Sound Insulation Measurements Research Articles

Study of Acoustic Prototypes Based on Plastic Cap Waste

This paper presents the initial prototypes of solutions designed using plastic caps, seeking acoustic applications for both airborne sound insulation and the acoustic conditioning of rooms. Plastic caps are a waste product from the packaging sector and they constitute a major waste problem, given that, if they are not attached to the packaging, they get lost during the recycling cycle and end up in landfill. Finding an application for this waste that can provide acoustic improvements is a sustainable alternative. This paper shows the results of airborne sound insulation measurements obtained in a scaled transmission chamber and sound absorption measurements obtained in a scaled reverberation chamber for different combinations of single and double plastic caps and combinations with thin sheets of sustainable materials, such as jute weaving, textile waste, hemp felt and cork board. Tests have shown that obtaining sound reduction index values of up to 20 dB is possible with plastic cap configurations, or even up to 30 dB is possible at some frequencies with combinations of caps and certain eco-materials. With regard to the sound absorption coefficient tests, close to unity absorption values have been achieved with the appropriate configuration at frequencies that can also be selected. The results indicate that these panels can be eco-solutions for airborne sound insulation as lightweight elements, or they can be used for the conditioning of rooms, tailoring the sound absorption maximums to the desired frequencies.

Advancing sustainable construction through comprehensive analysis of thermal, acoustic, and environmental properties in prefabricated panels with recycled PET materials

Acoustic and thermal insulation materials play a crucial role in the construction industry as they ensure high-performance applications. This study analyzes three recycled insulations (two derived from PET and one is EPS with graphite additives) for innovative prefabricated panels. A multiphysics, multiscale, and multiobjective approach was developed to analyze the performance of the individual materials and three prototype prefabricated panels incorporating them, combined with numerical analysis enabling the thermal transmittances assessment of a full-scale panel. Thermal investigations were conducted at both small and large scales to assess their performance. Additionally, acoustic sound insulation measurements at both scales and a LCA analysis were carried out. Thermal conductivity of the insulation layer ranges from 0.026 to 0.043 Wm−1K−1. Furthermore, the sound transmission loss exhibits a positive trend with increasing frequencies, reaching approximately 10 dB after 1600 Hz for the 15 cm thick PET insulation. EPS performs exceptionally well at low frequencies, with sound insulation peaks reaching almost 40 dB around 400 Hz. At the large scale, the weighted sound reduction index showed a 3.5 dB increase compared to the reference. The environmental assessment emphasized that 80 % of global warming potential comes from material extraction, stressing the importance of using recycled materials.

Assessing the low-frequency measurement procedure for the measurement of impact sound insulation using the rubber ball

ISO 16283-2 includes a procedure for measuring field impact sound insulation at low frequencies using a tapping machine to improve the repeatability, reproducibility, and relevance of results in the 50, 63, and 80 Hz one-third octave bands in small receiving rooms (volumes less than 25 m3). However, the low-frequency measurement procedure with excitation from a standardized rubber ball was not included because the link between measurements of Li,Fmax from the central region and corners had not been established at the time of writing. This paper assesses the use of the low-frequency measurement procedure with a rubber ball source through measurements of Li,Fmax in a vertical transmission suite at the Building Research Institute (Japan). It also provides analysis of the modal sound field in the receiving room due to rubber ball excitation of the concrete slab. The results indicated that the low-frequency measurement procedure was beneficial in this 60 m3 room to estimate the room average sound pressure level below 80 Hz. Future work could therefore evaluate the low-frequency procedure in the field with different room volumes and floor constructions.

