Building Acoustics

Speech intelligibility is usually evaluated, by the use of objective parameters, in unoccupied rooms due to practical considerations. However, under normal conditions, the room occupancy can increase or decrease the values of speech intelligibility by the effect of the additional sound absorption present in the room or by the change in S/N ratio. Measurements were carried out in six churches with and without occupancy. The results show that occupancy induces a mean increase for the speech intelligibility of ∆STI (STIoccup- STIunoccup) of 0.050 with the use of a public address system (PA) and 0.035 without a PA. This increase is caused mainly by the reduction of the room reverberation time, due to the increased sound absorption and by the reduction of the additional RT induced by the PA (using loudspeakers with strong directivity oriented towards the congregation area). The variations in the speech intelligibility values with occupancy can be predicted in churches by employing new empirical formulations. The decrease in S/N ratio (due to the background sound level augmentation by the presence of people and by sound level decrease with distance in the congregation area), or the poor directivity and orientation of the sound sources, could reduce the speech intelligibility gain in particular cases. Other effects induced by the congregation, such as the variations of humidity and temperature, generally have negligible effect on speech intelligibility.

This paper outlines and evaluates a non-destructive experimental technique used to obtain in-situ measures of the real part of the bending wavenumber in the two principal directions of a wood joist floor. In-situ measured wavenumbers are compared to those obtained from beam samples cut from the floor sheathing to identify the frequency range when the joists significantly affect vibration response in the floor sheathing. Wavenumber measurements confirm the highly orthotropic nature. Measurements indicate that the wavenumbers in the direction parallel to the joists are a function of location between the joists. Lower wavenumbers in this direction can be expected closer to the joists. Some discussion is given regarding the rates of attenuation with distance that can be expected parallel and perpendicular to the joists given the variation in wavenumbers, however this will be the topic of a separate paper, Part 2.

Structure-borne sound transmission at a subfloor/joist connection typical of wood frame buildings is investigated experimentally and theoretically. The first part of this paper investigates the influence of the fastener spacing on the vibration attenuation across a joist. For this purpose, measurements were carried out on a small floor section for various coupling conditions of the joist. The experimental results suggested the existence of an effective coupling area characterizing the screwed joist/floor connection. In the second part of this study, a calculation model is developed based on Statistical Energy Analysis (SEA) and plate strip theory for the idealized case of a rigid line connection. The presented model is verified experimentally on a Plexiglas structure and a subfloor/joist connection. The experimental validation showed fair agreement between measured and calculated data, but revealed that more work is required to improve the prediction accuracy in realistic situations.

Direct and indirect measurements of the vibration response of several wood-framed walls and floors were made. The data indicate that these building elements do not behave like a homogeneous and isotropic system but rather exhibit a response typical of a periodic plate/beam structure. There is localization of energy near the excitation point and very strong attenuation with distance in the direction normal to the framing members. This region of high attenuation is followed by one of considerably reduced attenuation. A systematic study of a floor/ceiling assembly indicated that the onset of this second attenuation region was caused by the presence of a butt joint in the plate. It is speculated that the weak bending-to-bending coupling caused by the butt joint reduced the bending energy enough so that wave conversion from in-plane to bending at each plate/beam joint accounted for the presence (and in some cases near-constant level) of bending energy after the butt joint.

This article presents the results of an acoustic study in open premises in banks, where the main problem is to guarantee the confidentiality of the conversations between the customers and the bank advisor. The open architectural concept considered here is a generalisation the “Garden office”: although it does give concrete expression to the desire for openness and availability to the public, it poses new difficulties on an acoustic level. How can we in fact avoid the conversations being heard in an area that has neither doors nor complete partitions and for which the main characteristic is precisely to have as few partitions as possible? Based on measurements carried out in premises of this type, we have been able to establish the quantities that best characterise the situation. We observed that the intelligibility still remained good despite the attenuation brought about by the addition of screens, which obviously meant that the confidentiality could not be guaranteed. Once this was established, a certain amount of acoustic layouts were defined – which should already be defined during the pilot phase - that were able to reconcile the need for openness to the public with the confidentiality of the conversations.

