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  • 1.
    Andersson, Patrik B. U.
    et al.
    Chalmers, Sweden.
    Lindberg, Eskil
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Boundary Element Method for Intensity Potential Approach: Predicting the Radiated Sound Power from Partially Enclosed Noise Sources2012In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 98, no 4, p. 588-599Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Two-sided multi-port techniques for characterisation of in-duct samples with non-linear acoustic properties2013In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 99, no 3, p. 359-378Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Bolin, Karl
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prediction Method for Wind-Induced Vegetation Noise2009In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 95, no 4, p. 607-619Article in journal (Refereed)
    Abstract [en]

    This article examines the sound generated when the wind interacts with vegetation. A wind field model has been coupled to a new method for predicting sound from vegetation. This includes predictions from coniferous, deciduous and leafless trees. The proposed prediction method and an earlier model have been compared with measurements which show improved agreement, in particular in the region below 1 kHz. Comparisons between five measurement sites and predictions show satisfactory agreement for wind speeds up to 8.5 m/s. Fluctuations in the vegetation noise level due to wind turbulence can also be accurately estimated.

  • 4.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bluhm, Gosta
    Nilsson, Mats E.
    Listening Test Comparing A-Weighted and C-Weighted Sound Pressure Level as Indicator of Wind Turbine Noise Annoyance2014In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 100, no 5, p. 842-847Article in journal (Refereed)
    Abstract [en]

    A listening test was conducted to investigate whether A-or C-weighed sound levels are most suitable as indicator of annoyance due to wind turbine noise. The tests consisted of fifteen different wind turbine noises presented at eight sound levels together with pink noise signals as reference sounds. A total number of 31 persons performed the listening test divided into two subgroups. The first group comprising of 20 students conducted the test in a semi anechoic chamber, and the second group of 11 residents annoyed by wind turbine noise in their homes, conducted the test in their own homes. Results from both subgroups showed that A-weighed sound levels were a more accurate description of wind turbine noise annoyance than C-weighed sound levels. The residents found the same wind turbine noises more annoying than the students, indicating a higher sensitivity to wind turbine noise among persons a priori annoyed by this noise and exposed to this source in their residential settings.

  • 5.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Kedhammar, Anders
    Nilsson, Mats E.
    The Influence of Background Sounds on Loudness and Annoyance of Wind Turbine Noise2012In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 98, no 5, p. 741-748Article in journal (Refereed)
    Abstract [en]

    Natural sounds may create pleasant soundscapes that mask wind turbine noise. To explore this, a listening test was performed to investigate the influence of background sounds on perceived loudness and annoyance of wind turbine noise. A magnitude estimation method was used to measure perceived loudness and annoyance of wind turbine noise heard together with and without natural ambient sounds. Results indicate that decreased loudness and annoyance occurs if the level of the background sound exceeds the level of the wind turbine noise. The loudness experiment revealed that ambient sounds influenced the perception of wind turbine noise to a higher degree than predicted from a model of energetic masking. Annoyance ratings were less altered by background sound than perceived loudness. The results of the present listening study indicates that masking of wind turbine noise by positive natural sounds may be used as a complement to conventional noise control measures to improve the sound environment in areas exposed to wind turbine noise.

  • 6.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Khan, S.
    Determining the potentiality of masking wind turbine noise using natural ambient noise2006In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959Article in journal (Other academic)
  • 7.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, Mats E
    Karolinska Institutet, Inst. för Miljömedicin.
    Khan, Shafiquzzaman
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    The Potential of Natural Sounds to Mask Wind Turbine Noise2010In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 96, no 1, p. 131-137Article in journal (Refereed)
    Abstract [en]

    Wind turbine (WT) noise may cause annoyance, especially in relatively quiet areas with low ambient levels. As a compliment to conventional noise control at the source, addition of wanted sounds may reduce the loudness of WT noise by auditory masking. In order to test this, two masking experiments were conducted with two WT noises as target sounds and three natural sounds as maskers (wind in coniferous or deciduous trees and sea waves). In the first experiment, 30 listeners determined the detection thresholds of WT noise in the presence of the natural sounds using a threshold tracking method. In the second experiment, the same group of listeners matched the loudness of partially masked WT noise with the loudness of unmasked WT noise. The results showed that detection thresholds for WT-noise in the presence of natural sounds from trees and sea waves were around -8 to -12 dB S/N-ratio. Furthermore, a reduction of perceived loudness of WT-noise was found for S/N-ratios up to 2 dB. These results were compared with predictions from two models of partial masking (steady and time variant). In general, empirically determined detection thresholds and partial loudness matches were higher than predictions from the two models.

