Relation between sound absorption power and vibrational modes of the micro-perforated thin aluminum plate, which is set with air space in a cylindrical enclosure, is studied. The sound field in that enclosure is excited by a speaker set at the one end, and vibration displacement over the thin plate is measured by laser displacement meter through glass plate set at the other end. Sound absorption coefficient of the perforated plate is also measured by two microphones method with and without dumping. Those results show that vibarational modes affect the sound absorption power, that calculation with the assumption of no vibration is not always suitable and that dumping is effective to prevent steep depression of sound absorption coefficient by resonant vibration.

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An acoustic transparent wall was developed and applied to a ceiling mounted ventilation fan to reduce its noise radiation. The acoustic transparent wall is a plate through which sound can pass easily but flow cannot pass. If the casing of a ventilating fan is constructed by an acoustic transparent wall, the noise generated by the fan is expected to be radiated into the ceiling and hardly into the room. It is composed of a thin film, clothes and wire nets. In this paper, their appropriate combinations were studied and its noise reducing effect was proved. A trial application of this technique to a real machine obtained 3〜4 dB noise reduction.

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Some ceiling-mounted ventilators have the function of sound attenuation by a resonant effect in a chamber consisting of a rectangular outer cover and a cylindrical fan unit. In order to control the resonant properties in a reactive manner and maximize the sound attenuation effect of that resonant system, we have experimentally studied the properties of modeled resonant systems attaching a plate (or plates) of arbitrary shape in the resonant chamber. In this study, we separate the chamber by a partial shutting plate at the end of the inner cylinder modeling a fan unit into two spaces that are approximately expected to behave as a Helmholtz resonator of two degrees of freedom. We show the variations of the resonant properties experimentally obtained by modulating the shapes and dimensions of the plate, and verify the resonant frequencies by a simple analytical approximation. In this model, the second resonant frequency can be widely changed depending on the clearance between two spaces without attenuation of resonant effect.

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In recent years, with the never ending progress in technology related to audio visual equipments and PC, etc., there is an increasing trends of using the reproduction sound of contents such as music and speech even for household purposes. Since all the phenomena occurring in nature need to be considered in relative frame of reference, a pleasant and enjoyable sound to the listener may appear as a noise to the people (non-listener) around the owner of sound player. Therefore, the aim of the present work is to develop a sound field control technology which confined the sound field to the listener only. In this regard, the author first focused his attention to the relation between the vibration area of the speaker and the attenuation ratio. Based on that is proposed a method to change attenuation ratio so that sound pressure level remain same in the near field, but its level reduces in the far field. In this technique, the primary and secondary sound source of different vibration area is interacted by using anti-phase of the primary sound source. Based on the experiment and theoretical estimation the performance of the present technique is verified.

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Several studies have been made on active noise control for noise barrier. However their systems were insufficient to attenuate the noise at a little diffraction area. In this paper, a new concept of active noise barrier was proposed, which has a lot of active cells, on the top of barrier and being controlled individually by the feed forward method. The characteristics of this system is that they have the reference microphones just in front of the speakers and the control points at a little far away from the speakers. Here, this system was theoretically proved to be effective. And, the feasibility of this system was proved by experiments in an anechoic room and BEM simulations.

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This paper describes the investigation of an active feedback noise control system in an enclosure surrounded by rigid walls. A higher-order model is required for identification in a rigid-walled sound field because several sound pressure peaks can exit. Since the rigid-walled sound field can be expressed by the superposition of a large number of orthogonal acoustic modes, it is expected that identification can be achieved using a lower-order model for each mode independently based on the modal decomposition technique. Therefore, we propose an active control system with feedback controllers to suppress multiple mode amplitudes independently based on the modal decomposition technique. In the present paper, we verify the characteristics of the proposed system to control four modes numerically and experimentally. The obtained results show that reduction of mode amplitude at each natural frequency can be achieved independently without any mode couplings.