Modifications to the New Zealand Building Code are currently being considered, which may create a requirement to assess impact noise horizontally not just vertically. The test would be similar to vertical tests as described in ISO 140-7:1998, but sound pressure levels are proposed to be measured instead in the closest living space in an adjacent apartment which shares a common floor system. This work seeks to identify and validate different mathematical and computational methods for predicting the results of horizontal impact tests. Three methodologies were tested: finite element method software, statistical energy analysis and an analytical solution derived from the governing partial differential equations. These methods were applied to two different floor systems: a concrete double tee floor and a concrete floor supported by concrete beams and columns. Limitations were found for all of the methods, and caution is advised when using these to design to horizontal impact noise criteria.

The goal of this letter is to comments on the article "Empirical Prediction of Speech Levels and Reverberation in Classrooms" by Hodgson (2001). Hodgson proposed an empirical equation for prediction of classroom early decay time. Hodgson EDT equation with regard to the classroom ceiling height was theoretically discussed and it was concluded that when a classroom ceiling height is decreased or increased, it is not reasonable to judge about the acoustical condition of the new space based on the Hodgson EDT equation if the average absorption coefficient of the additional walls is equal to the average absorption coefficient of the original space.

The new Brazilian building performance standard is a landmark in terms of housing regulation in Brazil. Nevertheless, due to the standard recent release, it becomes essential to make its requirements compatible with users’ needs. This work has the objective to evaluate the acoustic performance requirements of buildings based on the users’ perceptions of acoustic comfort. In order to do this, field tests were performed and surveys were applied to the users. The results demonstrate that the requirements defined by the Brazilian norm are unsuitable to meet the users’ necessities. The correlation analysed shows a clear perception of the habitants in relation to the transmitted noise through the slabs and walls. These unsatisfactory results concern the acoustic performance of impact noise between slabs, as well as internal and external walls, showing that construction companies must implement new solutions that can provide greater acoustic performance to achieve acoustic comfort to the users.

ISO 16251-1 standard describes an alternative method for the experimental obtaining of acoustic parameters reduction of the impact sound pressure level ( ΔL) and weighted reduction of the impact sound pressure level ( ΔL w ) for soft floor coverings through vibration measurements on a small floor mock-up. The application of the methodology to floating floor systems is of great interest, since, compared to the conventional method (ISO 10140-3), it is less costly and would require smaller specimens. However, previous studies have revealed an influence of the modal behavior of the slab on the sound insulation in the frequency range, causing the ΔL curves to show abrupt oscillations (peaks and valleys), thus deviating from the reliable insulation values and decreasing their accuracy. This study proposes the use of ISO 16251-1 for the evaluation of floating floor systems investigating the main factors that influence the accuracy of laboratory tests and the performance of the devices, namely dynamic stiffness of the resilient layer, total loss factor, and dimensions in the floating slab area. The results of ΔL and ΔL w obtained according to ISO 16251-1 were compared to those of two analytical models and the conventional method for 17 samples of floating mortar screeds of 0.96 and 0.36 m ² areas, 10.8–340.6 MN m ⁻³ dynamic stiffness, and 0.04–0.39 total loss factor. The 0.96 m ² samples showed less abrupt oscillations in the ΔL curves than those of 0.36 m ² , and the oscillations recorded for resilient layers of above 68.4 MN m ⁻³ stiffness were minimal when the larger floating slab was used.

The acoustical characteristics of a room are traditionally determined using omnidirectional impulse response measurements, yielding information about sound reflections in terms of magnitude and time, but not direction. However, the direction of reflections is often important, and thus the need for a practical, low cost measurement system for determining this. In this paper we present the performance of a low cost measurement system utilising an inexpensive microphone array, namely the Core Sound TetraMic, for the determination of 3D room impulse responses. These can then be visualised, for example, as a "hedgehog pattern". Experiments undertaken in an anechoic chamber indicate that the accuracy of directional estimation of this system is in the region of ± 7.5°.

