Change search
Refine search result
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Baro, Simone
    et al.
    Politecn Milan, Dept Mech Engn, Milan, Italy..
    Corradi, Roberto
    Politecn Milan, Dept Mech Engn, Milan, Italy..
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Caracino, Paola
    Pirelli Tyre, Milan, Italy..
    Fioravanti, Anna Paola
    Pirelli Tyre, Milan, Italy..
    Modelling of a lined tyre for predicting cavity noise mitigation2019In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 155, p. 391-400Article in journal (Refereed)
    Abstract [en]

    Tyre cavity resonance can significantly affect vehicle interior noise at frequencies around 200 Hz. The insertion of a sound absorbing liner inside the tyre is known to be an efficient countermeasure, in fact nowadays tyre manufacturers are already producing tyres implementing this kind of solution. The present work, through analytical and numerical models, supported by material testing, provides a methodology for predicting the dag performance of a lined tyre, taking into account tyre/lining geometry and sound absorbing material properties. The results reported in the paper show that for fixed material characteristics, the attenuation of the cavity resonance is mostly influenced by the volume of the lining treatment. Moreover, the numerical model developed for discontinuous treatments, suggests that for fixed volume and material properties, the cavity resonance attenuation can be increased by choosing a proper layout. Elsevier Ltd. All rights reserved.

  • 2.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Modified impedance tube measurements and energy dissipation inside absorptive materials2013In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 71, no 12, p. 1480-1485Article in journal (Refereed)
    Abstract [en]

    Impedance tube is an important tool to measure acoustic properties of a material, for which two methods have been standardized. The methods for a "modified" impedance tube have been developed recently to measure material properties in the condition of an anechoic termination. Instead of commonly used two-load or two-source methods, a method with direct and inverted configuration in cooperation with the single-microphone method is suggested in this paper. With the help of transfer matrix method, combined effect of several materials placed in series can be predicted from individual properties. A simple recurrence formula is obtained to relate the acoustic properties of a multilayer structure with the reflection and transmission coefficients of each layer. Very good agreements are obtained between the prediction and the direct measurements. Energy dissipations inside porous materials for different situations are studied and compared.

  • 3.
    Feng, Leping
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Orrenius, Ulf
    Engineering methods to predict noise levels at reference points with known source properties2015In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 96, p. 68-74Article in journal (Refereed)
    Abstract [en]

    Two engineering methods are proposed to predict the sound pressure levels at a given point when the sound power level of a noise source is known and the transfer function between the source and the reference point can be obtained. The first method is applicable when the source is surrounded by many reflectors, or inside a box-like structure. A single monopole with average transfer function is suggested for this situation. For a source with a strong directivity placed in an essentially free space, the "box-source" method is recommended to take into account of the source directivity. The total sound power is in this case divided into five independent noise sources which are obtained via ordinary sound power measurement methods. Experimental verifications are made for several cases in laboratory. Satisfactory results are obtained for both methods.

  • 4.
    Garnell, Emil
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Banwell, Guy
    DYSON, Tetbury Hill, Malmesbury SN16 0RP, England..
    The use of the two-port method to characterize high-speed small fans2019In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 146, p. 155-163Article in journal (Refereed)
    Abstract [en]

    One way to obtain a complete characterization of a sound source in a duct is to measure two-port data, comprising of the source scattering matrix and the source cross-spectrum. The present paper discusses in detail the design and construction of a two-port rig to characterize high speed small fans. A new post-processing method is suggested for the source cross-spectrum data and is compared to an earlier published method. The new method is shown to behave better in highly reflective cases, but is more sensitive to flow noise. In some cases, the duct diameter is not equal to the diameter of the test object. An adaptor can then be used to match the diameters, but it will modify the two-port results. In the present paper a method to remove the adaptor influence on the measured scattering matrix and source vector is presented, and validated by measurements.