Need for a new test method for determining the acoustic performance of road traffic noise reducing devices

Noise reducing devices such as sound barrier walls are common ways to mitigate traffic noise problems in residential areas next to arterial roads or railways. The basic performance of noise reducing devices is sound insulation and absorption. However, the existing measurement methods are not adequate for characterizing sound insulation and absorption performances of noise reducing devices. The sound insulation measurement method is different from the actual installation condition of the noise reducing devices that transmit the sound to the free field, and the sound absorption coefficient measurement method does not include the transmitted sound energy. This study raised the problem of the current acoustic performance measurement method of noise-reducing devices and arises the need for a new measurement method to complement it.

Effects of sound insulation and light reflection of desktop partitions on subjective impression during conversation

In recent years, transparent desktop partitions have often been placed in public spaces to prevent the spread of COVID-19. Moreover, to clarify the view during conversation, surface materials with low light-reflectivity are developed for the partitions. In this paper, we conducted sound insulation measurements for partitions with four different materials, and two psychological experiments in order to examine the audio-visual effects on the ease of conversation. First, in non-visual conversation between two persons, better subjective evaluation of speech transmission was confirmed for partitions with lower surface density which have less insertion loss. However, in normal audio-visual conversation, the low light-reflective partitions got higher evaluations of not only visual but also auditory impressions, regardless of sound insulation performance. In addition, subjective evaluations among different materials varied in the quiet condition more remarkably than in the noisy condition.

Investigation of alternative methods for measuring and evaluating airborne sound insulation

The reproducibility of airborne noise insulation testing is poor, as documented by various interlaboratory studies. This is compounded by the definition of Sound Transmission Class (STC), the dominant single-number rating used in North America, which over-emphasizes the wall performance at and around the 125 Hz third-octave band. Small variations in performance at these frequencies can result in substantial changes in STC rating. To address these concerns, changes to both the measurement method and the single number ratings may be appropriate. For the former, the authors have begun an investigation of measuring the vibro-acoustic characteristics of walls, including measuring the vibration on the surfaces of the separating assembly and the flanking assemblies. This may result in increased precision of sound insulation measurements. For the latter issue, the authors have performed statistical evaluation of published wall sound insulation tests to clarify the effects of idiosyncrasies in the definition of STC and investigated whether different rating methods may better describe the performance of wall assemblies.

Effect of Diffusing Elements in a Reverberation Room on the Results of Airborne Sound Insulation Laboratory Measurements

The main problem in the measurement of airborne sound insulation is the measurement of the sound power radiated by the barrier, in practice performed by measuring the sound pressure level and the acoustic absorption in the receiving room. Large variations of the sound pressure level in a reverberation room indicate the presence of dominating strong standing waves, so that it becomes necessary to install diffusing elements. In ISO 10140, the limits have been defined in which the reverberation time at frequencies at and above 100 Hz should be included. Sometimes, however, in the case of rooms with a large volume, obtaining the required parameters is difficult and sometimes even impossible. It should then be checked whether the measured sound insulation depends on the reverberation time. The paper presents the results of sound insulation measurements at various reverberation time lengths in subsequent stages of diffusing elements installation in the receiving room. An analysis of diffusing materials amount and arrangement influence on the uniformity of the sound pressure level distribution and reverberation time in the room as well as the value of the measured sound insulation was carried out. Uncertainty of sound insulation measurement with partial uncertainties was adopted as a criterion supporting the assessment of the obtained results.

Modeling field measurements of sound insulation for multi-layered CLT-based floor systems: A means of a prediction model using artificial neural networks

A neural network-based prediction tool is developed to calculate the standardized sound level differences and the standardized impact sound pressure levels for multi-layered CLT-floor systems. The data for this model is derived from 104 sound insulation measurements in one-third-octave bands from 50 Hz to 5 kHz taken from 15 buildings in Europe with different room sizes and functions. The network model is developed using various structural parameters such as floor components, wall types, junction types and interlayers, receiving room volume, surface separating area, and more. The network developed shows good performance in predicting standardized airborne and impact sound insulation curves over all frequencies. The weighted standardized level differences DnTw are estimated with an accuracy of 1 dB, while the standard impact sound pressure level LnTw′ is accurate up to 2 dB. The airborne predictions are correlated in the middle-frequency range (200–1000 Hz), while some deviations may occur in higher frequencies. Impact insulation estimations, on the other hand, are more accurate in the high-frequency range (1.25–5 kHz). A sensitivity study is conducted to understand the model’s dependence on parameters. In both types of estimations, the direct sound path through the floor is the most influential factor, with the flanking paths affecting the results in the second order. Additionally, the volume of the receiving room significantly affects impact estimations at low frequencies. The study’s results also emphasize the importance of a visco-elastic interlayer for accurate airborne predictions in all frequency ranges.