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Active noise control (ANC) around head is investigated in this paper. In this type control, an enough control effect cannot be got when an evaluating point is moving. Against this problem, authors proposed Geometrical Adjustment Method based on Direct Adaptive Algorithm. Geometrical Adjustment Method prevents the control effect to become worse just after movement starts. However, the control effect becomes worse if the evaluating point moves largely. ANC used Filter-Map is proposed against this problem. In this paper, a method to update the Filter-Map is investigated. Predetermined map reliability controls the update. Difference of the control effect caused by difference of map reliability is researched in numerical simulations and experiments. The result suggests that the map reliability should be changed by the control effect.

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Noise reduction along a railway line is very important for further speed-up of a high-speed train. In particular, the aerodynamic noise caused by a pantograph is one of the main noise sources, therefore it has become increasingly important to reduce the foregoing noise. As one method for aerodynamic noise reduction, installation of porous metal which covers an object surface was proposed before. According to some wind tunnel test results, the aerodynamic noise reduction effect by this method was verified and it has been clarified that this method is effective for high-speed pantographs. A field test shows that installation of porous metal is effective in reducing the aerodynamic noise of a high-speed pantograph. These test results are described in this paper.

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[in Japanese]

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Generally speaking, a great noise is generated due to rail vibration derived from train passage in rail joint, and an effective counter measure easy to install against the noise generated in rail joint is eagerly requested to develop. Concerning with the countermeasure against the noise radiated from rail, we have developed a new material named "Rail Noise Insulating Material" for standard lines, and have found out that the material is effective to reduce the noise radiated from rail and is easy to install. So, we have developed the new material to install rail joint, named "Noise Insulating Material for Rail Joint (NIMRJ)" that is based on Rail Noise Insulating Material. Taking into consideration the fact that in rail joints the maintenance of it is executed often, the developed material is formed as it is fixed to rail at the place distant from that in the direction vertical to that so that the maintenance can be executed with the material installed. As the results of impact test for evaluating the properties of this material, it has been revealed that the material is effective to reduce the noise radiated from rail, and it is better to cover fully the area between the level of rail bottom and ground level.

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This paper describes a structural adjustment method for subsystems bringing desired coupling loss factors (CLF) in statistical energy analysis (SEA). We had developed the structural design process based on the experimental SEA in order to reduce structure-borne sound in machinery. The process in a few days identifies which CLF should be changed for reducing noise radiated from machinery. The adjustment method is implemented using the finite element method and optimization algorithms. The finite element model represents a part of a whole system and comprises a junction and the neighboring SEA subsystems associated with the CLF to be changed. In this paper, the proposed method for the structural adjustment was demonstrated. The adjustment method was shown to work well in identifying a structural design of the subsystems which achieves the desired CLF.

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The narrow gauge railway vehicle is proceeding with making the drive-system noise which has the possibility to generate noise a low noise. However, so far, as for the measure which decreases the aerodynamics noise of the induction traction motor noise which is one of the sources of the drive-system noise, the way of finding an optimum by the trial and error using the actual device was caught. Therefore, the mechanism of the generation of the aerodynamics noise hadn't been complete as the fluid acoustic analysis but the environment was ready as the tool which analyzes a fluid sound. According to this, we can choose the optimum by fluid acoustic analysis before the production of the actual machine.

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In the present study, we try to reveal the instantaneous and three-dimensional flow structures in the suction sumps, because the strong unsteadiness and three-dimensionality of such flow. Specifically, we conduct consecutive flow-velocity measurements in a suction sump both by a three-dimensional particle tracking velocimetry (referred to as 3D-PTV) and an ultrasonic velocity profiler (UVP), assisting each other. As a result, we have confirmed a good agreement on time-mean three-dimensional velocity distributions between the 3D-PTV and the UVP. In addition, we reveal some typical flow fields in the sump by the 3D-PTV, and discuss the relationship between flow patterns and the air entrainment.

