In Japan, the development of large-scale wind power generation facilities has been promoted since about 2000. Nationwide investigations of the acoustic characteristics of wind turbine noise have been conducted at various wind farms. In this study, to examine the horizontal and vertical radiation characteristics of noise generated from wind turbines, field measurements of noise from a single wind turbine with a rated power of 1.5 MW have been performed. Some receiving points were set circularly around the wind turbine and mounted on a nearby lightning tower. Meteorological and associated wind turbine operational data were collected at 1 s intervals along with corresponding acoustic data. In addition, the sound pressure level distributions at distances of 50 m to 200 m from the wind turbine were investigated. Results revealed distinguishable horizontal directivity of wind turbine noise. The A-weighted sound pressure levels in the crosswind direction are almost 5 dB lower than those in the up-and downwind directions. Furthermore, it has been found that the sound directivity around the wind turbine could be expressed by a simple empirical formula, assuming the wind turbine to be a point source with combined bi-and omnidirectional patterns.

Field measurements of noise generated from two different wind turbines, one with an upwind rotor and one with a downwind rotor, have been performed. To examine the radiation characteristics of wind turbine noise, some receiving points were set around each wind turbine and the apparent A-weighted sound power levels were calculated from the obtained data at 200 ms intervals under various wind conditions. Wind turbine operational data were collected at 1 s intervals along with corresponding acoustic data. Additionally, a simple empirical formula for the sound directivity was proposed, assuming the directivity pattern of aerodynamic and mechanical sound to be bi-and omnidirectional, respectively. The results showed that the horizontal directivity of the A-weighted sound pressure level at the ground level for the two different wind turbines is almost the same, whereas the frequency dependence of the sound directivity is different for the individual wind turbines. Furthermore, obtaining data of the rotor rotational speed, output power, and nacelle direction is strongly recommended to assess the characteristics of noise emission, such as the changes in the sound power level, sound directivity, and tonal components of wind turbine noise.

To accurately estimate the noise at a signalized intersection, it is necessary to precisely reproduce the traffic volume, signal cycle and traffic noise for each vehicle behavior and driving state. Precise reproduction requires considerable effort, such as continuous calculations of vehicles and the setting of parameters such as engine speed, engine load and velocity. A simple method that involves using A-weighted sound power levels (L WA) under nonsteady running conditions has already been proposed for estimating noise at signalized intersections in a previous paper. In this study, the authors developed two simple methods for predicting noise in which the effects of acceleration and deceleration by signals is reflected. One method is based on a microsimulation traffic model, in which equivalent continuous A-weighted sound pressure levels (L Aeq) is calculated by adding the noise of vehicles passing a green signal and the noise of vehicles decelerating and stopping at a red signal then accelerating when the signal turns green. The other method is even simpler and involves the assumption that an intersection zone is an unsteady running section and that L WA for a nonsteady running section is larger than that for a steady running section. Noise predicting by the three simple methods is compared with actual measurements at 10 sites. The two new methods had slightly improved accuracy relative to the measured results.

Large variations occur in actual meteorological conditions according to the time and place, on which the atmospheric absorption of sound depends strongly. To examine the temporal variability of atmospheric sound absorption during the year, the attenuation coefficients for atmospheric absorption were calculated from meteorological data in various world regions. The hourly meteorological data at 10 international airports and the half-daily aerological data obtained at 3 observatories were used in the calculation. The results show that significant differences in atmospheric absorption with the place can be found. The seasonal changes in the attenuation coefficients depend on both the frequency of the sound and the place. In addition, the effects of atmospheric absorption on aircraft noise propagation were examined by performing simple simulated calculations. The Aweighted sound pressure levels and sound spectra of aircraft noise change instantaneously owing to atmospheric absorption, which depends on actual meteorological conditions.

Great number of bottles made by glass, plastic and metal are used to store beverages, liquid ingredients as water, milk, vinegar and also liqueur. Empty bottles after usage are collected for recycling use and resources. Many of them have narrow open mouth and look like typical shape in kinds of Helmholtz resonator. Authors thought that their reuse for functional building parts with sound absorption would be very valuable from points of view of green building and environmental policies, and authors then measured each resonance frequency and sound absorption coefficient of representative, including light-soft-plastic, bottles, with net capacity from 7 to 2000 ml, by setting on the edge of sound tube with diameter of 100 mm. Sound resonances with sound absorption coefficient of 0.3–1.0 at frequencies from 100 to 1000 Hz clearly depending on the capacity could be confirmed. It was also found that measured result was well matched to the numerical calculation based on acoustic impedance change at each section area gradually changed in bottle. It is thought that combination use of recycled bottles with independent resonance frequency is more effective than use of new uniform perforated plates for wide space where we need additional sound absorption in certain frequency range.