AN EXPERIMENTAL STUDY ON THE INFLUENCE OF INCIDENT CHARACTERISTICS ON SOUND INSULATION BETWEEN ROOMS

Study on the incident sound field in the insulation performance measurement for partition walls Part 2

Abstract

 Sound insulation between adjacent houses is one of the fundamental factors in the indoor environmental performance of apartment houses, and inspections are often carried out through level difference measurement at the completion stage of the buildings. Since the characteristics of sound fields due to room modes are considered to have strong influences on level differences at low frequencies, understanding sound transmission phenomenon including the factors due to sound fields is likely to lead to effective control of the sound insulation performance at sites.

 In the previous paper, the authors have proposed an experimental method for analyzing the characteristics of the incident sound fields in dwelling rooms under sound insulation measurement, and the method was validated in FE models. The aims of this paper are to validate the proposed method in actual rooms under sound insulation measurement and to investigate experimentally the influence of incident sound fields on the sound insulation between dwelling rooms using the proposed method.

 In the experiment, the proposed method was applied to test rooms separated by an RC wall, where the source rooms were arranged to three different planar geometries using removable partitions. The RC wall was first tested without lining (RC single wall) and then with additional linings (composite wall).

 First, the proposed method was validated through reconstruction of SPL from decomposed sound fields and evaluation of incident directivities.

 Next, sound field analysis using the proposed method was performed in the test rooms along with level difference measurement to investigate the relation between the incident sound field and the sound insulation characteristics. The measured results of level difference D and sound reduction index R for the RC single wall and the composite wall demonstrated that the variation of the incident sound fields due to room geometry affects the sound insulation characteristics at low frequencies. The results of the sound field analysis showed that the transmitted power at low frequencies for the RC single wall is influenced by the matching of the modes between the source and receiving room, particularly by the proximity of the modes close to the normal direction to the wall.

 Furthermore, the sound insulation performance of the composite wall was broken down into sound reduction index R for the RC wall without additional lining and sound reduction improvement index ΔR by the additional lining to clarify the influence of incident characteristics. To analyze the influential factors on ΔR, the oblique incidence absorption coefficients of the composite wall were obtained using the proposed method. The result exhibited the influence of the matching between the incident characteristics and the oblique incidence resonance frequency f(θ) of the wall on the low frequency resonance transmission, suggesting a possibility that strong normal incident power in the frequency range near the normal resonance frequency of the composite wall leads to a decrease in ΔR.