  • 5. Hynninen, Antti
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Determination of in-duct sound power beyond the plane wave range using wall-mounted microphones2015In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 99, p. 24-30Article in journal (Refereed)
    Abstract [en]

    When studying the acoustic wave propagation in a duct, the frequency range can be divided into the low frequency plane wave range and the high frequency range with non-plane waves. In the low frequency range, the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct, the lower the frequency limit of the non-plane waves. Therefore, also taking into account the three-dimensional acoustic wave propagation is important, especially when considering the duct systems used in large machines. In practice often a harsh environment and immobile structures restrict the use of standardized noise measuring methods. For instance to characterize the exhaust noise of medium speed internal combustion engines (IC-engines) in situ, the in-duct sound pressures are measured using wall-mounted microphones. Then the low frequency range source sound power can be estimated by wave decomposition ("two-microphone method"). Often a three-microphone array is used to cover a sufficiently large frequency range. One way to formulate the sound pressure and sound power relationship in the high frequency range is to weight the sound pressures at the duct wall in one-third octave bands. The aim of this study is to extend the classical plane wave formulation by determining these weighting factors, so that a three-microphone array also can be used beyond the plane wave range. The results from numerical approach are compared to experimental data.

  • 6.
    Jansson, Erik V.
    KTH, Superseded Departments, Speech, Music and Hearing.
    Violin frequency response: bridge mobility and bridge feet distance2004In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 65, no 12, p. 1197-1205Article in journal (Refereed)
    Abstract [en]

    Good violins have a broad hill in the 2-3 kHz range of their frequency response. This hill has previously been attributed to the first in-plane resonance of the violin bridge. Experiments prove, however, that the hill is the result of two forces acting in opposite directions at the bridge feet. The experiments reported here show that the hill can be "tuned" by altering the distance between the bridge feet. It can be tuned both in terms of frequency and level but the properties of the violin cannot be neglected.

  • 7.
    Kårekull, Oscar
    et al.
    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.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Prediction model of flow duct constriction noise2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 82, p. 45-52Article in journal (Refereed)
    Abstract [en]

    The scaling law for aerodynamic dipole type of sound from constrictions in low speed flow ducts by Nelson and Morfey is revisited. A summary of earlier published results using this scaling law is presented together with some new data. Based on this, an effort to find a general scaling law for the sound power for components with both distinct and non-distinct flow separation points are made. Special care is taken to apply the same scaling to all data based on the pressure drop. Results from both rectangular and circular ducts, duct flow velocities from 2 to 120 m/s and sound power measurements made both in ducts and in reverberation chambers are presented. The computed sound power represents the downstream source output in a reflection free duct. In particular for the low frequency plane wave range strong reflections from e.g. openings can affect the sound power output. This is handled by reformulating the Nelson and Morfey model in the form of an active acoustic 2-port. The pressure loss information needed for the semi-empirical scaling law can be gained from CFD simulations. A method using Reynold Average Navier Stokes (RANS) simulations is presented, where the required mesh quality is evaluated and estimation of the dipole source strength via the use of the pressure drop is compared to using the turbulent kinetic energy.

  • 8.
    Lindberg, Eskil
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Hörlin, Nils-Erik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    An experimental study of interior vehicle roughness noise from disc brake systems2013In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 74, no 3, p. 396-406Article in journal (Refereed)
    Abstract [en]

    An experimental study of the friction-induced noise generated by the disc brake system of a passenger car is presented. In particular, the brake noise usually referred to as wire brush or roughness noise is studied. This is, in terms of frequency spectral content a broadband phenomenon, resulting from the interaction of multiple asperities in the tribological contact. A new experimental method for measurements of disc brake roughness noise is proposed, and is used in a lab environment where the vehicle speed and the brake pressure are accurately controlled. The aim is to study the influence of vehicle speed and brake pressure on the roughness noise inside the vehicle. It is shown for the specific test case that the transmission from the source to the interior is a vibro-acoustic structure-borne phenomenon. Measurements show that there is a, as expected, strong correlation between increased interior noise and both increased vehicle speed and brake pressure.

