Acoustic comfort is a concept hardly described in the literature. But it has been used in engineering typically to refer to low noise or annoyance in order to invoke no discomfort. Current standardized methods for airborne and impact sound reduction are deployed to assess acoustic comfort in dwellings. However, the measured sound pressure levels do not represent comfort. The latter should include further the human perception of the acoustic environment. Therefore, this article reviews studies that approached acoustic comfort through the association of objective and subjective field data, combining in situ acoustic measurements and survey responses from residents. We evaluated the studies using Bradford Hill’s criteria. Most researches focus on self-reported noise annoyance while some others on satisfaction responses. Many studies were found incomprehensibly described: often vital data of statistical evaluation or study design are lacking. The results indicate that noise is a significant issue in living environments, especially certain impact noise types. The use of extended low-frequency spectra down to 50 Hz was suggested for impact measurements in order to predict better self-reported noise response. Greater problems with low-frequency transmission are displayed in lightweight structures which perform inefficiently compared to heavyweight components. Harmonization of presented results and study design details should be taken into account for future articles.
This study concerns an overall evaluation of building envelopes, for what concerns the energy, acoustic and lighting performances. It combines different topics of energy and indoor comfort, with the aim to improve the livability of an existing building (a social housing) by means of a comprehensive retrofit of their envelopes. The novel contribution of this study is to apply some methods for energy retrofit of a building envelope in such a way that objectives are achieved within the state-of-the-art combination simulation, optimization approaches, and equations describing the calculations of sound insulation in buildings. The results showed that properties of building envelope like the value of transmittance of the glass window and thermal properties of materials have an impact on indoor environmental quality and energy performance.
A child with a developmental disability, such as autism spectrum disorder, has a high possibility of having atypical sensorial characteristics. Indeed, children with autism spectrum disorder often face great difficulties while listening to teachers’ instructions in noisy environments. Moreover, since some of their hearing is highly sensitive, specific or loud sounds may induce problematic behaviors. It is necessary to determine the acoustic requirements of a classroom by considering the atypical hearing properties of such children. In this study, we investigated the acoustic problems of schoolrooms for special-needs education and the methods to improve their sound environment. First, a questionnaire survey was conducted on the supervising teachers of the special-needs education class, and the children’s disorders, hearing properties, and problems caused by the acoustic environment were examined. Simultaneously, an observational survey of the school was performed and acoustic problems were overviewed. Second, as a means to find a method to improve the problems caused by sound, a small calming space was constructed with metal frames surrounded by sound-absorbing material. It was experimentally placed in a classroom so that children could take refuge in the quiet environment. The effectiveness of the space was investigated by an observational survey of the classroom and an interview survey of the teachers.
Listening effort describes the allocation of attentional and cognitive resources for successful listening. In adverse conditions, the mental demands for listening increase, interfering with other cognitive functions. This is especially relevant in learning spaces, where complex tasks that recruit more cognitive resources (e.g. memorization of information and comprehension) are performed by the students. This study focuses on the case of university classrooms and investigates the effects of different types of masking noise on both speech intelligibility and listening effort. Speech-in-noise tests in the Italian language were presented to 25 young adults with normal hearing (13 native and 12 non-native listeners) within an existing university classroom located in Bozen-Bolzano (Italy). The tests were presented in three listening conditions (quiet, stationary noise, and fluctuating noise), grouping the listeners around two locations within the classroom. The task performance was assessed using both speech intelligibility and two proxy measures of listening effort: response time and subjective ratings of effort. Longer response times and higher subjective ratings were taken to reflect increased listening effort. Results in noisy conditions were compared to the quiet condition. A disadvantage in task accuracy performance was found for non-native compared to native listeners; concerning response time, it was found that when the target signal is masked by a fluctuating noise, additional processing time is requested to non-native listeners compared to their native peers. The interaction was not pointed out by subjective ratings, supporting the hypothesis of a different sensitivity to listening conditions of the two proxy measures of listening effort.
This article reports numerical and experimental results concerning the estimation of the diffuse field sound absorption coefficient of several different materials under a synthetized diffuse acoustic field excitation in laboratory and in situ conditions. The proposed measurement method is based on a sound field reproduction approach and a synthetic array of acoustic monopoles facing the material to be tested. Numerical simulations are first conducted to optimize the geometrical parameters of the method and to compute theoretical sound absorption coefficients of the considered materials. Measurements on a set of six typical acoustic materials are then conducted following the standardized reverberant room method as well as the proposed approach in a hemi-anechoic room and in two realistic rooms. Albeit showing limitations in the low-frequency domain, the proposed method enables a significant reduction of the tested specimen dimensions compared with the reverberant room method and allows performing tests in non-ideal acoustic environments.