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We propose an experimental evaluation method of dipole sound based on the vortex sound theory. In order to obtain an unsteady two-dimensional flow field phenomena essential to apply the theory, we measured time series data of the flow field around a circular cylinder in a wind tunnel test by using dynamic PIV. The calculated sound pressure at the far field is validated by the correlation analysis with the measured sound pressure. Furthermore, we performed a correlation analysis between the source intensity defined as the integrand in the equation of the vortex sound theory and the measured sound pressure to clarify the relationship between the calculated dipole sound and measured flow field. It is shown that the estimated sound pressure can detect the Aeolian tone due to the Karman vortex shedding. Periodic fluctuation around the shear layer separation points and the vortex formation region in the wake causes the estimated dipole sound.

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In order to clarify the mechanism of aerodynamic noise generation, aerodynamic sound source was estimated with Lighthill theory. The sound source term of the Lighthill equation of the aerodynamic sound generated from a circular cylinder were compared with a numerical simulation and a wind tunnel experiment. The results showed the sound source term measured by the PIV experiments is qualitatively corresponding to the result by the LES analysis. The accuracy of the spectral analysis and the directivity analysis of the aerodynamic noise based on the PIV experiments is almost the same as that of the numerical simulations.

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Recently, it becomes imperative to evaluate fluid-induced noise for automobiles in operation as well as aero-dynamics performance. Though it is difficult to apply CFD analysis actual design because of a lot of computation abilities, we have to still rely on confirmation test employing wind tunnel, at present. For wind tunnel facilities to measure noise, open wind tunnels are generally used with anechoic room. It requires large anechoic room as well as more powerful blowers to compensate pressure drop due to anechoic room. In order to cape this problem, authors have been developing an unique technique, noise measurement trough, for wind tunnel to enable noise measurement at smaller closed type wind tunnel with pipes and gaps than open wind tunnels, as same as usual slotted wall. This paper describes this technique with some experimental data.

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Recently, it is necessary to give the additional value to a basic performance of the equipment to be lost of a remarkable difference. Then, it focus on the shutter sound of the camera in this research. It aims to give the quality of sound as an additional value by making comfortable shutter sound. In aiming at making comfortable shutter sound, sound quality evaluation is used. However, when the sound quality evaluation is repeated whenever the sound is changed by a simulation and a structural modification. Then, the regression in a sound quality evaluation result and psychoacoustic parameters is made by using regression analysis. Whether it is possible to provide the directionality of sound quality is verified without sound quality evaluation.

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A lot of attention has been directed at designing various sounds that are treated as noise, such as automobile acceleration sounds and cleaner sounds. The idea of sound being a normal part of product operation has permeated society. We focused on sound design and evaluated it with 11 kinds of button sounds. First, an impression was extracted by the semantic differential (SD) method, and the relevance of that impression was investigated by time frequency analysis. Next, we confirmed whether or not the impression changed when a sound that generated a bad impression was processed using an adaptive control into a sound that generated a good impression.

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In this study, we construct an impression evaluation model for button sounds generated when users press the buttons on car audio equipment using a neural network. The dynamic characteristics of 11 kinds of button sounds obtained by their wavelet transform frequencies and sound pressure values are fed into the network model inputs. The model responds with three factor scores, "esthetic", "force" and "metallic", and an evaluation value of "offensive - pleasant" as the outputs. By analyzing the synaptic weights of the neurons on the neural network after training, we confirmed the model acquired a mechanism that extracted four impression evaluation values from the sound characteristics. This result shows that the model is able to attain automation of button sound design.

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The production concept of car engine sound has been changing from finding a solution to noise to designing sound. Although many studies have been conducted on creating comfortable car-engine sound, the psychoacoustic effects of time-varying rate for accelerating-engine sounds are still unclear. Thus, we investigated the effects of increasing the frequency rate of car interior noise on auditory impressions using psychological and neurophysiological methods. Harmonic complex tones that simulate acceleration noise were used as stimuli. First, subjective evaluations were examined using the semantic differential (SD) method. Second, neuronal activities of the auditory cortex evoked by these stimuli were measured by magnetoencephalography (MEG). The results indicated that has a significant effect on subjective impressions and on neuronal activities of the auditory cortex.

