Wooden windows: Sound insulation evaluation by means of artificial neural networks

Windows are the weakest part of a façade in terms of acoustic performance: the weighted sound insulation index (R_w), measured according to ISO 140-3, is the fundamental parameter to evaluate the façade acoustic insulation.The paper aims at developing an artificial neural network (ANN) model to estimate the R_w value of wooden windows based on a limited number of windows parameters; this is a new approach because acoustic phenomena are non-linear and affected by a plurality of factors and, therefore, usually investigated through experimentation.Data set is taken from experimental campaigns carried out at the Laboratory of Acoustics, University of Perugia. A multilayer feed-forward approach was chosen and the model was implemented in MATLAB. On the basis of the results obtained by means of a preliminary training and test campaign of several ANN architectures, five main parameters were selected as network inputs: window typology, frame and shutters thickness, number of gaskets, R_w of glazing; R_w value of the window is the network output. Different ANN configurations were trained and a root mean-square error less than 3% was obtained, comparable to measurement uncertainty.This approach allows to develop a model which, with input parameters varying within appropriate ranges, can easily estimate the acoustic performance of wooden windows without experimental campaign on prototypes, saving both money and time. If the training data set is large enough, the presented approach could be very useful for design and optimization of acoustic performance of new products.     

Experimental study for control of sound transmission through double glazed window using optimally tuned Helmholtz resonators

This paper presents an experimental investigation of passively control of sound transmission through a double glazed window by using arrangement of Helmholtz resonators (HRs), which are commonly used for narrow band control application. The laboratory experiments were performed placing the window between reverberation chamber and anechoic chamber. The window was subject to diffuse field, approximate normal wave and oblique wave acoustic excitations. Three sets of HRs were designed and installed in cavity of window. The sound control performances at far-field were measured. The control performances from varying the number of HRs, incident acoustic field, excitation sources (band-limited white noise and traffic noise examples) are presented and discussed in detail. It is shown that a considerable reduction of the transmitted sound pressure levels has been achieved around the mass–air–mass resonance frequency (50–120 Hz). The obtained reductions in the transmitted sound pressure illustrate the potentials of HRs for improving the sound insulation characteristics of double glazed window. The experimental results also indicate that only tuning the HRs to the mass–air–mass resonance frequency does not guarantee the best possible insulation of the sound transmission.     

Development of a 3D finite element acoustic model to predict the sound reduction index of stud based double-leaf walls

Building standards incorporating quantitative acoustical criteria to ensure adequate sound insulation are now being implemented. Engineers are making great efforts to design acoustically efficient double-wall structures. Accordingly, efficient simulation models to predict the acoustic insulation of double-leaf wall structures are needed. This paper presents the development of a numerical tool that can predict the frequency dependent sound reduction index R of stud based double-leaf walls at one-third-octave band frequency range. A fully vibro-acoustic 3D model consisting of two rooms partitioned using a double-leaf wall, considering the structure and acoustic fluid coupling incorporating the existing fluid and structural solvers are presented. The validity of the finite element (FE) model is assessed by comparison with experimental test results carried out in a certified laboratory. Accurate representation of the structural damping matrix to effectively predict the R values are studied. The possibilities of minimising the simulation time using a frequency dependent mesh model was also investigated. The FEA model presented in this work is capable of predicting the weighted sound reduction index R_w along with A-weighted pink noise C and A-weighted urban noise C_tr within an error of 1 dB. The model developed can also be used to analyse the acoustically induced frequency dependent geometrical behaviour of the double-leaf wall components to optimise them for best acoustic performance. The FE modelling procedure reported in this paper can be extended to other building components undergoing fluid–structure interaction (FSI) to evaluate their acoustic insulation.     

Sound reduction in samples of environmentally friendly building materials and their compositions

In order to reduce the negative effect on the environment, environmentally friendly materials are being chosen for the construction of buildings more and more frequently. The building materials that are now used more commonly are clay, straw and reeds. The sound insulation properties of these environmentally friendly materials have not yet been examined thoroughly. This paper presents most commonly used sound reduction indexes R_W that have been measured in the semi-anechoic chamber and determined during the simulation. It has been found that adobe, pressed straw and reeds (oriented parallel to the sound transmission) are suitable for low-frequency sound insulation. The material with the best sound reduction index was adobe. The sound reduction index R_W of a 200 mm thick adobe wall reached up to 43 dB.     

