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| 2. |
- Molin, Nils-Erik, et al.
(författare)
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Optical methods of today for visualizing sound fields in musical acoustics
- 2004
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 90:4, s. 618-628
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Tidskriftsartikel (refereegranskat)abstract
- Pictures that demonstrate physical phenomena are important in science, so also in musical acoustics. In optics, interference, diffraction and polarization phenomena are for instance often pictured in text books. Phase contrast methods are used in microscopy to visualize transparent objects. Such methods have numerous applications in medicine and biology. Shadowgraph, schlieren and different kinds of classical interferometry setups are used in fluid mechanics to study laminar flow, turbulence, convection, subsonic and supersonic flow, shock waves etc. Propagating sound fields often accompany supersonic flow and shock waves. Also transparent object fields like sound and temperature fields can be pictured using optical measuring methods. Merits of these methods are that they are contactless, nondisturbing and wholefield methods. In this paper, some modern optical methods are presented that has the sensitivity and spatial resolution needed to visualize and measure sound fields in musical acoustics. They are computerized, all-electronic methods that present pictures but also give quantitative measures. Harmonic vibrations, standing waves, repetitive sequences and transient wave propagation will be addressed. TV holography, pulsed TV holography and scanning laser Doppler vibrometry (LDV), or scanning vibrometry will be discussed. Speckle photography and correlation methods like digital speckle photography (DSP) and particle image velocimetry (PIV) will also be shortly presented
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| 3. |
- Tinnsten, Mats, et al.
(författare)
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Prediction and verification of acoustic radiation
- 2001
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Ingår i: Acustica - Acta Acustica. - 0001-7884. ; 87:1, s. 117-127
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the boundary element method (BEM) is used to determine acoustic-related quantities in open domains from vibrating structures. Two different types of structures have been analysed, a sphere and an engine transmission cover. The analysed acoustical quantities are pressure amplitude and pressure and intensity amplitude respectively. The numerical results were compared with the analytical and experimental results. In both cases, the sphere and the transmission cover, the input to the BEM program is the normal velocity of the structure surface. The analysed frequency range was in the case of the sphere 100-5000 Hz and a good agreement between numerical and analytical results was obtained up to frequency 3500 Hz. In the engine transmission cover case, the analysed frequency range was 434-3552 Hz with an overall good agreement between numerical and experimental results in the frequency range of 644-1848 Hz
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| 4. |
- Amiryarahmadi, Nata, 1982, et al.
(författare)
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Application of LMS Algorithm to Measure Low-Frequency Transient Forces from Human Walking
- 2016
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Ingår i: Acta Acustica united with Acustica. - : S. Hirzel Verlag GmbH. - 1610-1928 .- 1861-9959. ; 102:1, s. 23-34
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Tidskriftsartikel (refereegranskat)abstract
- Measurement and modeling of low frequency ground reaction forces (GRFs) from human walking have been the subjects of research in different fields from biomechanics to civil engineering and structural dynamics. Many of the existing models are developed based on experiments which alter natural walking by for example presence of force transducers, limitations in the speed and path of walking and replacing the real floor with a transducerfacilitated measurement rig. These alterations result in contact forces which do not represent real GRFs. In this study, a time-domain inverse measurement method based on LMS algorithm is used to measure low-frequency (
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| 5. |
- Amiryarahmadi, Nata, et al.
(författare)
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Identification of low-frequency forces induced by footsteps on lightweight floors
- 2016
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Ingår i: Acta Acoustica united with Acustica. - : S. Hirzel Verlag GmbH. - 1610-1928 .- 1861-9959. ; 102:1, s. 45-57
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Tidskriftsartikel (refereegranskat)abstract
- Despite many advantages of wooden buildings, low-frequency noise disturbance, mainly from human footsteps on timber floors, is a major hindrance for widespread application of wood in multi-storey buildings. In many cases the impact noise evaluations of the wooden floors according to ISO 140-7 and ISO 717-2 standards do not correspond to subjective experiences. This study aims to investigate the characteristics of footstep forces to support further studies related to discrepancies between standard evaluations and low-frequency noise disturbances in lightweight buildings. Transient footstep forces in vertical direction made by different walkers and different footwear on two floor structures were measured and compared. The vertical footstep forces were then compared with the impact forces made by a standard tapping machine. Analysis revealed that footstep forces contain large amplitudes at low frequencies (20 < f < 50) which are not included in the standard evaluation procedure. Therefore, by extending the frequency range of the standard measurements down to 20 Hz and designing an accurate adaptation term for evaluations, a better correlation between standard impact noise evaluations and acoustic performance of the lightweight buildings might be achieved.
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| 6. |
- Andersson, Patrik, 1974, et al.
