Žiūrovų salės akustika ir jos interjeras. Akustikos reguliavimo būdai

Abstract

The article deals with the sound absorption properties of a new-type isolated acoustic resonator and of such resonators’ system, which for the most part determine the acoustics of the hall. The sound absorption properties of an isolated resonator were investigated under natural conditions. A resonator with the dimensions of 1.8 x 2.4 x 1.8 m was made of chipboard 18 mm thick. Since the sound field of the resonator is uneven, measurements were made at four points. The investigations show that the reverberation time of the isolated resonator at low frequencies up 200 Hz is short, i.e. 0.1-0.3 s. However, when the frequencies become higher, it is increased sharply, reaching its maximum of 0.83 s at 630-1000 Hz. The sound absorption coefficient has a pronounced resonant character and is equal to 0.54 in the resonator slit at 250 Hz. At other points of measurement, the value of the coefficient is lower. The sound absorption is also maximal in the resonator slit and reaches as much as 12.4 sq.m, at 250 Hz. The influence of the resonator system on the acoustical indices of the hall was investigated in the acoustical model of the hall (M 1:25). Suspended ceiling with cross-shaped slits between the 50 cm long planes (the distance between the ceiling and the rigid surface is 100 cm) reduces the reverberation time by 1.7-2.5 s in the frequency range of 50-250 Hz, whereas at high frequencies - by about 0.1 s only. The influence of the slits on the reverberation time weakens along with the increase in the slit width. The sound absorption reaches its maximum of 120 sq.m, at 200-250 Hz. The investigations show that the new-type resonant suspended ceiling with cross-shaped slits between the planes absorb the low-frequency sound well without any use of a sound-absorbing material.