Study on acoustic improvements by sound-absorbing panels and acoustical quality assessment of teleconference systems

Abstract

With the development of information and communications technology, conferences and remote education using teleconference systems have become common. When a teleconference system is used, the sound heard in a receiving room includes the acoustic characteristics of both the utterance and receiving rooms, in addition to the characteristics of the transmission via the teleconference system and Internet. Even today, when the digital technology is widely used, quality problems related to sound transmission remain; in particular, the influence of the reverberation of the conference room causes deterioration of the sound quality. Studies aiming to improve the quality of the signal transmission have been conducted; however, there are no acoustic countermeasure methods considering the acoustic characteristics of the two rooms connected by a teleconference system and performing the sound quality evaluation. In this study, focusing on a teleconference system sharing video and audio between two separate rooms, we evaluated the improvement in the sound transmission performance due to the addition of sound absorption to the conference room by examining the correspondence between the subjective assessment results and acoustical physical indexes. Additionally, the acoustical physical indexes that allow evaluating the quality of the sound transmitted via the teleconference system were also examined by comparing with the result of a subjective assessment. Intelligibility tests were conducted, listening difficulty ratings were evaluated, and the impulse response, STI, Clarity (C50), and reverberation time were measured in an actual teleconference system. We observed that, before the addition of sound absorption, the sound was difficult to listen to due to the acoustic characteristics of both of the utterance and receiving rooms. However, by suppressing reverberation in both the utterance and receiving rooms by using sound-absorbing panels, the difficulties in listening was improved. By examination of the correspondence between the subjective assessment results and acoustical physical indexes, we proved that STI and Clarity (C50) are highly correlated with intelligibility. On the other hand, reverberation time was found to be uncorrelated with the intelligibility of the rooms of teleconference systems.