This paper describes an application of active control of sound diffracted by a barrier. The basis of this application is the cancellation of the sound pressure at the diffraction edge, which behaves like a virtual source to the diffracted field. Several points on the edge were canceled simultaneously by several secondary sources to get a large attenuation over a wide area. While many factors appear to influence the effectiveness of active control, the points of cancellation on the diffraction edge and the arrangement of the secondary sources were studied. The optimum conditions for control were investigated using numerical simulation. These conditions were then confirmed experimentally using multichannel adaptive signal processing. It was found that control is stable and effective when the intervals of the points of cancellation on the edge are shorter than half of the wavelength, and that attenuation is greatest when the secondary sources are nearest the primary source.

In this paper, we revisit the acoustics education program using mobile devices to better understand urban environments. We begin with a summary of our past projects to demonstrate a model case of the concept. In these projects, the output was mainly supposed to be a noise map with measured sound pressure levels (SPLs) and sound spectra. This methodology can obviously be applied to larger-scale urban studies. Including measured sound spectra can be another advantage. Next, current problems in measurement accuracy due to recent device developments are explained and the required examinations are stated. Finally, the accuracy of the current versions of the applications as well as recently available devices are discussed. The results of this study provide information regarding the measurement accuracy of mobile devices, and some suggestions for their practical use are given, which are also useful for additional studies pertaining to the urban acoustic environment.

In an introductory course for environmental/architectural acoustics in universities, it is often used the teaching method based on soundscape, in which students are asked to make a sound map with listening their surrounding acoustic environment. However, if objective measurement of sound pressure level or frequency spectrum can be introduced in such a course, it will interest students in environmental acoustics, and enable them to discuss the acoustic environment more profoundly. Measurement apparatuses are usually expensive and difficult to be used in such a course. Therefore, we consider to use a smartphone: using a smartphone with acoustic measurement applications, it can be possible to introduce an objective measurement in such an introductory course for beginners. In this study, first some applications for acoustic measurement are examined to confirm their accuracy as well as the effect of a simple handmade windscreen. Secondly, using suitable applications, as a possible work in the course, sound maps with measurement results by a smartphone are made and their examples are shown. Finally, some issues to introduce this method in actual courses are discussed.

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