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Recently, global warming becomes serious problem all over the world. One reason for the greenhouse gas is CO2 in the exhaust gas from automobile. It is necessary to develop high- efficient engine such as hybrid system using internal combustion engine and electric motor or only electric motor. The purpose of this research is to analyze the sound quality of electric vehicles and to grasp influence of acceleration sound quality by a change of motor sound in electric vehicle. First, the acceleration sound that changed the sound pressure level and a rotation number of the motor are examined by semantic differential method. Then, the evaluation result is connected with physical parameters. Moreover, the sound quality of the electric vehicle is characterized for next-generation.

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This study was attempted to improve the sound quality of the small fan for information technology devices such as PC. In order to investigate the relation between various noises emitted from small fan and the design parameters, camber ratio, camber position and wing section of the axial fans were changed. On the other hand, a paired comparison method was chosen for jury test and the results were compared with sound quality metrics. It is known that the annoying feeling has the strong positive correlation with loudness. Therefore, the loudness of the tested fan was kept constant so that the correlation between the annoying feeling and the sound quality other than the loudness can be clarified. As a result, annoying feeling has positive correlation with roughness under the same loudness condition. In addition, it was also found that the roughness was increased with the camber ratio.

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Ventilating fans usually have silencers connecting to the suction side and to the delivery side of the fan. A fan with a silencer box designed to save space in duct systems has been developed and produced. A study to develop a quieter multi-blade centrifugal fan with a silencer box has been examined for exchanging the ordinal fan with a silencer box for a newly designed fan with the box. It was uncertain in the initial stage that air-rubbing noise from surface flow over the absorptive liner inside the silence box was the main noise source induced by higher flow velocity in the passage of the silencer. However, the result of analysis of the computational fluid dynamics with respect to this ordinal fan system indicated that the separated flow of the silencer splitter induced a biased flow at the inlet of the fan impeller. It was also estimated that this biased flow at the inlet acted as the dominant aerodynamic noise source. The situation of the biased flow at the inlet of the impeller was recognized by flow visualization using the tuft method. Various shapes of the silencer splitter designed by trial and error were studied with numerical flow analysis and experiments taking into account flow visualization and noise measurements to determine which shape improved the separated flow and the biased flow at the inlet of the fan impeller. In the final stage, we identified an optimal design for the silencer splitter which does not induce the biased flow at the inlet

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We have developed a method for separating airborne and structure-borne noise. Our method combines beamforming and adaptive filtering using active noise control. Separation is possible by calculating pressure distribution from beamforming, which uses data obtained from a microphone array and vibration sensors, and removing the vibration components using an adaptive filter This method can be used to efficiently solve noise and vibration problems when they are first detected and thus shorten the development of a machine. We used a shaker and speaker to demonstrate that our method is useful to separate noise sources. Results showed that our method separated airborne and structure-borne noise with an accuracy of ±2 dB or less.

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The railway noise from conventional narrow-gauge lines in Japan mainly consists of rolling noise and traction-motor fan noise. Rolling noise is generated by vertical vibration of the wheel and rail, which is induced by a relative displacement between them due to the roughness on their surfaces. Through the field tests, it is found that the excitation of rolling noise is determined by both the wheel/rail roughness and the vibratory behaviour of rolling stocks and tracks. Then, the theoretical model, such as TWINS, for rolling noise is applied to Japanese railways, and the predictions show good agreement with the measured results. In terms of noise spectra, the rail has greater contribution to rolling noise than the wheel in much of the frequency range. An attempt to estimate the effect of track parameters on rolling noise has been made by using the TWINS model. For the railpad, the stiffness has influence on the balance between the rail and sleeper components of noise. The additional damping for the rail makes the rail component of noise reduced effectively.

