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  • 1.
    Frenne, Nicklas
    et al.
    Luleå tekniska universitet.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Acoustic time histories from vibrating surfaces of a diesel engine2006In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 67, no 3, p. 230-248Article in journal (Refereed)
    Abstract [en]

    An experiment on a diesel engine provides for validation of a method that retrieves source strength spectra, source strength time histories and sound pressure time histories of the engine's complex partial sources. The method is based on empirical transfer function measurements and inverse matrix calculations briefly described in the article. Different simplifying source models were selected by comparison of calculated and measured auto spectra. The results show: (1) indication of time efficient measurements of source strength spectra, (2) the importance of correct source models in the case of separated source strength time histories, and (3) spectra of separated sound pressure time histories. Listening tests reported that it is possible to detect well differentiated sounds of the partial sources as a result of the method.

  • 2.
    Horoshenkov, K. V.
    et al.
    Department of Civil and Environmental Engineering, University of Bradford.
    Hughes, D. C.
    Department of Civil and Environmental Engineering, University of Bradford.
    Cwirzen, A.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    The sound speed and attenuation in loose and consolidated granular formulations of high alumina cements2003In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 64, no 2, p. 197-212Article in journal (Refereed)
    Abstract [en]

    Clinkers of high alumina cements are separated into three granular formulations with particle sizes in the range 0.6-0.71 mm, 0.71-1.18 mm and greater than 1.18 mm. These are used to manufacture consolidated samples of porous concrete in an autoclave. The acoustic and microscopic properties of loose and consolidated porous samples of concrete are investigated using both experimental methods and mathematical modelling. Values of porosity, flow resistivity, tortuosity and parameters of the pore size distribution are determined and used to predict closely the sound speed, acoustic attenuation and normal incidence absorption coefficient of these materials. It is shown that high alumina cements do not require additional binders for consolidation and that the structural bonds in these cements are developed quickly between individual clinkers in the presence of water. The hydration product build-up during the consolidation process is insignificant which ensures good acoustic performance of the consolidated samples resulting from a sufficient proportion of the open pores. The value of porosity in the consolidated samples was found to be around 40%, which is close to that measured in some commercial acoustic absorbers. This work provides a foundation for the development of acoustically efficient and structurally robust materials, which can be integrated in environmentally sustainable concrete and masonry structures. © 2002 Elsevier Science Ltd. All rights reserved.

  • 3.
    Johansson, Carin
    Luleå tekniska universitet.
    Design and evaluation of an impact noise laboratory1994In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 42, no 1, p. 75-84Article in journal (Refereed)
    Abstract [en]

    An acoustic laboratory has been constructed in order to measure sound transmission through floors. It has been erected inside an existing building. Apart from the costs being considerably less than if a new building had been constructed, this has meant that several other advantages have been obtained. The design and location of the laboratory have been partially governed by activities already existing in the building. This article presents the construction from the point of view of building technique and of acoustics. In an effort to eliminate flank transmission in the frequency range 100–3150 Hz the construction has been dimensioned with vibration dampers having a natural frequency fo = 10 Hz. For the same reason and in order to increase the sound insulation the walls and ceiling have been lined with radiation reducing material. Comparative calculations and measurements have been carried out which show how the results have been affected by this procedure. The radiated effect from the various surfaces is shown in the form of graphs. The ratios of the receiving room dimensions are chosen so that the natural frequencies in the low-frequency region 100, 125 and 160 Hz are spaced fairly uniformly Despite the economic limitations and a limited amount of space the laboratory meets the requirement set by the International Standards ISO 140 with a good margin.