  • 8.
    Coja, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    An effective waveguide model for pre-compressed vibration isolatorsIn: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959Article in journal (Refereed)
  • 9.
    Dahl, Sofia
    KTH, Superseded Departments, Speech, Music and Hearing.
    Playing the accent: comparing striking velocity and timing in an ostinato rhythm performed by four drummers2004In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 90, no 4, p. 762-776Article in journal (Refereed)
    Abstract [en]

    Four percussion players’ strategies for performing an accented stroke were studied by capturing movement trajectories.The players played on a force plate with markers on the drumstick, hand, and lower and upper arm. Therhythmic pattern – an ostinato with interleaved accents every fourth stroke – was performed at different dynamiclevels, tempi and on different striking surfaces attached to the force plate. The analysis displayed differencesbetween the movement trajectories for the four players, which were maintained consistently during all playingconditions. The characteristics of the players’ individual movement patterns were observed to correspond wellwith the striking velocities and timing in performance. The most influential parameter on the movement patternswas the dynamic level with increasing preparatory heights and striking velocity for increasing dynamic level. Theinterval beginning with the accented stroke was prolonged, the amount of lengthening decreasing with increasingdynamic level.

  • 10.
    Demoucron, Matthias
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    Askenfelt, Anders
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    Caussé, Rene
    IRCAM CNRS STMS.
    Measuring Bow Force in Bowed String Performance: Theory and Implementation of a Bow Force Sensor2009In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 95, no 4, p. 718-732Article in journal (Refereed)
    Abstract [en]

    A sensor has been developed which allows measurement of the force exerted by the bow on the string ( bow force) during violin performance. The bow force is deduced from measurement of the transversal force at the termination of the bow hair at the frog. The principle is illustrated with an experiment that demonstrates how the bending of the stick and variations in bow hair tension influence the measurements. The design of the sensor is described and performance characteristics are discussed. A thorough calibration procedure is described and tested. Finally, the use of the sensor is demonstrated through measurements in real playing situations.

  • 11. Durup, E
    et al.
    Jansson, Erik Valter
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    The quest of the violin Bridge-Hill2005In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 91, no 2, p. 206-213Article in journal (Refereed)
    Abstract [en]

    Good violins have a Bridge-Hill, i.e. a hump between 2 and 3 kHz in their frequency responses, both in radiated sound and in bridge mobility. Experiments have proved that the Hill is not confined to the bridge only. Present experiments show that the Hill can be modelled by a plate-bridge and a rectangular spruce plate with f-holes shaped as up-side-down Us. The flaps, the wings cut free by the up-side-down Us and especially their areas determine the peak frequency of the Hill. By tuning the bridge and the wings of a complete violin the Hill is obtained and can be tuned within a wide frequency range.

  • 12. Echternach, Matthias
    et al.
    Birkholz, Peter
    Sundberg, Johan
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics. University College of Music Education, Stockholm, Sweden.
    Traser, Louisa
    Korvink, Jan Gerrit
    Richter, Bernhard
    Resonatory Properties in Professional Tenors Singing Above the Passaggio2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 102, no 2, p. 298-306Article in journal (Refereed)
    Abstract [en]

    Introduction: The question of formant tuning in male professional voices has been a matter of discussion for many years. Material and Methods: In this study four very successful Western classically trained tenors of different repertoire were analysed. They sang a scale on the vowel conditions /a,e,i,o,u/ from the pitch C4 (250 Hz) to A4 (440 Hz) in their stage voice avoiding a register shift to falsetto. Formant frequencies were calculated from inverse filtering of the audio signal and from two-dimensional MRI data. Results: Both estimations showed only for vowel conditions with low first formant (F1) a tuning F1 adjusted to the first harmonic. For other vowel conditions, however, no clear systematic formant tuning was observed. Conclusion: For most vowel conditions the data are not able to support the hypothesis of a systematic formant tuning for professional classically trained tenors.

