Reverberation Time Calculation

Modeling a room of

Height H = m = ft

Length L = m = ft

Width W = m = ft

With absorption coefficients:

= , = , = for average of =
gives an effective absorbing area of = m2 = ft2
for a room of volume V = m3 = ft3.
The corresponding reverberation time is = seconds

RT60 is the amount of time, in seconds, for reverb to decay 60 dB below the initial value. Predictions are based on using known surface materials and their absorption coefficients, calculated in 1-octave frequency bands using Sabine equations. The table shows the numbers for an untreated space. Through design and acoustic treatment, the preferred RT60 values should fall between 0.35 and 0.5 seconds for each band, matching as close as possible.

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

 

Below are two links for a more in depth on this subject, this is just a very basic Rt60 calculator.

HyperPhysics is an exploration environment for concepts in physics which employs concept maps and other linking strategies to facilitate smooth navigation. It is a continually developing base of instructional material in physics outlined in a short and pedagogic manner. A visit is highly recommended.

EASE, Enhanced Acoustic Simulator for Engineers has developed over several versions into the de facto standard for sound system modeling software.Originated by Dr. Wolfgang Ahnert of ADA (Acoustical Design Ahnert)

HyperPhysics
EASE