  • 4.
    Johansson, Carin
    Luleå tekniska universitet.
    Low-frequency impact sound insulation of a light weight wooden joist floor1995In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 44, no 2, p. 133-147Article in journal (Refereed)
    Abstract [en]

    This article describes the results of a project for the development of a lightweight wooden joist floor. The project concerns the further development of an earlier joist construction, in which very good laboratory and field results were obtained in the frequency range 100–3150 Hz. The work was carried out to investigate how impact sound at frequencies under 100 Hz is affected if the construction is made more rigid by various means. Attention was concentrated on the effect of increasing the rigidity of joists and boards. The report cover laboratory experiments as well as measurements in the field.

  • 5.
    Johansson, Carin
    et al.
    Luleå tekniska universitet.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Development of a lightweight wooden joist floor with high impact noise insulation1994In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 43, no 1, p. 67-79Article in journal (Refereed)
    Abstract [en]

    This article describes the results of a project for the development of a lightweight wooden joist floor. The work has been carried out by the optimization of each of the variables which are important for sound insulation and has resulted in the construction of a framing of joists which has good impact sound insulation, small dimensions, can be constructed in a simple way at low cost and can be assembled in an easy and safe way. Forty-five different constructions and combinations were tested in the laboratory. The optimal construction was finally tested in several blocks of flats. In order for the construction to meet the Swedish Building Standards for sound insulation, the impact noise index Ii must not exceed 63 dB. The final construction had an index Ii of 52 dB in the laboratory and 53–58 dB in the field, and was thus approximately 10 dB better that the standard limit for impact noise between adjoining flats. The total weight of the construction is only 60 kg/m2 and the total thickness is 342 mm. Furthermore the framing of joists is economical and practical to manufacture in factories, is easy to transport without deformation and is easy to install in the building on the site.

  • 6. Johansson, Örjan
    et al.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    Klopotek, Manfred
    Luleå tekniska universitet.
    Source characterization of the lower front-end of a diesel engine1996In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 49, no 4, p. 383-404Article in journal (Refereed)
    Abstract [en]

    The lower front end of a diesel engine is a major noise source. Describing the source mechanisms of this area is problematic as it consists of a rotating torsional vibration damper in front of the timing transmission cover and the oil sump. This experimental study focuses on the acoustic interaction phenomena between the damper and the structure behind it. To describe the source mechanisms a test series of different modifications by conventional lead wrapping technique is performed. The vibration behaviour of each substructure is determined by operational deflection shape measurements and the source strength for each modification is determined by near-field sound intensity measurements. The results show the contributions from different substructures and describes the interference effects due to coherent radiation. It is concluded that the radiation is dominated by the timing transmission cover structure behind the damper. At some frequencies though, the torsional vibration damper in combination with the timing transmission cover behind it, causes the high radiation. This effect is mainly due

  • 7.
    Johnsson, Roger
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Odelius, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    A new test track for automotive squeak and rattle (S&R) detection2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 80, p. 79-85Article in journal (Refereed)
    Abstract [en]

    The perceived quality of interior sounds is of increasing importance in the automotive industry since it is important for the customer perception of vehicle quality. Squeak and rattle (S&R) is a group of intermittent interior noise that reduce the sense of quality dramatically. To identify and solve S&R problems the car manufacturers do both simulations and tests in laboratory of complete vehicles as well as subsystems. As a complement, to laboratory testing and for verification, complete vehicle tests at proving grounds are done. In order to systematically test for vehicle S&R noise at proving grounds there is a need for a new type of test track that in a controlled and repetitive ways excite vehicles at different frequencies. This paper describes such a new test track, called the Frequency Sweep Test Track (FSTT). The test track is based on sweep excitation and improves the precision when detecting and solving S&R issues. Different design considerations such as sweep waveform, frequency range and sweep rate are discussed. The track design is evaluated using a quarter-car model including a tandem ellipsoid tyre model. In a case study a FSTT was built and the excitation of a car was measured. The track excited the expected frequency range and the track operated well in detecting a rattle in the dashboard of an executive production car and at which frequency the rattle occurred.

