| 1. |
- Arvidsson, Emma, et al.
(författare)
-
The Difference in Subjective Experience Related to Acoustic Treatments in an Ordinary Public Room : A Case Study
- 2021
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- In ordinary public rooms absorbent ceilings are normally used. However, reflective material such as diffusers can also be useful to improve the acoustic performance for this type of environment. In this study, different combinations of absorbers and diffusers have been used. The study investigates whether a test group of 29 people perceived sound in an ordinary room differently depending on the type of treatment. Comparisons of the same position in a room for different configurations as well as different positions within one configuration were made. The subjective judgements were compared to the room acoustic measures T20, C50 and G and the difference in the values of these parameters. It was found that when evaluating the different positions in a room, the configuration including diffusers was perceived to a greater extent as being similar in the different positions in the room when compared to the configuration with absorbers on the walls. It was also seen that C50 was the parameter that mainly affected the perception, with the difference needing to be 2 dB to recognize a difference. However, the room acoustic measurements could not fully explain the differences obtained in perception. In addition, the subjective sound image created by different types of treatments was also shown to have an important impact on the perception.
|
|
| 2. |
- Arvidsson, Emma, et al.
(författare)
-
The Effect on Room Acoustical Parameters Using a Combination of Absorbers and Diffusers : An Experimental Study in a Classroom
- 2020
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 2:3
-
Tidskriftsartikel (refereegranskat)abstract
- Several room acoustic parameters have to be considered in ordinary public rooms, such as offices and classrooms, in order to present the actual conditions, thus increasing demands on the acoustic treatment. The most common acoustical treatment in ordinary rooms is a suspended absorbent ceiling. Due to the non-uniform distribution of the absorbent material, the classical diffuse field assumption is not fulfilled in such cases. Further, the sound scattering effect of non-absorbing objects such as furniture are considerable in these types of rooms. Even the directional characteristic of the sound scattering objects are of importance. The sound decay curve in rooms with absorbent ceilings often demonstrate a double slope. Thus, it is not possible to use reverberation time as room parameter as a representative standalone acoustic measure. An evaluation that captures the true room acoustical conditions therefore needs supplementary parameters. The aim of this experimental study is to show how various acoustical treatments affect reverberation time T20, speech clarity C50 and sound strength G. The experiment was performed in a mock-up of a classroom. The results demonstrated how absorbers, diffusers and scattering objects influence room acoustical parameters. It is shown that to some extent the parameters can be adjusted individually by using different treatments or combination of treatments. This allows for the fine-tuning of the acoustical conditions, in order to fulfill the requirements for achieving a high-quality sound environment.
|
|
| 3. |
- Eddin, Mohamad Bader, et al.
(författare)
-
Prediction of Sound Insulation Using Artificial Neural Networks—Part I : LightweightWooden Floor Structures
- 2022
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 4:1, s. 203-226
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 4. |
- Kissner, Carolin, et al.
(författare)
-
ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction-Part I-Influence of the RANS Simulation
- 2020
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 2:3, s. 539-578
-
Tidskriftsartikel (refereegranskat)abstract
- A benchmark of Reynolds-Averaged Navier-Stokes (RANS)-informed analytical methods, which are attractive for predicting fan broadband noise, was conducted within the framework of the European project TurboNoiseBB. This paper discusses the first part of the benchmark, which investigates the influence of the RANS inputs. Its companion paper focuses on the influence of the applied acoustic models on predicted fan broadband noise levels. While similar benchmarking activities were conducted in the past, this benchmark is unique due to its large and diverse data set involving members from more than ten institutions. In this work, the authors analyze RANS solutions performed at approach conditions for the ACAT1 fan. The RANS solutions were obtained using different CFD codes, mesh resolutions, and computational settings. The flow, turbulence, and resulting fan broadband noise predictions are analyzed to pinpoint critical influencing parameters related to the RANS inputs. Experimental data are used for comparison. It is shown that when turbomachinery experts perform RANS simulations using the same geometry and the same operating conditions, the most crucial choices in terms of predicted fan broadband noise are the type of turbulence model and applied turbulence model extensions. Chosen mesh resolutions, CFD solvers, and other computational settings are less critical.
|
|
| 5. |
- Nilsson, Erik, et al.
(författare)
-
Sound Reduction of Ventilation Ducts through Walls : Experimental Results and Updated Models
- 2021
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 3:4, s. 695-716
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Autio, Hanna, et al.
(författare)
-
A Novel Algorithm for Directional Scattering in Acoustic Ray Tracers
- 2023
-
Ingår i: Acoustics. - 2624-599X. ; 5:4, s. 928-947
-
Tidskriftsartikel (refereegranskat)abstract
- It is vital to consider acoustic scattering when using geometrical acoustic simulation techniques, such as ray tracing. However, there are few methods for modelling scattering, and most rely on strong assumptions of uniformity on the distribution of scattered energy. In this paper, a model for directional scattering in ray tracers is presented. The model is based on an idealized model of a 1D scatterer, which is then used to extend the most commonly used scattering algorithm in ray tracers today. The developed algorithm is implemented in a ray tracer and tested to evaluate its performance compared to existing methods. It is found that the directional scattering algorithm can be used to replicate measured effects on room acoustic parameters caused by changes in the orientation of 1D scatterers.
|
|
| 7. |
- Autio, Hanna, et al.
(författare)
-
An Iterative Ray Tracing Algorithm to Increase Simulation Speed While Maintaining Overall Precision
- 2023
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 5:1, s. 320-342
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Nilsson, Erik, et al.
(författare)
-
Acoustical Treatments on Ventilation Ducts through Walls : Experimental Results and Novel Models
- 2022
-
Ingår i: Acoustics. - : MDPI AG. - 2624-599X. ; 4:1, s. 276-296
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