Measurement of airborne sound insulation of building components by near-field acoustic holography

Taking the architectural acoustic design of a stadium and gymnasium in a sports center as an example, the acoustic parameters of large stadiums under different working conditions were explored. In order to improve the reliability of acoustic design of large stadiums, the acoustical environment of stadiums is simulated and matched with the design standard value by using the sound absorbing materials arranged in limited positions.

Dilatation wave velocities estimated from the plateau in sound insulation of cross-laminated timber (CLT) plates

There are four inherent problems when predicting the airborne sound insulation of cross-laminated timber (CLT) plates. (1) The internal loss factor of wood products is high and therefore difficult to measure using the structural reverberation time technique. (2) Solid wood is a low-density building material compared to reinforced concrete or masonry construction. (3) Timber is orthotropic. (4) Orthotropic behaviour includes low shear moduli. CLT plates, similarly to thick masonry or concrete plates, exhibit thick plate behaviour in the high frequency range (f>1600Hz). The high frequency sound insulation data of nine plates is examined. Transitions to a thick plate seems to occur in all measurements. However, a clearly observable plateau is only visible for six of the nine plates. Simple methods are applied to extract information about the CLT plates from this high frequency (f>1600Hz) measured data. The data extracted from the plate is compared to typical values for equivalent isotropic plates, where the bending stiffness is assumed to be B_iso=√(B_x B_y ). The results are discussed in the context of laboratory measurement of sound insulation.

Applicability of ISO 16283-3 for field measurement of sound insulation of partially open windows

Façade sound insulation regulations are typically focused on closed windows. However, many people prefer open windows for ventilation purposes, or simply because of the psychological effect of having an open window. As such it is important to be able to correctly quantify the sound insulation, also with open windows. The international standard ISO 16283-3 describes a field method for test of façade sound insulation of facades or façade elements, e.g. a window, which is further explained in the scope: "The element methods aim to estimate the sound reduction index of a façade element, for example, a window. The most accurate element method uses a loudspeaker as an artificial sound source. Other less accurate element methods use available traffic noise". However, the standard is probably primarily meant for closed windows, and not for open windows. The applicability of ISO 16283-3 for open windows is therefore under investigation for such conditions which are included in an additional Danish environmental noise guideline. Generally, it can be concluded that the traffic noise method is applicable, but care should be taken by using the loudspeaker method for partially open windows, since the results depend highly on the window opening position compared to the loudspeaker position.

Objective and subjective analysis of the acoustic performance of a ZEB test-building

The paper describes an experimentation campaign, including both objective and subjective analysis, carried out in a Zero-Energy full-scale test building and aiming at analysing the acoustic performance of the construction and the acoustic comfort of the rooms. The objective analysis consists of sound insulation measurements of facades and partitions, noise level measurements of service equipment and environmental noise level monitoring. The subjective analysis is based on a survey carried out on 100 participants to collect the answers about their evaluation of the acoustic quality in two different test rooms. The outcomes of the questionnaire were compared to the outcomes of the measurements in order to find a relationship between the subjective and objective data.