  • 8.
    Lennström, David
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Olsson, Magnus
    Volvo Car Corporation, Dept. 91600/PV2C2.
    Wullens, Frédéric
    Volvo Car Corporation, Dept. 91600/PV2C2.
    Nykänen, Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Validation of the blocked force method for various boundary conditions for automotive source characterization2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 102, p. 108-119Article in journal (Refereed)
    Abstract [en]

    Vibro-acoustic source characterization is an essential task in vehicle development to enable prediction of receiver response. For structure-borne noise, the interface forces in multiple degrees of freedom due to internal loads are often quantified for root cause analyses in a single system assembly, as in transfer path analysis (TPA). However, for a reliable prognosis of the acoustic performance of a known component such as a motor or pump, a receiver-independent source characterization is required, and the method of acquiring blocked forces from in-situ measurements has been shown to be a preferred technique for such purposes. The benefits of the method are the characterization of the intrinsic properties of the source and the possibilities of measuring the component attached to receivers with varying dynamic properties.There is to date a limited number of validation cases where blocked forces from in-situ measurements are acquired for automotive source–receiver assemblies. In this study the blocked forces of a vacuum pump in nine degrees of freedom were determined when connected to a bracket whose boundary conditions were modified in order to achieve four assemblies with different source/receiver dynamic properties. The results show that the blocked forces are transferable, i.e. the receiver response in one assembly was predicted in a wide frequency range by combining source–receiver transfer functions of that assembly with blocked forces estimated in another assembly. Furthermore, an in-situ blocked force TPA was applied to a double-isolated complete vehicle source–receiver case of an electric rear axle drive with interior compartment sound pressure as target. The reconstructed magnetic tonal harmonics agreed with the measured target response in the frequency range 50–500 Hz, which further motivates the use of the blocked force principles for TPA and source requirements specifications.

  • 9.
    Ljunggren, Fredrik
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Simmons, Christian
    Luleå University of Technology.
    Högberg, Klas
    WSP Acoustics, Ullevigatan 19, 41140 Gothenburg.
    Correlation between sound insulation and occupants’ perception: Proposal of alternative single number rating of impact sound2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 85, p. 57-68Article in journal (Refereed)
    Abstract [en]

    Traditionally, multi-family houses have been constructed using heavy, homogenous materials like concrete and masonry. But as a consequence of the progress of lightweight building systems during the last decades, it has been questioned whether standardized sound insulation evaluation methods still are appropriate.An extensive measurement template has been applied in a field survey where several vibrational and acoustical parameters were determined in ten Swedish buildings of various constructions. In the same buildings, the occupants were asked to rate the perceived annoyance from a variety of natural sound sources. The highest annoyance score concerned impact sounds, mainly in the buildings with lightweight floors.Statistical analyses between the measured parameters and the subjective ratings revealed a useful correlation between the rated airborne sound insulation and Rw′+C50–3150 while the correlation between the rated impact sound insulation and Ln,w′+CI,50–2500 was weak. The latter correlation was considerably improved when the spectrum adaptation term with an extended frequency range starting from 20 Hz was applied. This suggests that frequencies below 50 Hz should be considered when evaluating impact sound in lightweight buildings.

  • 10.
    Ljunggren, Fredrik
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ågren, Anders
    Development of a new damper to reduce resonant vibrations in lightweight steel joist floors2002In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 63, no 11, p. 1267-1280Article in journal (Refereed)
    Abstract [en]

    Floor vibrations annoying to humans often occur in lightweight constructions. A number of methods to solve the problem of resonant vibrations are reported in the literature. Tuned mass damper, semi-active tuned vibration absorber and active control system are all examples of existing methods. A new method has been tested in laboratory environment on a prefabricated floor containing a resilient ceiling with a size up to 6.8×4.8 m2. The method takes advantage of small pieces of visco-elastic material connected between the ceiling joists and the primary beams. A finite element model is used to calculate the correct amount of visco-elastic material. The new damper is especially effective in damping mode shapes where the ceiling oscillates out of phase relative to the floor but shows improvements for other mode shapes as well.

