Concept and development of a novel timber spring for impact sound reduction in timber floor slabs

The influence of static pressure and temperature on sound reduction indices, impact sound pressure levels, improvements of impact sound pressure levels and sound reduction indices, and relative installation noise levels is investigated. Theory revealed a systematic influence on sound reduction index and normalized impact sound pressure level. Firstly, the sound power radiated by a vibrating structure is directly proportional to the sound impedance in air and therefore to static pressure and temperature to the power of −0.5. Secondly, the sound pressure produced in a room by a sound source also depends on sound impedance, i.e. on static pressure and temperature. Since the excitation of a test specimen is not influenced by static pressure or temperature, the two effects are not compensated by any other mechanism, thus temperature and static pressure also influence sound reduction index and normalized impact sound pressure level. Experimental verification involved measurement of sound reduction index in a small test suite at static pressures between 307 and 970 hPa. Measurement results for single-shell structures showed the expected behaviour, whereas results for double-shell structures revealed a considerable scatter with a tendency towards even larger temperature and static pressure influences. For comparison of the acoustic properties of building elements, it is therefore advisable to introduce a normalized sound reduction index and a normalized impact sound pressure level, with both referred to reference conditions of static pressure and temperature. Improvements in impact sound pressure levels and sound reduction index, and relative installation noise levels are determined from changes in sound level differences. Since each difference is influenced in the same manner by meteorological conditions, the resulting improvement is independent of static pressure and temperature, as long as the differences were determined under the same meteorological conditions.

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

The direct sound transmission through a simple, massive, homogeneous building element with and without lining is investigated experimentally and compared with analytical and empirical models from the literature. A 150 mm thick concrete floor and a 100 mm thick floating floor were measured in the floor transmission facility of the National Research Council Canada, i.e. without flanking sound transmission. In addition to the sound reduction index and the normalized impact sound pressure level, loss factors, radiation efficiencies, and mean squared velocities were recorded in the laboratory. The measured data is compared to established models of sound transmission. A focus is placed on the calculation model of ISO 12354-1 (Appendix B), which uses calculated radiation efficiencies and loss factors to predict the sound reduction index of heavy, homogeneous building elements. Some difficulties with the calculation model and the examples in the standard are discussed. In principle, the results in this study show that the calculation model of ISO 12354-1 gives good estimates when the correct input parameters are used. However, deviations between the calculated and the measured loss factors and radiation efficiencies have large effects on the accuracy of the estimates, particularly in the region around the coincidence frequency.

The relationship between the normalized impact sound pressure level (NISPL) and the sound transmission loss (TL) of a floor ceiling assembly has been understood since 1963 (Heckl, and Rathe) and confirmed in 1971 (Ver), both for concrete based buildings. This concept has even made its way into ISO 12354-2. This paper will analyze approximately eight hundred floor/ceiling assemblies that Pliteq has measured in the lab to see if this relationship holds for other types of assemblies and where it might fall short. In a related topic, there has been discussion at ISO to create a delta sound reduction index (R) and normalized impact sound level (Ln) for added ceilings similar to the Delta IIC for floor coverings. The Ln/R are similar to the TL and NISPL in ASTM. The same data set will be queried to see if this is a valid approach for real world constructions in North America.

It has been shown via laboratory measurements that the airborne and impact sound insulation of a concrete floor structure with a suspended plasterboard ceiling can be improved by using elastic ceiling suspension systems. The weighted airborne sound reduction index R w was increased by 7dB and the normalized impact sound pressure level L n,w was decreased by 15 dB when using elastic ceiling hangers as opposed to fixed hangers. In order to study the effect of elastic ceiling hangers on sound insulation further and to make it easier to compare different suspension systems especially in the low frequency range, a calculation model applying the finite element method (FEM) and parametric calculation methods was created. The calculation model was validated using measured data. The calculation results were then used to predict the improvement of sound insulation achieved with the different suspended ceilings. Additionally, the calculation model was used to examine the phenomena around the performance of the different ceiling hangers. The calculation results confirm the observations made from the laboratory measurements; switching from fixed ceiling hangers to elastomer ceiling hangers improved the performance of the suspended ceiling by more than 10 dB, with significant improvements beginning from the low frequencies.