The acoustic quality of classrooms is crucial for children’s listening skills and consequently for their learning. Listening abilities in kids are still developing, and an environment with inadequate acoustic characteristics may create additional problems in speech perception and phonetic recognition. Background noise or reverberation may cause auditory processing problems and greater cognitive effort. There are also other elements which can make difficulty in listening and understanding in noisy environments an even more serious problem, such as learning disabilities, mild to severe hearing loss or bilingualism. Therefore, it is important to improve the acoustic quality of the classrooms, taking into account the specific needs of children in terms of signal-to-noise ratio and reverberation time, in order to ensure a proper quality of listening. The aim of this work is to analyse, through the review of previous studies, the impact that the acoustic of classrooms has on children’s listening skills and learning activities.
This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.
Studies in the literature suggest that factors influencing soundscape perception are based heavily on sound environments and auditory perception. Nevertheless, in studying the soundscape perception of people living in certain acoustic environments, cultural, social and habitual criteria should be taken into consideration. Residential environments are where people spend most of their time. Therefore, understanding the soundscape perception in the residential context is significant for indoor soundscape studies. This research investigates the residential soundscape perception differences of two different culture groups living in Ankara, Turkey. A total of 405 Arab and Turkish residents are included in the study. The questionnaire findings are statistically analysed using one-way analysis of variance and t-test. The results suggest that the sound environment in a house setting is equally important for both culture groups, while the Arab residents showed a higher satisfaction level from their present sound environment in their residences. Furthermore, statistically significant differences have been found based on cultural variances of the two groups regarding the overall soundscape perception, sound source loudness, frequency of occurrence, and sound favourability evaluations.
External shading devices are widely used in recent buildings because they reduce the greenhouse effect due to the solar irradiation through transparent surfaces and the glare effects in interiors. The acoustic effects of these devices have not been well investigated in the literature. In this article, we use a bi-dimensional pressure acoustics finite element model of a shading device attached to a building façade, in frequency domain, to analyse the effects both in the indoor and in the outdoor environments. The finite element model was validated with experimental measurements carried out in a semi-anechoic chamber and then extended to an urban scale to evaluate the effect in the reduction of outdoor noise due to traffic. To improve the acoustic effect of the shading device, a sound absorbing material was added to the bottom side of each louvre. Results of the simulations show that external shading devices tend to increase the sound pressure level over the building façade, while the introduction of the sound absorbing material behind each louvre reduces this problem. The dependencies of the sound pressure level reduction to the geometrical factors of the shading device were investigated by means of the finite element model. The installation of louvres on a building façade can affect also the sound pressure level over a façade of a building placed 20 m away, across a road. In this article, both the effect over the façade of the opposite building and the effect over the urban area between the two buildings are analysed.
Noise is the most frequent reason for complaints about environmental conditions in the workplace. It is associated with individual health and well-being and decreased productivity and performance. This study identified a set of acoustic strategies for open-plan workplaces and examined a case study applying those to four open-plan offices in the United States. The set of measures was defined based on a literature review and a focus group interview with 17 experts. A total of four topics were identified as key performance indicators of proper acoustic environments in the open-plan workplaces. A total of 19 items were then developed within these 4 topics as the protocols for planning acoustic strategies for workplace health and well-being. In the case study, the level of acoustic performance for workplace health and well-being was highest in the Dallas office (27.5 points out of a total of potential 40.0) followed by the Minneapolis office (26.0). Both offices outperformed the other offices in achieving space planning principles to control noises and occupant noise control in open spaces for acoustical privacy. A further examination on the relationships between acoustic strategies and other health and well-being key performance indicators in these offices suggests that guidance to increase occupants’ auditory comfort, well-being, and performance should be sought by designers in a holistic and integrative way.
Breakout from a flexible rectangular duct depends on its structural properties as well as acoustic properties of the medium. Majority of duct breakout noise prediction models in the literature consider an ideal duct (without joint). However, ducts used in applications have joints. So, current research interest is to study the effect of duct joint in predicting the breakout noise and its influence on modal parameters. For this purpose, duct with a joint is considered in the experimental study and an ideal duct for numerical analysis. As a first step, an experimental setup is developed to measure breakout noise in terms of transverse transmission loss and radiation efficiency, and furthermore an experimental modal analysis is performed to measure modal parameters of the duct. Numerical analysis is performed on an ideal rectangular duct (without considering the joint condition) to calculate the breakout noise and modal parameters. Both, experimental and numerical results are compared, and it is observed that joint has a less significant influence on breakout noise as compared with modal parameters.
