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 Wallace C. Sabine (Sabin) (1868 - 1919) came up with the formula in "Collected Papers on Acoustics" appeared in print 1922: RT60 = k × V / A with k = (24 × ln 10) / c20 = 0,161 (metric) V = room volume in m3    A = α × S = equivalent absorption surface in m2 RT60 = reverberation time in s    S = absorbing surface in m2 A = α1 × S1 + α2 × S2 + α3 × S3 + . . .          c20 = 343 m/s at 20°C RT60 is the reverberation time, the sound pressure level of a signal needs to decay to the value of (-) 60 dB. k is a constant that equals 0.161 when the units of measurement are expressed in meters and 0.049 when units are expressed in feet. A = S × α is the total surface absorption A of a room expressed in sabins. It is the sum of all the surface areas in the room multiplied by their respective absorption coefficients. The absorption coefficients α express the absorption factor of materials at given frequencies. V is the volume of the enclosure. The figures used in this calculator come from the table of absorption coefficients for various materials.

 Width Length Height feet meters
 Walls Material Windows, doors and other surfaces Deflection Material Size How many Front Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface × Back Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface × Left Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface × Right Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface × Ceiling Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface × Floor Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Metal or wood seats Upholstered seats Audience in seats Concrete-unpainted Concrete-painted Brick Plaster on lath Plywood paneling Drapery-lightwt Drapery-heavywt Terrazzo Wood floor Carpet on concrete Carpet on pad Ac. tile suspended Ac. tile on concrete Gypsum board Glass-large panes Glass-windows Marble or Tile Water Surface Metal or wood seats Upholstered seats Audience in seats × 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Estimated RT60 of this room is   seconds.

 Download Absorption Coefficient Chart for Microsoft Excel 5.0 or higher(Over 450 materials listed)

 Some usefull Absorbtion Coefficients Dimensions are given in imperial or metric, as originally published. Material 125Hz 250Hz 500Hz 1kHz >2kHz >4kHz 50mm Acoustic Foam 0.08 0.25 0.6 0.9 0.95 0.9 100mm Acoustic Foam 0.2 0.7 0.99 0.99 0.99 0.99 50mm Mineral Wool (Med Density) 0.2 0.45 0.7 0.8 0.8 0.8 Plaster on brick 0.013 0.015 0.02 0.03 0.04 0.05 Cotton drapes draped to half area. 15oz/sq yd 0.07 0.37 0.49 0.81 0.65 0.54 Foam backed carpet on concrete 0.05 0.16 0.44 0.7 0.6 0.4 Heavy carpet + heavy foam underlay on concrete 0.15 0.25 0.5 0.6 0.7 0.8 Coarse concrete 0.36 0.44 0.31 0.29 0.39 0.25 Painted concrete 0.01 0.05 0.06 0.07 0.09 0.08 Wood floor 0.15 0.11 0.10 0.07 0.06 0.07 Window glass 0.35 0.25 0.18 0.12 0.07 0.04 Plate glass 0.18 0.06 0.04 0.03 0.02 0.02 6mm glass 0.1 0.06 0.04 0.03 0.02 0.02 Plaster on brick 0.013 0.015 0.02 0.03 0.04 0.05 9mm Plasterboard over 20mm air gap 0.3 0.2 0.15 0.05 0.05 0.05 Brickwork 0.05 0.04 0.02 0.04 0.05 0.05 Vinyl flooring 0.03 0.04 0.05 0.04 0.05 0.05 Breeze block 0.25 0.40 0.6 0.5 0.75 0.5 LF panel absorber 0.28 0.22 0.17 0.09 0.10 0.11 Perforated Helmholz absorber, 4-inch depth, mineral wool damping, 0.79% perforation. 0.4 0.84 0.4 0.16 0.14 0.12 Perforated Helmholz absorber,8-inch depth, mineral wool damping, 0.79% perforation. 0.98 0.88 0.52 0.21 0.16 0.14 Broad-band absorber, 1-inch fibreglass slab at mouth of 7-inch deep cavity 0.67 0.98 0.98 0.93 0.98 0.96 Padded seat (unoccupied) 0.1 0.2 0.25 0.3 0.4 0.3

 Bron: HyperPhysics