  • 13.
    Feng, Leiping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Modified honeycomb panels to improve sound insulation properties2005In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 91, no 2, p. 386-388Article in journal (Refereed)
    Abstract [en]

    A modified honeycomb panel with improved bonding technique is presented in this paper. The idea is to keep the basic mechanical properties of a honeycomb panel while to eliminate the coincidence phenomenon of the whole system by using modified bonding technique. A specimen was made and measurement was performed. Results show that the coincidence phenomenon of the whole system disappears and the weighted intensity sound reduction index is 4 dB higher than that of the corresponding honeycomb panel with similar surface density and static strength.

  • 14.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Tone-like signal in the wind-induced noise of perforated plates2012In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 98, no 1, p. 188-194Article in journal (Refereed)
    Abstract [en]

    In some special situations the wind-induced noise of perforated plates may show strong power enhancement in a certain frequency band and hence exhibits a "tone-like" character. This problem is investigated experimentally in laboratory and some test results are presented in this paper. It is shown that the "tone-like" phenomenon happens only when the incident angle of the wind is relatively large to the perforated panel; say between 60 and 80 degrees. There seems an "optimum" wind speed corresponding to the size of the holes for this phenomenon. The peak frequency of the tone-like signal is mainly determined by the thickness of the plate and the size of the holes and can be roughly estimated from the geometry of the plate and the wind speed. The condition when the tone-like phenomenon may happen seems very much dependent on the perforation pattern along the wind direction. Same perforated plate may produce totally different sound in the same wind condition if the orientation of the plate is changed. Randomized hole size and distribution may help to reduce the tone-like signal and hence the total wind-induced noise. Possible explanations of the phenomenon are discussed.

  • 15.
    Finnveden, Svante
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Spectral finite element analysis of stationary vibrations in a beam – plate structure1996In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 82, p. 478-497Article in journal (Refereed)
  • 16.
    Friberg, Anders
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Schoonderwaldt, Erwin
    Juslin, Patrik N.
    CUEX: An algorithm for automatic extraction of expressive tone parameters in music performance from acoustic signals2007In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 93, no 3, p. 411-420Article in journal (Refereed)
    Abstract [en]

    CUEX is an algorithm that from recordings of solo music performances extracts the tone parameters for tempo, sound level, articulation, onset velocity, spectrum, vibrato rate, and vibrato extent. The aim is to capture the expressive variations in a music performance, rather than to identify the musical notes played. The CUEX algorithm uses a combination of traditional methods to segment the audio stream into tones based on fundamental frequency contour and sound level envelope. From the resulting onset and offset positions, the different tone parameters are computed. CUEX has been evaluated using both synthesized performances and recordings of human performances. For the synthesized performances, tone recognition of 98.7% was obtained in average. The onset and offset precision was 8 ms and 20 ms, respectively, and the sound level precision about 1 dB. Various applications of the CUEX algorithm are discussed. For human performances, the recognition was 91.8% in average.

  • 17.
    Gaborit, Mathieu Maël
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Université du Maine, France.
    Schwan, L.
    Dazel, O.
    Groby, J. -P
    Weisser, T.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Coupling FEM, bloch waves and TMM in meta poroelastic laminates2018In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 104, no 2, p. 220-227Article in journal (Refereed)
    Abstract [en]

    The propagation of airborne plane waves in the presence of a meta poroelastic laminate, that is a poroelastic matrix coated with thin elastic layers at its facings and periodically-embedded with inclusions, is studied. Using the Finite Element Method (FEM) only would result in a drastic increase of the degrees of freedom due to the fine mesh required to account for the very thin coatings. Here, the approach relies on: The Bloch wave expansion of the fields in air; the modal Transfer Matrix Method to account for the coatings; and the coupling with the FEM model of the poroelastic matrix and the resonant inclusions. The model is developed for reflection and transmission problems and it can account for coatings with multiple layers. The procedure induces the addition of the Bloch coefficients in the FEM's linear system at a negligible additional computational cost. It is applied to the meta poroelastic laminates with poroelastic inclusions and rubber shell inclusions. The results are compared with those from the Multiple Scattering Theory and an excellent agreement between the methods is found. The approach offers a numerically-efficient way to account for coatings applied to meta poroelastic layers, and finds applications in industrial prototypes where coatings are widely used.