In order to obtain reliable estimations of the impact sound insulation between rooms, it is necessary to know the acoustic performance of each element composing the floors. The contribution of the flanking transmissions, the attenuation of floating floors and the weighted normalized impact sound pressure level of the basic structure need to be determined in order to apply the simplified calculation method according to the EN ISO 12354-2 standard. With the aim of verifying the range of validity of the calculation method proposed by the EN ISO 12354-2 standard for typical basic beam floor structures, a research based on on-site measurements was conducted. This paper provides an analysis in terms of spectrum trend, predicted average weighted normalized impact sound pressure level and reduction of impact sound pressure level obtainable with a generic floating floor typology. The study can represent a starting point for a correct estimation of the impact sound insulation in new buildings and renovation plans.

Erratum: “Separation of Resonant and Non-Resonant Components-Part I: Sound Reduction Index” Jeffrey Mahn There was an error in the calculation of the shape factor for the non-resonant radiation efficiency σNR according to Annex B of EN12354 which was used for the evaluation presented in the paper. Although there are other formulas for calculating the radiation efficiency, it seemed reasonable to assume that a person calculating the apparent sound reduction index using EN12354 would use on the equations presented in the standard. The error in the calculation of σNR affected the calculations of the resonant component of the sound reduction for methods including: Method Gerretsen (eqn 2), C proposed (eqn 10), C A (eqn 16), C AnnexB (eqn 14) and C Villot (eqn 17). The correction of the error resulted in the resonant component of the sound reduction index calculated according to Method Gerretsen to be predicted in 5 of the 18 1/3 octave bands evaluated for the steel panel instead of none of the 1/3 octave bands. The resonant component for the MDF panel using Method Gerretsen could only be calculated in 2 of the 18 1/3 octave bands. When the measured sound reduction index was shifted to the bottom of the confidence interval, the use of Method Gerretsen predicted the resonant component in all of the 1/3 octave bands for the steel plate, but none of the 1/3 octave bands for the MDF plate which was evaluated. Therefore, the original conclusion that subtracting the non-resonant component from the total, measured sound reduction index is an unreliable means of calculating the resonant component was not affected by the correction of the error. Figure 8 of the paper compared the resonant components of the sound reduction index calculated using correction factors. The discussion of Figure 8 showed noted that the predictions of the resonant component of the sound reduction index were within 11 dB of each other with the exception of CAnnex B and CVillot. When the error in the calculation of the non-resonant radiation efficiency was corrected, the difference between the predictions was reduced to 8 dB as shown in Figure 1. [Figure: see text] Despite the error in the calculation of the non-resonant radiation efficiency, the overall conclusions of the paper remain the same. The application of the correction factors to the total, measured sound reduction index can result in a range of values for the resonant component of the sound reduction index as shown in the figure. Definitive guidance is needed for the determination of the resonant component of the sound reduction index in future revisions of EN12354 or ISO15712.

Lightweight profiled metal cladding systems generally have poor acoustic insulation characteristics, and traditional theories for evaluating noise transmission through building elements are usually not applicable to double-skin profiled systems because of their orthotropic nature. Based on extensive experimental observations, a new method for predicting the sound reduction index (SRI) of commercial double-skin cladding systems is proposed. The method combines existing theory for orthotropic flat plates with finite element analysis to account for the pronounced ‘‘dips‘‘ in the SRI at midfrequencies, which are caused by the resonances of the profile geometry. The predicted SRI was shown to compare well with measurements on 15 cladding systems used in the experimental work. The method was further extended to cover commercial double-skin cladding constructions. Analytical equations were formulated to account for the orthotropic nature of the cladding sheets, the sound bridging through fixing supports, and the sound reduction through the in-fill insulation. Comparisons of predictions against sound reduction measurements were made on a wide range of commercial cladding products. Good agreement between predictions and measurements was found.