One important challenge of the wooden constructions is to achieve a high quality of acoustic insulation, especially decreasing the impact noise in the low-frequency range. In order to avoid over-designed solutions and expensive experimental tests in the design phase, reliable prediction tools are called for. This article is an initial investigation of modeling the ISO standardized tapping machine on a cross-laminated timber floor, using finite element method. The wooden-based floor was first calibrated in terms of its dynamic properties. The influence of the material properties of the cross-laminated timber floor was discussed. The force generated by the tapping machine was then introduced in the established cross-laminated timber model. The model was finally validated by comparing the simulation results with the measured accelerations.
EU Environmental Noise Directive recognized the importance of identifying and preserving “quiet areas.” Even if the majority of EU member states have not yet defined what is a quiet area, many researchers have started to investigate the topic using the so-called “soundscape” approach. Designing or preserving a “quiet area” in urban settings can be a challenging task. Schools and universities located in urban areas are often surrounded by areas with high traffic and noise pollution that affect the overall and sonic quality of the external spaces, which should represent pleasant areas where students can relax or study. In this study, the assessment of the soundscape and of the overall environment of the external area of the Literature Department of Roma TRE University (Italy) was investigated and discussed by analysing the acoustic, psychoacoustic and perceptual data collected. The results obtained by a summer measurement campaign were compared with the previous winter outcomes. Moreover, it was investigated how natural features, visual aspects and thermal conditions can affect the users’ judgment about the overall and the sonic environment; in particular, the Tranquility Rating Prediction Tool was evaluated, both in winter and summer. The measurements campaign revealed that the obtained values are comparable under winter and summer conditions. Due to this, the differences observed in the perception of the sonic and overall environment are ascribable to higher human voice component, more pleasant visual aspects and climate conditions during the summer. This trend was confirmed by tranquility rating values.
In modern constructions, service equipment is the most used and complex technology. Air and liquid flow inside piping or conduit provides conditioning, well-being and comfort within buildings. Nevertheless, fluid movements inject both structure-borne and airborne noise, causing annoyance on people living inside edifices. In order to avoid this issue, the model provided by ISO 12354-5 standard could be used. Unfortunately, the standard describes very well the process in order to calculate the resulting noise caused by air flow service equipment, but it does not offer clear definitions of parameters related to waste water installations. As a consequence, very few researches and studies are available at present because of the difficulty on initial data set and on interpretation of requested parameters. In this article, the ISO 12354-5 method for waste water pipe source is critically analysed, modified and then applied to real case studies. Considerations on coupling terms are proposed, discussed and used in the standard equations, calculating the theoretical values and providing possible solutions for all missing data; results demonstrate how the suggested modified models matched very well measurements outcomes.
The construction of a new worship space in cross-laminated timber provides a good opportunity to include acoustic needs in the whole design development. The surface porosity and the lightweight of wooden elements may be carefully considered in order to improve the intelligibility of priests’ voice. In this work, a practical approach for obtaining a global acoustic comfort using sustainable materials is provided, using geometrical acoustic simulations. Material properties and architectural geometries were taken into account in order to evaluate subjective reverberation, speech intelligibility, and spatial perception over the whole audience. Results show how the sound energy distribution in the case study follows the sound field models proposed by scholars and how the ceiling shape—inspired by industrial sheds—contributes to the acoustic comfort of the faithfuls.
Nowadays, lightweight building structures are widely used by the construction industry as a more natural and cost-effective method. The purpose of this study is to compare between sound pressure level and vibration velocity method for sound reduction index determination for single- and double-leaf gypsum board partitions. The sound pressure level method was carried out according to the requirements of ISO 140-3:1997, and the vibration velocity method (V) was carried out according to some criteria of ISO 10848-1:2006. Regarding double-leaf partitions, measurements were carried out with the leaves separated by 5- and 10-cm air gaps. The effect of cavity filling with absorbing materials was studied experimentally. The space between the leaves was filled with Rockwool and polyurethane to illustrate the effect of cavity absorption on the sound reduction index behavior. It was found that there is good agreement between the two methods. Also, cavity filling with a 10-cm absorbing material such as Rockwool increases the sound reduction index at the critical frequency by 7 dB using sound pressure method and 4 dB using vibration velocity method.
The low-frequency properties of a room (where statistical methods in the standards cannot be applied directly) are often hard to estimate due to strong modal behaviour. The situation gets complicated by the fact that variations in the furnishing can have an impact on the modal patterns and therefore can also influence the results of measurements at certain points, in spite of the room properties being the same. The latter can hinder the achievement of acoustic comfort in dwellings, even if they comply with the current regulations, especially due to the fact that low-frequency noise is left outside the scope, since the standards currently in force do not require measurements below 100 Hz (albeit Sweden set 50 Hz as lower limit). This article aims to study variations of the sound field that results of varying the position of three moderately absorbing boards, which emulate how very sparse furniture can impact the sound field when relocated in the room. Furthermore, the potential of numerical models as prediction tools for such problems is pointed out.
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.
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.