Fig 5. Designed and measured values of reverberation time in hall under different conditions
TABLE I Values of reverberation time
Absorption at frequencies of 
      125 c/s 250 c/s 500 c/s 1000 c/s 2000 c/s 4000 c/s 8000 c/s  
Surface Area Ft2 Material α Total absorption α Total absorption α Total absorption α Total absorption α Total absorption α Total absorption α Total absorption  
Hall Ceiling 4800 Concrete slab on trusses 0.02 95 0.02 95 0.03 145 0.13 145 0.14 190 0.04 190 0.04 190  
Hall Floor 4800 Concrete Floor with Cane Chairs 0.05 240 0.07 335 0.1 480 0.15 720 0.2 960 0.2 960 0.2 960  
Side Walls (Front) 1400 Cement plaster 0.03 40 0.03 40 0.04 55 0.04 55 0.05 70 0.05 70 0.05 70  
Side Walls (rear) 1200 Mineral wool behind perforated plyboard on air gap 0.7 840 0.8 960 0.8 960 0.7 840 0.5 600 0.4 480 0.3 360  
Side Partition 1000 Plyboard on air gap 0.6 600 0.4 400 0.3 300 0.2 200 0.15 150 0.1 100 0.05 50  
Rear Partition 380 Resonators - 250 - 200 - 150 - 100 - 75 - 50 - 30  
Doors 300 Wood frame 0.2 60 0.15 45 0.1 30 0.07 20 0.05 15 0.03 10 0.02 5  
Stage Furnishing Curtain etc - - - 250 - 300 - 400 - 500 - 550 - 600 - 600  
Air content 125000 ft2 - 0 0 0 0 0 0 0.001 125 0.002 250 0.006 750 0.01 1250  
Total       2375   2375   2520   2705   2860   3210   3515  
Additional absorption due to full audience     0.35 1680 0.43 2065 0.4 1920 0.35 1680 0.4 1920 0.4 1920 0.4 1920  
two-thirds full       1120   1380   1280   1120   1280   1280   1280  
one-third full       560   690   640   560   640   640   640  
                                   
Expected reverberation time full audience       1.3   1.2   1.2   1.2   1.1   1   0.9  
two-thirds full       1.5   1.4   1.4   1.4   1.3   1.2   1.1  
one-third full       1.9   1.9   1.7   1.6   1.5   1.4   1.3  
no audience       2.4   2.4   2.1   2   1.9   1.7   1.5  
Measured reverberation time no audience       2.3   2.3   1.9   2   1.9   1.6   1.2  

This image is embedded in ...