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Ray tracing is a frequently used method for acoustic simulations, valued for its calculation speed and ease of use. Although it is fast, there are no fully ray tracing-based real-time simulation methods or engines. Under real-time restrictions, ray tracing simulations lose precision and the variance inherent in the random simulation method has too much impact on the outcome. In this paper, an algorithm called iterative ray tracing is presented that reduces the negative effects of real-time restrictions by iteratively improving the initial calculation and increasing the precision over time. In addition, new estimates of the expected value and variance of ray tracing simulations are presented and used to show the iteration steps in the new algorithm reduce variance, while maintaining the expected value. Simulations using iterative ray tracing are compared to measurements and simulations using the classical ray tracing method, and it is shown that iterative ray tracing can be used to improve precision over time. Although more testing is needed, iterative ray tracing can be used to extend most ray tracing algorithms, in order to decrease the adverse effects of real-time restrictions.

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.

Sound reduction is complex to estimate for acoustical treatments on ventilation ducts through walls. Various acoustical treatments are available for ventilation ducts, including internal lining (absorption along the inner perimeter), external lagging (external sound insulation), silencer, and suspended ceilings. Previous studies have examined how silencers and the internal lining affect the sound transmission of ventilation ducts. However, there are few theories to predict the effect of external lagging in combination with ventilation ducts and how the total sound reduction is affected. This article aims to investigate different acoustical treatments and develop theoretical models when external lagging with stone wool is used to reduce flanking sound transmission via the surface area of ventilation ducts. Theoretical models are developed for external lagging and compared with measurement data. Measurements and theory are generally in good agreement over the third-octave band range of 100–5000 Hz. The developed models clarify that the distance closest to the wall has the main impact on sound reduction for a combined system with a wall and a ventilation duct. Suspended ceilings and silencers are found to be enough as acoustical treatments for certain combinations of ventilation ducts and walls. However, external lagging seems to be the only effective solution in offices and schools when a large ventilation duct passes through a wall with high sound reduction.

Cross-laminated timber (CLT) floors with supplementary layers or floating floors comprise a common solution in new multistory timber structures. However, bare CLT components provide poor sound insulation, especially in low frequencies during structure-borne sound propagation. Thus, floor configurations in wooden buildings deploy more layers for improved acoustic behavior. Twelve contemporary CLT floors were analyzed after laboratory measurements of airborne sound reduction and impact sound transmission utilizing the following indicators: Rw, Rw, 100, Rw, 50, Ln,w, Ln,w,100, and Ln,w,50 (per ISO 10140, ISO 717). An increase in sound insulation was achieved thanks to added total mass and thickness, testing layers of the following: elastic mat for vibration isolation, wool insulation, gypsum boards, plywood, concrete screed, and wooden parquet floor. The results indicate that multilayered CLT floors can provide improvements of up to 22 dB for airborne sound and 32 dB for impact sound indicators compared with the bare CLT slab. Floating floor configurations with dry floor solutions (concrete screed) and wooden parquet floors stand out as the optimal cases. The parquet floor provides a 1–2 dB improvement only for impact sound indicators in floating floor setups (or higher in three cases).

In ordinary public rooms, such as classrooms and offices, an absorbent ceiling is the typical first acoustic action. This treatment provides a good acoustic baseline. However, an improvement of specific room acoustic parameters, operating for specific frequencies, can be needed. It has been seen that diffusing elements can be effective additional treatment. In order to choose the right design, placement, and quantity of diffusers, a model to estimate the effect on the acoustics is necessary. This study evaluated whether an SEA model could be used for that purpose, particularly for the cases where diffusers are used in combination with an absorbent ceiling. It was investigated whether the model could handle different quantities of diffusing elements, varied diffusion characteristics, and varied installation patterns. It was found that the model was sensitive to these changes, given that the output from the model in terms of acoustic properties will be reflected by the change of diffuser configuration design. It was also seen that the absorption and scattering of the diffusers could be quantified in a laboratory environment: a reverberation chamber. Through the SEA model, these quantities could be transformed to a full-scale room for estimation of the room acoustic parameters.