  • 9.
    Lindborg, Per
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH. Nanyang Technological University, Singapore.
    A taxonomy of sound sources in restaurants2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 110, p. 297-310Article in journal (Refereed)
    Abstract [en]

    Restaurants are complex environments engaging all our senses. More or less designable sound sources, such as background music, voices, and kitchen noises, influence the overall perception of the soundscape. Previous research suggested typologies of sounds in some environmental contexts, such as urban parks and offices, but there is no detailed account that is relevant to restaurants. We collected on-site data in 40 restaurants (n = 393), including perceptual ratings, free-form annotations of characteristic sounds and whether they were liked or not, and free-form descriptive words for the environment as a whole. The annotations were subjected to cladistic analysis, yielding a multi-level taxonomy of perceived sound sources in restaurants (SSR) with good construct validity and external robustness. Further analysis revealed that voice-related characteristic sounds including a 'people' specifier were more liked than those without it (d = 0.14 SD), possibly due to an emotional crossmodal association mechanism. Liking of characteristic sounds differed between the first and last annotations that respondents made (d = 0.21 SD), which might be due to an initially positive bias being countered by exposure to a task inducing a mode of critical listening. Comparing the SSR taxonomy with previous classifications, we believe it will prove useful for field research, simulation design, and sound perception theory.

  • 10.
    Lindborg, PerMagnus
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics. Nanyang Technological University, Singapore.
    A taxonomy of sound sources in restaurantsIn: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910XArticle in journal (Refereed)
    Abstract [en]

    Restaurants are complex environments where all our senses are engaged. Physical and psychoacoustic factors have been shown to be associated with perceived environmental quality in restaurants. More or less designable sound sources such as background music, voices, and kitchen noises are believed to be important in relation to the overall perception of the soundscape. Previous research publications have suggested typologies and other structured descriptions of sound sources for some environmental contexts, such as urban parks and offices, but there is no detailed account that is relevant to restaurants. While existing classification schemes might be extendable, an empirical approach was taken in the present work. We collected on-site data in 40 restaurants (n = 393), including perceptual ratings, free-form annotations of characteristic sounds and whether they were liked or not, and free-form descriptive words for the environment as a whole. The annotations were subjected to analysis using a cladistic approach and yielded a multi-level taxonomy of perceived sound sources in restaurants. Ten different classification taxa were evaluated by comparing the respondents' Liking of sound sources, by categories defined in the taxonomy, and their Pleasantness rating of the environment as a whole. Correlation analysis revealed that a four-level clade was efficient and outperformed alternatives. Internal validation of the Pleasantness construct was made through separate ratings (n = 7) of on-site free-form descriptions of the environment. External validation was made with ratings from a separate listening experiment (n = 48). The two validations demonstrated that the four-level Sound Sources in Restaurants (SSR) clade had good construct validity and external robustness. Analysis  of the data revealed two findings. Voice-related characteristic sounds including a ‘people’ specifier were more liked than those without such a specifier (d = 0.14 SD), possibly due to an emotional crossmodal association mechanism. Liking of characteristic sounds differed between the first and last annotations that the respondents had made (d = 0.21 SD), which might be due to an initially positive bias being countered by exposure to a task inducing a mode of critical listening. We believe that the SSR taxonomy will be useful for field research and simulation design. The empirical findings might inform theory, specifically research charting the perception of sound sources in multimodal environments.