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A boiler and a heat exchanger are widely used in various plants such as power plants and chemical plants. However unexpected high level sounds are generated when these plants are operated and it becomes a serious problem. This kind of problem is called the acoustic resonance and it has been considered that the resonance generates when the frequency of the vortex shedding behind the tube bank coincides the natural frequency of the duct system. However it has also been thought of self-sustained tone. In general, the self excited phenomenon arises when the exciting energy becomes greater than the dissipating energy. Then in this paper, in order to clarify the mechanism of self sustained tone experimentally, the instability region is tried to obtained by varying the number of tube row and acoustic damping. As a result, it was clarified that the self-sustained tone generates when the number of tube rows is large and the acoustic damping is small.

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A road maintenance vehicle has often been used at night in order to avoid traffic confusion in major cities in Japan. The noise reduction of the road maintenance vehicle has been demanded from the environmental point of view. The suction truck used for cleaning a sewer is one of them. Since the weight of a truck increases even if it performs soundproofing measures with covering a suction truck with acoustic insulation etc., the recovered amount of salvaged material will be restricted. For this reason, the working efficiency of a suction truck will fall. On the other hand, a side brunch is lightweight and is simple structure. And there is no example, which loaded the side brunch to the suction machine in the past. In this paper, numerical analyses by BEM and experiments by using a real thing are conducted in order to reduce the noise of the real suction machine. As a result, noise reduction of 6dB overall level and 20dB of 160Hz component could be achieved.

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Recently, complaints of the excessive railway noise have increased from residents living in high-rise buildings facing railway tracks, both for tracks at grade and on elevated viaducts. Therefore, it is more important than before to predict railway noise at high places and develop countermeasures to reduce the noise. However noise reduction at high places with conventional noise barrier is difficult. In this paper, the effect of noise barriers constructed adjacent to rail on the noise is investigated. Through acoustic tests by using scale models, it is found that, by the noise barriers, the noise at high place is reduced effectively.

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A compression wave is generated ahead of a high-speed train, while entering a tunnel. This compression wave propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wavefront propagating along a tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. From the results, it is confirmed that the maximum pressure gradient of the wave along a very long tube depends on the detail wavefront as well as the initial maximum pressure gradient.

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A generating device of impulsive sound which contains low frequency components was developed. By discharging compressed air in a moment and inserting sound absorption materials into the tube used as an air tank, we could consequently generate an impulsive sound with high sound pressure level more than 150dB at 5 m distance and with wide frequency range of from 1 Hz to 1000 Hz. This paper reports the overview of this device and some experimental results obtained by using an impulsive low frequency sound.

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In this paper, we applied the Direct Adaptive Algorithm (DAA) to active noise control (ANC) of low-frequency impact noise with a dominance at the 63Hz to 125Hz. DAA can carry on the adaptive feedforward control without identifying the acoustical property of a secondary path. It can also reduce the noise even if the control position moves. We develop an impact noise generator for the experiment. A control effect is rated with difference of sound exposure level. From the simulations, an enough validity of control is shown after ten times of impact. The possibility of using ANC against the impact noise is shown from both the simulations and experiments.

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Various structural measures against vibration and noise were taken in a training ship, Oshima Maru. However, an unpleasant sound persisted in the mess hall, where crews take their breaks. In order to reduce the noise, active controllers were investigated. The algorithms were compared under the same conditions to investigate differences in their properties. Simulations for a control system were introduced using plant responses measured from a loudspeaker to a microphone in the mess hall inside Oshima Maru. After investigating the convergence speed in various gradient descent adaptation algorithms, the results were integrated with the actual plant response.

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An estimation method of sound source direction on the binaural microphones system is studied. The head related transfer functions (HRTF) were measured using a dummy head at three dimensional positions and stored in computer. When a sound signal from an unknown direction is generated, the detected sound signals on the right and left ear can be used to regenerate the source signal using the HRTF. The correlation coefficient calculation between the regenerated sound signals on the left and the right ear are carried out for all measured HRTF. The maximum value of the correlation coefficient value among the directions can be recognized as the correct direction of the generated source.

