| 1. |
- Forssén, Jens, 1968, et al.
(författare)
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Thick barrier noise-reduction in the presence of atmospheric turbulence: Measurements and numerical modelling
- 2002
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 63:2, s. 173-187
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric turbulence causes scattering of sound, which can reduce the performance of sound barriers. This is an important inclusion in prediction models to obtain a correct picture of the sound reduction at higher frequencies. Here a prediction method is applied that uses the strengths of the wind and temperature turbulence to estimate the scattered power into the shadow zone of a barrier. The predictions are compared to full-scale measurements on a thick barrier, where both acoustic and meteorological data were recorded simultaneously under both calm and windy conditions. Comparison between the measurements and the predictions indicate that the method gives reasonably accurate results for mid to high frequencies and a slight overestimation at very high frequencies.
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| 2. |
- Horoshenkov, K. V., et al.
(författare)
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The sound speed and attenuation in loose and consolidated granular formulations of high alumina cements
- 2003
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 64:2, s. 197-212
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Johansson, Carin
(författare)
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Design and evaluation of an impact noise laboratory
- 1994
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 42:1, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Johansson, Carin, et al.
(författare)
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Development of a lightweight wooden joist floor with high impact noise insulation
- 1994
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 43:1, s. 67-79
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Johansson, Carin
(författare)
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Low-frequency impact sound insulation of a light weight wooden joist floor
- 1995
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 44:2, s. 133-147
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Johansson, Örjan, et al.
(författare)
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Source characterization of the lower front-end of a diesel engine
- 1996
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 49:4, s. 383-404
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 7. |
- Ljunggren, Fredrik, et al.
(författare)
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Development of a new damper to reduce resonant vibrations in lightweight steel joist floors
- 2002
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 63:11, s. 1267-1280
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Sandberg, Ulf, 1946-
(författare)
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Road traffic noise : The influence of the road surface and its characterization
- 1987
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Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 21:2, s. 97-118
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Tidskriftsartikel (refereegranskat)abstract
- Unacceptable errors in the prediction of traffic noise occur in some cases when the road surface is largely different from that on which the prediction model is based. The reason is that tyre/road noise has appeared to be the dominating component of the noise from free-flowing traffic and that this noise is to a substantial extent dependent on the road surface.The mechanisms for tyre/road noise generation and its relation to road characteristics are described. Relevant road surface characterization methods are suggested. The major method is the measurement of the road texture profile and subsequent spectral analysis of the profile curve. Supplementary methods concern the measurement of acoustical and mechanical impedances. It is concluded that the road surface effect on traffic noise is extremely complicated and that it is very difficult to generalize any simple relations.For free-flowing traffic it is shown that the tested road surface types and conditions may influence the traffic noise by up to 11 dB(A). This calls for a correction term for the road surface in the prediction models. Despite the complicated relations, it appears feasible—within stringent limitations—to use a table where the correction term is a variable of vehicle type, vehicle speed as well as road surface type and condition.
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| 9. |
- Shi, Wanqing, et al.
(författare)
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An investigation of the characteristics of impact sound sources for impact sound insulation measurement
- 1997
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 51:1, s. 85-108
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Shi, Wanqing, et al.
(författare)
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Assessment of the sound insulation of a wood joist construction due to different types of impact sources
- 1996
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 48:3, s. 195-203
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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