(författare)
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Boundary Element Method for Intensity Potential Approach : Predicting the Radiated Sound Power from Partially Enclosed Noise Sources
- 2012
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Ingår i: Acta Acoustica united with Acustica. - : S. Hirzel Verlag. - 1610-1928 .- 1861-9959. ; 98:4, s. 588-599
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes the boundary element method for the intensity potential for prediction of high-frequency sound power flow through partial enclosures. The intensity potential approach is based on the local power balance in a lossless medium and the Helmholtz decomposition of the vector field of time-averaged sound intensity. The result is a Poisson equation for a scalar intensity potential. The intensity potential formulation and the boundary element method are both suitable for exterior problems. The governing equations of the intensity potential and the boundary element method for solving this problem are presented. Results from the proposed method are compared with experimental results, for the case of radiated sound power in one-third-octave bands from sources in a partial enclosure. The results show that the method is applicable for estimation of global radiated sound power in one-third-octave bands in the high-frequency range.
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| 7. |
- Andersson, Patrik, 1974, et al.
(författare)
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High Frequency Dynamic Behaviour of Smooth and Patterned Passenger Car Tyres
- 2004
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Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 90:3, s. 445-456
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Tidskriftsartikel (refereegranskat)abstract
- Most traditional tyre models concern the low and middle frequency ranges. For improved accuracy in tyre/roadinteraction models it is necessary to include higher frequencies. Often only the radial direction is included, althoughthe tangential direction may be important, especially studying stick slip motion in the contact between tyreand road surface. Designing accurate and efifcient models requires insight into the behaviour of the tyre structureat higher frequencies to make the models as complete as necessary without creating tools that are computationallytoo costly. To add insight to this area, experimental studies were done on four different tyres with the sameinternal design but with different tread patterns. Point mobilities were measured and compared with two differenttyre models, a two-layer plate model based on the elastic field equations and an orthotropic plate model. Theresults of this study underline the importance of the local deformation when there are forces that act with smallexcitation areas on the tread. Adequate consideration of the tread properties in the tyre/road interaction modelsis thus of extreme importance to obtain the correct local contact force distribution. This is most important for thetangential driving point mobility. Tread patterns are shown mainly to modify the flexural stiffness in comparisonto smooth tyres, while block resonances are not expected to be located in the frequency range in which tyre/roadnoise is important.
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| 8. |
- Andersson, Patrik, 1974, et al.
(författare)
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Validation of a High Frequency Three-Dimensional Tyre Model
- 2005
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Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 91:1, s. 121-131
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Tidskriftsartikel (refereegranskat)abstract
- A high frequency three-dimensional tyre model based on the elastic field equations has been presented previously by Larsson [1]. This model makes it possible to calculate the response caused by a force in both the radial and tangential directions at high frequencies, including the local deformation at the excitation point. Now results from this tyre model have been compared with measured data. The effect of the measurement equipment has been included in the model and the model is demonstrated and validated against measured radial and tangential point and transfer mobilities. The agreement is good for radial point mobilities, capturing the local behaviour at the excitation point. The radial transfer mobilities also agree well with measured data. The tangential point and transfer mobilities also show good agreement with measured data in characteristics and levels, if the boundary conditions are changed. Finally, the benefits and limitations of the models are discussed.
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| 9. |
- Bengtsson, Johanna, 1974, et al.
(författare)
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Sound characteristics in low frequency noise and their relevance for the perception of pleasantness
- 2004
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Ingår i: Acta Acoustica. ; 90:1, s. 171-180
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Tidskriftsartikel (refereegranskat)abstract
- Noise sources with a dominant content of low frequencies (20-200 Hz) are found in many occupational environments. Work efficiency has been found in two earlier studies to be impaired to a larger degree when working in a low frequency ventilation noise than when working in a flat frequency ventilation noise at the same A-weighted sound pressure level. Other previous studies indicate that different sound characteristics found in low frequency noise are important for the way in which low frequency noise affects humans, and better knowledge of these characteristics could lead to better methods for assessing low frequency noise in occupational environments. The aim of this study was to evaluate the influence of frequency balance between low and high frequencies, which affects the slope of the frequency spectra, and the modulation frequency on subjects´ perception of a pleasant low frequency noise. The results showed that the subjects preferred either a higher or a lower modulation frequency as compared to that of the original low frequency noise, both choices leading to less perceivable modulations. Furthermore, the subjects preferred a lower relative content of frequencies below 500 Hz, but only as long as the original low frequency noise contained modulations and the variations were made within a constant A-weighted sound pressure level. The results are discussed in relation to improved guidelines and to the previously suggested theory of slope of the frequency spectra and problems involved with the implementation of that theory.
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| 10. |
- Bodén, Hans
(författare)
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Two-sided multi-port techniques for characterisation of in-duct samples with non-linear acoustic properties
- 2013
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 99:3, s. 359-378
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples accessible from both side such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested. The results of the experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.
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