This paper summarizes the progress that has been made in the application of sound intensity techniques related to the research of sound transmission loss in building acoustics. The modern development of sound intensity instruments began with the discovery of the fast Fourier transform and with the develpoment of techniques for filtering electrical signals using digital techniques. It was only after these techniques became well established, that instruments and procedures for the determination of sound intensity became available for laboratory and in situ measurements. Applications for these instruments and procedures quickly followed and are still pursued today. In this paper some of these developments are discussed, with emphasis on those directly related to sound transmission loss in buildings.

Sound absorbing materials are extensively used in the field of noise control engineering and architectural acoustics. Indeed they are, for an important part, responsible for the efficient sound insulation of partitions between rooms and of enclosures, for the acoustic comfort in rooms and industrial halls etc. Due to the continuing technological progress, research has been done and is still done in the motorcar, the aerospace and the manufacturing industries and others, to obtain absorbing materials who are simultaneously small in volume, have a low density, are rather cheap and have a good acoustic performance. From the other side it is necessary to develop precise and, from time to time, sophisticated theoretical models which take into account the complex physical phenomena of acoustic materials.

When measuring the absorption coefficient of acoustic materials in a reverberation room a lot of changing parameters can cause considerable errors in all different frequency bands of interest. Although the ISO-354 standard, 'Measurement of the sound absorption in a reverberant room', specifies the most essential details to increase the accuracy of the measurement results, important differences yet occur in repeatability and reproducibility measurements of the absorption coefficient.This paper describes the measurement of the absorption coefficient of different types of absorbing materials with total different absorption performances, taking into account the influence of equipment control, source and microphone positions, diffusers versus diffusity, the position of the absorbing material within the room, and the change in configuration of the reverberation room.Although values of the absorption coefficient have been systematically evaluated with Sabine's and Eyring's formula, the presented results and comparisons are obtained from Sabine's equation.

The method of measuring the impedance of a ground surface based on the spatial Hankel transform, can be divided into three parts. First the pressure field is sampled on two horizontal lines near to the surface, from beneath a cylindrical symmetric sound source till infinity. Next a Hankel transform is performed on the data of each horizontal line. Finally the impedance of the surface for an incident angle ranging from 0 to 90 deg, is calculated. In practice, due to the finite maximum, measuring distance oscillations occur in the impedance curve as a function of angle of incidence. This effect can be avoided by using a spatial window before transforming the data. A Kaiser–Bessel window is selected to give the best results. A side effect of using a window is a shift from the real impedance values. Further improvement can be obtained by calculating more data points for a horizontal value larger than the maximum measuring distance. The method and its improvements will be illustrated with measurements on outdoor ground surfaces.

A model is formulated to evaluate the modification of the acoustic impedance of a layer of isotropic porous material due to a porous facing which has been set upon it. The cases of a facing bonded to the frame of the layer and of an unbonded facing are presented successively. Two different kinds of facings, porous plates and porous elastic membranes, are considered. The modelling is performed at oblique incidence with a matrix representation of the layer obtained from the Biot theory, and this model can be used in the case of stratified porous materials. Measurements are compared to prediction in the case of a heavy facing made of glass fibres.

The propagation of plane waves in layered media including fluid, solid and porous layers is modelled with transfer matrices, the three Biot waves being taken into account in the porous layers.

L'ouvrage reprend les exposes tenus lors d'une Journee d'Etudes consacreea la nuisance causee par le bruit de la circulation routiere. Dans un premier temps, on situe le probleme au niveau de l'amenagement et de la gestion de la voirie. Ensuite, on envisage la lutte a la source : la limitationde bruit emis par les vehicules et l'usage de revetements routiers silencieux. La partie suivante est consacree aux mesures permettant d'eviter la dispersion du bruit. Cette partie comporte des reflexions theoriques sur la propagation du bruit de la circulation routiere. Un resume reprend les possibilites. Un test in situ de l'efficacite acoustique des ecrans antibruit en vue de leur reception est effectue. L'ouvrage se cloture par un apercu des mesures neerlandaises sur base de cas pratiques et l'etude de mesures pratiques tendant a limiter le bruit de la circulation par une construction et un urbanisme adequats.

The acoustic impedance of layered porous materials can be calculated using the Biot theory and a matrix formalism to characterize each layer. A comparison with experimental data will be made for layered systems of various types, including layered systems covered with a membrane. The experimental data have been obtained with a two-microphone technique, which calculates the acoustic impedance from pressure measurements at two different microphone locations above the sample.

A matrix formalism will be presented to describe the propagation of plane compressional waves in layered, fluid-loaded materials using the Biot theory. The three Biot waves have been taken into account and measuring equipment to determine the different elastic parameters of porous materials has been established. The model is then extended to include fluid and solid layers. Due to the matrix formalism, the reflection and transmission of plane acoustic waves on an arbitrary number of layers can easily be calculated. The model will be compared with measured data of the acoustic impedance of a layered system and with results for the transmission through a solid/porous/solid system. The proposed model can also be used to calculate the acoustic impedance of soil surfaces, which can be considered as a number of layers on an elastic half-space.