Case study of acoustic comfort improvement in conference room

Abstract

The Hall in Vilnius old town was rearranged for conference and meeting purposes during the last retrofitting. Unfortunately, the participants of events complained about poor acoustics and lack of speech intelligibility. Conducted acoustic measurements showed excessive reverberation time, especially at low frequencies. Technical task for acoustic criteria was formulated from performed analysis of hall properties and valid room acoustic requirements in different countries. During the pre-design stage was found that application of the required surface area of conventional acoustic materials is not possible to install due to the heritage status of the building and dome shape of the hall. The result of discussions with the architect was the idea of creating space sound absorbers with low-frequency absorption preferably. Fifteen different prototypes of absorbers were tested in the laboratory in order to adjust their spectrum to hall demands. The reverberation room with equipment, arrangement of test specimens, and measurement method was in compliance with ISO 354 requirements. Initial acoustic testing of selected prototypes in the conference hall confirmed their effectiveness of performance and pointed to relevant positions for installation. During the acoustic renovation, sixteen low-frequency space absorbers with a height of about 4 m were mounted around the oval hall. Repeatedly acoustic measurements were carried out in the conference hall using the MLS method in accordance with standard ISO 3382-1. The results showed decreasing in reverberation time after renovation from 3.7 s to 2.3 s at low frequencies, while the difference of reverberation time at mid and high frequencies was minor. Primary subjective evaluations also confirmed significant improvement of acoustic comfort in the conference room. Another important result was the obtaining of a more consistent reverberation time curve over the entire 125-4000 Hz frequency range.