  • 11. Ljunggren, Fredrik
    et al.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Potential solutions to improved sound performance of volume based lightweight multi-storey timber buildings2011In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 72, no 4, p. 231-240Article in journal (Refereed)
    Abstract [en]

    Lightweight building systems in general suffer from poor sound insulation, especially in the low frequency region. Since no reliable mathematical models that can predict the impact sound pressure level exists, the lightweight building design is to a high extent based upon previous experience and upon measurements. A special difficulty is related to experimental measurements since the variation among identical units must not be neglected. A modern volume based lightweight wooden buildingn concept has here been tested by numerous well controlled measurements, in laboratory as well as in more field like conditions. The volume construction technique offers new possibilities and challenges to improve sound insulation in light weight timber construction. The main purpose was to investigate how different constructional solutions in the floor, like plaster board, mineral wool, elastic glue, dividing board, floating floor etc., affect the sound insulation. Many of the tested modifications resulted in only marginally changed impact sound pressure level but parameters that substantially can improve the sound insulation were found in using elastic glue to mount the floor boards, to install extra board layers and to use floating floors.

  • 12.
    Löfdahl, Magnus
    et al.
    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.
    Nykänen, Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    An auralization model for structure-borne tire noise2015In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 96, p. 61-67Article in journal (Refereed)
    Abstract [en]

    In the automotive industry, a Noise, Vibration, and Harshness (NVH) issue such as road noise is an important factor for the perceived quality of a product. A useful method to address NVH problems and to reduce field-testing is to combine recordings and simulations into auralizations. The objective of this paper was to develop an auralization model of structure-borne tire noise based on operationally measured hub forces and validate it by comparison with artificial head recordings made under the same conditions. To create auralizations under the same condition as the recordings, the wheel hub forces used for the recordings were measured and filtered through experimentally measured binaural transfer functions from the same hub of the car to an artificial head in the cabin of the car. The auralization model was validated in a listening test where the criterion for considering the auralizations to be sufficiently similar to the recordings was that eight different tires should be ranked equally in a listening test regardless of whether the test was based on auralizations or recordings. Listening test results from ranking of tires with respect to the annoyance of interior sounds showed good agreement between auralizations and recordings. There were no significant differences between rankings based on recordings and auralizations – except for tires assessed to be very similar – at either 50 km/h or 70 km/h. The conclusion was that the use of auralizations for ranking of structure-borne tire noise gives results that match listening tests based on recordings, and this supports the validity of the auralization model.

  • 13.
    Löfdahl, Magnus
    et al.
    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.
    Nykänen, Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Mobility measurement in six DOFs applied to the hub of a car2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 83, p. 108-115Article in journal (Refereed)
    Abstract [en]

    Complex models are usually needed to predict functional performance of mechanical devices such as noise and vibration levels. A typical model is divided into substructures where each substructure is described either as a simulation or as an experimental model. When coupling substructures, information is needed that describes the boundary conditions at the attachment points of the various substructures. This can be hard to achieve, especially when full structural behavior including rotational degrees of freedom (DOFs) are needed. The objective of this study was to obtain the mechanical mobility matrix in six DOFs for a wheel hub of car, as an example of a complex mechanical structure, through an experimental approach based on the multiple-input multiple-output technique. Further, evaluation of the measurement quality was conducted without requirements for numerical simulation comparisons. A specially designed brake disc was fabricated for direct attachment of shakers and transducers. The quality of the 6-DOF mechanical mobility matrix was evaluated using reciprocities, coherence functions, and random error in the gain-factor estimates. The results showed good quality in the reciprocities, and the multiple coherences in each degree of freedom were close to one in the frequency range of 25–500 Hz. The random error can be reduced by increasing the number of averages.