  • 11.
    Lindborg, PerMagnus
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Music Acoustics. Nanyang Technological University, Singapore.
    Psychoacoustic, physical, and perceptual features of restaurants: A field survey in Singapore2015In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 92, p. 47-60Article in journal (Refereed)
    Abstract [en]

    Sound is a multi-faceted phenomenon and a critical modality in all kinds of sevicescapes. At restaurants, our senses are intensively stimulated. They are social places that depend on acoustic design for their success. Considering the large economic interests, surprisingly little empirical research on the psychoacoustics of restaurants is available. Contributing to theory building, this article proposes a typology of designed and non-designed sonic elements in restaurants. Results from a survey of 112 restaurants in Singapore are presented, with a focus on one element of the typology, namely interior design materials. The collected data included on-site sound level, audio recordings from which psychoacoustic descriptors such as Loudness and Sharpness were calculated, perceptual ratings using the Swedish Soundscape Quality protocol, and annotations of physical features such as Occupancy. We have introduced a measure, Priciness, to compare menu cost levels between the surveyed restaurants. Correlation analysis revealed several patterns: for example, that Priciness was negatively correlated with Loudness. Analysis of annotations of interior design materials supported a classification of the restaurants in categories of Design Style and Food Style. These were investigated with MANOVA, revealing significant differences in psychoacoustic, physical, and perceptual features between categories among the surveyed restaurants: for example, that restaurants serving Chinese food had the highest prevalence of stone materials, and that Western-menu places were the least loud. Some implications for managers, acoustic designers, and researchers are discussed. (C) 2015 Elsevier Ltd. All rights reserved.

  • 12.
    Nashed, Mina Wagih
    et al.
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, 1 Elsarayat St, Cairo 11517, Egypt..
    Elnady, Tamer
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, 1 Elsarayat St, Cairo 11517, Egypt..
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Modeling of duct acoustics in the high frequency range using two-ports2018In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 135, p. 37-47Article in journal (Refereed)
    Abstract [en]

    Design of duct networks is challenging because the design should consider the required flow rate, acceptable noise levels, and minimum pressure drop to achieve optimum performance. This paper presents acoustic analysis in high frequency range using sound power two-ports applied to Heating, Ventilation, and Air Conditioning (HVAC) systems. To simulate the acoustic behaviour one need to model three mechanisms; the sound power generated from sound sources (e.g. Fans), the regenerated sound power caused by the flow in different elements in the network (e.g. junctions), and the sound power loss across different elements of the network. The general approach considered here is based on two-port theory that divides the duct network into two-port elements. Each element can be described by 2 x 2 scattering matrix where the state variables are the acoustic power flow in both up and downstream directions. Junctions and branching are described by multi-port elements depending on the number of elements connected to this multiport. This algorithm is compared to measurements of HVAC system located in an academic building that shows good agreement. An advantage of this approach is the ability to use the same formalism of the two-port network theory to analyse the acoustic behaviour in both low and high frequency ranges beside the flow distribution and the pressure drop.

  • 13. Okasha, Ahmed
    et al.
    Elnady, Tamer
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Analysis of pipeline networks using two-ports2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 109, p. 44-53Article in journal (Refereed)
    Abstract [en]

    Majority of vibration problems arise in pipeline networks are attributed to the high-pressure pulsations. Pulsations are generated by fluid machines such as compressors and pumps. These pulsations turn into shaking forces at elements such as pipe bends and pipe reducers, which in turn excite vibrations in the connected piping network. High vibrations beyond the endurance limit of the pipe material may cause damage to pipes, supports, and equipment. In addition, if the source pulsation frequency coincides with one of the natural frequencies of the piping network, resonance will take place and the vibrations will be magnified to a large scale. Obviously, if these vibrations are not well controlled, they might cause damage to the whole system and foundation, and might lead to substantial financial losses. Thus, prediction of pulsations is important for safe and proper operation. In this paper, a pilot plant equipped with a reciprocating compressor, pipes, bends, and terminated by a vessel is built. The network is modeled using the two-port theory that splits the network into several cascaded elements, and predicts the response of the network. The prediction model uses the measured compressor source data as an input, which is determined by the indirect multi-load method that is usually used to characterize internal combustion engines. A pulsation suppression device is designed, modeled, manufactured and inserted into the pilot network. The pressure pulsations are measured with and without the pulsation suppression device, and compared to the predictions using the two-port theory.

