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  • 1.
    Carlson, Johan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Exploring interaction effects in two-component gas mixtures using orthogonal signal correction of ultrasound pulses2005Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 117, nr 5, s. 2961-2968Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Within Sweden and the EU, an increased use of biogas gas and natural gas is encouraged to decrease emission of carbon dioxide. To support more effective manufacturing, distribution, and consumption of energy gases, new methods for the measurement of the calorimetric value or the gas composition are needed. This paper presents a method to extract and visualize variations in ultrasound pulse shape, caused by interaction effects between the constituents of a two-component gas mixture. The method is based on a combination of principal component analysis and orthogonal signal correction. Pulse-echo ultrasound experiments on mixtures of oxygen and ethane in the concentration range from 20% to 80% ethane show that the extracted information could be correlated with the molar fraction of ethane in the mixture

  • 2.
    Cerdá, Salvador
    et al.
    Laboratory of Acoustics, Department of Applied Physics, University of Valencia.
    Romero, José
    Laboratory of Acoustics, Department of Applied Physics, University of Valencia.
    Navasquillo, Joaquin
    Laboratory of Acoustics, Department of Applied Physics, University of Valencia.
    Villarroel, Grover Zurita
    Luleå tekniska universitet.
    A study of knock and adiabatic process in multi-fuel engines2000Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 108, nr 5, s. 2594-2595Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    For both engine designers and control purposes, a better understanding of the knocking that occurs during combustion in engines can lead to optimal decisions which will make engines operate more efficiently. The rapid rise in diesel engines is recognized as an audible impulse noise, which is known as ``knock.'' The knock is caused by the spontaneous combustion of a significant volume of fuel/air mixture. The knock produces shock waves within the combustion chamber and results in a great number of combustion chamber resonance frequencies. The engine used in the experiments was a six-cylinder modified diesel engine running in ethanol conditions. The main purpose of this research is to determine the knock phenomena and the adiabatic process. To perform the data analysis a time-frequency spectral approach was used. The results revealed both radial and circumferential resonances. The most important adiabatic coefficients were carried out and used to calculate the heat release rate.

  • 3.
    Chaigne, Antoine
    et al.
    ENST, Signal Department.
    Lambourg, Christophe
    ENST, Signal Department.
    Schedin, Staffan
    Luleå tekniska universitet.
    Measurements and modeling of the transient acoustic field at impacted plates1998Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, nr 5, s. 2814-1815Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comparison between measured and simulated transient acoustic fields generated by thin impacted plates is reported. The plate is modeled by using finite difference methods and the radiated pressure is obtained by solving the Rayleigh integral [Ch. Lambourg and A. Chaigne, J. Acoust. Soc. Am. 101(A) (1997)]. The results are evaluated in the form of the spatial pressure distribution at instants short after the excitation. Experimentally, a lead bullet (0.5 g, 100 m/s) is fired towards a cantilever steel plate (300×30×1 mm). The duration of the impact is estimated by using a high-speed camera that can register several million frames per second. An interferometric comparison of the change in optical path length of two holographic recordings, captured before and shortly after the impact, gives a 2-D projection of the acoustic field. A double-pulsed ruby laser, emitting light pulses of short duration (30 ns), is used as light source [S. Schedin, A. O. Waahlin, and P. Gren, J. Acoust. Soc. Am 99, 700-705 (1996)]. A high degree of similarity is observed between measured and simulated sound field, except in the close vicinity of the impact point. It is presumed that the discrepancies are due to nonlinear effects which are not included in the model

  • 4.
    Jansson, Erik V.
    et al.
    Kungliga tekniska högskolan, KTH.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optical modal analysis compared to modal analysis with digital electronic equipment1988Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 84, nr 1, s. 136-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hologram interferometry and speckle interferometry have introduced powerful tools for "optical modal analysis." The vibration amplitudes at a single frequency are recorded simultaneously for all points of a surface. The excitation position and frequency are adjusted to give a normal mode by watching the vibration patterns in real time. In the common modal analysis with digital electronic equipment, the vibrations of a single point as a function of time are recorded for all frequencies simultaneously via the impulse response. Impulse responses for a large number of points are measured, analyzed, and recalculated to extract the normal modes. Investigations of two modes of a complicated object (a violin) using both methods showed differences. The position of the dominating antinodes agreed, but the distribution of the vibration amplitudes and especially the nodal lines did not always agree. The differences seem to depend mainly on methods. The differences imply that great cautiousness is motivated in interpreting unknown vibration modes of objects with complicated structures and boundaries. The real time observation with the optical modal analysis offers hereby advantages

