In order to predict equivalent continuous A-weighted sound pressure level (LAeq) of road traffic noise in the area facing roads, a grasp of the insertion loss of buildings against road traffic noise is needed. In the previous study, the authors proposed F2006 for predicting the insertion loss of detached houses against road traffic noise using a line sound source model. However, in order to predict LAeq at residential areas facing a curved road, a prediction method based on a point sound source model is needed. Therefore, a new prediction method of the insertion loss of detached houses against road traffic noise is proposed in this paper. The validity of the proposed prediction formula is verified through additional experiments. This simple method is applicable to the evaluation of the Environmental Quality Standards for Noise in Japan.
The reduced noise of electric and hybrid electric vehicles has been of particular concern because of the potential danger that these vehicles pose to pedestrians when their approach is inaudible against background noise. To address this issue, the use of additional warning sounds in such vehicles is being considered in various countries. The aim of this study was to examine the feasible level of the warning sounds in some urban environments. The levels of three candidate warning sounds (sound of car horn, engine sound, and band-pass noise) were adjusted by the study subjects against four types of urban background noise presented in a laboratory environment. The subjects were asked to adjust the level of the warning sounds so that they were reliably audible or just detectable. The results showed that the level of background noise and type of warning sound significantly affected the perception of the warning sounds, but there was no significant cross-cultural difference between the German and Japanese subject groups. The observations showed that a warning sound that was reliably audible in a particular environment might be inaudible in another environment approximately 10 to 20 dB noisier. The results were also compared with current recommended levels of warning sounds for quiet vehicles.
To determine noise radiation characteristics from a semi-underground road structure and to confirm the validity of a calculation method for road traffic noise, we previously carried out an in situ experiment using loudspeakers at a semi-underground road with reflective surfaces under construction. Thereafter, we carried out another experiment at the same experimental site, focusing on the effect of the pavement of an absorptive road surface and of setting absorptive louvers on the aperture part. In this report, experimental results on the effect of the pavement of an absorptive road surface are described. On the basis of the experimental results, the accuracy of a practical calculation method for noise around a semi-underground road, the hypothetical point source method, specified in the ASJ RTN-Model 2008, was discussed. Through the discussion, the practical calculation method was partially revised. That is, the effect of the absorption of the road surface was included in a correction term describing the sound power level of a hypothetical sound source that takes into consideration the multiple reflections between the ceiling and the road surface.
Eight- and 32-element ultrasonic array transducers using polyurea films are fabricated and experimentally tested in this study. Aromatic polyurea thin films, prepared by vapor deposition polymerization, are suitable for use as an ultrasonic transducer. In this paper, we present two types of polyurea array transducer with 20 and 200 μm pitches. The polyurea films were prepared through vapor deposition polymerization, and miniature electrode arrays were fabricated by a lithographic technique. Resonance frequencies of approximately 30, 65, and 100 MHz were observed in the electrical admittance. To examine the performances of the prototype array transducers, a pulse/echo test and phased array experiment were performed. From the experimental results, we found that the polyurea array transducers fabricated by the proposed method correctly operated as expected.
For practical applications of a thermoacoustic system using factory exhaust heat or solar heat, it is necessary to decrease the onset temperature ratio. In a previous study, a cascade thermoacoustic system with a number of prime movers connected in series was examined. This system can be driven at a lower onset temperature ratio than a conventional thermoacoustic system with a single prime mover. However, there are some problems with this system: it cannot be driven continuously and its thermal efficiency is low. Therefore, a parallel thermoacoustic engine was proposed. In this study, we compared the onset temperature ratios and thermal efficiencies of three systems: a normal thermoacoustic engine with a single prime mover, a cascade thermoacoustic engine, and a parallel thermoacoustic engine with two prime movers. The results indicated the parallel thermoacoustic engine to be advantageous in terms of the onset temperature ratio and thermal efficiency.