Sound Pressure Levels In Rooms Research Articles

Comparison of measurement methods of room sound energy for sound insulation performance evaluation at low frequencies

In the field measurement of acoustic performances, such as sound insulation and floor impact sound insulation, sound pressure level is usually measured to find the sound energy in a closed space. However, the sound pressure level at low frequencies such as the 63 Hz band depends on the measurement position due to the influence of the room eigenmodes, which leads to large uncertainties of the measured average sound pressure levels in rooms. In this study, several measurement methods of sound energy were applied to the low-frequency sound field of a mock-up room that simulates a source room in an RC apartment. Along with the standard sound pressure level measurement, the low-frequency procedure according to ISO 16283 series and acoustic energy density measurement using the combined particle velocity-pressure sensor were conducted, and their accuracies were evaluated based on the average sound pressure obtained by the grid-point measurement over the entire room.

Coupling Coefficient of Flux Density and Density Gradient of Reflected Sound Energy in Quasi-Diffuse Sound Fields

Sound pressure levels in rooms are determined by the energy of direct sound and the energy generated by reflections of sound from enclosures. In some areas of a room, the reflected sound energy exceeds the energy of the direct sound. For this reason, calculations of the energy characteristics of reflected sound energy are of great importance. In most rooms, the reflection of sound from enclosures has a specular-diffuse character. In this case, one part of the reflected energy transferred by specular reflected waves is distributed according to the laws of geometric acoustics, and the other part, scattered diffusely, according to Lambert’s law. The calculation of the specular component of the reflected energy is made by the methods of ray tracing, and the scattered energy is calculated by the statistical energy methods developed by the authors for the quasi-diffuse sound fields of the rooms. The basis of the latter methods is the relationship between the flux density of reflected sound energy and the density gradient of this energy. The accuracy of these methods depends on the accuracy of the adopted value of the coupling coefficient between the flux density and the density gradient of the reflected sound energy. Currently, there are different ideas about its magnitude. The paper presents the results of studies of coupling coefficients with regard to space-planning and acoustic characteristics of premises. The investigations were carried out using Kuttruff’s integral equation. Based on the results obtained, recommendations are given on the choice of the coupling coefficient.

Sound Pressure Levels in Rooms: A Study of Steady State Intensity, Total Sound Level, Reverberation Distance, a New Discussion of Steady State Intensity and Other Experimental Formulae

Sound Pressure Levels in Rooms: A Study of Steady State Intensity, Total Sound Level, Reverberation Distance, a New Discussion of Steady State Intensity and Other Experimental Formulae

Sound Pressure Levels in Rooms: A Study of Steady State Intensity, Total Sound Level, Reverberation Distance, a New Discussion of Steady State Intensity and other Experimental Formulae

In this publication we include all, or almost all, the valid formulas of sound levels in different types of rooms. We will explain all the theoretical basis of each of them, starting with reflected intensity, both classical and revised theories, the total sound level and its uses in concert venues. We will also deal with empirical formulas mainly for classrooms, churches and religious buildings and industrial use. However, the main significance of this work is not only the wide range of formulas exposed but also that we have found the explanation of why the reverberation radius, or distance radius, cannot exist in the revised theory. This finding can help that the revised theory of M. Barron be slightly modified to apply it to any room for several uses, other than concerts

On the efficacy of spatial sampling using manual scanning paths to determine the spatial average sound pressure level in rooms

In architectural acoustics, noise control and environmental noise, there are often steady-state signals for which it is necessary to measure the spatial average, sound pressure level inside rooms. This requires using fixed microphone positions, mechanical scanning devices, or manual scanning. In comparison with mechanical scanning devices, the human body allows manual scanning to trace out complex geometrical paths in three-dimensional space. To determine the efficacy of manual scanning paths in terms of an equivalent number of uncorrelated samples, an analytical approach is solved numerically. The benchmark used to assess these paths is a minimum of five uncorrelated fixed microphone positions at frequencies above 200 Hz. For paths involving an operator walking across the room, potential problems exist with walking noise and non-uniform scanning speeds. Hence, paths are considered based on a fixed standing position or rotation of the body about a fixed point. In empty rooms, it is shown that a circle, helix, or cylindrical-type path satisfy the benchmark requirement with the latter two paths being highly efficient at generating large number of uncorrelated samples. In furnished rooms where there is limited space for the operator to move, an efficient path comprises three semicircles with 45°-60° separations.

Reception plate method for characterisation of structure-borne sound sources in buildings: Installed power and sound pressure from laboratory data

In a companion paper, a laboratory method is described to obtain the structure-borne sound power of machines before they are installed in heavy-weight buildings. The laboratory method is based on the concept of the reception plate. In this paper, the method is shown to provide appropriate input data for the prediction of the installed structure-borne power, and thence the resultant sound pressure level in rooms removed from the room containing the machine. Case studies of two common sources are described: a whirlpool bath and a water cistern. It is shown that the method can be incorporated into recently proposed standard prediction models and that sound pressure levels in buildings can be predicted.