  • 5.
    Jansson, E.V.
    et al.
    Kungliga tekniska högskolan, KTH.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    On eigenmodes of the violin: electronic holography and admittance measurements1994Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 95, nr 2, s. 1100-1105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present experimental investigation, using recently assembled advanced electro-optical equipment for vibration analysis of three violins, was conducted to seek answers to three questions. A general or global question: Which parts of the violin body are vibrating the most? And two questions related to tonal quality: Are basic low-frequency vibration modes of a musically superior instrument different from those of an inferior violin? Can some special vibration properties be found to support the ``bridge hill?'' Optically obtained vibration modes were recorded as well as frequency responses in the form of admittance measurements. The investigation showed that the vibration modes found earlier are representative both for the inferior violin and the musically superior instruments, although discrepancies can be seen, both in eigenmode shapes and admittance responses. The experimental results are also in quite good agreement with published results of the modal analysis of a violin. Further, the experimental results indicate that the transversal vibrations are mainly within the plates, but at low frequencies, the vibrations of the edges and of the ribs can be large and in-plane as well as transversal. At higher frequencies, the transversal vibration amplitudes are small at the plate edges and larger inside. The top plate tends to have the largest amplitude of vibrations. In the 2.5-kHz range the violin with the most clear ``bridge hill'' tends to have the largest vibrations of the plates.

  • 6.
    Jiang, Biao
    Hangzhou Applied Acoustics Research Institute.
    Robust wideband adaptive beamforming using waveguide invariant focusing method2012Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 131, nr 4, s. 3487-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The waveguide invariant describing the dispersive propagation in underwater environment can provide useful information for signal processing. In this paper, waveguide invariant focusing is exploited to preprocess the received horizontal array signal, such that the moving target is aligned in a single rank-one signal subspace over the bandwidth, results a reduction of the number of the snapshots necessary for the adaptive beamforming, and the diagonal loading is optimized using the robust Capon method to further improve the robustness. Numerical results show that the proposed method can improve the detection performance with limited observation time. Moreover, passive ranging is accomplished when the beamforming output achieves the maximum over a scanned target range limit.

  • 7.
    Johansson, Örjan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lindegren, David
    Luleå tekniska universitet.
    Analysis of everyday sounds which are extremely annoying for children with autism2008Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 123, nr 5, s. 3299-Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Extreme sensitivity to noise is a problem that almost all autistic children suffer from. A sound that is extremely annoying does not need to be loud. However, the characteristics and temporal variations of these sounds are sparsely investigated. The aim of this study is to increase the knowledge about these extremely annoying sounds so they can be avoided by better design criteria for classrooms and venues like that. By interviewing teachers and parents a number of everyday sounds were identified and binaurally recorded. Examples are vacuum cleaners, ventilation noise, washing machines and pouring water. Detailed psychoacoustic analyses of this type of sounds were achieved by a listening test procedure in three parts. First 16 children composed different types of vacuum cleaner sounds trying to minimize annoyance in two different tests, a) keeping original sound pressure level. b) adjusting to acceptable loudness. In the second part, teachers working with autistic children performed a listening test to evaluate some of the composed sounds from part 1 and modified versions of them. The third part was performed by children to validate the results. The results showed that Roughness, Loudness and an index defined as High frequency tonality were the most important characteristics.

  • 8.
    Ling, Jun
    et al.
    Department of Electrical and Computer Engineering, University of Florida.
    Zhao, Kexin
    Department of Electrical and Computer Engineering, University of Florida.
    Li, Jian
    Department of Electrical and Computer Engineering, University of Florida.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Multi-input multi-output underwater communications over sparse and frequency modulated acoustic channels2011Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 130, nr 1, s. 249-262Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper addresses multi-input multi-output (MIMO) communications over sparse acoustic channels suffering from frequency modulations. An extension of the recently introduced SLIM algorithm, which stands for sparse learning via iterative minimization, is presented to estimate the sparse and frequency modulated acoustic channels. The extended algorithm is referred to as generalization of SLIM (GoSLIM). The sparseness is exploited through a hierarchical Bayesian model, and because GoSLIM is user parameter free, it is easy to use in practical applications. Moreover this paper considers channel equalization and symbol detection for various MIMO transmission schemes, including both space-time block coding and spatial multiplexing, under the challenging channel conditions. The effectiveness of the proposed approaches is demonstrated using in-water experimental measurements recently acquired during WHOI09 and ACOMM10 experiments.

