# Reverberation - Calculator

 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

## 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