  • 14.
    Nykänen, Arne
    et al.
    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.
    Sirkka, Anna
    Interactive Institute – Sonic Studio, Piteå.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Assessment of changes in preference ratings of auralized engine sounds caused by changes in frequency resolution of transfer functions2013In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 74, no 12, p. 1343-1353Article in journal (Refereed)
    Abstract [en]

    Auralization facilitates aural examination of contributions from different sound sources, individually and as parts of a context. Auralizations can be created by filtering sounds of perceptually salient sources through binaural transfer functions (BTFs) from source positions to a listening position. When such auralizations are used for product sound design it is essential to know that they are of sufficient quality. A basic requirement is that preference ratings are unaffected by the quality of the auralizations. The objective of this study was to measure changes in preference ratings of auralized engine sounds caused by changes in frequency resolution of used BTFs. Auralizations of engine sounds were created by filtering source sounds through BTFs measured from source positions to a driver’s position inside a truck cabin. The BTFs were altered by lowering the frequency resolution and by smoothing in the frequency domain. Preferences for the auralizations were compared using a modified version of the MUlti Stimulus test with Hidden Reference and Anchor, MUSHRA (ITU-R BS.1534-1). Since the use of a reference is only appropriate when a reference known to be most preferred exists the reference was removed, resulting in a MUlti Stimulus Test with Hidden Anchors (MUSTHA). For assessment of the differences between the auralizations a statistical method commonly used for assessing agreement between methods of clinical measurement was adopted. The lowest frequency resolutions resulting in acceptable agreement between preference ratings of auralizations made with high frequency resolution (1 Hz) BTFs and auralizations made with simplified BTFs were 32 Hz frequency resolution or smoothing with either 1/24 octave bandwidth filters or 63 Hz absolute bandwidth filters.

  • 15.
    Nykänen, Arne
    et al.
    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.
    Sirkka, Anna
    Scania, RTRN Acoustics, Truck Development.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Assessment of the change in similarity judgements of auralized engine sounds caused by changes in frequency resolution of transfer functions2011In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 72, no 2-3, p. 115-123Article in journal (Refereed)
    Abstract [en]

    Auralization facilitates aural examination of contributions from different sound sources, individually and as parts of a context. Auralizations can be created by filtering sounds of the perceptually most salient sources through binaural transfer functions (BTFs) from source positions to a listening position. When psychoacoustic analysis is based on auralizations, the auralizations need to give the same impression as real sounds. The objective of this study was to determine the frequency resolution required for auralizations to be perceptually equivalent to recordings made with an artificial head. Auralizations of the contribution of engine sounds to interior sounds of a truck were examined. In listening tests auralizations based on simplified BTFs were compared to artificial head recordings. The BTFs were simplified by lowering the frequency resolution and by smoothing in the frequency domain. Auralizations made through BTFs with a resolution of 4 Hz or higher or smoothed with maximum 1/96 octave moving average filters were perceived as similar to artificial head recordings.

  • 16.
    Nykänen, Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Sirkka, Anna
    Scania, Södertälje.
    Specification of component sound quality applied to automobile power windows2009In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 70, no 6, p. 813-820Article in journal (Refereed)
    Abstract [en]

    As cars become quieter the sound quality of components with electric motors becomes more important in the customer perception of vehicle quality. This has created a need to develop methods for the specification of component sounds. The objectives of this study were to identify perceptually important aspects, link them to acoustic metrics and, based on this, develop guidelines for the determination of requirements for power window sound. Seven prominent attributes were identified: dull, loud, annoying, steady, powerful, overall product quality and under-dimensioned. Effects of auditory stream segregation influenced the results. Power window sounds mainly consist of two sources: motor and window seal scratching. Subjects tended to judge only motor sound. Prediction models developed on isolated motor sound correlated well with judgements. Low loudness, sharpness and motor speed fluctuations led to perceived high product quality. The results emphasise the importance of handling auditory stream segregation and temporal variations in the sound design process.