  • 9.
    Ljunggren, Fredrik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Changed sound properties due to minor construction changes in a lightweight building2008Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 123, nr 5, s. 3763-Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    This paper relates to building acoustic measurement inside a two-story office house. The construction, which is known as lightweight, is prefabricated in volumes at a factory and is then transported to the building yard for assembling. It is build up of a wooden frame with particle boards and plaster boards attached. The building consists of a number of nominally, or almost nominally, identical rooms with assumed identical sound properties. In the projection stage, the construction was slightly modified in some of the rooms in order to see in what way the sound properties would be affected. In total eight impact sound pressure level measurements and eight sound reduction index measurements were performed and analysed for the different setups.

  • 10.
    Mace, P.R.
    et al.
    Institute of Sound and Vibration Research, University of Southampton.
    Jones, Richard W.
    Luleå tekniska universitet.
    Harland, N.R.
    Department of Mechanical Engineering, University of Auckland.
    Wave transmission through structural inserts2001Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 109, nr 4, s. 1417-1421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transmission of waves through two discontinuities in a one-dimensional waveguide system is considered. Attention is focused on transmission through a structural insert, which is defined here to be a waveguide segment which is inserted into an otherwise continuous structural member with different properties. A general expression for the net transmission through the insert is found. It has bandpass/stop characteristics and its frequency average is somewhat greater than that normally assumed due to the coherent interaction of the waves in the insert. The particular case is then considered where the insert comprises a three-layer composite beam inserted in a thin beam which vibrates in bending. The composite beam comprises two elastic faceplates and a core filled with a tunable electro- or magneto-rheological fluid. The net transmission and the stop bands depend on the properties of the insert. Since these properties are tunable by adjusting the field to which the tunable fluid is exposed, then so too are the transmission characteristics of the insert

  • 11.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, E.V.
    Kungliga tekniska högskolan, KTH.
    Transient wave propagation in wooden plates for musical instruments1989Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 85, nr 5, s. 2179-2184Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transient bending waves in three wooden plates are studied. A rectangular flat spruce plate (from a guitar top plate) and two arched violin plates (of spruce and maple, respectively) are impacted by a small ballistic pendulum. The impact point is at the center of the guitar plate and the bridge position of the violin plates. A sequence of holographic interferograms of the events is recorded using a double pulsed ruby laser as the light source. The holographic setup is a standard one. The elliptical shape of the interference fringes shows that wood is strongly anisotropic. The shape of the propagating pulse changes with time, which shows the dispersive behavior of bending waves in plates. A solution of the isotropic Euler plate equation for a flat plate is compared to experimental results of the guitar plate, assuming that this description is adequate along the main axes of this orthotropic plate. The shape of the propagating wave pattern and the elliptical rather than circular shape of the violin imply an interesting coincidence

  • 12.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jansson, Erik V.
    Royal Institute of Technology.
    Parameters of violin plates and their influence on the plate modes1988Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 83, nr 1, s. 281-291Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noncontact measuring methods and numerical calculations are used in a study of musical instruments. First, a simple method to determine the material parameters of a blank to a violin plate is presented. Eigenmodes of rectangular free-free violin wooden blanks are determined using optical nondestructive methods, Chladni patterns, or tapping. Assuming orthotropic material, the first three eigenmodes for such a blank are calculated using the finite element method (FEM). It is shown that the frequency of each eigenmode depends on separate elastic parameters. With this one variable dependence, it is a simple task to determine effective material parameters for quarter-cut standard wooden blanks when the frequencies and mass are known. Second, the violin maker's problem with the influence of material and geometrical parameters on the vibration modes is investigated. Numerical models and corresponding real violin plates are made from the spruce and the maple blanks. Good agreement between calculated and experimentally obtained plate modes is found. Calculations with a 10% variation in each parameter are thereafter used to give information about the influence of overall plate thickness variation, of local thickness variations, of changes in arch-height, and of material parameters. Third, boundary conditions for the plates when glued to the ribs are examined in a pilot experiment.