  • 18. Galembo, A.
    et al.
    Askenfelt, Anders
    KTH, Superseded Departments, Speech Transmission and Music Acoustics.
    Cuddy, L. L.
    Russo, F. A.
    Perceptual relevance of inharmonicity and spectral envelope in the piano bass range2004In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 90, no 3, p. 528-536Article in journal (Refereed)
    Abstract [en]

    Professionals consider the differences in the timbre of bass tones between large grand pianos and small uprights as significant. By tradition this difference has been attributed mainly to lower inharmonicity in grand pianos, due to longer bass strings. In this study, the importance of the spectral envelope, representing the dynamic balance between high-frequency and low-frequency energy in the spectrum, is contrasted against the importance of the level of inharmonicity. Results from two listening tests indicate that the inharmonicity is less important than the spectrum bandwidth in determining the timbre of piano bass tones.

  • 19.
    Göransson, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hörlin, Nils-Erik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Vibro-acoustic modelling of anisotropic porous elastic materials: A preliminary study of the influence of anisotropy on the predicted performancein a multi-layer arrangement.2010In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 96, p. 258-265Article in journal (Refereed)
    Abstract [en]

    During the recent years considerable efforts have been spent on developing numerical models and performing the necessary characterisation of elastic, dynamic and acoustic properties of porous materials. Originally having been considered to be isotropic, such materials have lately also been studied in terms of their anisotropic properties. In this paper, the influence of anisotropy on the vibroacoustic performance is illustrated and evaluated for a multi-layer configuration with varying boundary conditions between the porous material and a solid plate. The paper starts with a brief review of a recently published anisotropic, mixed displacement pressure weak formulation with a particular emphasis on the anisotropic properties. Using the material properties for a hypothetical porous foam model, the predicted response is evaluated. The influence of anisotropy is found to be significant in terms of response amplitude and apparent damping. For some boundary conditions the predicted response is an order of magnitude lower for the anisotropic material model, in particular for frequency ranges where the dynamics of the foam are significant.

  • 20.
    Hansen, Kjetil Falkenberg
    et al.
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID. KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Fabiani, Marco
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Bresin, Roberto
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Analysis of the acoustics and playing strategies of turntable scratching2011In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, no 2, p. 303-314Article in journal (Refereed)
    Abstract [en]

    Scratching performed by a DJ (disk jockey) is a skillful style of playingthe turntable with complex musical output. This study focuses on the description of some of the acoustical parameters and playing strategies of typical scratch improvisations, and how these parameters typically are used for expressive performance. Three professional DJs were instructed to express different emotions through improvisations, and both audio and gesturaldata were recorded. Feature extraction and analysis of the recordings are based on a combination of audio and gestural data, instrument characteristics, and playing techniques. The acoustical and performance parameters extracted from the recordings give a first approximation on the functional ranges within which DJs normally play. Results from the analysis show that parameters which are important for other solo instrument performances, suchas pitch, have less influence in scratching. Both differences and commonalities between the DJs’ playing styles were found. Impact that the findings of this work may have on constructing models for scratch performances arediscussed.

  • 21.
    Hassan, Osama
    Umea universitet, Department of Applied Physics and Electronics, Sweden .
    Experimental investigations on the force mobility of an elastic stratum on a rigid base2007In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 93, no 1, p. 164-166Article in journal (Refereed)
    Abstract [en]

    This paper attempts to investigate experimentally the influence of base conditions on the mobility of a stratum on a rigid base. The results are compared with the theoretical results as presented by the author in a previous publication. It is shown that the obtained measurement results reasonably agree with the theory and that the base conditions of stratum on a rigid base do have a significant influence on the force mobility, particularly at resonance.