Calculation of temporal evolution of sound pressure levels in rooms, based on diffuse reflection

This paper describes a model which enables the temporal evolution of sound pressure levels in rooms to be calculated. It is built on the assumption that sound waves are totally scattered when reflected by the walls. This model prescribes the sampling of all the surfaces of the room and defines a process of time discretization, process which enables the temporal evolution of energetic exchanges between each sample to be known. Ultimately, the model allows the sound pressure level to be calculated in every point of the room for each time sample Δt (echograms). Thanks to the echograms, some useful criterias for room acoustic studies can be evaluated : reverberation time, EDT, D50, C80,... Measurements and calculations have been carried out for different kinds of rooms. We will describe them in the second part of this paper.

Comparisons of predicted steady-state levels in rooms with extended- and local-reaction bounding surfaces

A combined beam-tracing and transfer-matrix model for predicting steady-state sound-pressure levels in rooms with multilayer bounding surfaces was used to compare the effect of extended- and local-reaction surfaces, and the accuracy of the local-reaction approximation. Three rooms—an office, a corridor and a workshop—with one or more multilayer test surfaces were considered. The test surfaces were a single-glass panel, a double-drywall panel, a carpeted floor, a suspended-acoustical ceiling, a double-steel panel, and glass fibre on a hard backing. Each test surface was modeled as of extended or of local reaction. Sound-pressure levels were predicted and compared to determine the significance of the surface-reaction assumption. The main conclusions were that the difference between modeling a room surface as of extended or of local reaction is not significant when the surface is a single plate or a single layer of material (solid or porous) with a hard backing. The difference is significant when the surface consists of multilayers of solid or porous material and includes a layer of fluid with a large thickness relative to the other layers. The results are partially explained by considering the surface-reflection coefficients at the first-reflection angles.

Application of acoustic radiosity methods to noise propagation within buildings

The prediction of sound pressure levels in rooms from transmitted sound is a difficult problem. The sound energy in the source room incident on the common wall must be accurately predicted. In the receiving room, the propagation of sound from the planar wall source must also be accurately predicted. The radiosity method naturally computes the spatial distribution of sound energy incident on a wall and also naturally predicts the propagation of sound from a planar area source. In this paper, the application of the radiosity method to sound transmission problems is introduced and explained.

Transmission of sound through suspended ceilings from HVAC terminal units

An ASHRAE project to investigate factors determining the sound pressure levels in rooms below ceilings concealing air-terminal units has been completed. Four terminal units installed close to the six ceiling types used were the major noise sources. They were supplemented by two simulators powered by loudspeakers. Sound power was measured for each device in the 156 cubic meter test room in its reverberant condition. The levels in the room were measured for each combination of source and ceiling tile. Sound pressure level was measured as a function of distance from two sources in the room below. The main intent of the project was to validate ARI Standard 885 which provides a calculation method for such situations. Differences among ceiling types were less than expected; leakage around the edges of each panel is a dominant transmission path. Ceiling attenuations at low frequencies were found to depend on the area of the lower face of the units. Sound levels in the room were essentially uniform when the source was above the ceiling. The decay of sound with distance from the sources below the ceiling was found to depend on the inverse of the room reverberation time.

Experimental evaluation of the accuracy of the Sabine and Eyring theories in the case of non-low surface absorption

The Sabine and Eyring diffuse-field theories are often used to predict the sound decay/reverberation time and steady-state sound-pressure levels in rooms. The Sabine theory can be considered to be an approximate version, valid for low surface absorption, of the Eyring theory, in principle valid for any surface absorption values. However, some practitioners believe that the Sabine theory is accurate for any absorption value. Further, there is some debate as to whether or not a 1−α factor should be included in the reverberant sound-pressure term of these theories. Experiments were done, in a 1:2.5 scale model reverberation room with surfaces of varying absorption. The results were compared with predictions by various versions of the Sabine and Eyring theories in order to evaluate their accuracies in the case of non-low surface absorption. It is concluded that the 1−α factor must be included to obtain accuracy. Eyring, but not Sabine, predictions were found to agree well with experiment, suggesting that only the Eyring theory can be accurate in the case of non-low absorption.

Equivalent absorption coefficient: A parameter for room sound pressure level prediction

The development of an equivalent absorption coefficient is described. Its use facilitates the calculation of A-weighted sound pressure levels in rooms. Thus for the modelling of the acoustic field only one set of calculations need to be performed rather than a separate one for each octave band and eventual A-weighted summation.

Recent advances in the understanding of acoustic transmission through the walls of air conditioning ductwork

Acoustic noise transmission through the walls of air conditioning ductwork has long been a neglected aspect of HVAC acoustics, but two recent ASHRAE-sponsored research projects have done much to rectify the situation. The results of this work are described here, and include both experimental data and prediction methods concerning interior/exterior noise transmission (“breakout”) through the walls of plain, unlined rectangular, flat-oval, and circular ducts; the measured and predicted breakout insertion loss (IL) of external acoustic wall lagging on ducts of these three geometries is also discussed. Noise transmission into ducts (termed “breakin”) is of importance too, and a simple theoretical treatment is available, enabling the breakin transmission loss (TL) of the duct walls to be found from the breakout TL. In addition, the calculation of sound pressure levels in rooms, from duct wall radiation, is discussed here. The prediction methods of the wall TL of rectangular and flat-oval ducts are simple to use and are fairly reliable; circular ducts are, however, difficult to cope with at present. The prediction of the IL of lagging on all duct geometries is straightforward and reasonably accurate. The “state of the art” in duct wall radiation is also discussed here.