  • 13.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wåhlin, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Jansson, Erik V
    Kungliga tekniska högskolan, KTH.
    Transient wave response of the violin body revisited1991Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 90, nr 4, s. 2192-2195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this investigation, the dispersive, transient wave propagation field of the top plate of a complete violin excited by a mechanically induced pulse at the top of the bridge is presented. A similar investigation has previously been made for excitation parallel with the top plate and is now completed with excitation perpendicular to the plate. From presented interferograms, it is seen that the top plate initially deforms in a nonsymmetric two-pole with centers at the two bridge feet. Shortly thereafter the two poles (valleys) are joined into one, but after 0.30 ms the displacement is still nonsymmetric with maximum motion at the bridge foot closest to the excitation point. From the measurements it can be concluded that for excitation parallel with the top plate, the plate between the f-holes acts mainly as a dipole, but with excitation perpendicular the same part acts mainly as a monopole. Thus the excitation of the top plate when playing the violin depends on the angle of the bow in relation to the top plate and should influence the tone character

  • 14.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wåhlin, Anders
    Jansson, E.V.
    Luleå tekniska universitet.
    Transient wave response of the violin body1990Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 88, nr 5, s. 2479-2481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments

  • 15.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    The effect of binaural processing techniques on speech quality ratings of assistive listening devices in different room acoustics conditions2008Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 123, nr 5, s. 3170-Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    External microphone systems, referred to as assistive listening devices (ALD), are used in classrooms for hearing impaired students. The objective is to investigate the effect of binaural processing techniques in different room acoustic conditions. A listening experiment was conducted with 10 normal hearing adults. Response variables were judgements of clarity, pleasantness, listening effort and overall speech quality. Design variables were binaural processing, room acoustics and ALD bandwidth. Stimuli were generated using the room acoustic modelling software CATT Acoustic. Three speech sources, two male voices and one female voice, were placed at a table in the centre of a room and one Brown noise source was placed in one corner of the room. Microphones were placed 0.5 m in front of each speech source. Target source was a random choice of one of the two male voices. The binaural processing was utilized by a simple HRTF filtering. Depending on the angle to the source from a fictitious listening position at the table, corresponding interaural time difference (ITD) and the interaural level difference (ILD) was applied to the signal. Stimuli were presented by loudspeakers using cross-talk cancellation. The hypothesis is that binaural processing will give a significant improvement in speech quality.

  • 16.
    Poll, Marijke Keus van de
    et al.
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Carlsson, Johannes
    Chalmers University of Technology, Department of Civil and Environmental Engineering.
    Marsh, John E.
    School of Psychology, University of Central Lancashire.
    Ljung, Robert
    Department of Building, Energy, and Environmental Engineering, University of Gävle, University of Gävle.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Schlittmeier, Sabine J.
    Work, Environmental and Health Psychology, Catholic University of Eichstätt-Ingolstadt.
    Sundin, Gunilla
    Akustikon Team in Norconsult AB.
    Sörqvist, Patrik
    Department of Building, Energy, and Environmental Engineering, University of Gävle, Centre for Built Environment, University of Gävle.
    Unmasking the effects of masking on performance: The potential of multiple-voice masking in the office environment2015Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 138, nr 2, s. 807-816Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Broadband noise is often used as a masking sound to combat the negative consequences of background speech on performance in open-plan offices. As office workers generally dislike broadband noise, it is important to find alternatives that are more appreciated while being at least not less effective. The purpose of experiment 1 was to compare broadband noise with two alternatives - multiple voices and water waves - in the context of a serial short-term memory task. A single voice impaired memory in comparison with silence, but when the single voice was masked with multiple voices, performance was on level with silence. Experiment 2 explored the benefits of multiple-voice masking in more detail (by comparing one voice, three voices, five voices, and seven voices) in the context of word processed writing (arguably a more office-relevant task). Performance (i.e., writing fluency) increased linearly from worst performance in the one-voice condition to best performance in the seven-voice condition. Psychological mechanisms underpinning these effects are discussed

  • 17.
    Romero, Jose
    et al.
    Laboratory of Acoustics, Department of Applied Physics, University of Valencia.
    Jimenez, Alicia
    Polytecnic University of Valencia.
    Sanchis, Antonio
    Polytecnic University of Valencia.
    Marin, Albert
    Polytecnic University of Valencia.
    Garcia, Amando
    Laboratory of Acoustics, Department of Applied Physics, University of Valencia.
    Villarroel, Grover Zurita
    Luleå tekniska universitet.
    Multivariate analysis of road traffic noise in Gandia (Spain) during 24 hours and its evolution in the last decades1998Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 103, nr 5, s. 3003-Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Road traffic noise is one of the most widespread and growing problems in urban areas. While it has long been known that hearing can be damaged by exposure to noise, it is also believed that continual noise, even at low or moderate intensity, can cause psychological discomfort and sleep disorders. Traffic noise levels in urban areas are increasing, and the areas affected by noise are spreading. As a result of these problems, legislation has been introduced by the city council to control the noise produced by individual vehicles with the aim of eventually producing traffic noise levels which are acceptable to the public. In this paper, therefore, aspects which connect the evolution of the road traffic noise in the last decades and the development of the infrastructure of the city are discussed. The study was carried out in Gandia (Spain), which is situated on the East Coast of the country, 65 kms from Valencia and 100 kms from Benidorn. The population has increased from 50 000 to 60 000 in the last 15 years, and the traffic distribution of the city has changed during this time, with a new bridge and some highways around the urban area. The main objective of this paper is to characterize the effects of the road traffic noise during 24 h (between 1983 and 1997), and including such aspects as traffic density and psychological aspects. The analysis part was performed by using multivariate analysis methods (MVA). Multivariate analysis methods can be used to investigate relationships between all the variables by extracting information from data with many variables and treating them simultaneously.

  • 18.
    Rossing, Thomas D.
    et al.
    Northern Illinois University.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Runnemalm, Anna
    Luleå tekniska universitet.
    Modal analysis of violin bodies viewed as three-dimensional structures2003Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 114, nr 4, s. 2438-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modal analyses of violins show several strong modes in the low frequency range. Holographic interferograms suggest that four strong modes can be interpreted as doublets having two and three nodal planes that intersect a cylinder with a roughly elliptical cross section at the bridge [A. Runnemalm, N.-E. Molin, and E. Jansson, J. Acoust. Soc. Am. 107, 3452-3459 (2000); M. Roberts and T. D. Rossing, Catgut Acoust. Soc. J. 3, 9-15 (1998)]. This is especially clear when the instrument is viewed simultaneously from three sides using mirrors, and the holographic system is made sensitive to in-plane motion as well. These doublets are not unlike those observed in cylindrical vibrators such as bells, and they remind us that a violin is a 3-dimensional object

  • 19.
    Runnemalm, Anna
    et al.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, Erik
    Kungliga tekniska högskolan, KTH.
    On operating deflection shapes of the violin body including in-plane motions2000Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 107, nr 6, s. 3452-3459Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier investigations have assumed only "out-of-plane" vibrations of the plates of the violin. The violin body can, however, be described as a thin-walled, double-arched shell structure and as such it may very well elongate in one direction as it contracts in another. Therefore, at least two orthogonal vibration components have to be included to describe the vibrations. The operating deflection shapes (ODSs) of a good, professionally made and carefully selected violin were therefore measured in several directions by TV holography to determine both "in-plane" and out-of-plane vibration components of the ODSs. The observations were limited to the frequency range 400-600 Hz, as this interval includes two most-prominent resonance peaks of bridge mobility and sound radiation as well as a third poorly radiating resonance. These three peaks clearly showed orthogonal vibration components in the ODSs. The vibration behavior of the violin body, sectioned in the bridge plane, was interpreted as the vibrations of an "elliptical tube" with nodal diameters. The number of nodal diameters increases from two to three in the selected frequency range. The TV holography measurements were supported by electrodynamical point measurements of bridge mobility, of air volume resonances, and by reciprocity, of radiation properties. Furthermore, a fourth mode, the air mode, A1, is involved indirectly in the sound radiation via influence on the body vibrations.

  • 20.
    Saldner, Henrik O.
    et al.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, Erik V.
    Kungliga tekniska högskolan, KTH.
    Vibration modes of the violin forced via the bridge and action of the soundpost1996Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 100, nr 2, s. 1168-1177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The action of the soundpost in a violin is not well understood and fundamental knowledge is needed. Therefore low-frequency forced modes, operating deflection shapes, 250-600 Hz of a violin were investigated. Harmonic, sine wave, excitation was applied via the bridge (resembling playing) or via the sound from a loudspeaker. The latter excitation gives a reciprocal measure of radiativity. The modes were investigated with TV-holography and electro-acoustical admittance measurements. A carefully selected violin was investigated without soundpost, with soundpost, and with the soundpost position shifted toward the centerline, Answers were sought to three questions: Which are the violin modes forced via the bridge? To what extent do they radiate sound? What is the action of the soundpost? The observed modes were mostly not pure normal modes but mode combinations. Generally there is a nodal line close to the soundpost position of the plates. Schelleng has hypothesized that the main action of the soundpost is to make the violin nonsymmetric. The first top plate mode with soundpost can be looked upon as a combination of the first symmetric top plate mode and the first asymmetric mode without soundpost, The first mode is an effcient radiator and the second mode transfers the string vibrations via the bridge to the top plate efficiently. The asymmetric first mode with the soundpost is thus both excited and radiates sound. Our experimental results make the hypothesis plausible, but show that body (global) modes play an important role too. In the range 500 to 600 Hz, a body mode, C3, constitutes a major part. The C3 mode has a nodal line close to the normal soundpost position and is especially interesting as it seems to form a quality mark of a good violin

  • 21.
    Sandell, Magnus
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Estimation of the spatial impulse response of an ultrasonic transducer using a tomographic approach1995Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 98, nr 4, s. 2094-2103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. These investigations can be extended to include the reflected echoes from point reflectors, which can be used in syntesizing echoes from reflectors of known shapes. The single point echo can be measured directly but there are however certain problems associated with this. This paper proposes an alternative method to estimate the echo from a point-like reflector by measuring the echoes from sliding halfplanes. Using a tomographic approach, the single point echo is estimated from these measurements. To perform the tomographic inversion, a truncated weighted Singular Value Decomposition (SVD) is used in order to catch essential features of the ultrasonic echoes, where the weight functions are chosen specially to suit our application. Numerical solutions are given for the chosen weight functions and an error analysis is carried out.

  • 22.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Rossing, Thomas D.
    Northern Illinois University.
    Transient wave response of a cymbal using double-pulsed TV holography1998Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 103, nr 2, s. 1217-1220Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using an electronic system for pulsed TV holography with a double-pulsed ruby laser, transient wave propagation during intervals from 30 to 480 µs after impact is recorded. The first observable bending waves, having wavelengths of about 5 mm, propagate at about 1700 m/s, and reach the edge of the cymbal in about 60 µs. These are quickly followed by waves of longer wavelength which scatter at the outer edge of the cymbal and also the central dome and result in standing waves. A phase unwrapping procedure is used to obtain a three-dimensional map of the wave field. Holographic film recordings similarly show scattering of transient bending waves at the central dome

  • 23.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Wåhlin, Anders
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient acoustic near field in air generated by impacted plates1996Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 99, nr 2, s. 700-705Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two-reference-beam double-pulsed holographic interferometry. The acoustic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itself. A subsequent phase-stepping procedure is used for quantitative evaluation of the registered two-dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the free end of the plate, where sound waves propagate into the air in oblique directions from the plate. At the region right above the free end no acoustic waves are observed. Supersonic flexural waves in the plates generate trace-matched acoustic waves in the surrounding air. Calculations of the corresponding two-dimensional transient acoustic fields are performed. Those are based on an analytical solution of the Kirchhoff plate equation. Calculated results reproduce the character of the observed transient acoustic waves quite well

  • 24.
    Wåhlin, Anders
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    On structure-borne sound: experiments showing the initial transient acoustic wave field generated by an impacted plate1994Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 96, nr 5, s. 2791-2797Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial propagating transient acoustic field in air generated by an impacted plate is visualized. The transient traveling flexural waves in the plate created by the impact are shown, simultaneously. The experiments are performed using double pulsed holographic interferometry. It is shown that flexural waves in a plate act as a series of traveling acoustic sources. Since the flexural waves in the plate are dispersive the trace matched acoustical waves further away from the impact source propagate at a smaller angle relative to the plate than those closer to the impact. An observer situated close to the plate and away from the impact point will first receive high-frequency components of the sound. A quantitative evaluation of the acoustic field also shows that if there is a transient increase in pressure on one side of the plate there will be a similar decrease on the other side.

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