콘서트홀에서 음향설계를 위한 벽체 확산체의 평가

Abstract

This study intends to provide broad understanding on diffusion characteristics of wall profiles of concert halls, especially in the aspect of acoustical designs. This study begins with the investigations of the scattering and diffusion properties of the various-shaped diffuser profiles and the effects of the wall scattering characteristics by diffusers on acoustical parameters of sound fields using scale model halls. In addition, new methods on in-situ diffusivity evaluation in practical spaces were proposed based on the wavelet theory and the counting number of peaks. The first part of this study contains the results of scattering and diffusion coefficients of diffusers in terms of the structural height and coverage density. The scattering coefficients measured in 1:10 scale reverberation chamber with the same scale diffusers, and the diffusion coefficients measured from a 1:10 goniometer were compared with the corresponding scattering characteristics and directivity patterns from the polar response. The optimum condition of the hemisphere diffuser specification maximizing the effect of scattering on a sound field was also investigated. The second part of this study deals with the effects of diffuser configurations in terms of location and profile on sound fields in concert halls. The effects of diffuser location and profile on concert hall acoustics were investigated in terms of diffuseness in the time domain for diffuser design. The design factors of diffusers in concert halls are geometrical shape, structural height, and surface coverage. Acoustical parameters such as RT, EDT, C80, and SPL were calculated from the impulse responses. As a result, diffusers commonly decreases in RT and SPL, but increased their uniformities. The third part of this study proposes the practical methods on in-situ diffusivity evaluations for concert halls. The numbers of peaks (Np) at -20 dB after the direct sound in measured impulse responses was calculated to evaluate the diffuseness in the halls. The concept of the number of peaks was rooted from the detecting reflections using wavelet theory. It was found that the diffusive lateral surfaces in the audience area close to the stage are more effective in increasing Np. Additionally, the effective hall shape and specific location for diffuser design were discussed through the experimental results of the scale model testing. The connection between Np evaluation and wavelet analysis was discussed. Finally, this study concludes the effects of wall diffusers in terms of both surface diffusivity and sound field diffusivity for better diffusion design of concert hall acoustics with summing up the above findings.|본 연구는 콘서트홀의 벽체 프로파일의 확산 특성에 대한 연구로서, 음향설계의 관점에서 측정법과 설계프로세스를 다루었다. 확산 표면의 물리적 특징으로서 형상, 높이, 점유밀도를 설계요소로 간주하였으며, 이를 바탕으로 실험실에서 측정할 수 있는 확산지표인 확산계수와 지향성 산란계수를 측정하였다. 설계요소에 따른 확산체의 확산 특성에 대해 평가하였고, 그 결과 실험실 측정 확산지표를 최대로 형성하기 위한 조건들을 비교하였다. 추가적으로 설계요소 변화에 따른 흡음율 변화를 검토한 결과, 확산체 높이 변화는 흡음율을 감소시키고, 확산체 점유면적 변화는 흡음율을 증가시키는 경향이 나타났다. 확산체의 방향성 변화는 표면적 증가량에 따른 함수로 표현할 수 있었다. 이를 바탕으로 축소모형 콘서트홀 모형을 이용하여 홀 평면형상, 확산체 위치 및 확산체 높이에 따른 음향 특성 변화를 평가하였다. 그 결과, 확산체 설치에 의해 잔향시간 및 음압의 감소가 공통적으로 나타났으며, 명료도는 증가하는 것으로 나타났다. 특히, 장방형 홀에서는 객석 전열에서는 음압이 증가하고 후열에서는 감소하는 특징을 보였으며, 확산체의 위치를 변화시켰을 때 무대와 가까운 측벽 절반의 구역이 음향 지표의 편차를 감소시키고, 초기감쇠시간 및 음압레벨이 다른 확산체 설치 위치에 비해 높은 것으로 나타났다. 현장확산 지표를 제안하기 위해 측정 임펄스 리스펀스를 웨이브릿 변환을 통해 확산음을 정량적으로 분석하였으며, 이 개념의 실용적인 적용을 위해 반사음개수를 평가하는 프로세스를 제안하여, 축소모형 콘서트홀에서 확산체 변화에 따라 분석하였다. 그 결과, 확산체 설치에 따라 웨이브릿 계수의 총합 및 반사음개수가 유의하게 증가하는 것으로 나타났으며, 측벽 절반의 구역의 확산체가 가장 높은 확산도를 보이는 것으로 나타났다. 실제 콘서트홀에서 측정한 음원을 이용하여 청감평가를 실시한 결과, 음압과 더불어 반사음개수가 주관적 확산도와 두번째로 높은 상관도를 보인 것으로 나타났다. 이상를 바탕으로 실험실에서 확산지표의 측정과 축소모형에서 반사음개수 측정을 통한 벽면 확산체의 설계 및 평가 방법을 제안하였다.; This study intends to provide broad understanding on diffusion characteristics of wall profiles of concert halls, especially in the aspect of acoustical designs. This study begins with the investigations of the scattering and diffusion properties of the various-shaped diffuser profiles and the effects of the wall scattering characteristics by diffusers on acoustical parameters of sound fields using scale model halls. In addition, new methods on in-situ diffusivity evaluation in practical spaces were proposed based on the wavelet theory and the counting number of peaks. The first part of this study contains the results of scattering and diffusion coefficients of diffusers in terms of the structural height and coverage density. The scattering coefficients measured in 1:10 scale reverberation chamber with the same scale diffusers, and the diffusion coefficients measured from a 1:10 goniometer were compared with the corresponding scattering characteristics and directivity patterns from the polar response. The optimum condition of the hemisphere diffuser specification maximizing the effect of scattering on a sound field was also investigated. The second part of this study deals with the effects of diffuser configurations in terms of location and profile on sound fields in concert halls. The effects of diffuser location and profile on concert hall acoustics were investigated in terms of diffuseness in the time domain for diffuser design. The design factors of diffusers in concert halls are geometrical shape, structural height, and surface coverage. Acoustical parameters such as RT, EDT, C80, and SPL were calculated from the impulse responses. As a result, diffusers commonly decreases in RT and SPL, but increased their uniformities. The third part of this study proposes the practical methods on in-situ diffusivity evaluations for concert halls. The numbers of peaks (Np) at -20 dB after the direct sound in measured impulse responses was calculated to evaluate the diffuseness in the halls. The concept of the number of peaks was rooted from the detecting reflections using wavelet theory. It was found that the diffusive lateral surfaces in the audience area close to the stage are more effective in increasing Np. Additionally, the effective hall shape and specific location for diffuser design were discussed through the experimental results of the scale model testing. The connection between Np evaluation and wavelet analysis was discussed. Finally, this study concludes the effects of wall diffusers in terms of both surface diffusivity and sound field diffusivity for better diffusion design of concert hall acoustics with summing up the above findings.