Teruo Iwase

Introduction of sound material in living environment 2004 (SMILE 2004): A sound source database for educational and practical purposes

Sound sources are used in various settings of education, research, and business that are related to architectural acoustics. Especially in educational scenarios, they are very effective for students to learn theories together with the experience of listening to actual sounds related to them. Sound Material In Living Environment (SMILE 2004), a sound source database published in 2004 in DVD form (Japanese only), is the culmination of our project. SMILE 2004 is intended as a collection of sample sounds for use in lectures on architectural acoustics at universities or industrial high schools. In addition, it is useful for measurements or demonstrations for academic or practical purposes. The database contains 913 digital sound files of real sounds and impulse responses, which cover the study fields of acoustics, noise control, and soundscapes. Each sound is accompanied by such information as the 1/1 octave band sound pressure levels and a brief explanation and photographs of the situation in which the sound ...

Observations of vibration velocity on wind turbine with propagated sound to surroundings

The authors newly tried measurements of the excited vibration on many parts of wind turbine such as outside surface of nacelle storing power generation system and tall tower by using a laser Doppler vibration meter. Observation and analysis of the natural vibration frequencies of blade in the stopping were done. Observations on sound in surroundings of wind turbine were also done. FFT analyses on them with high resolution to obtain detailed frequency characteristics and to know the relations between vibration velocity and propagated sound to surroundings were done in addition to ordinal spectral analyses. Sharp spectra at near 1 Hz as slightly lower or higher were appeared in the analysed results on blade and tower. In both the analyzed results of vibration velocity on wind turbine and propagated sound, a lot of sharp spectral peaks were recognized in wide frequency range from very low frequency to several hundreds of hertz with high coherencies between vibration velocity and propagated sound at their pea...

Experimental study on noise radiation from wind turbines

Noise emitted from wind turbines is composed of aerodynamic and mechanical sound and has directional radiation characteristics. To investigate the horizontal sound directivity around a wind turbine under various wind conditions, field measurements of noise generated from two different wind turbines have been performed over long periods. Wind turbine operational data such as the nacelle direction and rotor rotational speed were collected at 1 s intervals along with corresponding acoustic data. An empirical formula for the directivity correction was derived from the A-weighted sound pressure levels measured at the several receiving points around the wind turbine. We also focused on the amplitude modulation components of wind turbine noise in emission areas and compared the estimated rotor speeds by using measured sound pressure levels with actual values. The results showed that the directivity pattern of the A-weighted sound pressure level for two different wind turbines is almost the same, whereas the freq...

Acoustical diagnoses of porous drainage pavements

Road traffic noise reduction of drainage pavement with small air gaps among grains is well known. However, traffic flow over many years fills those gaps with mud and sand, thereby degrading the noise reduction effect. To regain that effect, cleansing or reconstructing the pavement is necessary after precise assessment of the air gaps. For that purpose, acoustical diagnoses of drainage pavement are proposed and test results are introduced. One method is to check sound absorption of the pavement surface, which normally has high absorption near frequencies of 1 kHz, which is related to the reduction of road traffic noise. The use of a particle velocity sensor together with a microphone greatly simplifies measurements and judgments. Another analysis method is based on sound propagation through air gaps in the pavement. Transmission characteristics clearly indicate pavement conditions. Low-attenuation sound transmissions are shown in a wide frequency range below 1 kHz for sound air gaps, and weak transmissions in a narrow frequency range are shown when air gaps are filled. These acoustic diagnostic methods are effective in investigating porous drainage pavement.

Effect of atmospheric absorption on aircraft noise propagation in various world regions during the year

The attenuation of sound due to atmospheric absorption depends strongly on environmental temperature and humidity. For that reason, it varies in response to changing meteorological conditions on a variety of time scales. To perform long‐term prediction of outdoor sound propagation more accurately, it is necessary to examine the fluctuation of the attenuation coefficients for atmospheric absorption during the year. Large variations occur according to the time and place in actual meteorological conditions, on which the attenuation coefficients depend strongly. The attenuation coefficients for atmospheric absorption were calculated from hourly meteorological data obtained at ten international airports throughout the world during a year using the calculation method described in ISO 9613‐1. Calculated results show that the variability characteristics of the attenuation coefficients during the year depend strongly upon both the sonic frequency and the place. The effects of atmospheric absorption on aircraft noi...

Measurements of acoustic impedance and their application to sound propagation calculations and audible simulations

Acoustic impedance is an important value that determines the boundary condition of each sound field, but collections of actual values are not sufficient for evaluation of many sound fields. First, measurements using a particle velocity sensor for acoustic impedance were tested on various fields. Such measurement results were applied to calculations of sound propagation. Frequency characteristics of sound propagation were obtained along such surfaces as fields of lawns and snow, and areas paved by porous asphalt for drainage. Those characteristics showed fair correspondence with inspected field measurement results. Then, fine calculations in the frequency domain were converted to the impulse response for each sound field model. Convolution operations based on the impulse response and on voice, music, and some noise sources readily produced an ideal sound field to the audible sound file. Furthermore, simulations of the noise, including noise reduction effects from a car running through a drainage pavement a...

An approach utilizing membrane materials to regulate modal characteristics of rooms

Abstract A passive approach, using membrane materials for regulating modal characteristics of rooms, is presented which improves undesirable acoustic properties in rooms at low frequencies without modifying room shape. Basic studies are conducted to examine the possibility of this approach through scale model experiment and computational analysis, where the effect on the modal distribution and the sound energy distribution in a rectangular room are investigated. The results show that the modal distribution is remarkably transformed depending on the surface density and the position of membranes. Moreover, they demonstrate some cases where high uniformity in the modal distribution and reduction in the spatial deviation of sound energy are achieved by using membranes even in the room originally having low uniformity. These findings indicate that the present approach works effectively under the proper installation of membranes, and, on the other hand, it requires the prediction of the effect in advance.