  • 14.
    Riber Marklund, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Dufek, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Development and comparison of spectral methods for passive acoustic anomaly detection in nuclear power plants2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 83, p. 100-107Article in journal (Refereed)
    Abstract [en]

    We have developed spectral signal processing methods for passive acoustic anomaly detection in nuclear power plants. Furthermore, we compared the developed and existing methods by applying them to stationary sounds recorded in a controlled environment. Our new methods show significant improvement, in particular concerning robustness against false alarms. The results also demonstrate that clear detection of a given sound at a given signal-to-noise ratio is highly dependent on the distribution of characteristic frequency content in the spectrum in relation to the background noise and the spectral uncertainty. Since the frequency monitoring principle used here is quite rigid, we stress the need for research on more flexible methods, also taking into account differences between experiments and real reactor systems.

  • 15.
    Rynell, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Chevalier, M.
    Åbom, Mats
    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. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    A numerical study of noise characteristics originating from a shrouded subsonic automotive fan2018In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 140, p. 110-121Article in journal (Refereed)
    Abstract [en]

    The characteristics of the noise radiated from a reduced automotive cooling module are numerically studied focusing on the interaction effects linked to the sound generation mechanisms and the acoustic scattering caused by the confined installation. The flow field is simulated by adopting the formulation of Improved Delayed Detached Eddy Simulation (IDDES), which is a numerical technique that enables large-scale structures to be resolved and the wall-bounded flow to be treated depending on the turbulent content within the boundary layer. By comparing the simulated fan performance to two sets of measurement data of a similar setup, the aerodynamic results obtained from IDDES are validated and conformed to the volumetric flow rate delivered for the pressure drop measured. The acoustic part of the study comprises evaluation of the sound source associated with the momentum distribution imposed on the surroundings at an interface slightly upstream of the fan. At the microphone positions upstream of the installation, the SPL falls within the SPL range measured and the acoustic power delivered by the fan conforms to the SWL obtained from the comparison method in the reverberation room. The system response function, estimated by subtracting the SWL for the free-field simulation from the SWL associated with the reduced automotive cooling module marks spectral humps at fixed frequencies, irrespectively of sound source. As such, the engineering approach to the spectral decomposition method earlier published, which enables the acoustical properties of the installation to be isolated from the source, is validated and found to hold.

  • 16.
    Rynell, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. Scania, Sweden.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, M.
    Scania AB, Sweden.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Acoustic characteristics of a heavy duty vehicle cooling module2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 111, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.

  • 17.
    Schenkman, Bo N.
    et al.
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH. Catholic Univ Louvain, Belgum.
    Nilsson, Mats E.
    Grbic, Nedelko
    Human echolocation: Acoustic gaze for burst trains and continuous noise2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 106, p. 77-86Article in journal (Refereed)
    Abstract [en]

    This study explored the ability of blind and sighted listeners to detect reflections, "echoes", of burst trains or continuous noise. Echo detection was compared by presenting 5 ms bursts, rates from 1 to 64 bursts, with a continuous white noise, all during 500 ms. Sounds were recorded in an ordinary room through an artificial binaural head, the loudspeaker 1 m behind it. The reflecting object was an aluminum disk, diameter 0.5 m, placed at 1 m. The sounds were presented to 12 blind and 26 sighted participants in a laboratory using a 2-Alternative-Forced-Choice methodology. The task was to detect which of two sounds contained an echo. In Experiment 2, 1.5 m distance sounds were presented to the blind only. At 1 m, detection for the blind increased up to 64 bursts/500 ms, but for the sighted up to 32 bursts. At 1.5 m, the peak performance for the blind was at 32 bursts. At the 1 m, but not at the 1.5 m distance, the blind performed best with continuous white noise. The overlap in time of signal and echo at 1 m for 64 bursts was 60%, but at 1.5 m 82%. Avoiding an overlap between emitted bursts and returning echoes seems important for echolocation, indicating that an acoustic gaze, analogous to in echolocating animals, may also exist in humans.