The artificial neural networks (ANN) approach is applied to estimate the acoustic performance for airborne and impact sound insulation curves of different lightweight wooden floors. The prediction model is developed based on 252 standardized laboratory measurement curves in one-third octave bands (50 - 5000 Hz). Physical and geometric characteristics of each floor structure (materials, thickness, density, dimensions, mass, and more) are utilized as network parameters. The predictive capability is satisfactory, and the model can estimate airborne sound better than impact sound cases especially in the middle frequency range (250 - 1000 Hz), while higher frequency bands often showed high errors. The forecast of the weighted airborne sound reduction index Rw was calculated with a maximum error of 2 dB. However, the error increased up to 5 dB in the worse case prediction of the weighted normalized impact sound pressure level Ln,w. A feature attribution analysis explored the essential parameters on estimation of sound insulation. The thickness of the insulation materials, the density of CLT material and the concrete floating floors and the total density of floor structures seem to affect estimations the most. A comparison between wet and dry floor solution systems indicated the importance of the upper part of floors to estimate airborne and impact sound in low frequencies. Keywords: airborne sound, impact sound, insulation, prediction model, artificial neural networks

The artificial neural networks approach is applied to estimate the acoustic performance for airborne and impact sound insulation curves of different lightweight wooden floors. The prediction model is developed based on 252 standardized laboratory measurement curves in one-third octave bands (50–5000 Hz). Physical and geometric characteristics of each floor structure (materials, thickness, density, dimensions, mass and more) are utilized as network parameters. The predictive capability is satisfactory, and the model can estimate airborne sound better than impact sound cases especially in the middle-frequency range (250–1000 Hz), while higher frequency bands often show high errors. The forecast of the weighted airborne sound reduction index Rw was calculated with a maximum error of 2 dB. However, the error increased up to 5 dB in the worse case prediction of the weighted normalized impact sound pressure level Ln,w. The model showed high variations near the fundamental and critical frequency areas which affect the accuracy. A feature attribution analysis explored the essential parameters on estimation of sound insulation. The thickness of the insulation materials, the density of cross-laminated timber slab and the concrete floating floors and the total density of floor structures seem to affect predictions the most. A comparison between wet and dry floor solution systems indicated the importance of the upper part of floors to estimate airborne and impact sound in low frequencies.

Advanced lightweight steel floor towards high sound insulation and fire resistance

This paper aims to develop an acoustic design methodology for CLT floor assemblies using artificial neural networks approach by integration of life cycle assessment (LCA). 72 Lab-based measurements are used to develop the acoustic prediction tool. They are related to 29 different CLT-based floor assemblies. The weighted sound reduction index (Rw), and the weighted normalized impact sound pressure level (Ln,w) are estimated with an accuracy of 2 dB. Then a LCA study is conducted on assemblies that are used to test the network model. The acoustic performance and their environmental impacts are compared to highlight trends that may guide decision-makers in the design phase. This paper initially found that CLT-based floor assemblies generally increase the environmental impacts to achieve better acoustic insulation. However, a good sound attenuation can be reached by selecting suitable acoustic solutions.