The Auditorio 400 is a new auditorium located inside the National Museum "Centro de Arte Reina Sofia" in Madrid. It is the work of the renowned French architect Jean Nouvel. This hall has acoustic problems derived from its innovative style and from the use of its space for multiple events. For these reasons, an acoustical study was carried out in order to analyse these problems and to provide solutions to the deficiencies found without the need of large structural and aesthetics changes to the current design by Jean Nouvel. This paper presents the results of the sound pressure level measurements inside the hall, as well as a survey carried out to evaluate the location of the acoustic problems. Finally, the survey presents the interesting coincidences between objective measures and subjective opinions.

This article will describe the different acoustic problems identified in Auditorio 400 and possible solutions to these acoustic deficiencies using variable acoustic systems such as movable panels with different absorption coefficients and reflectors suspended from the ceiling. Due to the various types of events that take place in this hall, the Auditorio 400 must have proper acoustics for speech as well as music presentations and concerts, and this implies different configurations of sound sources. The auditorium has an innovative style and the solution presented in this article maintains this architectonic and aesthetic style while still improving the acoustics of the venue.

The work reviews the design aspects related to window glazing constructions for combating the low frequency noise radiated by vehicular traffic and assimilates them in a cause and effect diagram. An experimental investigation is conducted in Reverberation chambers on various window glazing configurations to ascertain the performance of various parameters viz., depth of air space and effect of lamination on sound insulation characteristics. A pronounced dip attributed to mass-air-mass resonance consistent with theoretical formulation is observed when air gap is less that 30 mm in double glazings. Significant increase in (Rw+Ctr) value is observed in a sandwich constructions with 85 mm air gap or in sandwich constructions with either one double glazing or both are double.

Noise control is essential in an enclosed machine room where the noise level is regulated by the occupational safety and health act. In order to overcome noise hybridized by a direct and reverberant sound wave, a sound absorber in conjunction with an acoustical enclosure has been used. However, the traditional method for designing a sound absorber and an acoustical enclosure has proven to be time-consuming. In order to efficiently control the noise level specified by the Environmental Protection Agency, interest in shape optimization of a sound absorber as well as acoustical enclosure is coming to the forefront. In this paper, the numerical technique of particle swarm optimization ( PSO) in conjunction with the theoretical sound propagation model and the method of minimized variation square are applied in the following numerical optimizations. Before noise abatement is carried out, the accuracy of the mathematical model in a single-noise enclosed system will be checked by SoundPlan (a professional simulation package). Moreover, the noise abatement of five kinds of multi-equipment machine rooms using the PSO method has been exemplified and fully explored. The results reveal that both the acoustical panel and the acoustical enclosure can be precisely designed. Consequently, this paper may provide an efficient and rapid way of depressing both the direct and reflected sound wave by using a well-designed acoustical panel and acoustical enclosure in a complicated sound field.

One common method of obtaining the absorption properties of a sample of material is to measure the decay of sound in an enclosure partially lined with the sample. In order to infer absorption coefficients from decay rate measurements, it is assumed that the sound field in the enclosure is diffuse. When measurements are made in enclosures which are small compared with wavelength, and contain non-uniform absorption, the diffuse field may no longer be three-dimensional in nature. Descriptions are given of measurements made in a small rectangular enclosure with one surface lined with highly absorbent material, and the results presented. Predictions are made of the decay rates in this situation and compared with the experimental results. Finally, the different field states present during the decay are explored.

This report deals with a theoretical and experimental study of the low frequency sound absorption characteristics of perforated honeycomb sandwich panels. The derivations of formulae for absorption in terms of double perforation ratio and air gap are presented. Results show that the honeycomb absorber, with double perforated sheets, can be an effective low frequency absorber for frequencies down to 63 Hz. In addition, honeycomb panels have advantages over other low frequency absorbers in that they are light weight and strong.

Porous ceramic composite materials are fabricated for sound absorber materials. The ceramic composites are made from silica (SiO 2 ) with a filler mixture to change the pore structure. Natural fillers synthesized from sugarcane bagasse with compositions of 0.5, 0.75, and 1.0 g are considered for sound absorber fabrication. Each filler weight comes with three different fiber sizes, namely 212, 425, and 630 µm. Subsequently, a blowing agent made of Al 2 O 3 and CaCO 3 is added to create pores in the composite, while a binder made of a mixture of gypsum powder and Portland Composite Cement (PCC) is used to bind the whole ceramic composite materials. Sound absorption coefficients α of each sample are evaluated by using impedance tube measurements according to ISO 10534-2. The results suggest that adding 0.5, 0.75, and 1 g filler gives the composite an absorption coefficient of 50%–80%, 60%–90%, and 75%–90%, respectively.

