Gerrit Vermeir

Low-frequency airborne sound transmission through single partitions in buildings

Abstract The low-frequency (20–250 Hz) airborne sound transmission of single partitions is investigated. Three theoretical models are used for the prediction: an infinite plate model, a baffled plate model and a room-plate-room model. The calculation models are verified by detailed comparisons with experimental results obtained in the laboratory. A parametric study is carried out to examine the influence of the dimensions of the room and the partition. The results demonstrate the strong modal behaviour of the lowfrequency sound transmission. As a result, the low-frequency sound insulation depends not only on the properties of the test wall but also on the geometry and the dimensions of the room-wall-room system. In general, the large variation of the low-frequency insulation compromises the accuracy of prediction of the sound insulation in situ.

Measuring the free field acoustic impedance and absorption coefficient of sound absorbing materials with a combined particle velocity-pressure sensor

Acoustic surface impedance of sound absorbing materials can be measured by several techniques such as the impedance tube for normal impedance or the Tamura method for normal and oblique surface impedance. In situ, the acoustic impedance is mostly measured by use of impulse methods or by applying two-microphone techniques. All these techniques are based on the determination of the sound pressure at specific locations. In this paper, the authors use a method which is based on the combined measurement of the instantaneous sound pressure and sound particle velocity. A brief description of the measurement technique and a detailed analysis of the influence of the calibration, the source type, the source height, the sound incidence angle, and the sample size are included.

Frame-borne surface waves in air-saturated porous media

A Rayleigh-type surface wave at an air–air saturated porous layer interface is predicted and detected experimentally in the audible frequency range. Applications of this surface wave for the metrology of sound-absorbing media are suggested.

Sound transmission through finite lightweight multilayered structures with thin air layers

The sound transmission loss (STL) of finite lightweight multilayered structures with thin air layers is studied in this paper. Two types of models are used to describe the vibro-acoustic behavior of these structures. Standard transfer matrix method assumes infinite layers and represents the plane wave propagation in the layers. A wave based model describes the direct sound transmission through a rectangular structure placed between two reverberant rooms. Full vibro-acoustic coupling between rooms, plates, and air cavities is taken into account. Comparison with double glazing measurements shows that this effect of vibro-acoustic coupling is important in lightweight double walls. For infinite structures, structural damping has no significant influence on STL below the coincidence frequency. In this frequency region, the non-resonant transmission or so-called mass-law behavior dominates sound transmission. Modal simulations suggest a large influence of structural damping on STL. This is confirmed by experiments with double fiberboard partitions and sandwich structures. The results show that for thin air layers, the damping induced by friction and viscous effects at the air gap surfaces can largely influence and improve the sound transmission characteristics.

Designing spaces for every listener

Inclusive design aims at objects and environments that are accessible, usable and comfortable for all people throughout their entire lifespan. In architecture, this aim is usually associated with physical accessibility. Yet acoustic qualities may considerably impact usability and comfort as well, especially in spaces for listening. This case study explores the notion of acoustic comfort for all in the context of university education. One auditorium, situated in a historic building and subject to renovation in the near future, is studied in detail: acoustic obstacles are identified in collaboration with user/experts and are measured in situ; specific interventions are proposed in consultation with building professionals, technicians and conservation specialists and are tested using dedicated acoustic simulation software. The study draws attention to the importance of acoustic comfort for all and offers a first view of which solutions are possible and desirable and how these can be obtained.

Development of a hybrid wave based–transfer matrix model for sound transmission analysis

In this paper, a hybrid wave based-transfer matrix model is presented that allows for the investigation of the sound transmission through finite multilayered structures placed between two reverberant rooms. The multilayered structure may consist of an arbitrary configuration of fluid, elastic, or poro-elastic layers. The field variables (structural displacements and sound pressures) are expanded in terms of structural and acoustic wave functions. The boundary and continuity conditions in the rooms determine the participation factors in the pressure expansions. The displacement of the multilayered structure is determined by the mechanical impedance matrix, which gives a relation between the pressures and transverse displacements at both sides of the structure. The elements of this matrix are calculated with the transfer matrix method. First, the hybrid model is numerically validated. Next a comparison is made with sound transmission loss measurements of a hollow brick wall and a sandwich panel. Finally, numerical simulations show the influence of structural damping, room dimensions and plate dimensions on the sound transmission loss of multilayered structures.

Numerical investigation of the repeatability and reproducibility of laboratory sound insulation measurements

An extensive parametric study has been carried out with a wave based model to numerically investigate the fundamental repeatability and reproducibility of laboratory sound insulation measurements in the frequency range 50-200 Hz. Both the pressure method (according to ISO 10140-2) and the intensity method (according to ISO 15186-1 and ISO 15186-3) are investigated. The investigation includes the repeatability of the different measurement procedures, which depends on the influence of the microphone positions and the source position. The reproducibility of the sound insulation measurements in different test facilities is studied by looking at the influence of geometrical parameters like room and plate dimensions, aperture placement and aperture thickness. The results show that for small-sized test elements, the reproducibility of the intensity method is better. For heavy walls and lightweight double constructions, however, the predicted uncertainty is similar for the three measurement methods. The results of the reproducibility study are also used to investigate systematic differences between the pressure method and both

Free field measurements of the absorption coefficient for nonlocally reacting sound absorbing porous layers

A simple asymptotic approximation with two parameters (the plane wave reflection coefficient and a correction factor) has been derived by Brekhovskikh and Godin [Acoustics of Layered Media II. Point Sources and Bounded Beams (Springer, New York, 1992)], for the spherical field reflected by nonlocally reacting surfaces. In the present work, an expression for the correction factor is obtained for the case of a homogeneous and isotropic porous layer. A free field method for evaluating reflection and absorption coefficients with this approximation is presented. The evaluation of the absorption coefficient at normal incidence is performed on a porous layer on a rigid backing, and compared to measurements performed using a two microphone technique and an impedance tube.

Prediction of the sound field above a patchwork of absorbing materials

The aim of this paper is to investigate the acoustic performance of sound absorbing materials through a numerical wave based prediction technique. The final goal of this work is to get insight into the acoustic behavior of a combination of sound absorbing patches. In order to address a wide frequency range, a model based on the Trefftz approach is adopted. In this approach, the dynamic field variables are expressed in terms of global wave function expansions that satisfy the governing dynamic equations exactly. Therefore, approximation errors are associated only with the boundary conditions of the considered problem. This results in a computationally efficient technique. The main advantage of this method is the fact that the sound absorbing patches do not have to be locally reacting. In this article, the wave based method is described and experimentally validated for the case of normal incidence sound absorption identification in a standing wave tube. Afterwards, the method is applied to simulate some interesting setups of absorbing materials.

Diffuse transmission of structure-borne sound at periodic junctions of semi-infinite plates

Vibration attenuation at junctions of point connected plates is an important aspect of structure-borne sound transmission in many realistic structures. The vibrational response of point connected plates can be predicted using statistical energy analysis (SEA), where coupling loss factors are calculated based on mobility formulations. However, in the process of deriving the coupling loss factors for point connected systems, a number of assumptions and simplifications were introduced. In this paper, a more advanced calculation model, based on a wave approach for elastically coupled semi-infinite plates, is presented. Local rigid connections are modeled using an elastic interlayer characterized by a space-dependent stiffness. Periodic boundary conditions are assumed at the junction and the plate response is described using a Fourier decomposition technique. Calculation results obtained for two different junction geometries demonstrate the influence of the distance between the point connections on the structu...