Sound absorption properties and an estimation method of normal incidence absorption coefficient were investigated for the molded bark fiber in which pulp was mixed as a bonding material. First, the characteristic impedance and the propagation constant of the molded article were obtained as a function of f/σ (a ratio of frequency to airflow resistivity) in conformity with the method of Delany-Bazley. Furthermore, relational expressions between the bulk density and the airflow resistivity of the molded article were obtained for the bark fiber and the pulp which are the components of the molded article. The calculated values gave close agreement with the measured values after estimating normal incidence absorption coefficient from the bulk density and the sample thickness of the molded article by using those expressions. And, sound absorption properties of the molded article were clearly articulate, and the guideline of the compressing condition was obtained from the measured values and the estimated values by varying the bulk density and the sample thickness.
A road maintenance vehicle has been often used at night in order to avoid traffic confusion. Therefore it has created noise problems at night, and noise reduction of suction trucks used for cleaning the sewer have been in demand from the environmental point of view. On the other hand, a side branch is lightweight and has a simple structure. Then it is thought from our previous investigation that the drastic noise reduction can be achieved by applying the side branch to the piping system of the suction machine. In this paper, after piping is modeled, the sound field in piping is analyzed by numerical analysis. The installation position of the best side branch is forecast by the result. Furthermore the investigation of the effectiveness to mount the side branch in a real machine is our purpose. As a result, a noise reduction of overall level of 6 dB and 20 dB of a 155 Hz component could be achieved.
A GIS digital map on a scale of 1 to 2,500 is generally used for the evaluation of the Environmental Quality Standards for Noise in Japan at the area facing trunk roads. However, it has not been clarified yet whether the digital map with such a scale has an accuracy to apply for the noise estimation. The ground plan of the buildings on the digital map is a roof plan, because the digital map data is made on the basis of aerial photographs. It is feared that the noise estimated by using such a map may have some differences in the effects of buildings on the noise propagation from the real space. On the above view point, surveys and noise measurements are performed to reveal the effect of the accuracy of the digital map in a GIS on the estimation of the road traffic noise for the evaluation of the Environmental Quality Standards for Noise. As a result, buildings on the digital map are a little bigger than those in real spaces, and noise levels predicted by using the digital map are smaller than real noise levels. On the basis of this fact, a method to correct the building area of digital map data is proposed. An additional survey and noise measurement verify that the proposed method is useful for the evaluation of the Environmental Quality Standard for Noise.
Unique sound masking devices for toilets can be used in women's restrooms of public space in Japan. Such devices function to produce the sound of flushing water without actual flushing. A questionnaire survey to clarify the attitude of people toward such sound masking devices for toilets was conducted. The results showed that many Japanese women know such devices and often use them, that foreign women living in Japan also know such devices, and that Japanese men have heard of such devices. Many Japanese women are quite embarrassed at the thought that someone else can hear them while they are on the toilet. Many women noted the necessity of such devices and required a wide range of setting for toilets in public spaces. However, they are not satisfied with the sound quality of the playback toilet flush sounds of currently available devices.