Building Acoustics

Published by Multi-Science Publishing
Online ISSN: 1351-010X
Publications
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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°.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
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.
 
Article
A new sound absorbing material made from 100% softwood fibres by means of a foam-forming technique is introduced. In foam forming, a wet foam is created by mechanically mixing water, fibres and a surfactant. The air bubbles keep the wet fibres separate, and a highly porous fibre network is formed during drying. The sound absorption of foam-formed structures was measured by means of an impedance tube. The results showed that foam-formed softwood materials possessed a competitive sound absorption coefficient compared to different types of commercial sound absorber materials. The material is based on 100% softwood fibres without added binders and is semi-rigid and does not completely recover from compression. Improvement in the strength properties of softwood material can be obtained by using starch or cellulose microfibrils. The material could be used in indoor applications, for example, in replacing mineral wool acoustic ceiling panels or polyester non-woven materials in office acoustics products.
 
Article
In the first of a series of papers on the measurement of acoustical impedance of absorbing surfaces in-situ, the development of the theoretical methods for the determination of acoustic impedance by the two-microphone transfer function technique is outlined. Each method is based upon a model for propagation of sound above a plane. The impedance calculation models include an expression based on the Weyl-van der Pol equation for propagation over an impedance plane, an exact method based on specular reflection, and an approximate equation based upon specular reflection. The algorithm proposed by Vigran is also derived, and a plane wave model developed for comparison. Conditions under which the results from the different models are equivalent are discussed, along with the practical considerations in programming each model.
 
Article
In the second of a series of papers on the measurement of acoustical impedance of absorbing surfaces in-situ, geometrical and measurement errors for the two microphone transfer function technique are detailed. The effects of finite sample area on the impedance measured are considered, and experimental results show that for edge effects to be negligible, the minimum dimension of a sample should be two wavelengths. The method also becomes inaccurate when the transfer function tends to unity. This is shown to occur at low frequencies, but more importantly, at higher frequencies when an integral number of half wavelengths exists between the path length differences to the microphones. The results of the error analysis show that great care should be taken in determining the precise locations of the microphones. In particular, care should be taken in the alignment of the microphones with respect to the normal to the sample, since errors due to the alignment of the probe combine features of errors not only in the microphone positions, but also in the source location and the angle of sound incidence. In comparison with typical errors in the experimental geometry, errors due to the precision of typical transfer function estimates are very small.
 
Article
Egg cartons have popularly been used as sound absorbers because they are inexpensive, easy to install and easily available. However, acoustic experts have demonstrated that egg cartons are bad sound absorbers. This study developed Enhanced Egg Carton – Dry and Enhanced Egg Carton – Wet using additional recycled materials (shredded rice straw paper, textile waste, 2-cm cut rice straws) to improve the cartons’ sound absorption coefficient while retaining their original advantages. Enhanced Egg Carton – Dry and Enhanced Egg Carton – Wet were tested based on the ASTM C423-02 method of sound absorption measurement. Enhanced Egg Carton – Dry has a noise reduction coefficient of 0.6 and a sound absorption average of 0.59, while Enhanced Egg Carton – Wet has a noise reduction coefficient of 0.54 and sound absorption average of 0.54. The maximum sound absorption coefficients of Enhanced Egg Carton – Dry and Enhanced Egg Carton – Wet are, respectively, 0.77 at 500 Hz and 0.67 at 630 Hz. Enhanced Egg Carton – Dry has a sound absorption coefficient ⩾0.5, between 315 and 2500 Hz, which makes it able to absorb sound energy of the lower to upper mid-range frequencies. With their high sound absorptivity at mid-range frequencies, Enhanced Egg Carton – Dry and Enhanced Egg Carton – Wet are suitable for mosques and auditoriums, where the human voice is the dominant noise source and where an inexpensive sound absorber is needed. The production of Enhanced Egg Carton – Dry and Enhanced Egg Carton – Wet is so simple that users can do it themselves using basic home tools.
 
Article
Plastic is widely used all over the world and its production has been increasing continuously in recent years. But plastic presents significant problems about its end-of-life given its important environmental impact. These problems impose recycling policies which provide for the collection and recycling of plastic materials. In this work, the acoustic properties of a recycled polyethylene terephthalate-based material were analyzed. The material showed good sound-absorbing characteristics, especially at high frequencies. In addition, a numerical model based on the Gaussian regression was developed to simulate the sound absorption coefficient of the material. The model returned an R-Squared value of 0.97 demonstrating excellent performance.
 
Article
A compact multi-layered structure is proposed based on the coiled-up space concept for power transformer noise absorption at 100 and 200 Hz. Current methods of constructing multi-band absorbers are impractical for power transformer noise control due to the high coupling effect deteriorating their performance. To overcome this shortcoming, the proposed structure is composed of multiple connected layers creating two separate coiled ducts with adjustable dimensions to minimise the coupling effect. In the modelling stage, the geometrical features are optimised using the genetic algorithm to maximise the absorption coefficient and minimise the thickness. The proposed dual-tone absorber has a thickness of 43.5 mm which is significantly thinner than the existing conventional absorbers. The measurement results on a 3D-printed structure demonstrate the feasibility of the design.
 
Article
Sound absorption phenomenon of pseudostochastic diffusers was investigated in this paper. The mechanism of high absorption at low frequency was explained from the point view of energy dissipation due to nonlinear effects.
 
Article
In this paper we describe a method of calculation of the energy relations in halls where the existence of a non-uniform distribution of absorptive material in the room results in a non-diffuse sound field. The cases of halls used for concerts and speech have both been treated in order to derive new energy relations that yield known expressions when applied to a diffuse sound field. The importance of the initial reverberation time corresponding to the first portion of the decay has been verified showing that the main subjective parameters relating to the sound energy are influenced strongly by this portion, which is called the Early Decay Time if it is measured in the first 10 dB of the decay.
 
Article
The International Standards Organisation (ISO) is currently developing a standard by which the frequency dependent values of the sound absorption coefficient of building materials can be expressed as a single number rating. This paper describes the new rating procedure and relates it to measurement techniques currently employed. The practical implications are discussed and some examples of results presented. The new rating procedure was tested on various brickwork to be employed for building facades. Some of them were variants of common products, only differing in surface roughness; others were of new material not yet commercially available. Modifications to the production process allowed bricks with a perforated surface to be measured where the depth and the width of the holes could be varied to give a strong reactive absorption at various frequencies. The measurements were performed in an impedance tube, using both the conventional pure-tone technique and a variant of the transfer-function method, which is also described.
 
Article
This article presents some experimental results on Helmholtz resonators for large sound amplitudes with two general geometries of their necks: the resonators with classical (cylindrical) and quadratic nonlinear necks. Obtained results for large amplitudes show accelerated amplitude dependency of resonant frequencies of the resonators with modified shape of the neck compared to classical ones. This nonlinear response can be used as a passive controller system with nonlinear restoring forcing function for having broadband frequency absorption.
 
Article
The present study investigates an optimum combination of absorptive and diffusing treatments for achieving preferred acoustics in classrooms. The measurements were carried out in a 1/10 scale model classroom, adding different amounts of absorptive and diffusing materials to one or more of five surfaces of the room. Adding diffusers on 25% of the ceiling area with the other 75% absorptive was more beneficial for achieving higher G50 and G values than adding absorptive materials on the entire ceiling. Adding absorptive materials on the entire ceiling area and diffusers on the front or side wall was beneficial for achieving shorter T30, EDT values and higher C 50 values. Adding diffusers on the front or side wall slightly increased G50 and G values by more than 1 JND. Adding diffusers on the ceiling and lower front wall or side wall and adding diffusers on the ceiling a absorptive materials on the lower front wall were selected for consideration as the more successful treatments for classroom acoustic design.
 
Article
With the proposal of the D50 and the C80 two room acoustic parameters were introduced in which the time interval after the direct sound was taken into account. It is not widely known that comparable applications have a history which date back into the 17th century. Already B.C. Vitruvius had noticed that echoes occurred in theatres and that these were unwanted to create good hearing conditions. During the 17th and 18th century a theory on echoes arose in books about general physics and sound. This theory influenced the books about architectural acoustics written during the end of the 18th and the 19th century and consequently concert hall design at the end of the 19th century. Examples where the theory on echoes was used in the design are the Palais du Trocadero in Paris, the Neue Gewandhaus in Leipzig and the Salle Pleyel in Paris.
 
Article
The main objective of this study is to evaluate the acoustic behaviour of composites made by mixing cellulose acetate, from recycled cigarette butts, with polymers such as polyethylene and polypropylene, from recycled plastic containers and surgical masks, respectively. For this purpose, the spectra of the measured sound absorption coefficients and the calculated NRC and SAA indices of samples with thicknesses of 1.5, 3, 4.5, 6 and 7.5 cm are analysed. The results of both experiments reveal that the studied composites present a sound absorption capacity comparable to that of fibre glass and rock wool, being even more efficient for thicknesses greater than 4.5 cm. Moreover, the acoustical properties of the composites are predicted using the Miki model over the frequency range from 100 to 6400 Hz, showing very accurate predictions of the sound absorption spectrum at normal incidence.
 
Article
In auditoria, the acoustical properties of audience areas located under balconies are regarded as inferior to the main area. This is caused by the reduction of direct and reflected sound energy due to the smaller open area and the reduction of diffusive energy due to the limited acoustical space. In this paper, a new electro-acoustic system is proposed to compensate for this acoustical condition. The proposed system is a non-regenerative system and consists of directional microphones, head amps, a convolver, a matrix processor, amplifiers, and ceiling loudspeakers located under the balcony. The loudspeakers, located at positions corresponding to measurement points across the balcony, recreate the reflecting sound from above the balcony area, which otherwise fail to reach to the listeners under the balcony. The authors have examined the proposed system's performance via two methods: acoustical measurement using a full-scale model and a corresponding psycho-acoustical experiment. The results showed that the energy of the reflections from above the system was the same or more than that without the balcony, and the decay curve with the system was almost the same as that without the balcony. The MUSHRA method was used in the psycho-acoustical experiment, which focused on the evaluation of apparent source width (ASW) and listener envelopment (LEV). The results of the experiment show that the system is significantly better for all tests to the use of no system and that the system is superior to a standerd PA (delay system).
 
Article
Auditory perception has been proved to have an influence on how we live and move through places and on the use of public spaces. However, despite the numerous studies that have focused on the theme of soundscape and auditory perception of urban spaces, these aspects have not been studied in connection with the design of the building surrounding such spaces. This study focuses on the influence of façade design on acoustic characteristics of an urban space and on the subjective spatial perception of the users. Simulations and auralizations have been conducted through ODEON software (v.13) on the virtual model of a small square of Turin (Italy). Different absorption and scattering coefficients of façade upholsteries have been applied to the façades of the building surrounding the square, choosing from a pool of typical building façade materials. Results of a listening test have proved that the absorption coefficient of the façades has an influence on the subjective perception of space wideness. Moreover, multiple regression analysis has been conducted in order to find a mathematical relation between space wideness perception and objective acoustic parameters. It was shown that the relation between the perceptual aspects and the objective parameters is strongly dependent on the listening position.
 
Article
The localisation of acoustic sources using linear microphone arrays permits source positions and power levels to be evaluated. The identification of the positions of the principal sources is essential before noise reduction methods can be defined. The work presented here concentrates on problems associated with multiple and partially coherent sources. Conventional processing techniques have limited resolution for a restricted number of transducers which can be resolved using high resolution techniques. Experiments showed the limitations of high resolution methods when dealing with correlated sources. Techniques based on the use of reference signals from selected sources were studied to try and solve this problem. This approach consists of pre-processing the cross spectral matrix in a specific way using multiple-input multiple-output (MIMO) methods. This enables the independent contributions of sources to be localised even for relatively high values of inter-source correlation.
 
Article
Natural materials are a valid alternative to traditional synthetic materials in the fields of acoustic treatments and energy saving. Natural fibres have been used to produce sound-absorbing panels. This article reports the acoustical characterization of the following natural fibres: straw, hay, plant litter and different sized wood chips. The acoustic measurements were carried out with an impedance tube. The acoustic absorption values were measured in a frequency range between 200 and 2000 Hz.
 
Article
Most buildings such as hospitals, hotels, governmental offices, data processing rooms, etc, are equipped with internal combustion engines, diesel motors and generators to supply energy in emergencies. These same IC engines are used for industrial applications, building services and transportation. Exhaust noise are the predominant noise source with most internal combustion engines and thus exhaust systems incorporating mufflers have been designed to reduce the noise. This paper describes the analysis of several configurations of mufflers and also presents comparisons between the results for the transmission loss obtained by numerical modelling (FEM), Transfer Matrix Method (TMM) and measurements.
 
Article
Several acousticians have attempted to define a complete set of factors describing room acoustic quality, based on laboratory and/or real hall listening tests. After finishing a PhD thesis on room acoustic quality, the author has worked on new constructions of performance spaces, renovations as well as optimizations of existing spaces and the question can now be asked whether the widely used set of objective criteria and perceptual factors proves sufficient to describe the problems and challenges encountered. When working on high-quality acoustic spaces, the commonly used set of acoustic criteria is insufficient to describe all aspects and problems. Further descriptors are required with respect to both acoustic measurements and perceptual factors. Proposals for additional acoustic criteria and their link to the architecture of a space will be given, aiming to better describe the signature of a room with respect to both source presence and room presence. The concept of “stream segregation” into source presence and room presence is confirmed, but for both the “source” and “room” parts not only the magnitude (strength) needs to be considered but equally more detailed aspects like “lateralness” and direction of arrival, i.e. what could be called the “spatial center of gravity”. For example, changing the spatial center of gravity of the reverberation has very strong perceptual consequences. Another aspect that often tends to be neglected is the question of orchestral balance (for audience members but equally for musicians on stage) that can strongly be influenced by acoustic design decisions.
 
Article
The study and analysis of the processes that determine environmental sustainability of buildings are nowadays topics of great interest for the sustainable, economic and social development of the cities. The international context presents guidelines and protocols for the energy-environmental sustainability, often aimed to assigning a sustainability label to the buildings. In Italy one of the most used rating systems is the ITACA Protocol, recently updated by the Italian Standard UNI/Pdr 2019, which through a series of criteria identifies global indicators of the sustainability of the building examined. This paper presents the potential of the ITACA protocol which could be a method for designing innovative and efficient architectures. In particular, the aspects related to the acoustic comfort are examined and how these criteria change the overall performance of a building. The evaluation of the sustainability performance was applied to a school building. Results show that an optimal acoustic quality improve over to 2 point of the final protocol score.
 
Article
The experiment presented in this paper was to investigate and analyse the noise reduction at low frequency of porous material used to line the cavity between two panels of a double-panel structure. The effects of panel construction, fibreglass and cavity depth have also been studied. The structural-acoustic coupled system of a sandwich structure, backed by a rectangular acoustic cavity of rigid walls is discussed. It is found that the sound insulation of a combination of a stiff thick and a thin flexible plate panel, with air cavities and porous material in-between, is more effective than that of the conventional double-wall panel at low frequency.
 
Article
As many large buildings have been built worldwide recently, it is necessary to study how the acoustic environment in those buildings affects people in order to improve the acoustical comfort in them. The aim of this study is to explore the influence of acoustic environment on people in eight large-scale spaces, which are divided into three categories according to function, through grounded theory, and questionnaire. The results showed that “loud background noise,” “large number of sound sources,” “emotional change,” “mixed sounds,” and “sensible sound with certain spectrum component” were people’s main evaluation to the acoustic environment in large-scale spaces. Based on respondents’ perception, the influence of the acoustic environment in large-scale spaces could be classified into the following three aspects: emotional effect, influence on attention, and influence on thinking ability and behavior. Although the evaluation of the acoustic environment varied widely with the difference in spatial functions, same perception dimensions could be summarized.
 
Article
A new concept for building regulations together with sound and vibration classification standards are introduced. The regulations, which are harmonised with EC directives, specify general acoustic and vibration requirements. A new Norwegian Standard, NS 8175, was prepared in parallel with the new technical regulations. The standard specifies the detailed technical acoustic requirements and classes for the various types of buildings concerned. The sound insulation and noise criteria are given in four classes A, B, C and D. The classification system makes it possible to choose better acoustic qualities and climate in buildings. Another new standard, NS 8176, containing a measurement method for determining vibrations from heavy road and rail transport, and a similar classification system as for acoustic conditions, based on dose-effect relationship, is in preparation.
 
2 nd order reflection and receiving points for the von Kuster Hall soffit reflector design. On the receiving plane (the audience) the white dots indicate reflections arriving within the first 35 ms. The red dots represent reflections arriving between 35 and 50 ms.
1st order ray study of a concave lateral reflector in the Confederation Centre.
1st order ray study for the entire (concave) lateral reflector array in the Confederation Centre.
Reflectors above the proscenium arch. (Photo by Sarah Mackel)
Article
Non-rational uniform B-splines (NURBs) are liberating acoustic design. Geometrical acoustics is no longer limited to flat surfaces. For decades, curved surfaces in computer models had to be broken down into a series of contiguous flat surfaces; a procedure prone to inaccuracy. With NURBs this is no longer the case. A new software tool has been developed by the authors, called NRAT, intended to facilitate acoustic design in NURB based geometries. Two parameters have been developed to quantify the efficiency of reflectors as they are being designed. They are called Reflector Efficiency (RFE) and Receiver Coverage (RCC). The two are quoted together, much like a blood pressure reading might be. The two parameters are required for reasons that became apparent to the authors as the NRAT tool was being developed. A small reflector, perhaps one that might be part of an array, may have a very high percentage of its surface area effectively casting reflections to the audience (perhaps 85%) but those reflections may only cover a small proportion of the audience area (say, 12%). Conversely, a large reflector, for example the side wall of a shoe box shaped concert hall, may only have a small area casting reflections to the audience - in our experience, in the range of 6%. But this small zone efficiently casts reflections across the expanse of the audience, sometimes as much as 90% or more. The quantification of the two RFE/RCC scenarios presented above would be, respectively, "85 over 12" and "6 over 90". Two case studies are presented.
 
Article
The acoustic filter effects of periodic obstructions in a square section of duct are studied experimentally. The two-microphone transfer function method is employed to measure the transmission loss across the periodic elements of different profiles. The experiments aim to measure the Bragg Stop Band and the Resonance Scattering Stop Band and their interaction. The experimental data show that the Bragg effect is spatial dependent. The Resonance Scattering Stop Band is strongly affected by obstacles and demonstrates a possibly useful interaction between the Bragg Stop Band and the Resonance Scattering Stop Band. Results also indicate that for specific situations, the overall Resonance Scattering Stop Band contribution can be dominant and effective, both in terms of magnitude and bandwidth control. The asymmetric placement of the obstructing elements is shown to be nonreversible.
 
Article
This article continues the preliminary exploration of the sonic observations of Athanasius Kircher, namely, the first book of his Phonurgiæ Nova (1673), the Phonosophia anacamptica (Tronchin, Durvilli and Tarabusi). This book analyzes in particular sound propagation in enclosed spaces. In this work, Kircher also describes the statua citofonica, or ‘talking statue’, in relation to the magical effect created by aural illusion and the famous ancient Egyptian acoustical phenomenon and cultural sound-mark associated with the Colossus of Memnon, the famous lost sound phenomenon of the northern of the two colossi of Amenhotep III in the Theban Necropolis, near Luxor, Egypt, that reportedly emitted a sound with the first and final daily touch of sunlight at dawn and dusk. This article aims to describe, analyse and comment on the 17th century contributions of Athanasius Kircher by understanding his Phonosophia anacamptica and the contemporary intellectual context in which he worked. This article differs from our former work; for example, in this article, an earlier example of Francis Bacon’s methods of enquiry into acoustic phenomena illustrates differences with Kircher’s own line of inquiry. We show how Kircher accepts and embraces a Baroque fascination for the ‘marvellous world’ and the allegiance between science and magic, specifically with the mysterious magical affect of sound through the construction of interior listening strategies, or aural espionage, as in the Heidelberg Palace, the Villa Simonetta, and via talking statues such as the Colossus of Memnon.
 
Top-cited authors
Jian Kang
  • University College London
Bridget Shield
  • London South Bank University
Francesco Asdrubali
  • Università Degli Studi Roma Tre
Kirill V Horoshenkov
  • The University of Sheffield
Julie Dockrell
  • University College London