamaterials improve its vibroacoustic parameters in low and mid frequency range while preserving low mass and structure dimensions. While the foundational assumptions and lab validations highlight the advantages of these metamaterials, the practical application of these structures in real-world scenarios remains a challenge. The main aspect that is widely investigated is achieving maximum effectiveness while maintaining the simplicity of geometry to optimize mass production costs. This work presents a vibroacoustic metamaterial design with geometry adapted to serial production using injection molding. The proposed geometry allows for adjusting the effective frequency range of the structure after the production process. Due to the distinctive configuration of the elements and the grouping of unit cells, the design facilitates the generation of broadband and multi-band structures as well. Numerical simulations were employed to assess the impact of the proposed metamaterial on Sound Transmission Loss and other vibroacoustic parameters. Experimental validation of prototype effectiveness was conducted through Sound Reduction Index measurements in a diffuse field.

Changed sound properties due to minor construction changes in a lightweight building

This paper relates to building acoustic measurement inside a two‐story office house. The construction, which is known as lightweight, is prefabricated in volumes at a factory and is then transported to the building yard for assembling. It is build up of a wooden frame with particle boards and plaster boards attached. The building consists of a number of nominally, or almost nominally, identical rooms with assumed identical sound properties. In the projection stage, the construction was slightly modified in some of the rooms in order to see in what way the sound properties would be affected. In total eight impact sound pressure level measurements and eight sound reduction index measurements were performed and analysed for the different setups.

On the sound insulation of masonry wall façades

In this paper, laboratory measurements of sound reduction index for two types of cavity walls commonly used in façades are presented. The first type consists of “masonry–air cavity–brick” and the second one consists of “masonry–air cavity–-gypsum board”. Data are used to show that masonry walls with gypsum boards provide higher sound insulation than masonry cavity walls. The influence on sound reduction index of apertures made on external leaf of the wall to ventilate the cavity of the wall is also examined.

AN EXPERIMENTAL INVESTIGATION OF ACOUSTIC PARAMETERS OF THE LABORATORY FOR MEASURING SOUND INSULATION OF BUILDING ELEMENTS/STATINIO ELEMENTŲ GARSO IZOLIACIJAI MATUOTI SPECIALIAI ĮRENGTOS LABORATORIJOS AKUSTINIŲ PARAMETRŲ TYRIMAS IR DERINIMAS

The report deals with a task of investigating and adjusting acoustic parameters of the reverberant chambers of recently built laboratory for measuring sound insulation properties of building elements (windows, doors). The reverberation time values in the source and receiving empty rooms were measured at 16 one-third-octave frequency bands. It was determined that they significantly exceed the recommended ones. After a number of measurements the reverberation time was adjusted to the allowable limits. An optimum combination of loudspeaker positions in the source room with respect to the best acoustic field diffusivity has been experimentally found. Repeatability values r were calculated from the measurements of sound reduction index of plastic window conducted under repeatability conditions. At the 16 one-third-octave frequency bands they show a good precision of the test equipment.

AN EXPERIMENTAL INVESTIGATION OF ACOUSTIC PARAMETERS OF THE LABORATORY FOR MEASURING SOUND INSULATION OF BUILDING ELEMENTS

Summary The report deals with a task of investigating and adjusting acoustic parameters of the reverberant chambers of recently built laboratory for measuring sound insulation properties of building elements (windows, doors). The reverberation time values in the source and receiving empty rooms were measured at 16 one-third-octave frequency bands. It was determined that they significantly exceed the recommended ones. After a number of measurements the reverberation time was adjusted to the allowable limits. An optimum combination of loudspeaker positions in the source room with respect to the best acoustic field diffusivity has been experimentally found. Repeatability values r were calculated from the measurements of sound reduction index of plastic window conducted under repeatability conditions. At the 16 one-third-octave frequency bands they show a good precision of the test equipment.

Scale Model Investigation on the Influence of Boundary Conditions on the Airborne Sound Insulation of Lightweight Double Walls

Sound reduction index measurements were performed inside a 1:10 scale model of two adjoining rooms of a test facility in an acoustic laboratory, with the aim of investigating the influence of the boundary conditions on the acoustic performance of lightweight double walls. The model was built entirely of polymethyl methacrylate (PMMA). The specimen double walls were built using the same acrylic material. At first, measurements were performed on a single homogeneous panel, in order to check the reliability of the whole procedure and the repeatability of the measurements. A good correspondence was found between theoretically calculated values and measured values of the sound reduction index above the critical frequency. A second set of measurements was carried out on model double walls comprising two leaves, connected to each other only by a border frame running along the whole wall perimeter. It was found that the effect of the border frame is a reduction of the performance of the double wall, to under that of a single plate with the same total surface mass. A third set of measurements was carried out inserting vertical studs to connect the two leaves. It was found that the presence of the studs causes a general decrease of the sound reduction index values and a decomposition of the critical frequency. A fourth set of measurements was carried out on the same double wall using border frames made of different materials. The experimental results show that damped materials (wood, rubber) give a better performance than rigid materials (acrylic, aluminium).