Analytical modeling of the virtual sound insulation measurement suite and research on sound insulation test methods

With the development of modern industrial technology, it is an essential problem to calculate the noise reduction performance of the flexible partition walls. The sound insulation measurement model is modeled by the Spectral geometry method (SGM). Compared with the traditional ones, it is a method with higher calculation accuracy and faster convergence speed. The displacement of the panel and the sound pressure field inside the rooms are expressed as Fourier series with additional items. In order to simulate the real measurement environment, the sound source room and the receiving room are set as a reverberation chamber and an anechoic chamber with impedance boundaries, respectively. The coupling relationship is established by the Hamilton’s principle. Then the natural frequencies and the sound pressure level are compared with those derived by the finite element method (FEM). The results show that the analytical method has good accuracy and convergence. Moreover, the sound transmission loss (STL) of the partition could be obtained by the sound pressure method. Considering there is no accurate method for measuring the STL, this paper studies some factors affecting the sound insulation performance of the model by the parametric analysis method, such as the thickness of the panel, the length of the receiving room, the impedance of the receiving room and the parameters of medium.

Single-number values versus subjective judgment of airborne sound insulation in dwellings

There is a long history of adapting airborne sound insulation in buildings to the actual needs. A first pan-European work was published with COST Action TU0901: Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban Housing Constructions in which the differences between the sound insulation measure and the standard sound level difference were documented. Furthermore, ISO 16283-1: Field measurement of sound insulation in buildings and of building elements—Part 1: Airborne sound insulation states: Compared to DnT, R’ has a weaker connection to the subjective impression of airborne sound insulation. To investigate this relationship a simplified listening test and a computer-simulated variation studies of a synthesized airborne sound insulation were carried out. A test sound was generated from a speech, a music, and a noise signal, each of which was filtered by six frequency responses of solid structures. In a paired comparison task, 16 participants judged the loudness of the resulting 18 sounds. The results of the listening test show that perceived loudness is significantly correlated to the single number quantity DnT,w but less to the single number quantity R’w. This finding was confirmed across all signal types. Thus, the results confirm the statement in ISO 16283-1, that the single number quantity DnT,w has a stronger connection to the subjective impression of airborne sound insulation as the quantity R’w.

Analysis of the Acoustic Comfort in Hospital: The Case of Maternity Rooms

Hospitals include a variety of different spaces with different requirements and levels of sensitivity to noise but also different activities and equipment that can cause high noise levels. In this article, noise disturbance in hospitals is studied with reference to a case study in a maternity ward. The analysis is carried out by means of sound insulation measurements between bedrooms and between bedroom and corridor. Equivalent sound pressure level measurements were carried out continuously for two days and nights. The number of awakening events is examined for each hour of the two nights. In addition, the results of a questionnaire conducted on more than 100 patients are reported. The results of the study show that the main cause of noise disturbance is activity in the corridors and that this kind of disturbance is usually repeated throughout the night. This is made more critical by the poor acoustic performance of the doors, but also by the habit of keeping doors open or half-open to allow doctors to always control patients. The article proposes some possible solutions to reduce noise intrusion from the corridor to the rooms.

Timber hollow-box floors: Sound insulation measurement results and analysis

We performed measurements of the sound reduction index and impact sound pressure level for a range of lightweight floating floors installed on a hollow-box timber floor. The measurements were performed in the laboratory according to the relevant standards. We tested different configurations, varying the cavity filling of the bare floor and the assembly of the lightweight floating floor. We tested floating floors with a continuous elastic layer with high and low dynamic stiffness, floating floors on elastic load-bearing units and a basic vinyl covering of the bare floor. The results show that a wide range of sound insulation can be achieved, making the hollow-box floor elements suitable for different purposes. Best performance is achieved with elastic load-bearing units installed on the bare floor with gravel in the cavity. Detailed analysis of the achievable sound insulation improvement is also given. This shows that reasonably reliable predictions can be made using well-known equations from the literature. Key parameters are the resonance frequency of the system, determined by the mass per unit area of the bare floor and of the floating floor as well as the dynamic stiffness of the resilient layer, and the configuration of the elastic layer. The results and the highlighted prediction equation offer a solid basis to help develop solutions to meet different sound insulation requirements and make the hollow-box floor elements suitable for urban buildings with several purposes, ranging from office/commercial to educational and residential.

