Abstract:
The allowable upper limit of the background noise level for acoustic design of space depends on speech intelligibility requirement of that particular space. A classroom and a market will not allow the same amount of background noise to fulfill their acoustic requirements. Intelligibility is a quantification of the proportion of the substance of a speech message that can be adequately understood. It is often challenging for listeners to perceive speech in the presence of a background noise, especially when the listener is unfamiliar with the speech signal.
Maximum allowable noise levels for acoustic design of different spaces proposed in Bangladesh National Building Code (BNBC) based on standards used in English, which is only acceptable if speech intelligibility for Bangla and English act similarly against noise. Previous comparative studies on four languages, having different Consonant-to-Vowel ratio and tonal properties showed a different score in intelligibility test against noise. Therefore, it hypothesized that the languages that have a high consonant-to-vowel ratio might be more sensitive to the room acoustic conditions regarding speech intelligibility. Bangla and English have different phonetic structure, consonant-to-vowel ratio, and tonal properties; thus, it can postulate that the impact of noise on intelligibility might also vary. This study explores that speech intelligibility of Bangla affected more specifically by noise, compared to that of English. Based on these findings, the study propose an alternative to update BNBC standards for allowable upper limits of background noise levels for acoustic design of spaces for speech in Bangla.
The study can be broadly classified as an experimental research, which included a combination of experimental, computational and analytical methods in a quantitative approach. In the first phase, the research followed the experimental research methodology to prepare the stimulus and collect data through experiments in an acoustically controlled environment. In the second phase, a computational method was used to extract data, which was ultimately analyzed and synthesized to propose standards for maximum permissible background noise levels in different spaces.
From the derived data, a comparative analysis is done on similar studies for English. By synthesizing required speech intelligibility of space with the corresponding recommended Signal to Noise Ratio (SNR), a proposition is made for allowable upper limits of background noise levels for acoustic design of spaces for speech in Bangla language.