  • 17.
    Poll, Marijke Keus van de
    et al.
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Ljung, Robert
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Odelius, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Sörqvist, Patrik
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Disruption of writing by background speech: The role of speech transmission index2014In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 81, p. 15-18Article in journal (Refereed)
    Abstract [en]

    Speech transmission index (STI) is an objective measure of the acoustic properties of office environments and is used to specify norms for acceptable acoustic work conditions. Yet, the tasks used to evaluate the effects of varying STIs on work performance have often been focusing on memory (as memory of visually presented words) and reading tasks and may not give a complete view of the severity even of low STI values (i.e., when speech intelligibility is low). Against this background, we used a more typical office-work task in the present study. The participants were asked to write short essays (5 min per essay) in 5 different STI conditions (0.08; 0.23; 0.34; 0.50; and 0.71). Writing fluency dropped drastically and the number of pauses longer than 5 s increased at STI values above 0.23. This study shows that realistic work-related performance drops even at low STI values and has implications for how to evaluate acoustic conditions in school and office environments

  • 18.
    Shi, Wanqing
    et al.
    Luleå tekniska universitet.
    Johansson, Carin
    Luleå tekniska universitet.
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    An investigation of the characteristics of impact sound sources for impact sound insulation measurement1997In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 51, no 1, p. 85-108Article in journal (Refereed)
    Abstract [en]

    At the assessment of the impact sound insulation of a construction, a standard tapping machine is used as sound source. However, the current standard tapping machine has been criticised especially for measurement of wooden joist floors since the sounds generated by a tapping machine differ from those generated by actual footfall. This study has investigated the waveform and frequency spectra of human footfall (walking, running and jumping), of sand balls, sand bags and dropped tires, and of the standard tapping machine. It is shown that the frequency spectra differ between the standard tapping machine and actual footfall, especially at low frequencies. Results from other excitation sources such as a sand ball falling from a certain height showed concordance with actual footfall. This means that a sand ball drop as an impact source provides a better representation of actual human footfall than the standard tapping machine.

  • 19.
    Shi, Wanqing
    et al.
    Luleå tekniska universitet.
    Johansson, Carin
    Luleå tekniska universitet.
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    Assessment of the sound insulation of a wood joist construction due to different types of impact sources1996In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 48, no 3, p. 195-203Article in journal (Refereed)
    Abstract [en]

    The ISO standard tapping machine was specified as an impact source to assess the sound insulation of floors. The problem is that the noise spectrum produced by the tapping machine does not give similar spectra to that produced by an actual footfall. There are not enough low frequency components in the noise spectrum generated by the tapping machine and it does not, therefore, accurately reflect low frequency noise from the construction being measured. This study presents the impact sound power radiation from a wooden joist construction while applying different impact sources, actual footfall and the standard tapping machine. The sound power radiation obtained from the construction when the tapping machine is applied contains large discrepancies when compared with measurements obtained from an actual footfall at the lower frequency. Comparison of the sound power radiation from the wood joist construction generated by different impact sources showed very good agreement between an actual footfall and a sand ball falling from a certain height. This means that the use of the sand ball drop is a better method of assessing the low frequency impact sound insulation of a construction than using the standard tapping machine.

  • 20.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    The design and evaluation of a semi-anechoic engine test room1992In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 37, no 2, p. 151-161Article in journal (Refereed)
    Abstract [en]

    A low-cost hemi-anechoic laboratory for study of diesel engine emissions has been constructed. The laboratory has been equipped for research in acoustics as well as on exhaust emissions. The facilities for acoustic research are described. A low-budget wall absorber with durable, inexpensive and easily exchangeable wedges has been designed. Various ways of evaluating the acoustic properties of hemi-anechoic rooms are investigated. Finally, measurements are presented that show sound level decay with distance from a source and the standard deviation for sound level when the source and microphone are rotated in a so-called carousel measurement. For sound level decay measurements a special extremely low loudspeaker must be used to avoid interfering floor reflections. Carousel measurements give good results even for a standard loudspeaker. Our carousel measurements show that the absorbers are as appropriate as other more expensive absorbers for measurements up to 2 m from a sound source.

