We propose a method for predicting the absorption characteristics of a fibrous material, that is glass wool, covered with a perforated facing and an impermeable film, typically used for noise barriers. The method is based on Ingard and Bolt's model. It accounts for interactions among perforated facing, film and fibrous materials. The interaction occurs in areas where they are close to each other. That area was determined empirically as the coverage. The coverage is approximately 10 mm for a perforated facing with a 0.2 open area ratio. In the coverage, the perforated facing increases the acoustic impedance of film and fibrous material according to distance. The fibrous material causes acoustic resistance to the film when the film contacts the fibrous material. The formulae for their acoustic impedances were derived from many results of acoustic impedance measured using an impedance tube. The end correction of holes of the perforated facing was modified using the relationship between the measured values of resonance frequency for Helmholtz resonators with the perforated plate and their open area ratio. Results predicted by this method agree well with measured results obtained in most instances.

We investigated the improvement of sound insulation of a double-leaf partition using Helmholtz resonators. We proposed a method of predicting the sound reduction index R 0 at normal incidence using impedance transfer, under the assumption that the resonators installed in the air cavity between the two leaves were independent components of a wall, similarly to boards and studs. Furthermore, for experimentation, a small sample without studs was used to prevent flanking transmission through them. Theoretical and empirical examinations revealed that installing the resonators in the cavity in the following manner was sufficient to control sound insulation at low frequencies. High sound insulation occurred at the resonance frequency f 0 of resonators; the sound insulation decreased at higher and lower frequencies than f 0. The sound insulation at f 0 depended on the acoustic resistance of resonators. When an air layer existed behind the resonators, other peaks and dips appeared at higher frequencies than f 0. Installing both a fibrous absorber and resonators in the cavity was sufficient to recover the decreased performance of sound insulation owing to the installation of resonators.

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.

Acoustics 08 Paris materials, spatial averaging of reverberation time should be done. Using microphone rotator is recognized as one of the tool to do spatial averaging. This study compared results between three methods of spatial averaging of reverberation times measured in small rectangular test chamber (3m x 4m x 5m). The first method is averaging reverberation time measured at 5 of fixed position used as standard positions for testing, the second is at 72 fixed positions on the circle of microphone rotator, and the third is with microphone rotator (64 s/rotation). The result of comparison between three methods revealed that reverberation time measured by rotating microphone has more scatter than those measured by other method and presented different reverberation time from others especially at lower frequency bands. Simulation of microphone rotation with the decay curves measured at 72 fixed positions suggests that spatial distribution of steady state sound pressure level, rotation speed of microphone, and reverberation time of test chamber are key factors of errors. As a conclusion, the strict guideline for measurement of reverberation time with microphone rotator should be presented to minimize errors.