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In the near future, the mechanical systems using hydrogen energy such as a fuel cell vehicle will be widely used. From the point of safty measure, the hydrogen sensors are the necessities. In this paper, a new acoustic method of detecting hydrogen leakage is proposed. This acoustic method is effective in wide space such as a basement parking lot. Three-dimensional computer simulations of sound propagation using finite difference time domain FDTD method is carried out. A basic experiment using helium, instead of hydrogen is also carried out. The validity of the proposed method is shown from the results of simulation and experiment.

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It is necessary to establish the sound transmission analysis method in order to develop the hyper sonic type hydrogen gas flow meter. This method requires sound analyzing under the condition of flow with velocity distribution. We adopted FDTD method to solve this problem. FDTD method is one of the sound transmission analysis. We had FDTD program included a process to calculate movement of the particle in the gas using one dimensional difference. Then we compared the result of FDTD simulation with the experimental result and theoretical value, and estimated this FDTD program.

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From the viewpoint of global warming prevention, it is expected that sewage sludge will be used effectively as low-calorific energy resources. Then, experiments of the pyrolysis of dry sewage sludge using the fluidized-bed reactor were carried out. It was found that reaction temperature and the amount of supply steam have an influence over the pyrolysis oil yield and composition. From these results, it suggests that oil production process from sewage sludge with Internally Circulating Fluidized-bed Gasifier (ICFG) can be formed.

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This paper report the actual performance of the shaft sliding type screw-press dehydrator enables low sludge moisture. In the 16 year of the Heisei era, as for the Ministry of the Environment, the combustion improver technology was admitted to the new recycle technology. The combustion improver means the dehydration sludge by which about 70% of water content was dehydrated, and it doesn't require supplement fuel when burning up at refuse incinerator plants. We achieved the low sludge moisture by dehydrating human waste carried in the treatment plant as well as excess activated sludge together, because while dehydration is difficult for the excess sludge, the human waste is capable of dehydration. Previously, when low sludge moisture dehydration was performed by a screw-press-dehydratoz the performance was difficult because sludge was blocked in a dehydrator On the other hand, the shaft sliding type screwpress dehydrator could settle this problem because to possess the mechanism that shaft slides. This dehydrator has five cases of operation good record of performance by fiscal year 2007, by the all cases.

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Sapporo Plastics Recycling Co., Ltd. (SPR) which started commercial operation of liquefaction plant for waste plastics containing PVC and PET in 2000 has been entered into 9th year this year. Presently, thermal degradation residue and hydrochloric acid other than hydrocarbon oil have been produced as a by-product. As a result, SPR has achieved high recycling rate, in addition, more than 90% of the recycled products have been reused in Hokkaido. Current issues of recycling municipal plastic containers and wrapping are highlighted in this paper.

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Thermal gasification and reforming technologies applicable over a wide temperature range were investigated for high efficiency and calorific value of gas from organic waste such as woody debris. Using laboratory-scale catalytic reformers and gasifier, durability of reforming catalyst and availability of catalyst regeneration were discussed. Commercial Ni-based catalyst and calcined limestone (CaO) were applied to the reforming reaction. From the results of woody waste gasification and reforming, produced hydrogen concentration was sustained at a high catalyst temperature of 1123 K, which prevented the catalyst from deactivating. Moreover, the results indicate that catalyst regeneration by air oxidation at the same temperature would be effective for enhancing the catalytic activity.

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Milling of cellulosic woody biomass as preprocessing is one of the key technologies for ethanol production by an enzymatic hydrolysis process. The vibratory mill with gear type disks, which improves the vibratory cutting rod mill and could impact to woody cell wall directly, has been developed in order to make suitable woody powder for saccharification process and to realize the large volume milling process with high milling efficiency. And the Japanese cedar powder milled by the vibratory mill with gear type disks realized over 60% saccharification efficiency of holocellulose in 60min mill process time. In this study, the feature of woody powder particle after mill was investigated by the scanning electron microscope. And effect of the particle feature for the saccharification efficiency was examined. As a result, it seemed that cracks on the particle were connected the saccharification efficiency.

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