  • 21.
    Ågren, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Experimental study of repeatability errors in 3D sound intensity measurements in narrow frequency bands1994In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 43, no 2, p. 95-111Article in journal (Refereed)
    Abstract [en]

    When investigating the 2D or 3D intensity of complex ‘real life’ noise sources, rather than the intensity normal to a surface, to obtain more detailed information about the radiated sound field great care has to be taken both in measuring and in interpreting the results. In this study it is shown that in measurements of 3D intensity for fixed points and in narrow frequency bands, large errors can be expected for a well-defined simple source if the positioning is imprecise and for a complex source even if the positioning device and the probe are of highest quality. Comparisons have been made between a two-microphone and a six-microphone probe, hand-held and robot-controlled. The comparisons show that, except for the case of an ideal measurement with a simple source and a high-precision robot, significant errors can be expected for all the tested measurement cases. The measurements also show that the positioning of the microphone is of major importance for the repeatability accuracy. The accuracy obtained with a 3D-probe is notably better than with a 1D-probe. The errors when measuring the complex source with a robot-controlled 3D-probe, however, are still so high, especially for the non-dominant directions, that interpretations have to be made with great care. Under non-ideal measurement conditions, the errors are found to be exponentially dependent upon the sound field pressure/intensity relationship (the pI-index).

  • 22.
    Öqvist, Rikard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics. Tyréns AB.
    Ljunggren, Fredrik
    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.
    Walking sound annoyance vs. impact sound insulation from 20 Hz2018In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 135, p. 1-7Article in journal (Refereed)
    Abstract [en]

    There is a need to develop single number quantities (SNQ) of impact sound insulation that correlate better with walking sound annoyance. Previous research has indicated that impact sound insulation should be evaluated from 20 Hz in lightweight constructions, using modified spectrum adaptation terms. The purpose of our study was to verify whether frequencies between 20 and 50 Hz are important for perceived walking sound annoyance and to verify whether the proposed spectrum adaptation terms improve correlation with perceived walking sound annoyance. Binaural recordings of walking sound in one heavy and one lightweight construction were evaluated in a two-part listening test. The need to include frequencies from 20 Hz when evaluating lightweight constructions was verified. Both tested constructions achieved similar performance in terms of LnT,w and LnT,w + CI,50-2500, while a significant mismatch in the rated annoyance was observed. The correlation between SNQ and subjective response was considerably improved, when the impact sound insulation was evaluated from 20 or 25 Hz using a flat frequency-weighting factor.

  • 23.
    Öqvist, Rikard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ljunggren, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    On the uncertainty of building acoustic measurements: Case study of a cross-laminated timber construction2012In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 73, no 9, p. 904-912Article in journal (Refereed)
    Abstract [en]

    If variations and uncertainty in building acoustic measurements can be controlled, construction costs can potentially be reduced since the building will not have to be acoustically over-designed. Field measurements of impact and airborne sound insulation were carried out for an industrially prefabricated cross-laminated timber (CLT) system of plate elements. The results from 18 rooms, forming three groups with respect to size, were compared to a similar study dealing with a prefabricated Volume Based Building (VBB) system. Large variations were found at frequencies below 100 Hz which is crucial for the low frequency adaptation terms connected to the weighted sound insulation indices. The measurement uncertainty was investigated by analysing the repeatability, measurement direction and the time dependence of the sound source. The variations due to the measurement procedure were found to be small compared to the total variations. It was also indicated that the variations in sound insulation are smaller with a prefabricated system compared to on-site production, since less work is required at the building site

1 - 23 of 23
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