The joint between a heavyweight construction and the surrounding building frame can be rigid or resilient. It is often believed that a resilient joint improves sound insulation. The purpose of this study was to investigate how the joint resiliency of a single-leaf heavyweight construction affects the sound reduction index and the total loss factor. A masonry wall of 10 m2 (220 kg/m2 calcium silicate block wall) was built three times (A−C) in laboratory using three different joint types between the wall perimeter and the test opening frame: A - All four joints rigid; B - Three joints resilient and one rigid; C - All four joints resilient. The sound reduction index was determined using both pressure and intensity method. The total loss factor was determined by measuring the structural reverberation time using hammer impacts. The sound reduction index reduced significantly with increasing level of resiliency. For joint type A, the weighted sound reduction index, Rw, was 50 dB while it was 45 dB for B and 43 dB for C. Correspondingly, the total loss factor reduced from A to C, i.e., with increasing joint resiliency. The effect of joint type was evident above the coincidence frequency (250 Hz) of the block wall. Resilient joint prevented the energy transmission from the wall to the building frame, which increased the sound radiation to the air, which was reflected as reduced sound reduction index. The results imply that the joints of a heavyweight construction shall be rigid if high sound reduction index is desired above the coincidence frequency. On the other hand, the increased joint resiliency improved the sound reduction index at most frequency bands below the coincidence frequency. Resilient joints around heavyweight construction can be beneficial in situations where the reduction of low-frequency noise is of primary concern.

As the demand for sustainable materials in acoustic applications grows, mesoporous charcoal—produced via biomass pyrolysis—has emerged as a promising material for acoustic absorption and thermal insulation. This study investigates its acoustic properties using impedance tube and anechoic chamber measurements, alongside comparisons with mass law predictions. Charcoal samples, characterized by pore sizes ranging from 2 to 50 nm and fraction sizes from 1 to 4 cm, were tested across varying thicknesses (5 cm, 10 cm, and 17 cm) and frequencies (315 Hz to 5000 Hz). The Johnson-Champoux-Allard-Lafarge (JCAL) model was used to derive key acoustic parameters. These parameters were instrumental in explaining the material's behaviour in different acoustic environments.Impedance tube measurements revealed sound absorption coefficients below 0.1 for most samples, attributed to the material’s low porosity (φ= 0.19) and fine pore structure. In contrast, anechoic chamber tests demonstrated increased sound reduction, with a17 cm thick construction (fraction size 1 cm) achieving a sound reduction index (SRI) of 35 dB at 5000 Hz, significantly exceeding the transmission loss (TL) predicted by mass law, which calculated a TL of only 8.28 dB under similar conditions. Statistical analysis further revealed that SRI increases with particle size and thickness, ranging from 9.17 for 1 cm particles to 18.38 for 4 cm particles. The highest SRI of 28.00 was observed for 1 cm particles at 17 cm thickness, while bulk density results highlighted an inverse relationship with particle size: 1 cm particles had a bulk density of 550 kg/m³ compared to 323.33 kg/m³ for 4 cm particles. These findings highlight mesoporous charcoal's potential in sustainable acoustic applications, particularly in the context of circular economy principles. Its production from biomass, combined with the eco-friendly properties it brings to noise insulation, aligns with the goals of sustainable material cycles. Optimizing parameters such as pore size, fraction size, and thickness can further increaseits acoustic performance, making it a promising material for eco-friendly construction and noise control.

Ventilation ducts can have a negative effect on the sound reduction index between two rooms if they pass through the dividing structure without treatments. The overall sound reduction of a ventilation duct is dependent on several factors including the transmission loss when sound is breaking in and out from the duct. This study aims to model the sound reduction of a combined system with a separating wall and a ventilation duct through it. Three walls, characterized according to ISO 717-1, are combined with three different ventilation ducts, two circular and one rectangular with different dimensions. Laboratory measurement data are used to determine the sound reduction of the different configurations and the type of treatments needed for each configuration. A proposed model with existing theory for describing sound transmission losses of circular and rectangular ventilation ducts predicts the shape of the measurement data for many frequency bands. A new theory part is developed through an iterative process for circular ducts, which is based on measurements with previous methods and studies as a guide because the existing prediction scheme is somewhat perplexing. For rectangular ducts, the existing theory has been updated to better match measurement data. The application of the proposed theory and model in this article shows similar results when compared to measurements. The difference in weighted sound reduction index between developed theories and measurement data is 0–1 dB for every configuration.