  • 22.
    Hassan, Osama
    Umea universitet, Department of Applied Physics and Electronics,Sweden .
    Force mobility of an elastic stratum over a rigid base: Part I. Approximate solution2006In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 92, no 3, p. 378-389Article in journal (Refereed)
    Abstract [en]

    An approximate approach to derive the input mobility of an infinite elastic stratum on a rigid base is investigated. The excitation is due to a vertical force, which is applied via a small massless indenter with a circular base, fixed to the stratum. Two cases are investigated: a stratum with a fixed base and a stratum with a frictionless base. General expressions for the mobilities are derived from the equations of motion of an isotropic elastic medium. Using a numerical approach, the analytical results are evaluated up to a Helmholtz number k(L)d = 10, where k(L) is the wave number of the P- wave and d is the stratum depth. For small Helmholtz numbers, asymptotic expressions are derived analytically; the two evaluations agree well up to a Helmholtz number of 0.2 for the frictionless base and to 0.5 for the fixed base. It is shown that the mobilities for the two cases differ significantly at small Helmholtz numbers. This is mainly due to the influence of a propagating wave, which can exist only in the case of a frictionless base. It is also shown that the local deformations in the vicinity of the indenter are built up by low-frequency, non-propagating Lamb modes. Finally, the dispersion relations are evaluated up to a Helmholtz number k(L)d = 16.

  • 23.
    Hassan, Osama
    Umea universitet, Department of Applied Physics and Electronics, Sweden .
    Force mobility of an elastic stratum over a rigid base: Part II. Exact solution2006In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 92, no 3, p. 390-397Article in journal (Refereed)
    Abstract [en]

    The second part of this paper deals with the exact solution for the force mobility of an infinite elastic stratum with respect to a vertical force. The stratum rests on a rigid and frictionless foundation. The upper surface of the stratum is excited by a circular weightless indenter with a prescribed velocity; otherwise this surface is stress-free. The mixed boundary conditions result in dual integral equations, which are solved using analytical and numerical techniques. An exact analytical solution for the force mobility of the stratum is determined by using the method of resolvent kernel together with the residue theorem. The results are validated by comparisons with the results from a numerical solution using the quadrature method. It is shown that the results from an approximate solution as presented in the first part, where the prescribed velocity is exchanged for a presumed stress distribution, agrees well with the present results for low frequencies up to approximately the first thickness resonance, but not for higher frequencies.

  • 24.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Du, Lin
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Optimum Sound Attenuation in Flow Ducts Based on the "Exact" Cremer Impedance2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 102, no 5, p. 851-860Article in journal (Refereed)
    Abstract [en]

    The Cremer impedance (Acustica 3, 1953) [1] is the locally reacting boundary condition that maximizes the attenuation of a certain mode in a uniform wave guide taken as the lowest order mode or "plane" wave. This paper presents the analysis of the "exact" Cremer impedance model, i.e., the high frequency asymptotic results proposed by Tester for uniform mean flow (JSV 28(2), 1973) [2] are extended to lower frequencies. It is shown that significantly larger attenuation per unit length can be obtained using the exact instead of the asymptotic solution. However, for sufficiently low frequencies the "exact" Cremer solution and optimum attenuation is requiring a wall impedance with a negative real part, i.e. an active boundary. In addition, the effect of a finite length on the resulting attenuation is studied using a finite element method for solving the convected wave equation. Finally, it is demonstrated how a silencer can be built that realize the optimum Cremer impedance at a given frequency by using a micro-perforated panel and locally reacting cavities. The performance of the optimized silencer is determined experimentally and the results are compared to the prediction of the finite element model.

  • 25.
    Karlsson, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    On the Use of Linear Acoustic Multiports to Predict Whistling in Confined Flows2011In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, no 1, p. 24-33Article in journal (Refereed)
    Abstract [en]

    The use of linear acoustic multiport models to analyse the existence of flow driven instabilities, that is - self-sustained oscillators or whistles - is addressed. By combining the scattering and reflection matrices for a system and searching for eigenfrequencies (zeros) in the critical half-plane, the existence of exponentially growing instabilities can be determined. In practice, the available frequency domain data are only known along the real axis; then the search for zeros may be done via the so-called Nyquist stability criterion generalized to an N-degree of freedom system. The method has been validated by two test cases, a T-junction and a Herschel-Quincke tube. In both cases, the occurrence and the frequencies of the self-sustained oscillations were correctly predicted.