Bistable sound insulator with an abrupt stiffness shift using magnetic-coupled dielectric elastomer actuator

Aiming at noise isolation in low frequency range, this paper presents a novel kind of membrane sound insulator featuring a bistable actuation, by combining magnets and multilayer dielectric elastomer actuator (DEA). With a critical applied voltage on DEA, it deforms and the magnets attract in terms of a bistable snapping, which leads to an abrupt stiffness shift, and consequently regulates the sound transmission loss peak frequency. An electromechanical model is established to reveal the bistable characteristics and to study the effect of voltage and structure parameters for design optimization. The sound-insulation measurement experiment verifies the tunable acoustic performance. The sound-insulation peak frequency has a maximum shift of 142, 130, and 141 Hz under voltages of 2000, 2500, and 3000 V, respectively, showing an advancing figure of merit compared with the existed acoustic metamaterial based on dielectric elastomer.

Effect of installation conditions on laboratory sound insulation measurement and an equivalent method for simply supported boundary

This paper investigated the effect of installation conditions on laboratory sound insulation measurement, and proposed an equivalent method for simply supported boundary. First, taking a typical thin plate as an example, an equivalent method for simply supported boundary of the thin plate in the sound insulation opening is studied. Second, through the measurement (in Opening #1) and simulation of vibration characteristics, the feasibility of equivalent simply supported boundary of thin plates with different materials and sizes is analysed. Then, based on modal test and the method of rational fraction polynomial analysis, the composition and main influencing factors of additional damping in the process of approximate simply supported boundary equivalence are further investigated. Finally, repeated measurements and verification are carried out in another Opening #2. The repeatability and reproducibility of sound insulation test results of the same aluminium plate in Opening #1 and Opening #2 are analysed. The results demonstrate that the approximate simply supported boundary method in the sound insulation measurement in this study is convenient and efficient. It is especially suitable for sound insulation tests of small, thin panels without a specific use.

Validation of the Low-Frequency Procedure for Field Measurement of Façade Sound Insulation

In the ISO 16283 series for field measurement of sound insulation, a low-frequency procedure is specified for determining indoor average sound pressure level, which is the so-called corner method. In the procedure, additional measurements are required in the corners in addition to the default measurements in the central zone, and the indoor average level is corrected with the highest level in the corners. However, this procedure was empirically proposed, and its validity is not fully examined for façade sound insulation. In this paper, detailed experiments were performed in a mock lightweight wooden house for validating the low-frequency procedure for façade sound insulation measurement. The results suggest that a correction with energy-averaging level of all corners is more reliable than with the maximum level, and the uncertainty in the default procedure is sufficiently improved with additional measurements in four non-adjacent corners. Moreover, the effect of the detailed position of the microphone around the corner was clarified for a more specific instruction.

Validation of a 1:8 Scale Measurement Stand for Testing Airborne Sound Insulation.

This paper contains a detailed description of the design and validation of a measurement stand for testing the airborne sound insulation of specimens made at a small scale. The stand is comprised of two coupled reverberation rooms in which the geometry represents the full-size reverberation rooms used at the AGH University of Science and Technology at a 1:8 scale. The paper proves that both the scaled measurement stand and the testing methodology conform to the ISO 10140 standards, and that the obtained measurement uncertainty does not exceed the maximum values specified in ISO 12999-1. Moreover, the calculated uncertainty of measurements obtained for the 1:8 scale stand is comparable with the typical uncertainty given in ISO 12999-1 and the uncertainty obtained on the full-scale measurement stand. In connection with the above, the authors have proved that by using the scaled-down measurement stands, one can obtain reliable and repeatable results of measurements of airborne sound insulation.