Preliminary Quantification of the Acoustic Properties of Some Selected Lecture Theatres in Federal University of Technology, Yola – Nigeria

Abstract

The reverberation times of some selected lecture theatres in Federal University of Technology, Yola which are the major contributory factors to their acoustic properties have been studied. The selected halls chosen as representatives are LT I, SMIT LT I and LT III having room volumes of 1473.4, 2156.4 and 763.0 m3 respectively. Using acoustic standards the reverberation times were computed using the Sabine formula. The result shows that the reverberation times were 4.20, 1.80 and 2.17 s respectively when they were unoccupied. To understand their acoustic behavior when occupied, the reverberation times were recomputed with assumed human audience at various capacities. When full audience was assumed, their reverberation times reduced to 1.80, 0.90 and 0.62 s for LT I, SMIT LT I and LT III respectively. The values reduced further to 0.86, 0.80 and 0.46 s respectively when the audience was increased 50% above their normal capacities. The reverberation times dropped to 0.68, 0.67 and 0.36 s respectively on doubling the audience. This results shows that in its unoccupied state, the reverberation time of 4.20 s for LT I is too high for lecture theatre which by standard should have a reverberation time of about 1.0 s. On the other hand, occupying LT III 50 % above its normal capacity means that the sound power level would rapidly decay and consequently would render audibility problematic. The reverberation times of 0.9 and 0.62 s at full occupation of SMIT LT I and LT III showed their reverberation times were still under the generally preferred value for speech rooms like lecture theatres. This is also true of all the theatres when assumed filled, one-half times above their seating capacities. Under all conditions of the investigation, it was observed that SMIT LT I seemed to show more compatibility in the reverberation time. This could be attributed to the upholstered finishes on the chairs that have higher absorption coefficient than wood in the other theatres and possible choice of room volume to absorption power ratio.