  • 18.
    Seifzadeh, Alireza
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Pietrzyk, A.
    Volvo Cars Corporation, Gothenburg Sweden.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Ramakrishnan, R.
    Department of Architectural Science, Toronto Canada.
    Effect of coupling between passenger compartment and trunk of a car on coupled system natural frequencies using acoustic frequency response function2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 76, p. 310-318Article in journal (Refereed)
    Abstract [en]

    Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources.

  • 19.
    Seifzadeh, Alireza
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Pietrzyk, A.
    Volvo Cars Corporation, Gothenburg Sweden.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Ramakrishnan, R.
    Department of Architectural Science, Toronto Canada.
    Experimental investigation of coupling effects of passenger compartment and trunk of a car on coupled system natural frequencies using noise transfer function2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 83, p. 16-21Article in journal (Refereed)
    Abstract [en]

    The parcel shelf of a car has several holes for speakers and electrical devices. In addition, air ventilation holes are installed on the trim that covers the parcel shelf. The effect of the holes between the two cavities, passenger compartment and the trunk, and the natural frequencies of double cavities connected by the neck (parcel shelf) are very vital and useful to noise-vibration-harshness engineers, as the low frequency resonances contribute to the booming noise inside the car. In the present study, the coupling effect of the passenger compartment and the trunk connected through the holes on the parcel shelf in between, has been investigated experimentally using noise transfer function. The first and second coupled system modes are measured at around 40 Hz and 70-80 Hz respectively. By increasing the effective size of the holes on the parcel shelf, the first and second natural frequencies of coupled modes can be shifted to higher values. The current study has verified that holes act as point sources in the low frequency ranges. It was concluded that the coupled acoustic modes, in the low frequency range, are strongly controlled by fluid-structure interaction as well as changes in the panels mass and stiffness in the car interior space. The shift in the natural frequencies of connected cavities can be useful in the prediction of the interior noise in an automobile as well as provide a verification tool for conventional numerical techniques such as finite element methods.

  • 20. Temiz, Muttalip Askin
    et al.
    Tournadre, Jonathan
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Eindhoven University of Technology, Netherlands.
    Hirschberg, Avraham
    Modelling vibro-acoustic coupling in flexible micro-perforated plates by a patch-impedance approach2017In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 125, p. 80-90Article in journal (Refereed)
    Abstract [en]

    This study proposes a Finite Element (FE)-based efficient numerical model of the vibro-acoustic coupling in flexible micro-perforated plates (f-MPPs) where each perforation is described as an imposed impedance boundary condition (uniform impedance patch) on the plate. This approach opens the possibility of predicting the influence of perforation distribution on the acoustic performance of f:MPP. Micro perforated plates have been a topic of interest as a promising sound absorber in a wide range of applications, from room acoustics to combustion systems. One great advantage of these plates is that it gives the designer the freedom of choice on material in production. Depending on the material and the dimensions, the acoustical modes of the medium can couple with the structural modes of the plate. This coupling changes the number of absorption peaks, frequency and amplitude of the Helmholtz resonance of the system, therefore the coupling becomes an extra parameter in the design process. Current analytical models superpose the mechanical impedance of the plate with the acoustic impedance of the perforations to compute this coupling. This approach works fairly well for plates with uniform perforation distribution. This study proposes a numerical method which assumes perforations as discrete impedance patches on the flexible plate so that they can be considered separately. The method couples the solution of the Helmholtz equation in air with shell plate theory to model the vibro-acoustic effects and the impedance patches are represented as imposed transfer impedance boundary conditions. The assessment of the method is performed in terms of comparing the calculated absorption coefficient values from the simulations of several test cases, fundamental theories and measurement results from the literature. The simulation results agree both with these theoretical limits and measurement results. The use of the method is illustrated by considering an example of the influence of modification of the spatial distribution of perforations on the sound absorption of a membrane.