  • 26.
    Kernen, Ulrica
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Hassan, Osama
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Airborne Sound Insulation of a Thin Plate of Finite Dimensions2005In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 91, no 4, p. 732-739Article in journal (Refereed)
    Abstract [en]

    An analytical model for predicting the sound reduction index of a single plate is presented. The plate is assumed to be excited by a diffuse sound field and the velocity distribution of the plate is derived from the Kirchoff plate equation in the frequency domain. The resulting Fourier transform is evaluated using residue calculus and the solution is verified numerically. The analytical model is valid for a wide frequency range, both below, above and at the critical frequency. Special interest is paid to the area dependency of the sound reduction index. Calculated results are presented for a 0.5 m(2), 1.7 m(2) and 4.4 m(2) plate of 16 rum chipboard. These results, which agree well with measured values, show that the sound reduction index decreases with increasing area in the whole frequency range.

  • 27.
    Lopez Arteaga, Ines
    et al.
    Department of Mechanical Engineering, Eindhoven University of Technology.
    Hirschberg, A.
    Van Hirtum, A.
    Ruty, N.
    Pelorson, X.
    Physical modeling of buzzing artificial lips: The effect of acoustical feedback2006In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 92, no 6, p. 1047-1059Article in journal (Refereed)
    Abstract [en]

    The influence of the up- and downstream acoustics on the buzzing behavior of artificial lips has been studied. In the presence of a long downstream pipe, the oscillation frequency is well predicted by means of a model assuming a single mechanical degree of freedom for the lips. A minimum of the threshold pressure for buzzing is observed when the lips are just closed at rest. The magnitude of this threshold pressure is underestimated by the model. In order to fit experiments the quality factor of the lip resonance has to be reduced by a factor two compared to the measured quality factor. In the absence of downstream pipe the threshold pressure increases by a factor three and a jump in oscillation frequency from one mechanical lip-mode to another one is observed as the lung pressure is increased. An attempt to describe this behavior by means of a 2-mass-model fails.

  • 28.
    Ramanathan, Sathish Kumar
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Orrenius, Ulf
    Predicting the sound transmission loss of honeycomb panels using the wave propagation approach2011In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, no 5, p. 869-876Article in journal (Refereed)
    Abstract [en]

    The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.

  • 29.
    Sack, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    On Acoustic Multi-Port Characterisation Including Higher Order Modes2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 192, no 5, p. 834-850Article in journal (Refereed)
    Abstract [en]

    Methods to design test-procedures for acoustic multi-ports in ducts with a focus on pressure sampling positions for accurate modal decomposition are demonstrated. Acoustic fields up- and downstream of an in-duct acoustic element are excited by external sources and decomposed into transmitted and reflected aeroacoustic modal pres- sure amplitudes in order to first determine the acoustic scattering of the element. Secondly, the determination of the element source strength requires tests with no external sources, but with known terminations and scattering data. Unfavourable source and sensor positions lead to mode coupling and to ill-conditioned or even singular decomposition matrices, which results in high amplifications of uncertainties within the wave decomposition. An unoptimised but over-determined assembly is compared with a setup containing a minimum of sensors but with optimised positions. Lower uncertainty amplification, despite the usage of fewer sensors, is achieved for most frequencies, especially after the cut-on of t he higher order acoustic modes. A genetic algorithm (GA) is used to achieve this optimised setup by minimising the condition number of the decomposition matrix, which is a multi-dimensional optimisation problem with numerous local minima. To estimate the stability of the optimised configuration, a Monte-Carlo Method (MCM) is deployed to introduce normal distributed complex pressure un- certainties into the decomposition. In order to estimate the wave number, different approaches are compared - namely the classical non-dissipative wav e number estimate, an extended Kirchhoff method for viscous-thermal damping and an eigenvalue solution of the Linearised Navier Stokes Equations by Dokumaci. The presented de- composition method is not only applicable to measurement data but is equally useful to post-process results from numerical computation.