Development of multiple drywall with high sound insulation performance

Experimental studies for the development of multiple drywalls with a high sound insulation performance are performed. Firstly, a means of preventing the sound insulation deterioration due to the coincidence effect at high frequencies is investigated by layering two plasterboards with different physical characteristics. Based on the results, a double drywall with a sound insulation performance of R_w = 61 is developed. Further more, a double drywall of R_w = 64 , a triple drywall of R_w = 86 and a quadruple drywall of R_w = 90 are developed.     

An experimental study on the effect of rolling shutters and shutter boxes on the airborne sound insulation of windows

The façade of a room is usually composed of different construction elements, one of which is the window. This fulfils both an aesthetic function and closes the wall opening. In order to improve thermal behaviour and control solar radiation, the window is fitted with different protection features, such as the shutter. In climate zones with many hours of sunlight, windows in residential buildings commonly incorporate a rolling shutter. Traffic noise and higher standards of energy saving, comfort, durability and sustainability in buildings means that windows now have to comply with stricter requirements, including their sound insulation from airborne noise. This work contains a summary of studies carried out on the sound insulation from airborne noise in several types of windows (double side-hung casement and double horizontal sliding sash) with built-on shutter and prefabricated box. For each type of window, an analysis was made of the effects of the interior finishings in the shutter box, the shutter position (whether fully retracted or extended) and the weighted sound reduction index of windows for traffic noise in accordance with EN ISO 717-1.     

The prediction of the vibration reduction index Kij for brick and concrete rigid junctions

The vibration reduction index, K_ij, is related to the transmission of the vibrational power over a junction between structural elements. Two empirical models are proposed to evaluate K_ij, on the basis of statistical evaluations of numerous in-field tests carried out on rigid junctions between floors made by concrete beams and ribbed slab with brick blocks and brickwork walls, a type of junction that is frequently encountered in Southern European and Mediterranean buildings. These models can be applied in order to calculate the sound insulation properties, such as the normalized impact sound pressure level, , and the apparent sound reduction index, R′, of walls and floors in buildings.The first model allows the single number value of the vibration sound reduction index of a junction to be calculated, on the basis of the real properties of the materials that constitute the junction. A new quantity, the “essential” mass per unit area, was introduced to implement the model.The second model provides an estimation of the K_ij as a function of frequency, subdivided between BB-junction, as ribbed slab with brick blocks floor-brick wall, and CB-junction, i.e. concrete beam-brick wall.     

Standardised acoustic characterisation of sonic crystals noise barriers: Sound insulation and reflection properties

This work presents sound insulation and sound reflection measurements conducted over sonic crystal noise barriers according to the European standards EN 1793-2, EN 1793-5 and EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to window out all diffraction components and to verify the points of strength and weakness of the application of standardised measurements to sonic crystals. Diffuse field measurements in laboratory are also done for comparison purposes. Since the target frequency range for traffic noise spectrum is centred at around 1000 Hz, a finite element based parametric investigation is performed to design unit cells capable of generating band gaps in the one-third octave bands ranging from 800 Hz to 1250 Hz. Then, 3 × 3 m sonic crystal noise barriers are installed in the Laboratory of the University of Bologna and sound insulation and sound reflection measurements are performed according to the mentioned active standards for normal incidence. Sound insulation is measured for diffuse incidence too. The two methods give different results. The method more directly comparable to calculations is the free-field one. However, if on the one hand the application of a time window allows to compute the transmitted or reflected component only, on the other hand the time window itself limits the maximum width of the sample for which all reflections of the n-th order having a significant spectral content are included, and thus results critical in the analysis of this kind of noise barriers. Nevertheless, the standardised measurements allow a direct comparison between the performance of sonic crystals and common noise barriers.     

A model comparison of the absorption coefficient of a Microperforated Insertion Unit in the frequency and time domains