  • 21.
    Vieira, Tiago
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI.
    Sandberg, Ulf
    VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. VTI.
    Acoustical performance of winter tyres on in-service road surfaces2019In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 153, p. 30-47Article in journal (Refereed)
    Abstract [en]

    Exposure to excessively high noise levels is a relevant health problem in Europe and road traffic noise is the most widespread noise source. When considering cold climate countries, the available scientific literature on noise emission properties of winter tyres is still very limited. In order to contribute into filling this knowledge gap, this paper investigates the acoustical performance of different types of tyres, with focus on winter tyres, on different road surfaces, at different speeds, and with different states of wear. The results indicate that studded winter tyres have, indeed, an increased noise level at frequencies between 315 Hz and 10 kHz, having a significantly different response especially at frequencies higher than 4 kHz. The acoustical response also depends on the tyre type when comparing different road surfaces, as a result of conflicting vibrational and aerodynamic noise generation mechanisms. Additionally, the relationship between labelled and measured values was explored, however, no statistically significant relationship was found between them (and labelling is not applied for studded tyres). A frequency spectrum correction was attempted based on previous measurements on an ISO track, which reduced the difference between measured and labelled values, however, further investigation is still required to properly understand differences between label and road measurements, where the label is determined on a test track with a special, smooth surface.

  • 22. Williams, P.
    et al.
    Kirby, R.
    Hill, J.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Malecki, C.
    Reducing low frequency tonal noise in large ducts using a hybrid reactive-dissipative silencer2018In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 131, p. 61-69Article in journal (Refereed)
    Abstract [en]

    Noise generated by fans or turbines normally consists of a combination of narrow and broadband noise. To lower transmitted noise levels, it is attractive to use a combination of reactive and dissipative elements. However, this approach presents a number of challenges for larger systems. This is because reactive elements are commonly placed around the duct circumference where they are normally only effective up to the frequency at which the first higher order mode cuts on in the duct. For larger systems, this means that reactive elements work only in the low, and often very low, frequency range, whereas dissipative elements, which are distributed across the duct cross-section, generally work well in the medium to high frequency range. This can cause noise problems in the low to medium frequency range in larger systems. This article presents an alternative approach for delivering noise attenuation over the low to medium frequency range that is suitable for application in larger duct systems. This approach takes advantage of those splitter silencer designs commonly used in larger systems to integrate a reactive element into the splitter design. This delivers a hybrid splitter that uses a combination of dissipative and reactive elements so that the reactive element partitions the main airway. This has the advantage of introducing a quasi-planar transverse sound pressure field for each resonator in the low to medium frequency range, including frequencies above the first cut-on. It is demonstrated using predictions and measurements taken for a number of example silencers, that this approach enables reactive elements to work over an extended low to medium frequency range, including at frequencies above the first cut-on mode in the main duct. Accordingly, it is shown that a hybrid dissipative-reactive splitter design is capable of delivering improved levels of attenuation in the crucial low to medium frequency range.

  • 23. Zhou, H.
    et al.
    Lopez-Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Eindhoven University of Technology, Netherlands.
    Nijmeijer, H.
    Broadband planar nearfield acoustic holography based on one-third-octave band analysis2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 109, p. 18-26Article in journal (Refereed)
    Abstract [en]

    Planar nearfield acoustic holography (PNAH) is usually based on narrow-band, single frequency analysis, which is time consuming when the source behavior over a broad frequency range is of interest, as is the case with many industrial sources. In this paper a method, broadband planar nearfield acoustic holography based on one-third-octave band analysis (BPNAH), is described. Data relating to the complex band pressure on the hologram is obtained by combining the root-mean-square pressure corresponding to a one-third-octave band with the phase of the pressure corresponding to a single frequency line. Numerical simulations and measurements show that the BPNAH method allows a significant reduction in processing time, while keeping a similar accuracy to the conventional reconstruction, which is based on the summation of frequency by frequency in the corresponding band. As a simple, time-saving and robust technique, the BPNAH method is particularly well adapted to industrial studies.

1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf