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  • 1.
    Allam, Sabry
    et al.
    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).
    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).
    Noise control for cooling fans on heavy vehicles2012In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 60, no 6, p. 707-715Article in journal (Refereed)
    Abstract [en]

    In this paper two different objects for fan passive noise control have been examined: heat exchangers and inlet/outlet parallel splitter silencers based on micro-perforated panels. The first object is theoretically and experimentally examined while the second is only examined experimentally. Throughout this paper two measurement methods were used. The ISO 15186-1:2000 to test the acoustic transmission for a diffuse field and plane wave testing in a duct of a sample cut from each heat exchanger type. Based on an anisotropic equivalent fluid model a theoretical model for the heat exchanger acoustic transmission is presented. A new type of splitter silencers based on micro-perforated plates, which can add damping up 10-20 dB in the frequency range of interest (<5 kHz), are also presented.

  • 2. 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).
    Simulation of the particle oxidation catalyst POC (R) acoustics2014In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 62, no 5, p. 368-374Article in journal (Refereed)
    Abstract [en]

    The reduction of the exhaust noise from internal combustion engine (IC-engine) is mainly managed by proper silencer design, while less attention is paid to the acoustic performance of the after treatment devices (ATD). It is known from the earlier studies, that the transmission loss of a typical ATD unit can be quite significant. An ATD unit for diesel engines is classically assembled from several specific parts such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POC (R)). The POC (R) substrate studied in this paper is of type POC-X, which consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. In this paper acoustic two-port simulation models for POC-X are proposed. First model is built up starting from the classical Kirchhoff solution for prediction of the acoustic wave attenuation in narrow channels. According to experimental studies, correction factors to the narrow channel two-port model are proposed. Second model is derived by treating the filter as a lumped acoustic resistance, dependent on the flow resistivity coefficients obtained from the pressure drop measurements.

  • 3.
    Kari, Leif
    KTH, Superseded Departments, Vehicle Engineering.
    Dynamic transfer stiffness measurements of vibration isolators in the audible frequency range2001In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 49, no 2, p. 88-102Article in journal (Refereed)
    Abstract [en]

    An indirect measurement method for blocked dynamic transfer stiffness of vibration isolators in the audible frequency range, up to 1000 Hz, including static preload and all six degrees of freedom is presented, Techniques for improving the stiffness accuracy are discussed in some detail, To suppress (unwanted) coupling effects between different degrees of freedom an improved excitation and terminating arrangement is adopted. Source correlation technique and stepped sine excitation are applied, increasing the signal-to-noise ratio. Computationally, a heavy blocking mass is replaced by its effective mass in the high frequency region, while using an overdetermined stiffness equation system. This is possible by applying various blocking masses, measuring acceleration at several positions and repeating the measurements. The method applied to a cylindrical vibration isolator at four axial preloads, results in smooth stiffness magnitude and phase curves, displaying antiresonances, resonances and the expected preload dependence, The test rig flanking transmission is shown to be negligible, while applying an auxiliary isolator decoupled test set-up, embedded in a heavy rigid frame construction, The stiffness error due to non-vanishing motion of the blocking mass is also shown to be negligible,

  • 4.
    Khan, M. Shafiquzzaman
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Dickson, Crispin
    KTH, Superseded Departments, Vehicle Engineering.
    Evaluation of sound quality of wheel loaders using a human subject for binaural recording2002In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 50, no 4, p. 117-126Article in journal (Refereed)
    Abstract [en]

    The sound quality of four different models of wheel loaders was evaluated using twenty-eight experienced male operators as subjects. Using these human subjects, sounds were recorded binaurally and played back through headphones. Tachometer recordings were also made from the engines and transmissions in order to trace the origins of amplitude peaks in the signals. There were two sessions (viz. lift and transportation) for each wheel loader. Altogether, there were eight sessions for all four wheel loaders. Tachometer signals indicated that peaks were dominated mainly by pinion and drop box for the transport sounds, whereas the peaks of hydraulic orders (i.e., between 250 and 1000 Hz) were dominant for the lift sounds. The dominant peaks were damped by either 3 or 6 dB, thus creating new modified sounds. Both original and modified sounds were then played randomly and separately for all sessions using a paired comparisons method. The results showed that the pinion and drop box were causing annoyance for the transportation sounds, while the hydraulic orders were causing annoyance for the lift sounds. The results also revealed that damping the tonal components created by the drop box reduced the annoyance response more significantly than damping the tonal components made by the pinion. This indicates that the tonal components in higher frequencies were more annoying than the tonal components in lower frequencies. In the final part of the study, multivariate analysis was applied in order to model annoyance of noises from the four different models of wheel loaders for both sessions (i.e., lift and transportation) on the basis of the sound quality descriptors. Annoyance prediction models for all sessions were developed based on the articulation index and a newly developed descriptor, viz. tonal ratio. The new descriptor identifies the tonal components by comparing the sound pressure level of each 1/3-octave band of the peaks between 125 and 3150 Hz with the two 1/3-octave-band levels adjacent to it.

  • 5.
    Khan, M. Shafiquzzaman
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Hogstrom, C.
    Determination of sound quality of HVAC systems on trains using multivariate analysis2001In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 49, no 6, p. 276-283Article in journal (Refereed)
    Abstract [en]

    An attempt was made to develop a model describing annoyance of noises generated by HVAC (Heating Ventilation Air Conditioning) systems on trains. The work was performed in three sequential parts. The first part contained the recording and reproduction of the HVAC noises. A binaural recording technique was applied and headphones were used for the reproduction. The second part of the study included both subjective and objective evaluations of the recorded noises. In the subjective evaluation 33 subjects judged nine different noise stimuli on annoyance scales. In the objective evaluation several sound quality descriptors and the third-octave-band levels were calculated. In the final part of the study, multivariate analysis was applied to modeling annoyance of the HVAC noises on the basis of the sound quality descriptors and third-octave-band levels. An annoyance prediction model was developed based on sharpness, a sound quality descriptor that describes the high frequency content in the sound, and a newly developed descriptor, tonal ratio. The new descriptor identifies the tonal components by comparing the sound pressure level between 125 and 800 Hz with the two third-octave-band levels adjacent to it. The interpretation of the results is that high frequency content and tonal components are the main contributors to the annoyance of HVAC noises and is where the main focus should be addressed in order to improve the sound quality of future HVAC systems.

  • 6.
    Khan, M. Shafiquzzaman
    et al.
    Luleå tekniska universitet.
    Johansson, Örjan
    Lindberg, Walter
    Luleå tekniska universitet.
    Sundbäck, Ulrik
    Annoyance of idling diesel engine noise evaluated by multivariate analysis1995In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 43, no 6, p. 197-207Article in journal (Refereed)
  • 7.
    Khan, M. Shafiquzzaman
    et al.
    Luleå tekniska universitet.
    Johansson, Örjan
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    Development of an annoyance index for heavy-duty diesel engine noise using multivariate analysis1997In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 45, no 4, p. 157-167Article in journal (Refereed)
  • 8.
    Khan, M. Shafiquzzaman
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Trapenskas, D.
    Johansson, O.
    Technical Note: Effects of different fuels on annoyance from diesel engine sounds2000In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 48, no 3, p. 102-106Article in journal (Refereed)
    Abstract [en]

    Annoyance judgments of engine sounds under six different fuel conditions were investigated using forty subjects. An equal number of males and females participated in the listening test. Thirty stereophonic recorded sounds were randomly presented to the subjects through a pair of loudspeakers. All sounds were recorded in a hemi-anechoic room. The listening test was conducted using a sequential rating method known as the method of successive Intervals. Tests for effects of the different fuels were made on the basis of non-parametric statistics. Engine sounds for an ethanol fuel with 9% Beraid were rated as least annoying whereas engine sounds for a mixture of diesel and ethanol fuels were rated as most annoying, The differences In annoyance judgments for different fuels at the same engine running speed could not be predicted using the annoyance index developed in an earlier study based on loudness, sharpness and harmonic ratio.

  • 9.
    Khan, M.S.
    et al.
    Luleå tekniska universitet.
    Trapenskas, Donatas
    Luleå tekniska universitet.
    Johansson, Örjan
    Technical note: Effects of different fuels on annoyance from diesel engine sounds2000In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 48, no 3, p. 102-106Article in journal (Refereed)
    Abstract [en]

    Annoyance judgments of engine sounds under six different fuel conditions were investigated using forty subjects. An equal number of males and females participated in the listening test. Thirty stereophonic recorded sounds were randomly presented to the subjects through a pair of loudspeakers. All sounds were recorded in a hemi-anechoic room. The listening test was conducted using a sequential rating method known as the method of successive Intervals. Tests for effects of the different fuels were made on the basis of non-parametric statistics. Engine sounds for an ethanol fuel with 9% Beraid were rated as least annoying whereas engine sounds for a mixture of diesel and ethanol fuels were rated as most annoying, The differences In annoyance judgments for different fuels at the same engine running speed could not be predicted using the annoyance index developed in an earlier study based on loudness, sharpness and harmonic ratio.

  • 10.
    Larsson, Krister
    et al.
    SP Technical Research Institute of Sweden.
    Simmons, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics. Simmons akustik & utveckling.
    Measurements of structure-borne sound from building service equipment by a substitution method: Round robin comparisons2011In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 59, no 1, p. 75-86Article in journal (Refereed)
    Abstract [en]

    A pilot project has been performed with a round robin comparison (inter-laboratory test), where a modified heavy-duty washing machine has been circulated for tests among 6 laboratories. The main goal of this pilot project was to find out whether a simple substitution method could be applied to estimate the structure-borne sound pressure level of some typical building service equipments. First, the vibration levels of a heavy low mobility test floor are measured when a machine with high internal mobility operates on this floor. Then, the vibration levels are measured at the same positions on the same floor when a standardized tapping machine (ISO 140-7) operates in the same positions as the test machine. The differences between the vibration level are then calculated. The difference may be used to compare the performance of different machines at one site or to estimate the sound pressure level in other buildings with heavy floors. In its simplest form, this can be made in the same way as for floorings, i.e., first calculating the normalized impact sound pressure level (EN 12354-2) and then subtracting the vibration level difference of the actual machine compared to the tapping machine. It remains to apply this method in the field and to compare estimated sound pressure levels with measured.

  • 11.
    Ljunggren, Fredrik
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Öqvist, Rikard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Simmons, Christian
    Luleå tekniska univesitet.
    Uncertainty of in situ low frequency reverberation time measurements from 20 Hz: An empirical study2016In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 64, no 6, p. 706-715Article in journal (Refereed)
    Abstract [en]

    Measuring reverberation time is normally one of the steps within the procedure of determining sound insulation in dwellings where 100 or 50 Hz usually serves as the lower frequency limit. However, even lower frequencies have become a matter of interest as research in the field recently indicated that the range 20-50 Hz seems to be of great importance when it comes to the perception of impact sound in lightweight buildings. A major issue in this context is then whether it is appropriate to measure and evaluate reverberation time at such low frequencies. This paper presents an empirical study of reverberation time measurements made in two rooms using more than 100 microphone positions in each. The measurement uncertainty with respect to microphone position and combinations of positions are compared for the frequency bands from 16 to 1600 Hz. Furthermore, it is analyzed how many microphone positions are needed in order to, with a reasonable probability, end up with an uncertainty in the related standardized impact sound level insulation L′n,T within ±1 dB

  • 12.
    Löfdahl, Magnus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Nykänen, Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johnsson, Roger
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Assessment of changes in automotive sounds caused by displacements of source and listening positions2012In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 60, no 3, p. 283-292Article in journal (Refereed)
    Abstract [en]

    Artificial head recordings are commonly used to measure and evaluate soundquality. In sound quality assessments, spatial qualities are crucial both forcorrect localization and separation of sources. Changes in locations of thesource and/or the receiver will alter the character of the sound since the binauraltransfer functions will alter. However, in complex environments (i.e. not freefield conditions) such as a car compartment, the required accuracy in positioningof sources and receivers cannot be drawn from previous studies of localizationblur. Therefore, examples of automotive sounds were reproduced through aloudspeaker in a source position outside a car and recorded with an artificialhead inside the car. Changes in perceived sound character caused by displacements of either the source or the receiver position were studied through a listening test. Just noticeable displacements were determined and perceiveddifferences compared to a reference position were rated. In addition, binauraltransmissibility functions of airborne sounds were measured and comparedwith the listening test results. The results showed that artificial head recordingsand measurements of binaural transmissibility functions were affected by smalldisplacements in location of both the source and the receiver. However, it washard to assess perceived differences from measured binaural transmissibilityfunctions. This highlights the importance of performing listening tests. Basedon this study, the recommended maximum inaccuracy in positioning of sourcesand receivers for binaural measurements in cars is 1 cm, in order to avoid audibleeffects.

  • 13. Nilsson, Mats E.
    et al.
    Alvarsson, Jesper
    Radsten-Ekman, Maria
    Bolin, Karl
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Auditory masking of wanted and unwanted sounds in a city park2010In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 58, no 5, p. 524-531Article in journal (Refereed)
    Abstract [en]

    Auditory masking of unwanted sounds by wanted sounds has been suggested as a tool for outdoor acoustic design. Anecdotal evidence exists for successful applications, for instance the use of fountain sounds for masking road traffic noise in urban parks. However, basic research on auditory masking of environmental sounds is lacking. Therefore, we conducted two listening experiments, using binaural recordings from a city park in Stockholm exposed to traffic noise from a main road and sound from a large fountain located in the center of the park. In the first experiment, 17 listeners assessed the loudness of the road traffic noise and fountain sounds from recordings at various distances from the road, with or without the fountain turned on. In the second experiment, 16 listeners assessed the loudness of systematic combinations of a singular fountain sound and a singular road traffic noise. The results of the first experiment showed that the fountain sound reduced the loudness of road traffic noise close to the fountain, and that the fountain sound was equally loud or louder than the road traffic noise in a region 20-30 m around the fountain. This suggests that the fountain added to the quality of the city park soundscape by reducing the loudness of the (presumably unwanted) traffic noise. On the other hand, results from the second experiment showed that road traffic noise was harder to mask than fountain sound, and that the partial loudness of both sources was considerably less than expected from a model of energetic masking. This indicates that auditory processes, possibly related to target-masker confusion, may reduce the overall masking effect of environmental sounds.

  • 14.
    Nilsson, Mats E.
    et al.
    Stockholms universitet, Psykologiska institutionen.
    Alvarsson, Jesper
    Stockholms universitet, Psykologiska institutionen.
    Rådsten-Ekman, Maria
    Stockholms universitet, Psykologiska institutionen.
    Bolin, Karl
    KTH.
    Auditory masking of wanted and unwanted sounds in a city park2010In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 58, no 5, p. 524-531Article in journal (Refereed)
    Abstract [en]

    Auditory masking of unwanted sounds by wanted sounds has been suggested as a tool for outdoor acoustic design. Anecdotal evidence exists for successful applications, for instance the use of fountain sounds for masking road traffic noise in urban parks. However, basic research on auditory masking of environmental sounds is lacking. Therefore, we conducted two listening experiments, using binaural recordings from a city park in Stockholm exposed to traffic noise from a main road and sound from a large fountain located in the center of the park. In the first experiment, 17 listeners assessed the loudness of the road traffic noise and fountain sounds from recordings at various distances from the road, with or without the fountain turned on. In the second experiment, 16 listeners assessed the loudness of systematic combinations of a singular fountain sound and a singular road traffic noise. The results of the first experiment showed that the fountain sound reduced the loudness of road traffic noise close to the fountain, and that the fountain sound was equally loud or louder than the road traffic noise in a region 20-30 m around the fountain. This suggests that the fountain added to the quality of the city park soundscape by reducing the loudness of the (presumably unwanted) traffic noise. On the other hand, results from the second experiment showed that road traffic noise was harder to mask than fountain sound, and that the partial loudness of both sources was considerably less than expected from a model of energetic masking. This indicates that auditory processes, possibly related to target-masker confusion, may reduce the overall masking effect of environmental sounds.

  • 15.
    Nilsson, Mats E.
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Alvarsson, Jesper
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Rådsten-Ekman, Maria
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Bolin, Karl
    Auditory masking of wanted and unwanted sounds in a city park2010In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 58, no 5, p. 524-531Article in journal (Refereed)
    Abstract [en]

    Auditory masking of unwanted sounds by wanted sounds has been suggested as a tool for outdoor acoustic design. Anecdotal evidence exists for successful applications, for instance the use of fountain sounds for masking road traffic noise in urban parks. However, basic research on auditory masking of environmental sounds is lacking. Therefore, we conducted two listening experiments, using binaural recordings from a city park in Stockholm exposed to traffic noise from a main road and sound from a large fountain located in the center of the park. In the first experiment, 17 listeners assessed the loudness of the road traffic noise and fountain sounds from recordings at various distances from the road, with or without the fountain turned on. In the second experiment, 16 listeners assessed the loudness of systematic combinations of a singular fountain sound and a singular road traffic noise. The results of the first experiment showed that the fountain sound reduced the loudness of road traffic noise close to the fountain, and that the fountain sound was equally loud or louder than the road traffic noise in a region 20-30 m around the fountain. This suggests that the fountain added to the quality of the city park soundscape by reducing the loudness of the (presumably unwanted) traffic noise. On the other hand, results from the second experiment showed that road traffic noise was harder to mask than fountain sound, and that the partial loudness of both sources was considerably less than expected from a model of energetic masking. This indicates that auditory processes, possibly related to target-masker confusion, may reduce the overall masking effect of environmental sounds.

  • 16.
    Pedersen, Eja
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Ecology and Environmental Science.
    Health aspects associated with wind turbine noise: Results from three field studies2011In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 59, no 1, p. 47-53Article in journal (Refereed)
    Abstract [en]

    Wind farms are a new source of environmental noise. The impact of wind turbine noise on health and well-being has not yet been well-established and remains under debate. Long-term effects, especially, are not known, because of the short time wind turbines have been operating and the relatively few people who have so far been exposed to wind turbine noise. As the rate of new installations increases, so does the number of people being exposed to wind turbine noise and the importance of identifying possible adverse health effects. Data from three cross-sectional studies comprising A-weighted sound pressure levels of wind turbine noise, and subjectively measured responses from 1,755 people, were used to systematically explore the relationships between sound levels and aspects of health and well-being. Consistent findings, that is, where all three studies showed the same result, are presented, and possible associations between wind turbine noise and human health are discussed.

  • 17. Preis, Anna
    et al.
    Hafke-Dys, Honorata
    Szychowska, Malina
    Stockholm University, Faculty of Social Sciences, Department of Psychology, Perception and psychophysics. Adam Mickiewicz University, Poznan, Poland.
    Kocinski, Jedrzej
    Felcyn, Jan
    Audio-visual interaction of environmental noise2016In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 64, no 1, p. 34-43Article in journal (Refereed)
    Abstract [en]

    Currently research into the psychological evaluation of noise in daily life is car- ried out without taking into account the sense of sight. The human senses interact with each other; thus some information coming from one sense can be skipped or ignored in favor of information coming from another sense, leading to completely different reactions or behavior. The aim of this paper is to verify, on the basis of psychophysical experiments, how a human being processes audio-visual informa- tion coming from the different environmental noises which can be encountered in daily life. The experiment was divided into three parts: auditory, visual, and audio-visual. In each part of the experiment, the ICBEN scale (0–10) was used to rate the presented stimuli. In the first part only audio stimuli were pre- sented, and subjects were asked to rate their annoyance with the sound. In the second part of the experiment, the participants were asked to rate how pleasant the presented video clips were. Finally, in the last part of the experiment, parti- cipants were presented with a compatible and incompatible mix of audio and visual stimuli and asked to rate their annoyance. We found that several audio stimuli were assessed differently, to a significant extent, by listeners after video clips were added to them. © 2016 Institute of Noise Control Engineering.

  • 18. Rämmal, Hans
    et al.
    Lavrentjev, Jueri
    Sound reflection at an open end of a circular duct exhausting hot gas2008In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 56, no 2, p. 107-114Article in journal (Refereed)
    Abstract [en]

    Sound reflection from hot flow duct openings is a classical problem in acoustics. In practice this is important for effective modelling and prediction off noise radiation from engine exhaust systems, burner pipelines, exhaust nozzles etc. Despite several experimental and theoretical investigations in the field, there is still limited experimental data available to validate the existing theory. In the present study, experimental investigations of plane acoustic wave reflections at duct openings where a hot jet flows into relatively cold surrounding media have been carried out. Heated air with well determined and homogenous chemical consistency along the duct axis was used as a testing media inside the duct during the experiments. The studied jet temperatures exhausting from the pipe ranged from room temperature up to 500 degrees C. The standard two-microphone technique was applied to determine the reflection properties at the duct opening. The experimental results for the reflection coefficient magnitude and phase have been compared with Munt's theory and good correlation was found. This result is a first experimental validation of the theory for hot flow conditions.

  • 19.
    Simmons, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Uncertainties of room average sound pressure levels measured in the field according to the draft standard ISO 16283-1: Experiences from a few case studies2012In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 60, no 4, p. 405-420Article in journal (Refereed)
    Abstract [en]

    A draft standard was presented by a working group within ISO in April 2011. It describes six methods to simplify the measurement of a spatially averaged sound pressure level in a room, in order to determine an airborne sound insulation between two rooms. The draft standard is intended to replace ISO 140 part 4. The proposed methods are based on various spatial sampling techniques, where a microphone is moved continuously or kept steady at ?xed positions in differ¬ent parts of the room. The uncertainty of the average is to a large extent related to the ability of the sampling method to sample sound pressure levels uniformly from all parts of the room. The uncertainties of the simpli?ed methods of the draft standard have been estimated empirically by means of measurements made in ?ve rooms with different acoustic conditions. The result of each type of simpli?ed method is compared to an average of sound pressures recorded in a dense mesh of microphone positions throughout the permitted space in the same room. Some results that may be useful when an averaging method is to be decided: • the standard deviations may actually be higher above 100 Hz than below, the 160 and 200 Hz third octave bands may even contain the most uncer¬tain results • the ?xed positions method is practical and may be used in all types of room • the special corner method gave higher average sound pressure levels and lower uncertainties compared to the other methods • moving microphone methods are dif?cult to apply in small furnished rooms where there is not enough space to complete several indepen¬dent microphone paths • moving microphone methods may be sensitive to operator generated background noise • microphone positions should be spread over the entire room volume. This study has not estimated the uncertainty of the sound pressure level differ¬ence between two adjacent rooms, used for sound reduction index estimates.

  • 20.
    Zurita-Villarroel, G.
    et al.
    Luleå tekniska universitet.
    Haupt, Dan
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Reconstruction of cylinder pressure through multivariate data analysis: for prediction of noise and exhaust emissions2004In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 52, no 4, p. 154-163Article in journal (Refereed)
    Abstract [en]

    A new approach for reconstructing diesel engine cylinder pressure is presented. The technique is based on vibration measurements on the engine surface with subsequent reconstruction of the cylinder pressure by direct use of multivariate data analysis (MVDA). In order to investigate and evaluate the usefulness of the proposed technique, data from earlier experiments with four in-line, six cylinder, heavy-duty diesel engines have been used. One of the engines, running on ethanol, was tested according to a three factorial central composite face at different speeds and loads, as well as different blends of ethanol/ignition improver. The other engines, running on ordinary diesel, were tested with various loads and speeds. All of the measurements, i.e. cylinder pressure, sound pressure levels, vibration, and exhaust emissions, were performed simultaneously. The results demonstrated that MVDA models could accurately reconstruct cylinder pressures for all six cylinders in a diesel/ethanol engine. The differences between predicted and observed maximum cylinder pressure for 800 rpm were just 0-5%. The investigations also showed the potential of the method to estimate noise emissions and emission of NO x from the ethanol engine; a single partial least square (PLS) model could be used to predict noise and exhaust emissions at three different loads

  • 21.
    Ågren, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Klopotek, Manfred
    Luleå tekniska universitet.
    Noise reduction of diesel engines with internal stiffeners1997In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 45, no 1, p. 1-13Article in journal (Refereed)
    Abstract [en]

    In recent years there has been an increased interest from truck manufacturers in reducing the noise from internal combustion engines through stiffening solutions like bearing beams, ladder frames, and bedplates. This paper presents a short literature review of experiences published on the topic. Results of an experimental study of engine modifications with a bearing beam, a ladder frame, and an isolated oil sump are presented as well. The beam and the frame were designed so that they can be installed together without vibration propagating connections and to give high stiffness in the areas where they are most effective. The study was performed on a relatively light 9-liter six-cylinder diesel engine with an engine block of deep skirt type. The influence of the engine modifications was investigated through measurements of sound intensity, sound pressure, running modes, internal and external vibrations, and mobility. The results show that a ladder frame effectively reduces the noise from a deep skirt engine and that the reductions are substantially increased by isolation of the oil sump. The results also show where the components of the ladder frame are effective and that a bearing beam can be an unsuitable solution for deep skirt engines as resonances are shifted to higher frequencies that can be more effectively transferred and radiated.

  • 22.
    Öqvist, Rikard
    et al.
    Tyréns AB, Umeå, Sweden.
    Ljunggren, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Variations in sound insulation from 20 Hz in lightweight dwellings2018In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 66, no 1, p. 56-65Article in journal (Refereed)
    Abstract [en]

    The objective of this study is to quantify the total variations in impact and airborne sound insulation from 20 and 50 Hz, respectively, within a wood-based building system. Field measurements in 70 rooms have been statistically analyzed, in weighted metrics and in third octave bands. Since 1994, the Swedish building code permits wood-based high-rise multifamily dwellings. However, the low frequency sound insulation soon turned out to be insufficient, and complaints were more common in lightweight buildings compared to traditional heavy constructions. Therefore, in 1999, the extended frequency range 50–3150 Hz was introduced in the requirements, an action that mitigated the problem, but only to some extent. Consequently, the lightweight industry often aims one sound class (4 dB) higher than the minimum requirements to obtain satisfactory performance. The Swedish research program Aku20 (2014–2017) showed that the correlation between measured and perceived impact sound insulation in lightweight constructions was significantly improved, when even lower frequencies (20–50 Hz) were included. In this context, the variations of low frequency field measurements and corresponding safety margins need to be investigated.

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