The absorption coefficient of acoustic materials can be measured either in the frequency or the time domain. At normal incidence, a sample of the material is fitted within an impedance tube and the absorption coefficient is calculated in the frequency domain from the measurement of the transfer function between two microphones [ISO 10534-2. Acoustics - determination of sound absorption coefficient and impedance in impedance tubes - Part 2: transfer function method. ISO, Geneva, Switzerland; 1996]. When the acoustic material must be characterized at oblique incidence or in situ (noise barriers, for instance) the absorption coefficient is calculated from measurements of the loudspeaker-microphone impulse response in the time domain, both in free field and in front of the sample [CEN/TS 1793-5. Road traffic noise reduction devices - test method for determining the acoustic performance - Part 5: intrinsic characteristics - in situ values of sound reflection and airborne sound insulation. CEN, Brussels, Belgium; 2003, ISO 13472-1. Acoustic measurement of sound absorption properties of road surfaces in situ - Part I: extended surface method. ISO, Geneva, Switzerland; 2002]. Since the absorption is an intrinsic property of the acoustic material, its measurement in either domain must provide the same result. However, this has not been formally demonstrated yet. The aim of this paper is to carry out a comparison between the absorption coefficient predicted by the impedance model of a Microperforated Insertion Unit and the absorption coefficient predicted from a simulated reflection trace taken into account the finite length of the time window.     

Sound insulation property of Al–Si closed-cell aluminum foam sandwich panels

Al–Si closed-cell aluminum foam sandwich panels (1240 mm × 1100 mm) of different thicknesses and different densities were prepared by molten body transitional foaming process in Northeastern University. The experiments were carried out to investigate the sound insulation property of Al–Si closed-cell aluminum foam sandwich panels of different thicknesses and different densities under different frequencies (100–4000 Hz). Results show that sound reduction index (R) is small under low frequencies, large under high frequencies; thickness affects the sound insulation property of material obviously: when the thicknesses of Al–Si closed-cell aluminum foam sandwich panels are 12, 22, and 32 mm, the corresponding weighted sound reduction indices (R_W) are 26.3, 32.2, and 34.6 dB, respectively, the rising trend tempered; the increase of density of Al–Si closed-cell aluminum foam can also increase the sound insulation property: when the densities of aluminum foam are 0.31, 0.51, and 0.67 g/cm³, the corresponding weighted sound reduction indices (R_W) are 28.9, 34.3, and 34.6 dB, the increasing value mitigating.     

Active control of aircraft fly-over sound transmission through an open window

This paper presents an experimental work on active control of sound transmission through a restricted opening bottom hinged window. The main goal of the work is to demonstrate the feasibility of the active technique to limit the loss of attenuation due to the aperture of windows, and its application to aircraft fly-over incident noise. The experimental window is placed in an exposed façade of a dwelling close to an airport and subject to fly-by aircraft noise. The active control is configured to cancel the pressure at the aperture using a single-input single-output feedforward adaptive system. As a result, a reduction of sound transmission is achieved with low power consumption. In global terms, an increase of almost 3 dB of transmission loss (with respect to the partially opened window insulation values) in the low frequency range (below 160 Hz and according to the National Danish Method for evaluating low frequency noise) is demonstrated, which is equivalent to a reduction of 50% in the loss of insulation caused by opening the window.     

Evaluation and analysis of the environmental noise of Messina, Italy

In this paper, the results of a study on the environmental noise pollution of the city of Messina (Italy) are presented. The investigation has included a preliminary classification of the territory in six acoustically homogeneous areas according to Italian noise regulations. On the basis of the resultant acoustic zoning 35 sites were selected for an experimental survey. This last has been carried out by extensive measurements of the main indexes for noise pollution (L_eq, L₁, L₁₀, L₅₀, L₉₀, L₉₉) and of the traffic flow and composition. Results indicate that: (a) main roads of Messina are overloaded by traffic flow during day-time period and that in all the examined sites daily average sound levels due to road traffic exceed environmental standards by about 10 dBA; (b) environmental noise exhibits a certain degree of spatial variance resulting primarily from the peculiar geo-morphological structure of the town and from the transport infrastructure and (c) more than 25% of residents should be highly disturbed by road traffic noise.     

Urban ambient outdoor and indoor noise exposure at home: A population-based study on schoolchildren

To investigate residential exposure to environmental noise among children in an urban area, a noise measurement campaign was performed at the residences of 44 schoolchildren. Outdoor and indoor noise levels were simultaneously recorded during one week inside and outside each child’s bedroom and in the other room where each child spent most of his or her time, called “the main room”. Associations between equivalent noise levels and familial or environmental characteristics were explored.The recorded equivalent continuous sound levels (L_Aeq) were prone to large variability between dwellings regardless of the measurement location and time of day. Factors linked to outdoor noise level differed from those associated with indoor noise level. Indoor noise levels were associated with the number of children present and noise sources present in the dwelling, whereas outdoor L_Aeq depended significantly on the socio-economic status (SES) of the household. An association was found between the type of view from the window and outdoor L_Aeq, but no significant association was observed between view from the window and indoor L_Aeq. These results support a complex link between noise exposure and the characteristics of the dwelling and of the family, and highlight the contribution of the indoor noise sources to the ambient noise level.Considering the observed acoustic levels and their variability, the sensitivity of children to noise, and the length of time they spend at home, research efforts are needed to better quantify noise exposure at home if the actual burden of noise on child health is to be identified.     

Annoyance and self-reported sleep disturbances due to structurally radiated noise from railway tunnels

In Norway, the requirement for structure borne noise from tunnels is L_pAFmax = 32 dB inside dwellings. According to the Norwegian Standard 8175 it is expected that up to 20% of the exposed population are disturbed by the noise at this level. However, the scientific basis for this noise limit is poor. The aim of this study was to determine the degree of annoyance and self-reported sleep disturbances as a function of L_pAFmax. In the present study, 521 dwellings exposed to structural sound from railway rock-tunnels were identified. A questionnaire was sent to one randomly selected person above 18 years of age from each dwelling. The results showed that both noise induced annoyance and reported sleep disturbances were significantly related to L_pAFmax. Other factors that increased the annoyance were high pass-by frequency of freight trains per day, and degree of sound insulation of the windows. At L_pAFmax = 32 dB, 20% were slightly or more than slightly annoyed, and 4% were moderately or more than moderately annoyed. According to the pre-existing assumption that up to 20% of the exposed population are disturbed by the noise at this level, the present results give support to the Norwegian noise limit L_pAFmax = 32 dB inside dwellings of structure borne noise from railway tunnels.     

含空气层与多孔材料的复合结构隔声特性研究

基于高速列车减振降噪需求,本文应用Biot提出的多孔弹性介质声传播理论,采用传递矩阵法理论推导了典型分层结构的隔声量计算公式,给出了空气层与多孔材料对分层复合结构隔声特性的影响。将传递矩阵与遗传算法相结合,对特定中低频段内的复合结构隔声特性进行了优化。研究结果表明:空气层和多孔材料有助于分层复合结构隔声量的提高,特别是空气层对低频隔声有很好的促进作用,另外空气层与多孔材料的分配情况也影响着隔声效果。含有空气层的复合结构在提高隔声量的同时降低了结构的总体重量,实现了高速列车隔声材料低能耗和轻量化的设计目标。     

Acoustic insulation capacity of Vertical Greenery Systems for buildings

Vertical Greenery Systems (VGS) are promising contemporary Green Infrastructure which contribute to the provision of several ecosystem services both at building and urban scales. Among others, the building acoustic insulation and the urban noise reduction could be considered. Traditionally vegetation has been used to acoustically insulate urban areas, especially from the traffic noise. Now, with the introduction of vegetation in buildings, through the VGS, it is necessary to provide experimental data on its operation as acoustic insulation tool in the built environment. In this study the acoustic insulation capacity of two VGS was conducted through in situ measurements according to the UNE-EN ISO 140-5 standard. From the results, it was observed that a thin layer of vegetation (20–30 cm) was able to provide an increase in the sound insulation of 1 dB for traffic noise (in both cases, Green Wall and Green Facade), and an insulation increase between 2 dB (Green Wall) and 3 dB (Green Facade) for a pink noise. In addition to the vegetation contribution to sound insulation, the influence of other factors such as the mass factor (thickness, density and composition of the substrate layer) and type of modular unit of cultivation, the impenetrability (sealing joints between modules) and structural insulation (support structure) must be taken into account for further studies.     

Specification of component sound quality applied to automobile power windows

As cars become quieter the sound quality of components with electric motors becomes more important in the customer perception of vehicle quality. This has created a need to develop methods for the specification of component sounds. The objectives of this study were to identify perceptually important aspects, link them to acoustic metrics and, based on this, develop guidelines for the determination of requirements for power window sound. Seven prominent attributes were identified: dull, loud, annoying, steady, powerful, overall product quality and under-dimensioned. Effects of auditory stream segregation influenced the results. Power window sounds mainly consist of two sources: motor and window seal scratching. Subjects tended to judge only motor sound. Prediction models developed on isolated motor sound correlated well with judgements. Low loudness, sharpness and motor speed fluctuations led to perceived high product quality. The results emphasise the importance of handling auditory stream segregation and temporal variations in the sound design process.