  • 30.
    Sandqvist, Henrik
    KTH, Superseded Departments, Mechanics.
    Theoretical studies of shock waves in nonlinear, dispersive and dissipative media2004In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 90, no 4, p. 662-678Article in journal (Refereed)
    Abstract [en]

    Propagation of waves in nonlinear, dispersive and dissipative media, as described by Korteweg-de Vries-Burgers' equation (KdVB), have been studied. The focus of the investigation has been to study analyticaly, the structure of a shock wave that is broken down by dispersive and dissipative phenomena. To be able to use the inverse scattering transform (IST) to get analytical solutions for Korteweg-de Vries' equation (KdV), an N-wave was used as model for the initial shock. The IST is used to transform KdV, which is a nonlinear differential equation, into Marchenko's equation that is a linear Volterra integral equation. A zeroth order iteration solution, which reconstructs the initial waveform, is presented. For positive times, this solution shows a decaying shock front which slows down, leaving an oscillating tail behind. In the early stages, the behaviour of the leading and the tailing shock of the N-wave are similar but soon the structure caused by the tailing shock is disrupted by the oscillating tail of the leading shock. This solution is valid for moderate values of the dispersion coefficient. In order to obtain solutions for smaller values of the dispersion coefficient, asymptotic analysis is used. The corresponding asymptotic analysis for Burgers' equation, with a small dissipation coefficient, is quoted for comparison. An asymptotic analysis is also made for KdVB, in the case for which dispersion as well as dissipation is important.

  • 31. Scholte, R.
    et al.
    Lopez Arteaga, Ines
    Eindhoven University of Technology.
    Roozen, N. B.
    Nijmeijer, H.
    Wavenumber domain regularization for near-field acoustic holography by means of modified filter functions and cut-off and slope iteration2008In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 94, no 3, p. 339-348Article in journal (Refereed)
    Abstract [en]

    Planar Near-field Acoustic Holography (PNAH) is an acoustic imaging method based on the inverse solution of the wave equation. Wavenumber domain low-pass filtering is an essential operation in the PNAH process. An increasingly higher wavenumber filter cut-off results in a "blow-up" of the inverse solution, which is a characteristic of an ill-posed problem. On the other hand, lower cut-off wavenumbers result in spatial acoustic data at very low resolution, where highly detailed information is discarded. Thus, an optimal solution for the cut-off wavenumber somewhere in between is needed. This paper introduces two modified filter functions, namely a modified exponential and a modified Tikhonov filter, that are specifically designed for application in PNAH and compares them with a number of more general applied filter functions. Regularization methods are introduced that exploit the k-space to obtain near-optimal low-pass filter parameter selection at high computational efficiency. These filter functions are discussed and their parameters are selected by k-space application of L-curve, Generalised Cross-Validation and the newly introduced and well-applicable Cut-Off and Slope iteration. Simulations of various sources show that the optimal regularization method is highly dependent on the type of source, the spatial distribution and measurement noise. Finally, a robust regularization strategy is proposed which automatically produces high quality results for a wide range of practical conditions.

  • 32.
    Schoonderwaldt, Erwin
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    On the Use of Skewness in Violin Bowing: Should the Bow be Straight or Not?2010In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 96, no 4, p. 593-602Article in journal (Refereed)
    Abstract [en]

    Bowing parallel to the bridge is by many players considered as the golden standard. However, in practice straight bow strokes are rarely observed, and the bow can be considerably slanted even in the performance of renowned players. In any case, the angle of the bow with the violin (skewness) is likely to form an important control parameter, which has hardly been addressed in scientific studies of violin performance. In the current study measurements of skewness in violin and viola performance are presented, and possible explanations of the observed behavior are offered. The results provide strong indications of that skewness fulfills an important function in controlling bow-bridge distance, integrated in players' performance strategies.

  • 33.
    Schoonderwaldt, Erwin
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    The violinist's sound palette: Spectral centroid, pitch flattening and anomalous low frequencies2009In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 95, no 5, p. 901-914Article in journal (Refereed)
    Abstract [en]

    The string player controls variations in spectral content mainly via bow velocity, bow-bridge distance and bow force. Many combinations of the bowing parameters influence the pitch noticeably as well, in particular close to the upper bow-force limit in the Schelleng diagram. The influence of the bowing parameters on the spectral content and pitch were studied systematically by use of a monochord and a bowing machine. Bow force was found to be the totally dominating parameter in determining the spectral centroid. Bow-bridge distance and bow velocity serve essentially as indirect control parameters of spectral content by giving the player access to playable areas with high or low bow forces in the Schelleng diagram. Clear areas of pitch flattening could be distinguished below the upper bow-force limits in the Schelleng diagrams, confirming the role of pitch flattening as a practical bow-force limit in playing. The conditions for anomalous low frequencies (ALF), S-motion and other, higher types of string motion were analyzed, and it was shown that secondary waves might play an important role in their creation.