Helmholtz absorbers are a common solution for controlling the low-frequency modes found in small rooms. These devices only perform in a narrow spectrum range with the tuning depending on each room’s geometrical configurations. Consequently, their development still operates on a case-by-case basis. A possible alternative to optimize the production of these acoustic solutions is the development of a tunable Helmholtz absorber capable of changing its geometrical configurations according to each room’s acoustic needs. The present work shares the results of tests performed on varied samples of different configurations of absorbers. The samples were chosen aiming the control of the three first modes of each direction in rooms with volume ranging from 20 to 60 m³. The research revealed that the use of a single tunable absorber has the potential to produce sound absorption coefficients higher than 0.8 in almost the entirety of the frequency spectrum considered.

The question of the arrangement of sound absorbers has been under study for some time. In our approach we conducted a sequence of experiments in a reverberation chamber to determine the optimal sound absorption for different configurations of suspended absorbers using various air spaces and a central dividing panel between them. The results obtained were compared with measurements of the panels, tested against a solid backing as specified in ISO-R-354. It is shown that a porous absorber is more efficient at high frequencies if it is suspended in the sound field rather than against a solid backing. It was also found that the efficiency of an air space between the two porous sheets that compose a suspended absorber is moderately increased when a central divider is used. The statistical precision of the test was also investigated.

Acoustic characterization of sound absorbing materials requires the measurement of one to five non-acoustical parameters, depending on the assumed impedance model. The measurement of five non-acoustical parameters, in the case of more refined impedance models, is sophisticated and time-consuming. As an alternative, a much simpler measurement of the normal incidence sound absorption in an impedance tube can be carried out, and the non-acoustical parameters can be estimated by minimizing the difference between the measured and modeled absorption curves. This inverse procedure requires the choice of the impedance model and the inversion method. The aim of the article is to review the goodness of simulating annealing for estimating the non-acoustical parameters of Miki and Champoux–Stinson models of two granular absorbers. Three of these non-acoustical parameters, common to the two models, are also measured, so that a comparison between measured and estimated parameters can be performed.

In the third of a series of papers on the measurement of acoustical impedance of absorbing surfaces using the two-microphone transfer function technique, the influence of surface absorption mechanism upon the measured impedance is described. The results from measurements of the impedance of bulk reactors are compared with values obtained from theoretical models. Materials investigated are an inhomogeneous polyurethane foam, a distributed resonance absorber, and a twin layer foam. This paper also investigates how the measurement technique behaves with samples which are bulk reacting and have surface roughness. A rough surfaced polyurethane foam sample is used. The results indicate that at frequencies for which the surface irregularities are small in comparison to the wavelength, the material can be accurately characterised by the acoustical impedance acting at an effective plane. For higher frequencies it is thought that the measuring technique becomes inaccurate due to scattering of sound by the surface roughness, and the consequent breakdown of the sound field prediction methods.

In the fourth and final of a series of papers on the measurement of acoustical impedance of absorbing surfaces using the two-microphone transfer function technique, the application of the technique to the measurement of a suspended ceiling and to soft grassland is described. Real materials often exhibit extended reaction, and detailed experimental data is currently difficult to obtain for such samples. But for precise sound field predictions, accurate acoustical data is required. The suspended ceiling tiles investigated are extended reaction panels and measurements are performed in-situ. Consequently, no restrictions on the sample area, edge conditions, or homogeneity are applied. Comparisons with theoretical models are presented. These investigations indicate that the panel absorber can be described by its surface impedance, and that the two-microphone transfer function technique can be used to successfully measure this characteristic in-situ. The surface impedance of soft grassland is also successfully measured using both normal and oblique incident sound. These measurements are compared with theoretical models, which are then used to obtain information concerning the structure of the ground, without invasive sampling.