  • 34.
    Schoonderwaldt, Erwin
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Guettler, Knut
    Askenfelt, Anders
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    An empirical investigation of bow-force limits in the Schelleng diagram2008In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 94, no 4, p. 604-622Article in journal (Refereed)
    Abstract [en]

    An experimental study of the upper and lower bow-force limits for bowed violin strings is reported. A bowing machine was used to perform bow strokes with a real violin bow on steel D and E strings mounted on a rigid monochord and on a violin. Measurements were systematically performed for 11 values of relative bow-bridge distance and 24 values of bow force at four bow velocities (5, 10, 15 and 20 cm/s). The measured string velocity signals were used to compile Schelleng diagrams, showing the distribution of different classes of string motion (multiple slipping, Helmholtz motion, raucous motion). It was found that the maximum bow-force limit for Helmholtz motion corresponded well to Schelleng's equation in modified form, taking the shape of the (hyperbolic) friction curve into account. The minimum bow force was found to be independent of bow velocity, which is in clear contradiction to Schelleng's prediction. Observations and simulations suggested that the breakdown of Helmholtz motion at low bow forces involves a mechanism related to ripple and corner rounding which was not taken into account in Schelleng's derivation of minimum bow force. The influence of damping showed only qualitative agreement with Schelleng's predictions.

  • 35.
    Ternström, Sten
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics.
    Pabon, Peter
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics. Royal Conservatoire, The Hague, Netherlands.
    Södersten, M.
    The Voice Range Profile: its function, applications, pitfalls and potential2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 102, no 2, p. 268-283Article in journal (Refereed)
    Abstract [en]

    An overview is given of the current status of the computerised voice range profile (VRP) as a voice measurement paradigm. Its operating principles are described, and sources of errors and variability are discussed. The features of the VRP contour and its characterisaï¿œtion are described. Methods for performing statistics on VRP contour and interior data are considered. Examples are given of clinical, pedagogical and research applications. Finally, issues with the models used to interpret VRP data are discussed. It is concluded that, while the VRP offers a convenient frame of reference for a multitude of voice assessment metrics, it also exposes the many degrees of freedom in the voice to an extent that challenges us to improve our models of how the voice functions over a large range and in a dynamic setting.

  • 36. Van Hirtum, A.
    et al.
    Cisonni, J.
    Ruty, N.
    Pelorson, X.
    Lopez Arteaga, Ines
    Eindhoven University of Technology.
    Van Uittert, F.
    Experimental validation of some issues in lip and vocal fold physical models2007In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 93, no 2, p. 314-323Article in journal (Refereed)
    Abstract [en]

    Insight into vocal fold and lip oscillation mechanisms is important for the understanding of phonation and the sound generation process in brass musical instruments. In general, a simplified analysis of the physical 3D fluid-structure interaction process between the living tissues and the airflow is favoured by most workers. Several simple models (lumped parameter models) have been proposed and these represent the tissues as a distribution of elastic mass(es). The mass-spring-damper system is acted on by a driving force resulting from the pressure exerted by the airstream. The results from these theoretical models have been validated 'in-vitro' using rigid or deformable replicas mounted in a suitable experimental set-up. Previous research by the authors focused on the prediction of the pressure threshold and oscillation frequency of an 'in-vitro' replica, in the absence and presence of acoustical feedback. In the theoretical model a lip or vocal fold is represented as a simple lumped mass system. The model yielded accurate prediction of the oscillation threshold and frequency. In this paper a new 'in-vitro' set-up is presented, which overcomes some of the limitations of the previous study. By the use of a digital camera synchronised with a light source and of pressure sensors, this set-up allows 1) measurement of the area of the replica opening and 2) imposition of independent initial conditions, such as height of the initial opening and internal pressure in the replica. The impact of these findings on physical modelling is discussed.

1 - 36 of 36
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